This document lists the standard bug patterns reported by SpotBugs.

Bad practice (BAD_PRACTICE)

Violations of recommended and essential coding practice. Examples include hash code and equals problems, cloneable idiom, dropped exceptions, Serializable problems, and misuse of finalize. We strive to make this analysis accurate, although some groups may not care about some of the bad practices.

JUA: Asserting value of instanceof in tests is not recommended. (JUA_DONT_ASSERT_INSTANCEOF_IN_TESTS)

Asserting type checks in tests is not recommended as a class cast exception message could better indicate the cause of an instance of the wrong class being used than an instanceof assertion.

When debugging tests that fail due to bad casts, it may be more useful to observe the output of the resulting ClassCastException which could provide information about the actual encountered type. Asserting the type before casting would instead result in a less informative "false is not true" message.

If JUnit is used with hamcrest, the IsInstanceOf class from hamcrest could be used instead.

AA: Assertion is used to validate an argument of a public method (AA_ASSERTION_OF_ARGUMENTS)

Assertions must not be used to validate arguments of public methods because the validations are not performed if assertions are disabled.

See SEI CERT rule MET01-J. Never use assertions to validate method arguments for more information.

CT: Be wary of letting constructors throw exceptions. (CT_CONSTRUCTOR_THROW)

Classes that throw exceptions in their constructors are vulnerable to Finalizer attacks

A finalizer attack can be prevented, by declaring the class final, using an empty finalizer declared as final, or by a clever use of a private constructor.

See SEI CERT Rule OBJ-11 for more information.

CNT: Rough value of known constant found (CNT_ROUGH_CONSTANT_VALUE)

It’s recommended to use the predefined library constant for code clarity and better precision.

NP: Method with Boolean return type returns explicit null (NP_BOOLEAN_RETURN_NULL)

A method that returns either Boolean.TRUE, Boolean.FALSE or null is an accident waiting to happen. This method can be invoked as though it returned a value of type boolean, and the compiler will insert automatic unboxing of the Boolean value. If a null value is returned, this will result in a NullPointerException.

SW: Certain swing methods need to be invoked in Swing thread (SW_SWING_METHODS_INVOKED_IN_SWING_THREAD)

(From JDC Tech Tip): The Swing methods show(), setVisible(), and pack() will create the associated peer for the frame. With the creation of the peer, the system creates the event dispatch thread. This makes things problematic because the event dispatch thread could be notifying listeners while pack and validate are still processing. This situation could result in two threads going through the Swing component-based GUI — it’s a serious flaw that could result in deadlocks or other related threading issues. A pack call causes components to be realized. As they are being realized (that is, not necessarily visible), they could trigger listener notification on the event dispatch thread.

FI: Finalizer only nulls fields (FI_FINALIZER_ONLY_NULLS_FIELDS)

This finalizer does nothing except null out fields. This is completely pointless, and requires that the object be garbage collected, finalized, and then garbage collected again. You should just remove the finalize method.

FI: Finalizer nulls fields (FI_FINALIZER_NULLS_FIELDS)

This finalizer nulls out fields. This is usually an error, as it does not aid garbage collection, and the object is going to be garbage collected anyway.

UI: Usage of GetResource may be unsafe if class is extended (UI_INHERITANCE_UNSAFE_GETRESOURCE)

Calling this.getClass().getResource(...) could give results other than expected if this class is extended by a class in another package.

AM: Creates an empty zip file entry (AM_CREATES_EMPTY_ZIP_FILE_ENTRY)

The code calls putNextEntry(), immediately followed by a call to closeEntry(). This results in an empty ZipFile entry. The contents of the entry should be written to the ZipFile between the calls to putNextEntry() and closeEntry().

AM: Creates an empty jar file entry (AM_CREATES_EMPTY_JAR_FILE_ENTRY)

The code calls putNextEntry(), immediately followed by a call to closeEntry(). This results in an empty JarFile entry. The contents of the entry should be written to the JarFile between the calls to putNextEntry() and closeEntry().

IMSE: Dubious catching of IllegalMonitorStateException (IMSE_DONT_CATCH_IMSE)

IllegalMonitorStateException is generally only thrown in case of a design flaw in your code (calling wait or notify on an object you do not hold a lock on).

CN: Class defines clone() but doesn’t implement Cloneable (CN_IMPLEMENTS_CLONE_BUT_NOT_CLONEABLE)

This class defines a clone() method but the class doesn’t implement Cloneable. There are some situations in which this is OK (e.g., you want to control how subclasses can clone themselves), but just make sure that this is what you intended.

CN: Class implements Cloneable but does not define or use clone method (CN_IDIOM)

Class implements Cloneable but does not define or use the clone method.

CN: clone method does not call super.clone() (CN_IDIOM_NO_SUPER_CALL)

This non-final class defines a clone() method that does not call super.clone(). If this class (“A“) is extended by a subclass (“B“), and the subclass B calls super.clone(), then it is likely that B‘s clone() method will return an object of type A, which violates the standard contract for clone().

If all clone() methods call super.clone(), then they are guaranteed to use Object.clone(), which always returns an object of the correct type.

DE: Method might drop exception (DE_MIGHT_DROP)

This method might drop an exception. In general, exceptions should be handled or reported in some way, or they should be thrown out of the method.

DE: Method might ignore exception (DE_MIGHT_IGNORE)

This method might ignore an exception. In general, exceptions should be handled or reported in some way, or they should be thrown out of the method.

Dm: Method invokes System.exit(…) (DM_EXIT)

Invoking System.exit shuts down the entire Java virtual machine. This should only been done when it is appropriate. Such calls make it hard or impossible for your code to be invoked by other code. Consider throwing a RuntimeException instead.

Nm: Use of identifier that is a keyword in later versions of Java (NM_FUTURE_KEYWORD_USED_AS_IDENTIFIER)

The identifier is a word that is reserved as a keyword in later versions of Java, and your code will need to be changed in order to compile it in later versions of Java.

Nm: Use of identifier that is a keyword in later versions of Java (NM_FUTURE_KEYWORD_USED_AS_MEMBER_IDENTIFIER)

This identifier is used as a keyword in later versions of Java. This code, and any code that references this API, will need to be changed in order to compile it in later versions of Java.

JCIP: Fields of immutable classes should be final (JCIP_FIELD_ISNT_FINAL_IN_IMMUTABLE_CLASS)

The class is annotated with net.jcip.annotations.Immutable or javax.annotation.concurrent.Immutable, and the rules for those annotations require that all fields are final. .

Dm: Method invokes dangerous method runFinalizersOnExit (DM_RUN_FINALIZERS_ON_EXIT)

Never call System.runFinalizersOnExit or Runtime.runFinalizersOnExit for any reason: they are among the most dangerous methods in the Java libraries. — Joshua Bloch

NP: equals() method does not check for null argument (NP_EQUALS_SHOULD_HANDLE_NULL_ARGUMENT)

This implementation of equals(Object) violates the contract defined by java.lang.Object.equals() because it does not check for null being passed as the argument. All equals() methods should return false if passed a null value.

FI: Empty finalizer should be deleted (FI_EMPTY)

Empty finalize() methods are useless, so they should be deleted.

FI: Finalizer nullifies superclass finalizer (FI_NULLIFY_SUPER)

This empty finalize() method explicitly negates the effect of any finalizer defined by its superclass. Any finalizer actions defined for the superclass will not be performed. Unless this is intended, delete this method.

FI: Finalizer does nothing but call superclass finalizer (FI_USELESS)

The only thing this finalize() method does is call the superclass’s finalize() method, making it redundant. Delete it.

FI: Finalizer does not call superclass finalizer (FI_MISSING_SUPER_CALL)

This finalize() method does not make a call to its superclass’s finalize() method. So, any finalizer actions defined for the superclass will not be performed. Add a call to super.finalize().

FI: Explicit invocation of finalizer (FI_EXPLICIT_INVOCATION)

This method contains an explicit invocation of the finalize() method on an object. Because finalizer methods are supposed to be executed once, and only by the VM, this is a bad idea.

If a connected set of objects beings finalizable, then the VM will invoke the finalize method on all the finalizable object, possibly at the same time in different threads. Thus, it is a particularly bad idea, in the finalize method for a class X, invoke finalize on objects referenced by X, because they may already be getting finalized in a separate thread.

Eq: Equals checks for incompatible operand (EQ_CHECK_FOR_OPERAND_NOT_COMPATIBLE_WITH_THIS)

This equals method is checking to see if the argument is some incompatible type (i.e., a class that is neither a supertype nor subtype of the class that defines the equals method). For example, the Foo class might have an equals method that looks like:

public boolean equals(Object o) {
    if (o instanceof Foo)
        return name.equals(((Foo)o).name);
    else if (o instanceof String)
        return name.equals(o);
    else return false;
}

This is considered bad practice, as it makes it very hard to implement an equals method that is symmetric and transitive. Without those properties, very unexpected behaviors are possible.

Eq: equals method fails for subtypes (EQ_GETCLASS_AND_CLASS_CONSTANT)

This class has an equals method that will be broken if it is inherited by subclasses. It compares a class literal with the class of the argument (e.g., in class Foo it might check if Foo.class == o.getClass()). It is better to check if this.getClass() == o.getClass().

Eq: Covariant equals() method defined (EQ_SELF_NO_OBJECT)

This class defines a covariant version of equals(). To correctly override the equals() method in java.lang.Object, the parameter of equals() must have type java.lang.Object.

Co: Covariant compareTo() method defined (CO_SELF_NO_OBJECT)

This class defines a covariant version of compareTo(). To correctly override the compareTo() method in the Comparable interface, the parameter of compareTo() must have type java.lang.Object.

Co: compareTo()/compare() returns Integer.MIN_VALUE (CO_COMPARETO_RESULTS_MIN_VALUE)

In some situation, this compareTo or compare method returns the constant Integer.MIN_VALUE, which is an exceptionally bad practice. The only thing that matters about the return value of compareTo is the sign of the result. But people will sometimes negate the return value of compareTo, expecting that this will negate the sign of the result. And it will, except in the case where the value returned is Integer.MIN_VALUE. So just return -1 rather than Integer.MIN_VALUE.

Co: compareTo()/compare() incorrectly handles float or double value (CO_COMPARETO_INCORRECT_FLOATING)

This method compares double or float values using pattern like this: val1 > val2 ? 1 : val1 < val2 ? -1 : 0. This pattern works incorrectly for -0.0 and NaN values which may result in incorrect sorting result or broken collection (if compared values are used as keys). Consider using Double.compare or Float.compare static methods which handle all the special cases correctly.

RV: Negating the result of compareTo()/compare() (RV_NEGATING_RESULT_OF_COMPARETO)

This code negates the return value of a compareTo or compare method. This is a questionable or bad programming practice, since if the return value is Integer.MIN_VALUE, negating the return value won’t negate the sign of the result. You can achieve the same intended result by reversing the order of the operands rather than by negating the results.

ES: Comparison of String objects using == or != (ES_COMPARING_STRINGS_WITH_EQ)

This code compares java.lang.String objects for reference equality using the == or != operators. Unless both strings are either constants in a source file, or have been interned using the String.intern() method, the same string value may be represented by two different String objects. Consider using the equals(Object) method instead.

ES: Comparison of String parameter using == or != (ES_COMPARING_PARAMETER_STRING_WITH_EQ)

This code compares a java.lang.String parameter for reference equality using the == or != operators. Requiring callers to pass only String constants or interned strings to a method is unnecessarily fragile, and rarely leads to measurable performance gains. Consider using the equals(Object) method instead.

Eq: Class defines compareTo(…) and uses Object.equals() (EQ_COMPARETO_USE_OBJECT_EQUALS)

This class defines a compareTo(...) method but inherits its equals() method from java.lang.Object. Generally, the value of compareTo should return zero if and only if equals returns true. If this is violated, weird and unpredictable failures will occur in classes such as PriorityQueue. In Java 5 the PriorityQueue.remove method uses the compareTo method, while in Java 6 it uses the equals method.

From the JavaDoc for the compareTo method in the Comparable interface:

It is strongly recommended, but not strictly required that (x.compareTo(y)==0) == (x.equals(y)). Generally speaking, any class that implements the Comparable interface and violates this condition should clearly indicate this fact. The recommended language is “Note: this class has a natural ordering that is inconsistent with equals.”

HE: Class defines hashCode() and uses Object.equals() (HE_HASHCODE_USE_OBJECT_EQUALS)

This class defines a hashCode() method but inherits its equals() method from java.lang.Object (which defines equality by comparing object references). Although this will probably satisfy the contract that equal objects must have equal hashcodes, it is probably not what was intended by overriding the hashCode() method. (Overriding hashCode() implies that the object’s identity is based on criteria more complicated than simple reference equality.)

If you don’t think instances of this class will ever be inserted into a HashMap/HashTable, the recommended hashCode implementation to use is:

public int hashCode() {
    assert false : "hashCode not designed";
    return 42; // any arbitrary constant will do
}

HE: Class defines hashCode() but not equals() (HE_HASHCODE_NO_EQUALS)

This class defines a hashCode() method but not an equals() method. Therefore, the class may violate the invariant that equal objects must have equal hashcodes.

HE: Class defines equals() and uses Object.hashCode() (HE_EQUALS_USE_HASHCODE)

This class overrides equals(Object), but does not override hashCode(), and inherits the implementation of hashCode() from java.lang.Object (which returns the identity hash code, an arbitrary value assigned to the object by the VM). Therefore, the class is very likely to violate the invariant that equal objects must have equal hashcodes.

If you don’t think instances of this class will ever be inserted into a HashMap/HashTable, the recommended hashCode implementation to use is:

public int hashCode() {
    assert false : "hashCode not designed";
    return 42; // any arbitrary constant will do
}

HE: Class inherits equals() and uses Object.hashCode() (HE_INHERITS_EQUALS_USE_HASHCODE)

This class inherits equals(Object) from an abstract superclass, and hashCode() from java.lang.Object (which returns the identity hash code, an arbitrary value assigned to the object by the VM). Therefore, the class is very likely to violate the invariant that equal objects must have equal hashcodes.

If you don’t want to define a hashCode method, and/or don’t believe the object will ever be put into a HashMap/Hashtable, define the hashCode() method to throw UnsupportedOperationException.

HE: Class defines equals() but not hashCode() (HE_EQUALS_NO_HASHCODE)

This class overrides equals(Object), but does not override hashCode(). Therefore, the class may violate the invariant that equal objects must have equal hashcodes.

Eq: Abstract class defines covariant equals() method (EQ_ABSTRACT_SELF)

This class defines a covariant version of equals(). To correctly override the equals() method in java.lang.Object, the parameter of equals() must have type java.lang.Object.

Co: Abstract class defines covariant compareTo() method (CO_ABSTRACT_SELF)

This class defines a covariant version of compareTo(). To correctly override the compareTo() method in the Comparable interface, the parameter of compareTo() must have type java.lang.Object.

IC: Superclass uses subclass during initialization (IC_SUPERCLASS_USES_SUBCLASS_DURING_INITIALIZATION)

During the initialization of a class, the class makes an active use of a subclass. That subclass will not yet be initialized at the time of this use. For example, in the following code, foo will be null.

public class CircularClassInitialization {
    static class InnerClassSingleton extends CircularClassInitialization {
        static InnerClassSingleton singleton = new InnerClassSingleton();
    }
    static CircularClassInitialization foo = InnerClassSingleton.singleton;
}

SI: Static initializer creates instance before all static final fields assigned (SI_INSTANCE_BEFORE_FINALS_ASSIGNED)

The class’s static initializer creates an instance of the class before all of the static final fields are assigned.

It: Iterator next() method cannot throw NoSuchElementException (IT_NO_SUCH_ELEMENT)

This class implements the java.util.Iterator interface. However, its next() method is not capable of throwing java.util.NoSuchElementException. The next() method should be changed so it throws NoSuchElementException if is called when there are no more elements to return.

ME: Enum field is public and mutable (ME_MUTABLE_ENUM_FIELD)

A mutable public field is defined inside a public enum, thus can be changed by malicious code or by accident from another package. Though mutable enum fields may be used for lazy initialization, it’s a bad practice to expose them to the outer world. Consider declaring this field final and/or package-private.

ME: Public enum method unconditionally sets its field (ME_ENUM_FIELD_SETTER)

This public method declared in public enum unconditionally sets enum field, thus this field can be changed by malicious code or by accident from another package. Though mutable enum fields may be used for lazy initialization, it’s a bad practice to expose them to the outer world. Consider removing this method or declaring it package-private.

Nm: Method names should start with a lower case letter (NM_METHOD_NAMING_CONVENTION)

Methods should be verbs, in mixed case with the first letter lowercase, with the first letter of each internal word capitalized.

Nm: Non-final field names should start with a lower case letter, final fields should be uppercase with words separated by underscores (NM_FIELD_NAMING_CONVENTION)

Names of fields that are not final should be in mixed case with a lowercase first letter and the first letters of subsequent words capitalized. Names of final fields should be all uppercase with words separated by underscores (‘_’).

Nm: Class names shouldn’t shadow simple name of implemented interface (NM_SAME_SIMPLE_NAME_AS_INTERFACE)

This class/interface has a simple name that is identical to that of an implemented/extended interface, except that the interface is in a different package (e.g., alpha.Foo extends beta.Foo). This can be exceptionally confusing, create lots of situations in which you have to look at import statements to resolve references and creates many opportunities to accidentally define methods that do not override methods in their superclasses.

Nm: Class names shouldn’t shadow simple name of superclass (NM_SAME_SIMPLE_NAME_AS_SUPERCLASS)

This class has a simple name that is identical to that of its superclass, except that its superclass is in a different package (e.g., alpha.Foo extends beta.Foo). This can be exceptionally confusing, create lots of situations in which you have to look at import statements to resolve references and creates many opportunities to accidentally define methods that do not override methods in their superclasses.

Nm: Class names should start with an upper case letter (NM_CLASS_NAMING_CONVENTION)

Class names should be nouns, in mixed case with the first letter of each internal word capitalized. Try to keep your class names simple and descriptive. Use whole words-avoid acronyms and abbreviations (unless the abbreviation is much more widely used than the long form, such as URL or HTML).

Nm: Very confusing method names (but perhaps intentional) (NM_VERY_CONFUSING_INTENTIONAL)

The referenced methods have names that differ only by capitalization. This is very confusing because if the capitalization were identical then one of the methods would override the other. From the existence of other methods, it seems that the existence of both of these methods is intentional, but is sure is confusing. You should try hard to eliminate one of them, unless you are forced to have both due to frozen APIs.

Nm: Method doesn’t override method in superclass due to wrong package for parameter (NM_WRONG_PACKAGE_INTENTIONAL)

The method in the subclass doesn’t override a similar method in a superclass because the type of a parameter doesn’t exactly match the type of the corresponding parameter in the superclass. For example, if you have:

import alpha.Foo;
public class A {
    public int f(Foo x) { return 17; }
}
----
import beta.Foo;
public class B extends A {
    public int f(Foo x) { return 42; }
    public int f(alpha.Foo x) { return 27; }
}

The f(Foo) method defined in class B doesn’t override the f(Foo) method defined in class A, because the argument types are Foo‘s from different packages.

In this case, the subclass does define a method with a signature identical to the method in the superclass, so this is presumably understood. However, such methods are exceptionally confusing. You should strongly consider removing or deprecating the method with the similar but not identical signature.

Nm: Confusing method names (NM_CONFUSING)

The referenced methods have names that differ only by capitalization.

Nm: Class is not derived from an Exception, even though it is named as such (NM_CLASS_NOT_EXCEPTION)

This class is not derived from another exception, but ends with ‘Exception’. This will be confusing to users of this class.

RR: Method ignores results of InputStream.read() (RR_NOT_CHECKED)

This method ignores the return value of one of the variants of java.io.InputStream.read() which can return multiple bytes. If the return value is not checked, the caller will not be able to correctly handle the case where fewer bytes were read than the caller requested. This is a particularly insidious kind of bug, because in many programs, reads from input streams usually do read the full amount of data requested, causing the program to fail only sporadically.

RR: Method ignores results of InputStream.skip() (SR_NOT_CHECKED)

This method ignores the return value of java.io.InputStream.skip() which can skip multiple bytes. If the return value is not checked, the caller will not be able to correctly handle the case where fewer bytes were skipped than the caller requested. This is a particularly insidious kind of bug, because in many programs, skips from input streams usually do skip the full amount of data requested, causing the program to fail only sporadically. With Buffered streams, however, skip() will only skip data in the buffer, and will routinely fail to skip the requested number of bytes.

Se: Class is Serializable but its superclass doesn’t define a void constructor (SE_NO_SUITABLE_CONSTRUCTOR)

This class implements the Serializable interface and its superclass does not. When such an object is deserialized, the fields of the superclass need to be initialized by invoking the void constructor of the superclass. Since the superclass does not have one, serialization and deserialization will fail at runtime.

Se: Class is Externalizable but doesn’t define a void constructor (SE_NO_SUITABLE_CONSTRUCTOR_FOR_EXTERNALIZATION)

This class implements the Externalizable interface, but does not define a public void constructor. When Externalizable objects are deserialized, they first need to be constructed by invoking the public void constructor. Since this class does not have one, serialization and deserialization will fail at runtime.

Se: Comparator doesn’t implement Serializable (SE_COMPARATOR_SHOULD_BE_SERIALIZABLE)

This class implements the Comparator interface. You should consider whether or not it should also implement the Serializable interface. If a comparator is used to construct an ordered collection such as a TreeMap, then the TreeMap will be serializable only if the comparator is also serializable. As most comparators have little or no state, making them serializable is generally easy and good defensive programming.

SnVI: Class is Serializable, but doesn’t define serialVersionUID (SE_NO_SERIALVERSIONID)

This class implements the Serializable interface, but does not define a serialVersionUID field. A change as simple as adding a reference to a .class object will add synthetic fields to the class, which will unfortunately change the implicit serialVersionUID (e.g., adding a reference to String.class will generate a static field class$java$lang$String). Also, different source code to bytecode compilers may use different naming conventions for synthetic variables generated for references to class objects or inner classes. To ensure interoperability of Serializable across versions, consider adding an explicit serialVersionUID.

Se: The readResolve method must be declared with a return type of Object. (SE_READ_RESOLVE_MUST_RETURN_OBJECT)

In order for the readResolve method to be recognized by the serialization mechanism, it must be declared to have a return type of Object.

Se: Transient field that isn’t set by deserialization. (SE_TRANSIENT_FIELD_NOT_RESTORED)

This class contains a field that is updated at multiple places in the class, thus it seems to be part of the state of the class. However, since the field is marked as transient and not set in readObject or readResolve, it will contain the default value in any deserialized instance of the class.

Se: Prevent overwriting of externalizable objects (SE_PREVENT_EXT_OBJ_OVERWRITE)

The readExternal() method must be declared as public and is not protected from malicious callers, so the code permits any caller to reset the value of the object at any time.

To prevent overwriting of externalizable objects, you can use a Boolean flag that is set after the instance fields have been populated. You can also protect against race conditions by synchronizing on a private lock object.

Se: serialVersionUID isn’t final (SE_NONFINAL_SERIALVERSIONID)

This class defines a serialVersionUID field that is not final. The field should be made final if it is intended to specify the version UID for purposes of serialization.

Se: serialVersionUID isn’t static (SE_NONSTATIC_SERIALVERSIONID)

This class defines a serialVersionUID field that is not static. The field should be made static if it is intended to specify the version UID for purposes of serialization.

Se: serialVersionUID isn’t long (SE_NONLONG_SERIALVERSIONID)

This class defines a serialVersionUID field that is not long. The field should be made long if it is intended to specify the version UID for purposes of serialization.

Se: Non-transient non-serializable instance field in serializable class (SE_BAD_FIELD)

This Serializable class defines a non-primitive instance field which is neither transient, Serializable, or java.lang.Object, and does not appear to implement the Externalizable interface or the readObject() and writeObject() methods. Objects of this class will not be deserialized correctly if a non-Serializable object is stored in this field.

Se: Serializable inner class (SE_INNER_CLASS)

This Serializable class is an inner class. Any attempt to serialize it will also serialize the associated outer instance. The outer instance is serializable, so this won’t fail, but it might serialize a lot more data than intended. If possible, making the inner class a static inner class (also known as a nested class) should solve the problem.

Se: Non-serializable class has a serializable inner class (SE_BAD_FIELD_INNER_CLASS)

This Serializable class is an inner class of a non-serializable class. Thus, attempts to serialize it will also attempt to associate instance of the outer class with which it is associated, leading to a runtime error.

If possible, making the inner class a static inner class should solve the problem. Making the outer class serializable might also work, but that would mean serializing an instance of the inner class would always also serialize the instance of the outer class, which it often not what you really want.

Se: Non-serializable value stored into instance field of a serializable class (SE_BAD_FIELD_STORE)

A non-serializable value is stored into a non-transient field of a serializable class.

RV: Method ignores exceptional return value (RV_RETURN_VALUE_IGNORED_BAD_PRACTICE)

This method returns a value that is not checked. The return value should be checked since it can indicate an unusual or unexpected function execution. For example, the File.delete() method returns false if the file could not be successfully deleted (rather than throwing an Exception). If you don’t check the result, you won’t notice if the method invocation signals unexpected behavior by returning an atypical return value.

NP: toString method may return null (NP_TOSTRING_COULD_RETURN_NULL)

This toString method seems to return null in some circumstances. A liberal reading of the spec could be interpreted as allowing this, but it is probably a bad idea and could cause other code to break. Return the empty string or some other appropriate string rather than null.

NP: Clone method may return null (NP_CLONE_COULD_RETURN_NULL)

This clone method seems to return null in some circumstances, but clone is never allowed to return a null value. If you are convinced this path is unreachable, throw an AssertionError instead.

OS: Method may fail to close stream (OS_OPEN_STREAM)

The method creates an IO stream object, does not assign it to any fields, pass it to other methods that might close it, or return it, and does not appear to close the stream on all paths out of the method. This may result in a file descriptor leak. It is generally a good idea to use a finally block to ensure that streams are closed.

OS: Method may fail to close stream on exception (OS_OPEN_STREAM_EXCEPTION_PATH)

The method creates an IO stream object, does not assign it to any fields, pass it to other methods, or return it, and does not appear to close it on all possible exception paths out of the method. This may result in a file descriptor leak. It is generally a good idea to use a finally block to ensure that streams are closed.

RC: Suspicious reference comparison to constant (RC_REF_COMPARISON_BAD_PRACTICE)

This method compares a reference value to a constant using the == or != operator, where the correct way to compare instances of this type is generally with the equals() method. It is possible to create distinct instances that are equal but do not compare as == since they are different objects. Examples of classes which should generally not be compared by reference are java.lang.Integer, java.lang.Float, etc.

RC: Suspicious reference comparison of Boolean values (RC_REF_COMPARISON_BAD_PRACTICE_BOOLEAN)

This method compares two Boolean values using the == or != operator. Normally, there are only two Boolean values (Boolean.TRUE and Boolean.FALSE), but it is possible to create other Boolean objects using the new Boolean(b) constructor. It is best to avoid such objects, but if they do exist, then checking Boolean objects for equality using == or != will give results than are different than you would get using .equals(...).

FS: Format string should use %n rather than n (VA_FORMAT_STRING_USES_NEWLINE)

This format string includes a newline character (\n). In format strings, it is generally preferable to use %n, which will produce the platform-specific line separator. When using text blocks introduced in Java 15, use the \ escape sequence: String value = """ first line%n\ second line%n\ """;

BIT: Check for sign of bitwise operation (BIT_SIGNED_CHECK)

This method compares an expression such as ((event.detail & SWT.SELECTED) > 0). Using bit arithmetic and then comparing with the greater than operator can lead to unexpected results (of course depending on the value of SWT.SELECTED). If SWT.SELECTED is a negative number, this is a candidate for a bug. Even when SWT.SELECTED is not negative, it seems good practice to use ‘!= 0’ instead of ‘> 0’.

ODR: Method may fail to close database resource (ODR_OPEN_DATABASE_RESOURCE)

The method creates a database resource (such as a database connection or row set), does not assign it to any fields, pass it to other methods, or return it, and does not appear to close the object on all paths out of the method. Failure to close database resources on all paths out of a method may result in poor performance, and could cause the application to have problems communicating with the database.

ODR: Method may fail to close database resource on exception (ODR_OPEN_DATABASE_RESOURCE_EXCEPTION_PATH)

The method creates a database resource (such as a database connection or row set), does not assign it to any fields, pass it to other methods, or return it, and does not appear to close the object on all exception paths out of the method. Failure to close database resources on all paths out of a method may result in poor performance, and could cause the application to have problems communicating with the database.

ISC: Needless instantiation of class that only supplies static methods (ISC_INSTANTIATE_STATIC_CLASS)

This class allocates an object that is based on a class that only supplies static methods. This object does not need to be created, just access the static methods directly using the class name as a qualifier.

DMI: Random object created and used only once (DMI_RANDOM_USED_ONLY_ONCE)

This code creates a java.util.Random object, uses it to generate one random number, and then discards the Random object. This produces mediocre quality random numbers and is inefficient. If possible, rewrite the code so that the Random object is created once and saved, and each time a new random number is required invoke a method on the existing Random object to obtain it.

If it is important that the generated Random numbers not be guessable, you must not create a new Random for each random number; the values are too easily guessable. You should strongly consider using a java.security.SecureRandom instead (and avoid allocating a new SecureRandom for each random number needed).

BC: Equals method should not assume anything about the type of its argument (BC_EQUALS_METHOD_SHOULD_WORK_FOR_ALL_OBJECTS)

The equals(Object o) method shouldn’t make any assumptions about the type of o. It should simply return false if o is not the same type as this.

J2EE: Store of non serializable object into HttpSession (J2EE_STORE_OF_NON_SERIALIZABLE_OBJECT_INTO_SESSION)

This code seems to be storing a non-serializable object into an HttpSession. If this session is passivated or migrated, an error will result.

GC: Unchecked type in generic call (GC_UNCHECKED_TYPE_IN_GENERIC_CALL)

This call to a generic collection method passes an argument while compile type Object where a specific type from the generic type parameters is expected. Thus, neither the standard Java type system nor static analysis can provide useful information on whether the object being passed as a parameter is of an appropriate type.

PZ: Don’t reuse entry objects in iterators (PZ_DONT_REUSE_ENTRY_OBJECTS_IN_ITERATORS)

The entrySet() method is allowed to return a view of the underlying Map in which an Iterator and Map.Entry. This clever idea was used in several Map implementations, but introduces the possibility of nasty coding mistakes. If a map m returns such an iterator for an entrySet, then c.addAll(m.entrySet()) will go badly wrong. All of the Map implementations in OpenJDK 7 have been rewritten to avoid this, you should too.

DMI: Adding elements of an entry set may fail due to reuse of Entry objects (DMI_ENTRY_SETS_MAY_REUSE_ENTRY_OBJECTS)

The entrySet() method is allowed to return a view of the underlying Map in which a single Entry object is reused and returned during the iteration. As of Java 6, both IdentityHashMap and EnumMap did so. When iterating through such a Map, the Entry value is only valid until you advance to the next iteration. If, for example, you try to pass such an entrySet to an addAll method, things will go badly wrong.

DMI: Don’t use removeAll to clear a collection (DMI_USING_REMOVEALL_TO_CLEAR_COLLECTION)

If you want to remove all elements from a collection c, use c.clear, not c.removeAll(c). Calling c.removeAll(c) to clear a collection is less clear, susceptible to errors from typos, less efficient and for some collections, might throw a ConcurrentModificationException.

THROWS: Method intentionally throws RuntimeException. (THROWS_METHOD_THROWS_RUNTIMEEXCEPTION)

Method intentionally throws RuntimeException.
According to the SEI CERT ERR07-J rule, throwing a RuntimeException may cause errors, like the caller not being able to examine the exception and therefore cannot properly recover from it.
Moreover, throwing a RuntimeException would force the caller to catch RuntimeException and therefore violate the SEI CERT ERR08-J rule.
Please note that you can derive from Exception or RuntimeException and may throw a new instance of that exception.

THROWS: Method lists Exception in its throws clause. (THROWS_METHOD_THROWS_CLAUSE_BASIC_EXCEPTION)

Method lists Exception in its throws clause.
When declaring a method, the types of exceptions in the throws clause should be the most specific. Therefore, using Exception in the throws clause would force the caller to either use it in its own throws clause, or use it in a try-catch block (when it does not necessarily contain any meaningful information about the thrown exception).

For more information, see the SEI CERT ERR07-J rule.

THROWS: Method lists Throwable in its throws clause. (THROWS_METHOD_THROWS_CLAUSE_THROWABLE)

Method lists Throwable in its throws clause.
When declaring a method, the types of exceptions in the throws clause should be the most specific. Therefore, using Throwable in the throws clause would force the caller to either use it in its own throws clause, or use it in a try-catch block (when it does not necessarily contain any meaningful information about the thrown exception).
Furthermore, using Throwable like that is semantically a bad practice, considered that Throwables include Errors as well, but by definition they occur in unrecoverable scenarios.

For more information, see the SEI CERT ERR07-J rule.

PA: Primitive field is public (PA_PUBLIC_PRIMITIVE_ATTRIBUTE)

SEI CERT rule OBJ01-J requires that accessibility to fields must be limited. Otherwise, the values of the fields may be manipulated from outside the class, which may be unexpected or undesired behaviour. In general, requiring that no fields are allowed to be public is overkill and unrealistic. Even the rule mentions that final fields may be public. Besides final fields, there may be other usages for public fields: some public fields may serve as “flags” that affect the behavior of the class. Such flag fields are expected to be read by the current instance (or the current class, in case of static fields), but written by others. If a field is both written by the methods of the current instance (or the current class, in case of static fields) and from the outside, the code is suspicious. Consider making these fields private and provide appropriate setters, if necessary. Please note that constructors, initializers and finalizers are exceptions, if only they write the field inside the class, the field is not considered as written by the class itself.

PA: Array-type field is public (PA_PUBLIC_ARRAY_ATTRIBUTE)

SEI CERT rule OBJ01-J requires that accessibility of fields must be limited. Making an array-type field final does not prevent other classes from modifying the contents of the array. However, in general, requiring that no fields are allowed to be public is overkill and unrealistic. There may be usages for public fields: some public fields may serve as “flags” that affect the behavior of the class. Such flag fields are expected to be read by the current instance (or the current class, in case of static fields), but written by others. If a field is both written by the methods of the current instance (or the current class, in case of static fields) and from the outside, the code is suspicious. Consider making these fields private and provide appropriate setters, if necessary. Please note that constructors, initializers and finalizers are exceptions, if only they write the field inside the class, the field is not considered as written by the class itself.

PA: Mutable object-type field is public (PA_PUBLIC_MUTABLE_OBJECT_ATTRIBUTE)

SEI CERT rule OBJ01-J requires that accessibility of fields must be limited. Making a mutable object-type field final does not prevent other classes from modifying the contents of the object. However, in general, requiring that no fields are allowed to be public is overkill and unrealistic. There may be usages for public fields: some public fields may serve as “flags” that affect the behavior of the class. Such flag fields are expected to be read by the current instance (or the current class, in case of static fields), but written by others. If a field is both written by the methods of the current instance (or the current class, in case of static fields) and from the outside, the code is suspicious. Consider making these fields private and provide appropriate setters, if necessary. Please note that constructors, initializers and finalizers are exceptions, if only they write the field inside the class, the field is not considered as written by the class itself. In case of object-type fields “writing” means calling methods whose name suggest modification.

PI: Do not reuse public identifiers from JSL as class name (PI_DO_NOT_REUSE_PUBLIC_IDENTIFIERS_CLASS_NAMES)

It’s a good practice to avoid reusing public identifiers from the Java Standard Library as class names. This is because the Java Standard Library is a part of the Java platform and is expected to be available in all Java environments. Doing so can lead to naming conflicts and confusion, making it harder to understand and maintain the code. It’s best practice to choose unique and descriptive class names that accurately represent the purpose and functionality of your own code. To provide an example, let’s say you want to create a class for handling dates in your application. Instead of using a common name like “Date”, which conflicts with the existing java.util.Date class, you could choose a more specific and unique name like or “AppDate” or “DisplayDate”. A few key points to keep in mind when choosing names as identifier:

• Use meaningful prefixes or namespaces: Prepend a project-specific prefix or namespace to your class names to make them distinct. For example, if your project is named “MyApp”, you could use “MyAppDate” as your class name.
• Use descriptive names: Opt for descriptive class names that clearly indicate their purpose and functionality. This helps avoid shadowing existing Java Standard Library identifiers. For instance, instead of “List”, consider using “CustomAppList”.
• Follow naming conventions: Adhere to Java’s naming conventions, such as using camel case (e.g., MyClass) for class names. This promotes code readability and reduces the chances of conflicts.

See SEI CERT rule DCL01-J. Do not reuse public identifiers from the Java Standard Library.

PI: Do not reuse public identifiers from JSL as field name (PI_DO_NOT_REUSE_PUBLIC_IDENTIFIERS_FIELD_NAMES)

It is a good practice to avoid reusing public identifiers from the Java Standard Library as field names in your code. Doing so can lead to confusion and potential conflicts, making it harder to understand and maintain your codebase. Instead, it is recommended to choose unique and descriptive names for your fields that accurately represent their purpose and differentiate them from Standard Library identifiers. To provide an example, let’s say you want to create a class for handling dates in your application. Instead of using a common name like “Date”, which conflicts with the existing java.util.Date class, you could choose a more specific and unique name like or “AppDate” or “DisplayDate”. For example, let’s say you’re creating a class to represent a car in your application. Instead of using a common name like “Component” as a field, which conflicts with the existing java.awt.Component class, you should opt for a more specific and distinct name, such as “VehiclePart” or “CarComponent”. A few key points to keep in mind when choosing names as identifier:

• Use descriptive names: Opt for descriptive field names that clearly indicate their purpose and functionality. This helps avoid shadowing existing Java Standard Library identifiers. For instance, instead of “list”, consider using “myFancyList”
• Follow naming conventions: Adhere to Java’s naming conventions, such as using mixed case for field names. Start with a lowercase first letter and the internal words should start with capital letters (e.g., myFieldUsesMixedCase). This promotes code readability and reduces the chances of conflicts.

See SEI CERT rule DCL01-J. Do not reuse public identifiers from the Java Standard Library.

PI: Do not reuse public identifiers from JSL as method name (PI_DO_NOT_REUSE_PUBLIC_IDENTIFIERS_METHOD_NAMES)

It is a good practice to avoid reusing public identifiers from the Java Standard Library as method names in your code. Doing so can lead to confusion, potential conflicts, and unexpected behavior. To maintain code clarity and ensure proper functionality, it is recommended to choose unique and descriptive names for your methods that accurately represent their purpose and differentiate them from standard library identifiers. To provide an example, let’s say you want to create a method that handles creation of a custom file in your application. Instead of using a common name like “File” for the method, which conflicts with the existing java.io.File class, you could choose a more specific and unique name like or “generateFile” or “createOutPutFile”. A few key points to keep in mind when choosing names as identifier:

• Use descriptive names: Opt for descriptive method names that clearly indicate their purpose and functionality. This helps avoid shadowing existing Java Standard Library identifiers. For instance, instead of “abs()”, consider using “calculateAbsoluteValue()”.
• Follow naming conventions: Adhere to Java’s naming conventions, such as using mixed case for method names. Method names should be verbs, with the first letter lowercase and the first letter of each internal word capitalized (e.g. runFast()). This promotes code readability and reduces the chances of conflicts.

See SEI CERT rule DCL01-J. Do not reuse public identifiers from the Java Standard Library.

PI: Do not reuse public identifiers from JSL as method name (PI_DO_NOT_REUSE_PUBLIC_IDENTIFIERS_LOCAL_VARIABLE_NAMES)

When declaring local variables in Java, it is a good practice to refrain from reusing public identifiers from the Java Standard Library. Reusing these identifiers as local variable names can lead to confusion, hinder code comprehension, and potentially cause conflicts with existing publicly available identifier names from the Java Standard Library. To maintain code clarity and avoid such issues, it is best practice to select unique and descriptive names for your local variables. To provide an example, let’s say you want to store a custom font value in a variable. Instead of using a common name like “Font” for the variable name, which conflicts with the existing java.awt.Font class, you could choose a more specific and unique name like or “customFont” or “loadedFontName”. A few key points to keep in mind when choosing names as identifier:

• Use descriptive names: Opt for descriptive variable names that clearly indicate their purpose and functionality. This helps avoid shadowing existing Java Standard Library identifiers. For instance, instead of “variable”, consider using “myVariableName”.
• Follow naming conventions: Adhere to Java’s naming conventions, such as using mixed case for variable names. Start with a lowercase first letter and the internal words should start with capital letters (e.g. myVariableName). This promotes code readability and reduces the chances of conflicts.

See SEI CERT rule DCL01-J. Do not reuse public identifiers from the Java Standard Library.

ENV: It is preferable to use portable Java property instead of environment variable. (ENV_USE_PROPERTY_INSTEAD_OF_ENV)

Environment variables are not portable, the variable name itself (not only the value) may be different depending on the running OS. Not only the names of the specific environment variables can differ (e.g. `USERNAME` in Windows and `USER` in Unix systems), but even the semantics differ, e.g. the case sensitivity (Windows being case-insensitive and Unix case-sensitive). Moreover, the Map of the environment variables returned by java.lang.System.getenv() and its collection views may not obey the general contract of the Object.equals(java.lang.Object) and Object.hashCode() methods. Consequently, using environment variables may have unintended side effects. Also, the visibility of environment variables is less restricted compared to Java Properties: they are visible to all descendants of the defining process, not just the immediate Java subprocess. For these reasons, even the Java API of java.lang.System advises to use Java properties (java.lang.System.getProperty(java.lang.String)) instead of environment variables (java.lang.System.getenv(java.lang.String)) where possible.

If a value can be accessed through both System.getProperty() and System.getenv(), it should be accessed using the former.

Mapping of corresponding Java System properties:

See SEI CERT rule ENV02-J. Do not trust the values of environment variables.

Correctness (CORRECTNESS)

Probable bug - an apparent coding mistake resulting in code that was probably not what the developer intended. We strive for a low false positive rate.

CN: Super method is annotated with @OverridingMethodsMustInvokeSuper, but the overriding method isn’t calling the super method. (OVERRIDING_METHODS_MUST_INVOKE_SUPER)

Super method is annotated with @OverridingMethodsMustInvokeSuper, but the overriding method isn’t calling the super method.

NP: Method with Optional return type returns explicit null (NP_OPTIONAL_RETURN_NULL)

The usage of Optional return type (java.util.Optional or com.google.common.base.Optional) always means that explicit null returns were not desired by design. Returning a null value in such case is a contract violation and will most likely break client code.

NP: Non-null field is not initialized (NP_NONNULL_FIELD_NOT_INITIALIZED_IN_CONSTRUCTOR)

The field is marked as non-null, but isn’t written to by the constructor. The field might be initialized elsewhere during constructor, or might always be initialized before use.

VR: Class makes reference to unresolvable class or method (VR_UNRESOLVABLE_REFERENCE)

This class makes a reference to a class or method that cannot be resolved using against the libraries it is being analyzed with.

IL: An apparent infinite loop (IL_INFINITE_LOOP)

This loop doesn’t seem to have a way to terminate (other than by perhaps throwing an exception).

IO: Doomed attempt to append to an object output stream (IO_APPENDING_TO_OBJECT_OUTPUT_STREAM)

This code opens a file in append mode and then wraps the result in an object output stream like as follows:

OutputStream out = new FileOutputStream(anyFile, true);
new ObjectOutputStream(out);

This won’t allow you to append to an existing object output stream stored in a file. If you want to be able to append to an object output stream, you need to keep the object output stream open.

The only situation in which opening a file in append mode and the writing an object output stream could work is if on reading the file you plan to open it in random access mode and seek to the byte offset where the append started.

IL: An apparent infinite recursive loop (IL_INFINITE_RECURSIVE_LOOP)

This method unconditionally invokes itself. This would seem to indicate an infinite recursive loop that will result in a stack overflow.

IL: A collection is added to itself (IL_CONTAINER_ADDED_TO_ITSELF)

A collection is added to itself. As a result, computing the hashCode of this set will throw a StackOverflowException.

RpC: Repeated conditional tests (RpC_REPEATED_CONDITIONAL_TEST)

The code contains a conditional test is performed twice, one right after the other (e.g., x == 0 || x == 0). Perhaps the second occurrence is intended to be something else (e.g., x == 0 || y == 0).

FL: Method performs math using floating point precision (FL_MATH_USING_FLOAT_PRECISION)

The method performs math operations using floating point precision. Floating point precision is very imprecise. For example, 16777216.0f + 1.0f = 16777216.0f. Consider using double math instead.

CAA: Possibly incompatible element is stored in covariant array (CAA_COVARIANT_ARRAY_ELEMENT_STORE)

Value is stored into the array and the value type doesn’t match the array type. It’s known from the analysis that actual array type is narrower than the declared type of its variable or field and this assignment doesn’t satisfy the original array type. This assignment may cause ArrayStoreException at runtime.

Dm: Useless/vacuous call to EasyMock method (DMI_VACUOUS_CALL_TO_EASYMOCK_METHOD)

This call doesn’t pass any objects to the EasyMock method, so the call doesn’t do anything.

Dm: Futile attempt to change max pool size of ScheduledThreadPoolExecutor (DMI_FUTILE_ATTEMPT_TO_CHANGE_MAXPOOL_SIZE_OF_SCHEDULED_THREAD_POOL_EXECUTOR)

(Javadoc) While ScheduledThreadPoolExecutor inherits from ThreadPoolExecutor, a few of the inherited tuning methods are not useful for it. In particular, because it acts as a fixed-sized pool using corePoolSize threads and an unbounded queue, adjustments to maximumPoolSize have no useful effect.

DMI: BigDecimal constructed from double that isn’t represented precisely (DMI_BIGDECIMAL_CONSTRUCTED_FROM_DOUBLE)

This code creates a BigDecimal from a double value that doesn’t translate well to a decimal number. For example, one might assume that writing new BigDecimal(0.1) in Java creates a BigDecimal which is exactly equal to 0.1 (an unscaled value of 1, with a scale of 1), but it is actually equal to 0.1000000000000000055511151231257827021181583404541015625. You probably want to use the BigDecimal.valueOf(double d) method, which uses the String representation of the double to create the BigDecimal (e.g., BigDecimal.valueOf(0.1) gives 0.1).

Dm: Creation of ScheduledThreadPoolExecutor with zero core threads (DMI_SCHEDULED_THREAD_POOL_EXECUTOR_WITH_ZERO_CORE_THREADS)

(Javadoc) A ScheduledThreadPoolExecutor with zero core threads will never execute anything; changes to the max pool size are ignored.

Dm: Cannot use reflection to check for presence of annotation without runtime retention (DMI_ANNOTATION_IS_NOT_VISIBLE_TO_REFLECTION)

Unless an annotation has itself been annotated with @Retention(RetentionPolicy.RUNTIME), the annotation cannot be observed using reflection (e.g., by using the isAnnotationPresent method). .

NP: Method does not check for null argument (NP_ARGUMENT_MIGHT_BE_NULL)

A parameter to this method has been identified as a value that should always be checked to see whether or not it is null, but it is being dereferenced without a preceding null check.

RV: Bad attempt to compute absolute value of signed random integer (RV_ABSOLUTE_VALUE_OF_RANDOM_INT)

This code generates a random signed integer and then computes the absolute value of that random integer. If the number returned by the random number generator is Integer.MIN_VALUE, then the result will be negative as well (since Math.abs(Integer.MIN_VALUE) == Integer.MIN_VALUE). (Same problem arises for long values as well).

RV: Bad attempt to compute absolute value of signed 32-bit hashcode (RV_ABSOLUTE_VALUE_OF_HASHCODE)

This code generates a hashcode and then computes the absolute value of that hashcode. If the hashcode is Integer.MIN_VALUE, then the result will be negative as well (since Math.abs(Integer.MIN_VALUE) == Integer.MIN_VALUE).

One out of 2^32 strings have a hashCode of Integer.MINVALUE, including “polygenelubricants” “GydZG“ and “”DESIGNING WORKHOUSES”.

RV: Random value from 0 to 1 is coerced to the integer 0 (RV_01_TO_INT)

A random value from 0 to 1 is being coerced to the integer value 0. You probably want to multiply the random value by something else before coercing it to an integer, or use the Random.nextInt(n) method.

Dm: Incorrect combination of Math.max and Math.min (DM_INVALID_MIN_MAX)

This code tries to limit the value bounds using the construct like Math.min(0, Math.max(100, value)). However the order of the constants is incorrect: it should be Math.min(100, Math.max(0, value)). As the result this code always produces the same result (or NaN if the value is NaN).

Eq: equals method compares class names rather than class objects (EQ_COMPARING_CLASS_NAMES)

This class defines an equals method that checks to see if two objects are the same class by checking to see if the names of their classes are equal. You can have different classes with the same name if they are loaded by different class loaders. Just check to see if the class objects are the same.

Eq: equals method always returns true (EQ_ALWAYS_TRUE)

This class defines an equals method that always returns true. This is imaginative, but not very smart. Plus, it means that the equals method is not symmetric.

Eq: equals method always returns false (EQ_ALWAYS_FALSE)

This class defines an equals method that always returns false. This means that an object is not equal to itself, and it is impossible to create useful Maps or Sets of this class. More fundamentally, it means that equals is not reflexive, one of the requirements of the equals method.

The likely intended semantics are object identity: that an object is equal to itself. This is the behavior inherited from class Object. If you need to override an equals inherited from a different superclass, you can use:

public boolean equals(Object o) {
return this == o;
}

Eq: equals method overrides equals in superclass and may not be symmetric (EQ_OVERRIDING_EQUALS_NOT_SYMMETRIC)

This class defines an equals method that overrides an equals method in a superclass. Both equals methods use instanceof in the determination of whether two objects are equal. This is fraught with peril, since it is important that the equals method is symmetrical (in other words, a.equals(b) == b.equals(a)). If B is a subtype of A, and A’s equals method checks that the argument is an instanceof A, and B’s equals method checks that the argument is an instanceof B, it is quite likely that the equivalence relation defined by these methods is not symmetric.

Eq: Covariant equals() method defined for enum (EQ_DONT_DEFINE_EQUALS_FOR_ENUM)

This class defines an enumeration, and equality on enumerations are defined using object identity. Defining a covariant equals method for an enumeration value is exceptionally bad practice, since it would likely result in having two different enumeration values that compare as equals using the covariant enum method, and as not equal when compared normally. Don’t do it.

Eq: Covariant equals() method defined, Object.equals(Object) inherited (EQ_SELF_USE_OBJECT)

This class defines a covariant version of the equals() method, but inherits the normal equals(Object) method defined in the base java.lang.Object class. The class should probably define a boolean equals(Object) method.

Eq: equals() method defined that doesn’t override Object.equals(Object) (EQ_OTHER_USE_OBJECT)

This class defines an equals() method, that doesn’t override the normal equals(Object) method defined in the base java.lang.Object class. The class should probably define a boolean equals(Object) method.

Eq: equals() method defined that doesn’t override equals(Object) (EQ_OTHER_NO_OBJECT)

This class defines an equals() method, that doesn’t override the normal equals(Object) method defined in the base java.lang.Object class. Instead, it inherits an equals(Object) method from a superclass. The class should probably define a boolean equals(Object) method.

HE: Signature declares use of unhashable class in hashed construct (HE_SIGNATURE_DECLARES_HASHING_OF_UNHASHABLE_CLASS)

A method, field or class declares a generic signature where a non-hashable class is used in context where a hashable class is required. A class that declares an equals method but inherits a hashCode() method from Object is unhashable, since it doesn’t fulfill the requirement that equal objects have equal hashCodes.

HE: Use of class without a hashCode() method in a hashed data structure (HE_USE_OF_UNHASHABLE_CLASS)

A class defines an equals(Object) method but not a hashCode() method, and thus doesn’t fulfill the requirement that equal objects have equal hashCodes. An instance of this class is used in a hash data structure, making the need to fix this problem of highest importance.

UR: Uninitialized read of field in constructor (UR_UNINIT_READ)

This constructor reads a field which has not yet been assigned a value. This is often caused when the programmer mistakenly uses the field instead of one of the constructor’s parameters.

UR: Uninitialized read of field method called from constructor of superclass (UR_UNINIT_READ_CALLED_FROM_SUPER_CONSTRUCTOR)

This method is invoked in the constructor of the superclass. At this point, the fields of the class have not yet initialized.

To make this more concrete, consider the following classes:

abstract class A {
int hashCode;
abstract Object getValue();
    A() {
        hashCode = getValue().hashCode();
    }
}
class B extends A {
Object value;
    B(Object v) {
        this.value = v;
    }
    Object getValue() {
        return value;
    }
}

When a B is constructed, the constructor for the A class is invoked before the constructor for B sets value. Thus, when the constructor for A invokes getValue, an uninitialized value is read for value.

Nm: Very confusing method names (NM_VERY_CONFUSING)

The referenced methods have names that differ only by capitalization. This is very confusing because if the capitalization were identical then one of the methods would override the other.

Nm: Method doesn’t override method in superclass due to wrong package for parameter (NM_WRONG_PACKAGE)

The method in the subclass doesn’t override a similar method in a superclass because the type of a parameter doesn’t exactly match the type of the corresponding parameter in the superclass. For example, if you have:

import alpha.Foo;
public class A {
public int f(Foo x) { return 17; }
}
----
import beta.Foo;
public class B extends A {
public int f(Foo x) { return 42; }
}

The f(Foo) method defined in class B doesn’t override the f(Foo) method defined in class A, because the argument types are Foo‘s from different packages.

Nm: Apparent method/constructor confusion (NM_METHOD_CONSTRUCTOR_CONFUSION)

This regular method has the same name as the class it is defined in. It is likely that this was intended to be a constructor. If it was intended to be a constructor, remove the declaration of a void return value. If you had accidentally defined this method, realized the mistake, defined a proper constructor but cannot get rid of this method due to backwards compatibility, deprecate the method.

Nm: Class defines hashcode(); should it be hashCode()? (NM_LCASE_HASHCODE)

This class defines a method called hashcode(). This method does not override the hashCode() method in java.lang.Object, which is probably what was intended.

Nm: Class defines tostring(); should it be toString()? (NM_LCASE_TOSTRING)

This class defines a method called tostring(). This method does not override the toString() method in java.lang.Object, which is probably what was intended.

Nm: Class defines equal(Object); should it be equals(Object)? (NM_BAD_EQUAL)

This class defines a method equal(Object). This method does not override the equals(Object) method in java.lang.Object, which is probably what was intended.

Se: The readResolve method must not be declared as a static method. (SE_READ_RESOLVE_IS_STATIC)

In order for the readResolve method to be recognized by the serialization mechanism, it must not be declared as a static method.

Se: Method must be private in order for serialization to work (SE_METHOD_MUST_BE_PRIVATE)

This class implements the Serializable interface, and defines a method for custom serialization/deserialization. But since that method isn’t declared private, it will be silently ignored by the serialization/deserialization API.

SF: Dead store due to switch statement fall through (SF_DEAD_STORE_DUE_TO_SWITCH_FALLTHROUGH)

A value stored in the previous switch case is overwritten here due to a switch fall through. It is likely that you forgot to put a break or return at the end of the previous case.

SF: Dead store due to switch statement fall through to throw (SF_DEAD_STORE_DUE_TO_SWITCH_FALLTHROUGH_TO_THROW)

A value stored in the previous switch case is ignored here due to a switch fall through to a place where an exception is thrown. It is likely that you forgot to put a break or return at the end of the previous case.

NP: Read of unwritten field (NP_UNWRITTEN_FIELD)

The program is dereferencing a field that does not seem to ever have a non-null value written to it. Unless the field is initialized via some mechanism not seen by the analysis, dereferencing this value will generate a null pointer exception.

UwF: Field only ever set to null (UWF_NULL_FIELD)

All writes to this field are of the constant value null, and thus all reads of the field will return null. Check for errors, or remove it if it is useless.

UwF: Unwritten field (UWF_UNWRITTEN_FIELD)

This field is never written. All reads of it will return the default value. Check for errors (should it have been initialized?), or remove it if it is useless.

SIC: Deadly embrace of non-static inner class and thread local (SIC_THREADLOCAL_DEADLY_EMBRACE)

This class is an inner class, but should probably be a static inner class. As it is, there is a serious danger of a deadly embrace between the inner class and the thread local in the outer class. Because the inner class isn’t static, it retains a reference to the outer class. If the thread local contains a reference to an instance of the inner class, the inner and outer instance will both be reachable and not eligible for garbage collection.

RANGE: Array index is out of bounds (RANGE_ARRAY_INDEX)

Array operation is performed, but array index is out of bounds, which will result in ArrayIndexOutOfBoundsException at runtime.

RANGE: Array offset is out of bounds (RANGE_ARRAY_OFFSET)

Method is called with array parameter and offset parameter, but the offset is out of bounds. This will result in IndexOutOfBoundsException at runtime.

RANGE: Array length is out of bounds (RANGE_ARRAY_LENGTH)

Method is called with array parameter and length parameter, but the length is out of bounds. This will result in IndexOutOfBoundsException at runtime.

RANGE: String index is out of bounds (RANGE_STRING_INDEX)

String method is called and specified string index is out of bounds. This will result in StringIndexOutOfBoundsException at runtime.

RV: Method ignores return value (RV_RETURN_VALUE_IGNORED)

The return value of this method should be checked. One common cause of this warning is to invoke a method on an immutable object, thinking that it updates the object. For example, in the following code fragment,

String dateString = getHeaderField(name);
dateString.trim();

the programmer seems to be thinking that the trim() method will update the String referenced by dateString. But since Strings are immutable, the trim() function returns a new String value, which is being ignored here. The code should be corrected to:

String dateString = getHeaderField(name);
dateString = dateString.trim();

RV: Exception created and dropped rather than thrown (RV_EXCEPTION_NOT_THROWN)

This code creates an exception (or error) object, but doesn’t do anything with it. For example, something like

if (x < 0) {
new IllegalArgumentException("x must be nonnegative");
}

It was probably the intent of the programmer to throw the created exception:

if (x < 0) {
throw new IllegalArgumentException("x must be nonnegative");
}

RV: Code checks for specific values returned by compareTo (RV_CHECK_COMPARETO_FOR_SPECIFIC_RETURN_VALUE)

This code invoked a compareTo or compare method, and checks to see if the return value is a specific value, such as 1 or -1. When invoking these methods, you should only check the sign of the result, not for any specific non-zero value. While many or most compareTo and compare methods only return -1, 0 or 1, some of them will return other values.

NP: Null pointer dereference (NP_ALWAYS_NULL)

A null pointer is dereferenced here. This will lead to a NullPointerException when the code is executed.

NP: close() invoked on a value that is always null (NP_CLOSING_NULL)

close() is being invoked on a value that is always null. If this statement is executed, a null pointer exception will occur. But the big risk here you never close something that should be closed.

NP: Store of null value into field annotated @Nonnull (NP_STORE_INTO_NONNULL_FIELD)

A value that could be null is stored into a field that has been annotated as @Nonnull.

NP: Null pointer dereference in method on exception path (NP_ALWAYS_NULL_EXCEPTION)

A pointer which is null on an exception path is dereferenced here. This will lead to a NullPointerException when the code is executed. Note that because SpotBugs currently does not prune infeasible exception paths, this may be a false warning.

Also note that SpotBugs considers the default case of a switch statement to be an exception path, since the default case is often infeasible.

NP: Possible null pointer dereference (NP_NULL_ON_SOME_PATH)

There is a branch of statement that, if executed, guarantees that a null value will be dereferenced, which would generate a NullPointerException when the code is executed. Of course, the problem might be that the branch or statement is infeasible and that the null pointer exception cannot ever be executed; deciding that is beyond the ability of SpotBugs.

NP: Possible null pointer dereference in method on exception path (NP_NULL_ON_SOME_PATH_EXCEPTION)

A reference value which is null on some exception control path is dereferenced here. This may lead to a NullPointerException when the code is executed. Note that because SpotBugs currently does not prune infeasible exception paths, this may be a false warning.

Also note that SpotBugs considers the default case of a switch statement to be an exception path, since the default case is often infeasible.

NP: Method call passes null for non-null parameter (NP_NULL_PARAM_DEREF)

This method call passes a null value for a non-null method parameter. Either the parameter is annotated as a parameter that should always be non-null, or analysis has shown that it will always be dereferenced.

NP: Non-virtual method call passes null for non-null parameter (NP_NULL_PARAM_DEREF_NONVIRTUAL)

A possibly-null value is passed to a non-null method parameter. Either the parameter is annotated as a parameter that should always be non-null, or analysis has shown that it will always be dereferenced.

NP: Method call passes null for non-null parameter (NP_NULL_PARAM_DEREF_ALL_TARGETS_DANGEROUS)

A possibly-null value is passed at a call site where all known target methods require the parameter to be non-null. Either the parameter is annotated as a parameter that should always be non-null, or analysis has shown that it will always be dereferenced.

NP: Method call passes null to a non-null parameter (NP_NONNULL_PARAM_VIOLATION)

This method passes a null value as the parameter of a method which must be non-null. Either this parameter has been explicitly marked as @Nonnull, or analysis has determined that this parameter is always dereferenced.

NP: Method may return null, but is declared @Nonnull (NP_NONNULL_RETURN_VIOLATION)

This method may return a null value, but the method (or a superclass method which it overrides) is declared to return @Nonnull.

NP: Null value is guaranteed to be dereferenced (NP_GUARANTEED_DEREF)

There is a statement or branch that if executed guarantees that a value is null at this point, and that value that is guaranteed to be dereferenced (except on forward paths involving runtime exceptions).

Note that a check such as if (x == null) throw new NullPointerException(); is treated as a dereference of x.

NP: Value is null and guaranteed to be dereferenced on exception path (NP_GUARANTEED_DEREF_ON_EXCEPTION_PATH)

There is a statement or branch on an exception path that if executed guarantees that a value is null at this point, and that value that is guaranteed to be dereferenced (except on forward paths involving runtime exceptions).

DMI: Reversed method arguments (DMI_ARGUMENTS_WRONG_ORDER)

The arguments to this method call seem to be in the wrong order. For example, a call Preconditions.checkNotNull("message", message) has reserved arguments: the value to be checked is the first argument.

RCN: Nullcheck of value previously dereferenced (RCN_REDUNDANT_NULLCHECK_WOULD_HAVE_BEEN_A_NPE)

A value is checked here to see whether it is null, but this value cannot be null because it was previously dereferenced and if it were null a null pointer exception would have occurred at the earlier dereference. Essentially, this code and the previous dereference disagree as to whether this value is allowed to be null. Either the check is redundant or the previous dereference is erroneous.

RC: Suspicious reference comparison (RC_REF_COMPARISON)

This method compares two reference values using the == or != operator, where the correct way to compare instances of this type is generally with the equals() method. It is possible to create distinct instances that are equal but do not compare as == since they are different objects. Examples of classes which should generally not be compared by reference are java.lang.Integer, java.lang.Float, etc. RC_REF_COMPARISON covers only wrapper types for primitives. Suspicious types list can be extended by adding frc.suspicious system property with comma-separated classes:

<systemPropertyVariables>
              <frc.suspicious>java.time.LocalDate,java.util.List</frc.suspicious>
           </systemPropertyVariables>

VA: Primitive array passed to function expecting a variable number of object arguments (VA_PRIMITIVE_ARRAY_PASSED_TO_OBJECT_VARARG)

This code passes a primitive array to a function that takes a variable number of object arguments. This creates an array of length one to hold the primitive array and passes it to the function.

EC: equals() used to compare array and nonarray (EC_ARRAY_AND_NONARRAY)

This method invokes the .equals(Object o) to compare an array and a reference that doesn’t seem to be an array. If things being compared are of different types, they are guaranteed to be unequal and the comparison is almost certainly an error. Even if they are both arrays, the equals() method on arrays only determines if the two arrays are the same object. To compare the contents of the arrays, use java.util.Arrays.equals(Object[], Object[]).

EC: Call to equals(null) (EC_NULL_ARG)

This method calls equals(Object), passing a null value as the argument. According to the contract of the equals() method, this call should always return false.

EC: Call to equals() comparing unrelated class and interface (EC_UNRELATED_CLASS_AND_INTERFACE)

This method calls equals(Object) on two references, one of which is a class and the other an interface, where neither the class nor any of its non-abstract subclasses implement the interface. Therefore, the objects being compared are unlikely to be members of the same class at runtime (unless some application classes were not analyzed, or dynamic class loading can occur at runtime). According to the contract of equals(), objects of different classes should always compare as unequal; therefore, according to the contract defined by java.lang.Object.equals(Object), the result of this comparison will always be false at runtime.

SA: Self assignment of local rather than assignment to field (SA_LOCAL_SELF_ASSIGNMENT_INSTEAD_OF_FIELD)

This method contains a self assignment of a local variable, and there is a field with an identical name, e.g.:

    int foo;
    public void setFoo(int foo) {
        foo = foo;
    }

The assignment is useless. Did you mean to assign to the field instead?

INT: Bad comparison of int value with long constant (INT_BAD_COMPARISON_WITH_INT_VALUE)

This code compares an int value with a long constant that is outside the range of values that can be represented as an int value. This comparison is vacuous and possibly incorrect.

INT: Bad comparison of signed byte (INT_BAD_COMPARISON_WITH_SIGNED_BYTE)

Signed bytes can only have a value in the range -128 to 127. Comparing a signed byte with a value outside that range is vacuous and likely to be incorrect. To convert a signed byte b to an unsigned value in the range 0..255, use 0xff & b.

INT: Bad comparison of nonnegative value with negative constant or zero (INT_BAD_COMPARISON_WITH_NONNEGATIVE_VALUE)

This code compares a value that is guaranteed to be non-negative with a negative constant or zero.

BIT: Bitwise add of signed byte value (BIT_ADD_OF_SIGNED_BYTE)

Adds a byte value and a value which is known to have the 8 lower bits clear. Values loaded from a byte array are sign extended to 32 bits before any bitwise operations are performed on the value. Thus, if b[0] contains the value 0xff, and x is initially 0, then the code ((x << 8) + b[0]) will sign extend 0xff to get 0xffffffff, and thus give the value 0xffffffff as the result.

In particular, the following code for packing a byte array into an int is badly wrong:

int result = 0;
for (int i = 0; i < 4; i++)
    result = ((result << 8) + b[i]);

The following idiom will work instead:

int result = 0;
for (int i = 0; i < 4; i++)
    result = ((result << 8) + (b[i] & 0xff));

BIT: Bitwise OR of signed byte value (BIT_IOR_OF_SIGNED_BYTE)

Loads a byte value (e.g., a value loaded from a byte array or returned by a method with return type byte) and performs a bitwise OR with that value. Byte values are sign extended to 32 bits before any bitwise operations are performed on the value. Thus, if b[0] contains the value 0xff, and x is initially 0, then the code ((x << 8) | b[0]) will sign extend 0xff to get 0xffffffff, and thus give the value 0xffffffff as the result.

In particular, the following code for packing a byte array into an int is badly wrong:

int result = 0;
for (int i = 0; i < 4; i++) {
    result = ((result << 8) | b[i]);
}

The following idiom will work instead:

int result = 0;
for (int i = 0; i < 4; i++) {
    result = ((result << 8) | (b[i] & 0xff));
}

BIT: Check for sign of bitwise operation involving negative number (BIT_SIGNED_CHECK_HIGH_BIT)

This method compares a bitwise expression such as ((val & CONSTANT) > 0) where CONSTANT is the negative number. Using bit arithmetic and then comparing with the greater than operator can lead to unexpected results. This comparison is unlikely to work as expected. The good practice is to use ‘!= 0’ instead of ‘> 0’.

BIT: Incompatible bit masks (BIT_AND)

This method compares an expression of the form (e & C) to D, which will always compare unequal due to the specific values of constants C and D. This may indicate a logic error or typo.

BIT: Check to see if ((…) & 0) == 0 (BIT_AND_ZZ)

This method compares an expression of the form (e & 0) to 0, which will always compare equal. This may indicate a logic error or typo.

BIT: Incompatible bit masks (BIT_IOR)

This method compares an expression of the form (e | C) to D. which will always compare unequal due to the specific values of constants C and D. This may indicate a logic error or typo.

Typically, this bug occurs because the code wants to perform a membership test in a bit set, but uses the bitwise OR operator (“|”) instead of bitwise AND (“&”).

Also such bug may appear in expressions like (e & A | B) == C which is parsed like ((e & A) | B) == C while (e & (A | B)) == C was intended.

SA: Self assignment of field (SA_FIELD_SELF_ASSIGNMENT)

This method contains a self assignment of a field; e.g.

int x;
public void foo() {
    x = x;
}

Such assignments are useless, and may indicate a logic error or typo.

SA: Nonsensical self computation involving a field (e.g., x & x) (SA_FIELD_SELF_COMPUTATION)

This method performs a nonsensical computation of a field with another reference to the same field (e.g., x&x or x-x). Because of the nature of the computation, this operation doesn’t seem to make sense, and may indicate a typo or a logic error. Double-check the computation.

SA: Nonsensical self computation involving a variable (e.g., x & x) (SA_LOCAL_SELF_COMPUTATION)

This method performs a nonsensical computation of a local variable with another reference to the same variable (e.g., x&x or x-x). Because of the nature of the computation, this operation doesn’t seem to make sense, and may indicate a typo or a logic error. Double-check the computation.

SA: Self comparison of field with itself (SA_FIELD_SELF_COMPARISON)

This method compares a field with itself, and may indicate a typo or a logic error. Make sure that you are comparing the right things.

SA: Self comparison of value with itself (SA_LOCAL_SELF_COMPARISON)

This method compares a local variable with itself, and may indicate a typo or a logic error. Make sure that you are comparing the right things.

UMAC: Uncallable method defined in anonymous class (UMAC_UNCALLABLE_METHOD_OF_ANONYMOUS_CLASS)

This anonymous class defines a method that is not directly invoked and does not override a method in a superclass. Since methods in other classes cannot directly invoke methods declared in an anonymous class, it seems that this method is uncallable. The method might simply be dead code, but it is also possible that the method is intended to override a method declared in a superclass, and due to a typo or other error the method does not, in fact, override the method it is intended to.

IJU: JUnit assertion in run method will not be noticed by JUnit (IJU_ASSERT_METHOD_INVOKED_FROM_RUN_METHOD)

A JUnit assertion is performed in a run method. Failed JUnit assertions just result in exceptions being thrown. Thus, if this exception occurs in a thread other than the thread that invokes the test method, the exception will terminate the thread but not result in the test failing.

IJU: TestCase declares a bad suite method (IJU_BAD_SUITE_METHOD)

Class is a JUnit TestCase and defines a suite() method. However, the suite method needs to be declared as either

public static junit.framework.Test suite()

or

public static junit.framework.TestSuite suite()

IJU: TestCase defines setUp that doesn’t call super.setUp() (IJU_SETUP_NO_SUPER)

Class is a JUnit TestCase and implements the setUp method. The setUp method should call super.setUp(), but doesn’t.

IJU: TestCase defines tearDown that doesn’t call super.tearDown() (IJU_TEARDOWN_NO_SUPER)

Class is a JUnit TestCase and implements the tearDown method. The tearDown method should call super.tearDown(), but doesn’t.

IJU: TestCase implements a non-static suite method (IJU_SUITE_NOT_STATIC)

Class is a JUnit TestCase and implements the suite() method. The suite method should be declared as being static, but isn’t.

IJU: TestCase has no tests (IJU_NO_TESTS)

Class is a JUnit TestCase but has not implemented any test methods.

BOA: Class overrides a method implemented in super class Adapter wrongly (BOA_BADLY_OVERRIDDEN_ADAPTER)

This method overrides a method found in a parent class, where that class is an Adapter that implements a listener defined in the java.awt.event or javax.swing.event package. As a result, this method will not get called when the event occurs.

SQL: Method attempts to access a result set field with index 0 (SQL_BAD_RESULTSET_ACCESS)

A call to getXXX or updateXXX methods of a result set was made where the field index is 0. As ResultSet fields start at index 1, this is always a mistake.

SQL: Method attempts to access a prepared statement parameter with index 0 (SQL_BAD_PREPARED_STATEMENT_ACCESS)

A call to a setXXX method of a prepared statement was made where the parameter index is 0. As parameter indexes start at index 1, this is always a mistake.

SIO: Unnecessary type check done using instanceof operator (SIO_SUPERFLUOUS_INSTANCEOF)

Type check performed using the instanceof operator where it can be statically determined whether the object is of the type requested.

BAC: Bad Applet Constructor relies on uninitialized AppletStub (BAC_BAD_APPLET_CONSTRUCTOR)

This constructor calls methods in the parent Applet that rely on the AppletStub. Since the AppletStub isn’t initialized until the init() method of this applet is called, these methods will not perform correctly.

EC: equals(…) used to compare incompatible arrays (EC_INCOMPATIBLE_ARRAY_COMPARE)

This method invokes the .equals(Object o) to compare two arrays, but the arrays of incompatible types (e.g., String[] and StringBuffer[], or String[] and int[]). They will never be equal. In addition, when equals(…) is used to compare arrays it only checks to see if they are the same array, and ignores the contents of the arrays.

EC: Invocation of equals() on an array, which is equivalent to == (EC_BAD_ARRAY_COMPARE)

This method invokes the .equals(Object o) method on an array. Since arrays do not override the equals method of Object, calling equals on an array is the same as comparing their addresses. To compare the contents of the arrays, use java.util.Arrays.equals(Object[], Object[]). To compare the addresses of the arrays, it would be less confusing to explicitly check pointer equality using ==.

STI: Unneeded use of currentThread() call, to call interrupted() (STI_INTERRUPTED_ON_CURRENTTHREAD)

This method invokes the Thread.currentThread() call, just to call the interrupted() method. As interrupted() is a static method, it is more simple and clear to use Thread.interrupted().

STI: Static Thread.interrupted() method invoked on thread instance (STI_INTERRUPTED_ON_UNKNOWNTHREAD)

This method invokes the Thread.interrupted() method on a Thread object that appears to be a Thread object that is not the current thread. As the interrupted() method is static, the interrupted method will be called on a different object than the one the author intended.

DLS: Useless increment in return statement (DLS_DEAD_LOCAL_INCREMENT_IN_RETURN)

This statement has a return such as return x++; / return x--;. A postfix increment/decrement does not impact the value of the expression, so this increment/decrement has no effect. Please verify that this statement does the right thing.

DLS: Dead store of class literal (DLS_DEAD_STORE_OF_CLASS_LITERAL)

This instruction assigns a class literal to a variable and then never uses it. The behavior of this differs in Java 1.4 and in Java 5. In Java 1.4 and earlier, a reference to Foo.class would force the static initializer for Foo to be executed, if it has not been executed already. In Java 5 and later, it does not.

See Oracle’s article on Java SE compatibility for more details and examples, and suggestions on how to force class initialization in Java 5+.

IP: A parameter is dead upon entry to a method but overwritten (IP_PARAMETER_IS_DEAD_BUT_OVERWRITTEN)

The initial value of this parameter is ignored, and the parameter is overwritten here. This often indicates a mistaken belief that the write to the parameter will be conveyed back to the caller.

MF: Method defines a variable that obscures a field (MF_METHOD_MASKS_FIELD)

This method defines a local variable with the same name as a field in this class or a superclass. This may cause the method to read an uninitialized value from the field, leave the field uninitialized, or both.

MF: Class defines field that masks a superclass field (MF_CLASS_MASKS_FIELD)

This class defines a field with the same name as a visible instance field in a superclass. This is confusing, and may indicate an error if methods update or access one of the fields when they wanted the other.

FE: Doomed test for equality to NaN (FE_TEST_IF_EQUAL_TO_NOT_A_NUMBER)

This code checks to see if a floating point value is equal to the special Not A Number value (e.g., if (x == Double.NaN)). However, because of the special semantics of NaN, no value is equal to Nan, including NaN. Thus, x == Double.NaN always evaluates to false. To check to see if a value contained in x is the special Not A Number value, use Double.isNaN(x) (or Float.isNaN(x) if x is floating point precision).

ICAST: int value converted to long and used as absolute time (ICAST_INT_2_LONG_AS_INSTANT)

This code converts a 32-bit int value to a 64-bit long value, and then passes that value for a method parameter that requires an absolute time value. An absolute time value is the number of milliseconds since the standard base time known as “the epoch”, namely January 1, 1970, 00:00:00 GMT. For example, the following method, intended to convert seconds since the epoch into a Date, is badly broken:

Date getDate(int seconds) { return new Date(seconds * 1000); }

The multiplication is done using 32-bit arithmetic, and then converted to a 64-bit value. When a 32-bit value is converted to 64-bits and used to express an absolute time value, only dates in December 1969 and January 1970 can be represented.

Correct implementations for the above method are:

// Fails for dates after 2037
Date getDate(int seconds) { return new Date(seconds * 1000L); }
// better, works for all dates
Date getDate(long seconds) { return new Date(seconds * 1000); }

ICAST: Integral value cast to double and then passed to Math.ceil (ICAST_INT_CAST_TO_DOUBLE_PASSED_TO_CEIL)

This code converts an integral value (e.g., int or long) to a double precision floating point number and then passing the result to the Math.ceil() function, which rounds a double to the next higher integer value. This operation should always be a no-op, since converting an integer to a double should give a number with no fractional part. It is likely that the operation that generated the value to be passed to Math.ceil was intended to be performed using double precision floating point arithmetic.

ICAST: int value cast to float and then passed to Math.round (ICAST_INT_CAST_TO_FLOAT_PASSED_TO_ROUND)

This code converts an int value to a float precision floating point number and then passing the result to the Math.round() function, which returns the int/long closest to the argument. This operation should always be a no-op, since converting an integer to a float should give a number with no fractional part. It is likely that the operation that generated the value to be passed to Math.round was intended to be performed using floating point arithmetic.

NP: A known null value is checked to see if it is an instance of a type (NP_NULL_INSTANCEOF)

This instanceof test will always return false, since the value being checked is guaranteed to be null. Although this is safe, make sure it isn’t an indication of some misunderstanding or some other logic error.

DMI: Double.longBitsToDouble invoked on an int (DMI_LONG_BITS_TO_DOUBLE_INVOKED_ON_INT)

The Double.longBitsToDouble method is invoked, but a 32 bit int value is passed as an argument. This almost certainly is not intended and is unlikely to give the intended result.

BC: Impossible cast (BC_IMPOSSIBLE_CAST)

This cast will always throw a ClassCastException. SpotBugs tracks type information from instanceof checks, and also uses more precise information about the types of values returned from methods and loaded from fields. Thus, it may have more precise information than just the declared type of a variable, and can use this to determine that a cast will always throw an exception at runtime.

BC: Impossible downcast (BC_IMPOSSIBLE_DOWNCAST)

This cast will always throw a ClassCastException. The analysis believes it knows the precise type of the value being cast, and the attempt to downcast it to a subtype will always fail by throwing a ClassCastException.

BC: Impossible downcast of toArray() result (BC_IMPOSSIBLE_DOWNCAST_OF_TOARRAY)

This code is casting the result of calling toArray() on a collection to a type more specific than Object[], as in:

String[] getAsArray(Collection<String> c) {
    return (String[]) c.toArray();
}

This will usually fail by throwing a ClassCastException. The toArray() of almost all collections return an Object[]. They cannot really do anything else, since the Collection object has no reference to the declared generic type of the collection.

The correct way to do get an array of a specific type from a collection is to use c.toArray(new String[0]); or c.toArray(new String[c.size()]); (the former is slightly more efficient since late Java 6 updates).

There is one common/known exception to this. The toArray() method of lists returned by Arrays.asList(...) will return a covariantly typed array. For example, Arrays.asArray(new String[] { "a" }).toArray() will return a String []. SpotBugs attempts to detect and suppress such cases, but may miss some.

BC: instanceof will always return false (BC_IMPOSSIBLE_INSTANCEOF)

This instanceof test will always return false. Although this is safe, make sure it isn’t an indication of some misunderstanding or some other logic error.

RE: “.” or “|” used for regular expression (RE_POSSIBLE_UNINTENDED_PATTERN)

A String function is being invoked and “.” or “|” is being passed to a parameter that takes a regular expression as an argument. Is this what you intended? For example

• s.replaceAll(“.”, “/“) will return a String in which every character has been replaced by a ‘/‘ character
• s.split(“.”) always returns a zero length array of String
• “ab|cd”.replaceAll(“|”, “/“) will return “/a/b/|/c/d/“
• “ab|cd”.split(“|”) will return array with six (!) elements: [, a, b, |, c, d]

Consider using s.replace(".", "/") or s.split("\\.") instead.

RE: Invalid syntax for regular expression (RE_BAD_SYNTAX_FOR_REGULAR_EXPRESSION)

The code here uses a regular expression that is invalid according to the syntax for regular expressions. This statement will throw a PatternSyntaxException when executed.

RE: File.separator used for regular expression (RE_CANT_USE_FILE_SEPARATOR_AS_REGULAR_EXPRESSION)

The code here uses File.separator where a regular expression is required. This will fail on Windows platforms, where the File.separator is a backslash, which is interpreted in a regular expression as an escape character. Among other options, you can just use File.separatorChar=='\\' ? "\\\\" : File.separator instead of File.separator

DLS: Overwritten increment (DLS_OVERWRITTEN_INCREMENT)

The code performs an increment/decrement operation (e.g., i++ / i--) and then immediately overwrites it. For example, i = i++ / i = i-- immediately overwrites the incremented/decremented value with the original value.

BSHIFT: 32 bit int shifted by an amount not in the range -31..31 (ICAST_BAD_SHIFT_AMOUNT)

The code performs shift of a 32 bit int by a constant amount outside the range -31..31. The effect of this is to use the lower 5 bits of the integer value to decide how much to shift by (e.g., shifting by 40 bits is the same as shifting by 8 bits, and shifting by 32 bits is the same as shifting by zero bits). This probably isn’t what was expected, and it is at least confusing.

BSHIFT: Possible bad parsing of shift operation (BSHIFT_WRONG_ADD_PRIORITY)

The code performs an operation like (x << 8 + y). Although this might be correct, probably it was meant to perform (x << 8) + y, but shift operation has a lower precedence, so it’s actually parsed as x << (8 + y).

IM: Integer multiply of result of integer remainder (IM_MULTIPLYING_RESULT_OF_IREM)

The code multiplies the result of an integer remaining by an integer constant. Be sure you don’t have your operator precedence confused. For example i % 60 * 1000 is (i % 60) * 1000, not i % (60 * 1000).

DMI: Invocation of hashCode on an array (DMI_INVOKING_HASHCODE_ON_ARRAY)

The code invokes hashCode on an array. Calling hashCode on an array returns the same value as System.identityHashCode, and ignores the contents and length of the array. If you need a hashCode that depends on the contents of an array a, use java.util.Arrays.hashCode(a).

USELESS_STRING: Invocation of toString on an array (DMI_INVOKING_TOSTRING_ON_ARRAY)

The code invokes toString on an array, which will generate a fairly useless result such as [C@16f0472. Consider using Arrays.toString to convert the array into a readable String that gives the contents of the array. See Programming Puzzlers, chapter 3, puzzle 12.

USELESS_STRING: Invocation of toString on an unnamed array (DMI_INVOKING_TOSTRING_ON_ANONYMOUS_ARRAY)

The code invokes toString on an (anonymous) array. Calling toString on an array generates a fairly useless result such as [C@16f0472. Consider using Arrays.toString to convert the array into a readable String that gives the contents of the array. See Programming Puzzlers, chapter 3, puzzle 12.

DMI: Bad constant value for month (DMI_BAD_MONTH)

This code passes a constant month value outside the expected range of 0..11 to a method.

DMI: hasNext method invokes next (DMI_CALLING_NEXT_FROM_HASNEXT)

The hasNext() method invokes the next() method. This is almost certainly wrong, since the hasNext() method is not supposed to change the state of the iterator, and the next method is supposed to change the state of the iterator.

QBA: Method assigns boolean literal in boolean expression (QBA_QUESTIONABLE_BOOLEAN_ASSIGNMENT)

This method assigns a literal boolean value (true or false) to a boolean variable inside an if or while expression. Most probably this was supposed to be a boolean comparison using ==, not an assignment using =.

GC: No relationship between generic parameter and method argument (GC_UNRELATED_TYPES)

This call to a generic collection method contains an argument with an incompatible class from that of the collection’s parameter (i.e., the type of the argument is neither a supertype nor a subtype of the corresponding generic type argument). Therefore, it is unlikely that the collection contains any objects that are equal to the method argument used here. Most likely, the wrong value is being passed to the method.

In general, instances of two unrelated classes are not equal. For example, if the Foo and Bar classes are not related by subtyping, then an instance of Foo should not be equal to an instance of Bar. Among other issues, doing so will likely result in an equals method that is not symmetrical. For example, if you define the Foo class so that a Foo can be equal to a String, your equals method isn’t symmetrical since a String can only be equal to a String.

In rare cases, people do define nonsymmetrical equals methods and still manage to make their code work. Although none of the APIs document or guarantee it, it is typically the case that if you check if a Collection<String> contains a Foo, the equals method of argument (e.g., the equals method of the Foo class) used to perform the equality checks.

DMI: Vacuous call to collections (DMI_VACUOUS_SELF_COLLECTION_CALL)

This call doesn’t make sense. For any collection c, calling c.containsAll(c) should always be true, and c.retainAll(c) should have no effect.

DMI: D’oh! A nonsensical method invocation (DMI_DOH)

This particular method invocation doesn’t make sense, for reasons that should be apparent from inspection.

DMI: Collections should not contain themselves (DMI_COLLECTIONS_SHOULD_NOT_CONTAIN_THEMSELVES)

This call to a generic collection’s method would only make sense if a collection contained itself (e.g., if s.contains(s) were true). This is unlikely to be true and would cause problems if it were true (such as the computation of the hash code resulting in infinite recursion). It is likely that the wrong value is being passed as a parameter.

TQ: Value without a type qualifier used where a value is required to have that qualifier (TQ_UNKNOWN_VALUE_USED_WHERE_ALWAYS_STRICTLY_REQUIRED)

A value is being used in a way that requires the value to be annotated with a type qualifier. The type qualifier is strict, so the tool rejects any values that do not have the appropriate annotation.

To coerce a value to have a strict annotation, define an identity function where the return value is annotated with the strict annotation. This is the only way to turn a non-annotated value into a value with a strict type qualifier annotation.

TQ: Comparing values with incompatible type qualifiers (TQ_COMPARING_VALUES_WITH_INCOMPATIBLE_TYPE_QUALIFIERS)

A value specified as carrying a type qualifier annotation is compared with a value that doesn’t ever carry that qualifier.

More precisely, a value annotated with a type qualifier specifying when=ALWAYS is compared with a value that where the same type qualifier specifies when=NEVER.

For example, say that @NonNegative is a nickname for the type qualifier annotation @Negative(when=When.NEVER). The following code will generate this warning because the return statement requires a @NonNegative value, but receives one that is marked as @Negative.

public boolean example(@Negative Integer value1, @NonNegative Integer value2) {
    return value1.equals(value2);
}

TQ: Value annotated as carrying a type qualifier used where a value that must not carry that qualifier is required (TQ_ALWAYS_VALUE_USED_WHERE_NEVER_REQUIRED)

A value specified as carrying a type qualifier annotation is consumed in a location or locations requiring that the value not carry that annotation.

More precisely, a value annotated with a type qualifier specifying when=ALWAYS is guaranteed to reach a use or uses where the same type qualifier specifies when=NEVER.

For example, say that @NonNegative is a nickname for the type qualifier annotation @Negative(when=When.NEVER). The following code will generate this warning because the return statement requires a @NonNegative value, but receives one that is marked as @Negative.

public @NonNegative Integer example(@Negative Integer value) {
    return value;
}

TQ: Value annotated as never carrying a type qualifier used where value carrying that qualifier is required (TQ_NEVER_VALUE_USED_WHERE_ALWAYS_REQUIRED)

A value specified as not carrying a type qualifier annotation is guaranteed to be consumed in a location or locations requiring that the value does carry that annotation.

More precisely, a value annotated with a type qualifier specifying when=NEVER is guaranteed to reach a use or uses where the same type qualifier specifies when=ALWAYS.

TODO: example

TQ: Value that might not carry a type qualifier is always used in a way requires that type qualifier (TQ_MAYBE_SOURCE_VALUE_REACHES_ALWAYS_SINK)

A value that is annotated as possibly not being an instance of the values denoted by the type qualifier, and the value is guaranteed to be used in a way that requires values denoted by that type qualifier.

TQ: Value that might carry a type qualifier is always used in a way prohibits it from having that type qualifier (TQ_MAYBE_SOURCE_VALUE_REACHES_NEVER_SINK)

A value that is annotated as possibly being an instance of the values denoted by the type qualifier, and the value is guaranteed to be used in a way that prohibits values denoted by that type qualifier.

FB: Unexpected/undesired warning from SpotBugs (FB_UNEXPECTED_WARNING)

SpotBugs generated a warning that, according to a @NoWarning annotation, is unexpected or undesired.

FB: Missing expected or desired warning from SpotBugs (FB_MISSING_EXPECTED_WARNING)

SpotBugs didn’t generate a warning that, according to an @ExpectedWarning annotation, is expected or desired.

EOS: Data read is converted before comparison to -1 (EOS_BAD_END_OF_STREAM_CHECK)

The method java.io.FileInputStream.read() returns an int. If this int is converted to a byte then -1 (which indicates an EOF) and the byte 0xFF become indistinguishable, this comparing the (converted) result to -1 causes the read (probably in a loop) to end prematurely if the character 0xFF is met. Similarly, the method java.io.FileReader.read() also returns an int. If it is converted to a char then -1 becomes 0xFFFF which is Character.MAX_VALUE. Comparing the result to -1 is pointless, since characters are unsigned in Java. If the checking for EOF is the condition of a loop then this loop is infinite.

See SEI CERT rule FIO08-J. Distinguish between characters or bytes read from a stream and -1.

FL: Do not use floating-point variables as loop counters (FL_FLOATS_AS_LOOP_COUNTERS)

Using floating-point variables should not be used as loop counters, as they are not precise, which may result in incorrect loops. A loop counter is a variable that is changed with each iteration and controls when the loop should terminate. It is decreased or increased by a fixed amount each iteration.

See rule NUM09-J.

SING: Class using singleton design pattern directly implements Cloneable interface. (SING_SINGLETON_IMPLEMENTS_CLONEABLE)

If a class using singleton design pattern directly implements the Cloneable interface, it is possible to create a copy of the object, thus violating the singleton pattern.
Therefore, implementing the Cloneable interface should be avoided.

For more information, see: SEI CERT MSC07-J.

SING: Class using singleton design pattern indirectly implements Cloneable interface. (SING_SINGLETON_INDIRECTLY_IMPLEMENTS_CLONEABLE)

If a class using singleton design pattern indirectly implements the Cloneable interface, it is possible to create a copy of the object, thus violating the singleton pattern.
Therefore, implementing the Cloneable interface should be avoided. If that’s not possible because of an extended super-class, the solution would be overriding the clone method to unconditionally throw CloneNotSupportedException.

For more information, see: SEI CERT MSC07-J.

SING: Class using singleton design pattern implements clone() method without being an unconditional CloneNotSupportedException-thrower. (SING_SINGLETON_IMPLEMENTS_CLONE_METHOD)

This class is using singleton design pattern and does not implement the Cloneable interface, but implements the clone() method without being an unconditional CloneNotSupportedException-thrower. With that, it is possible to create a copy of the object, thus violating the singleton pattern.
Therefore, implementing the clone method should be avoided, otherwise the solution would be overriding the clone method to unconditionally throw CloneNotSupportedException.

For more information, see: SEI CERT MSC07-J.

SING: Class using singleton design pattern has non-private constructor. (SING_SINGLETON_HAS_NONPRIVATE_CONSTRUCTOR)

This class is using singleton design pattern and has non-private constructor (please note that a default constructor might exist which is not private). Given that, it is possible to create a copy of the object, thus violating the singleton pattern.
The easier solution would be making the constructor private.

SEI CERT MSC07-J rule

SING: Class using singleton design pattern directly or indirectly implements Serializable interface. (SING_SINGLETON_IMPLEMENTS_SERIALIZABLE)

This class (using singleton design pattern) directly or indirectly implements the Serializable interface, which allows the class to be serialized.
Deserialization makes multiple instantiation of a singleton class possible, and therefore should be avoided.

SEI CERT MSC07-J rule

SING: Instance-getter method of class using singleton design pattern is not synchronized. (SING_SINGLETON_GETTER_NOT_SYNCHRONIZED)

Instance-getter method of class using singleton design pattern is not synchronized. When this method is invoked by two or more threads simultaneously, multiple instantiation of a singleton class becomes possible.

SEI CERT MSC07-J rule

Experimental (EXPERIMENTAL)

Experimental and not fully vetted bug patterns

SKIPPED: Class too big for analysis (SKIPPED_CLASS_TOO_BIG)

This class is bigger than can be effectively handled, and was not fully analyzed for errors.

TEST: Unknown bug pattern (UNKNOWN)

A warning was recorded, but SpotBugs cannot find the description of this bug pattern and so cannot describe it. This should occur only in cases of a bug in SpotBugs or its configuration, or perhaps if an analysis was generated using a plugin, but that plugin is not currently loaded. .

TEST: Testing (TESTING)

This bug pattern is only generated by new, incompletely implemented bug detectors.

TEST: Testing 1 (TESTING1)

This bug pattern is only generated by new, incompletely implemented bug detectors.

TEST: Testing 2 (TESTING2)

This bug pattern is only generated by new, incompletely implemented bug detectors.

TEST: Testing 3 (TESTING3)

This bug pattern is only generated by new, incompletely implemented bug detectors.

OBL: Method may fail to clean up stream or resource (OBL_UNSATISFIED_OBLIGATION)

This method may fail to clean up (close, dispose of) a stream, database object, or other resource requiring an explicit cleanup operation.

In general, if a method opens a stream or other resource, the method should use a try/finally block to ensure that the stream or resource is cleaned up before the method returns.

This bug pattern is essentially the same as the OS_OPEN_STREAM and ODR_OPEN_DATABASE_RESOURCE bug patterns, but is based on a different (and hopefully better) static analysis technique. We are interested is getting feedback about the usefulness of this bug pattern. For sending feedback, check:

• contributing guideline
• mailinglist

In particular, the false-positive suppression heuristics for this bug pattern have not been extensively tuned, so reports about false positives are helpful to us.

See Weimer and Necula, Finding and Preventing Run-Time Error Handling Mistakes (PDF), for a description of the analysis technique.

OBL: Method may fail to clean up stream or resource on checked exception (OBL_UNSATISFIED_OBLIGATION_EXCEPTION_EDGE)

This method may fail to clean up (close, dispose of) a stream, database object, or other resource requiring an explicit cleanup operation.

In general, if a method opens a stream or other resource, the method should use a try/finally block to ensure that the stream or resource is cleaned up before the method returns.

This bug pattern is essentially the same as the OS_OPEN_STREAM and ODR_OPEN_DATABASE_RESOURCE bug patterns, but is based on a different (and hopefully better) static analysis technique. We are interested is getting feedback about the usefulness of this bug pattern. For sending feedback, check:

• contributing guideline
• mailinglist

In particular, the false-positive suppression heuristics for this bug pattern have not been extensively tuned, so reports about false positives are helpful to us.

See Weimer and Necula, Finding and Preventing Run-Time Error Handling Mistakes (PDF), for a description of the analysis technique.

LG: Potential lost logger changes due to weak reference in OpenJDK (LG_LOST_LOGGER_DUE_TO_WEAK_REFERENCE)

OpenJDK introduces a potential incompatibility. In particular, the java.util.logging.Logger behavior has changed. Instead of using strong references, it now uses weak references internally. That’s a reasonable change, but unfortunately some code relies on the old behavior - when changing logger configuration, it simply drops the logger reference. That means that the garbage collector is free to reclaim that memory, which means that the logger configuration is lost. For example, consider:

public static void initLogging() throws Exception {
    Logger logger = Logger.getLogger("edu.umd.cs");
    logger.addHandler(new FileHandler()); // call to change logger configuration
    logger.setUseParentHandlers(false); // another call to change logger configuration
}

The logger reference is lost at the end of the method (it doesn’t escape the method), so if you have a garbage collection cycle just after the call to initLogging, the logger configuration is lost (because Logger only keeps weak references).

public static void main(String[] args) throws Exception {
    initLogging(); // adds a file handler to the logger
    System.gc(); // logger configuration lost
    Logger.getLogger("edu.umd.cs").info("Some message"); // this isn't logged to the file as expected
}

Ulf Ochsenfahrt and Eric Fellheimer

Internationalization (I18N)

Code flaws having to do with internationalization and locale

Dm: Consider using Locale parameterized version of invoked method (DM_CONVERT_CASE)

A String is being converted to upper or lowercase, using the platform’s default encoding. This may result in improper conversions when used with international characters. Use the

• String.toUpperCase( Locale l )
• String.toLowerCase( Locale l )

versions instead.

Dm: Reliance on default encoding (DM_DEFAULT_ENCODING)

Found a call to a method which will perform a byte to String (or String to byte) conversion, and will assume that the default platform encoding is suitable. This will cause the application behavior to vary between platforms. Use an alternative API and specify a charset name or Charset object explicitly.

Malicious code vulnerability (MALICIOUS_CODE)

Code that is vulnerable to attacks from untrusted code

DP: Method invoked that should be only be invoked inside a doPrivileged block (DP_DO_INSIDE_DO_PRIVILEGED)

This code invokes a method that requires a security permission check. If this code will be granted security permissions, but might be invoked by code that does not have security permissions, then the invocation needs to occur inside a doPrivileged block.

DP: Classloaders should only be created inside doPrivileged block (DP_CREATE_CLASSLOADER_INSIDE_DO_PRIVILEGED)

This code creates a classloader, which needs permission if a security manage is installed. If this code might be invoked by code that does not have security permissions, then the classloader creation needs to occur inside a doPrivileged block.

FI: Finalizer should be protected, not public (FI_PUBLIC_SHOULD_BE_PROTECTED)

A class’s finalize() method should have protected access, not public.

MS: Public static method may expose internal representation by returning a mutable object or array (MS_EXPOSE_REP)

A public static method returns a reference to a mutable object or an array that is part of the static state of the class. Any code that calls this method can freely modify the underlying array. One fix is to return a copy of the array.

MS: May expose internal representation by returning a buffer sharing non-public data (MS_EXPOSE_BUF)

A public static method either returns a buffer (java.nio.*Buffer) which wraps an array that is part of the static state of the class by holding a reference only to this same array or it returns a shallow-copy of a buffer that is part of the static stat of the class which shares its reference with the original buffer. Any code that calls this method can freely modify the underlying array. One fix is to return a read-only buffer or a new buffer with a copy of the array.

EI: May expose internal representation by returning reference to mutable object (EI_EXPOSE_REP)

Returning a reference to a mutable object value stored in one of the object’s fields exposes the internal representation of the object. If instances are accessed by untrusted code, and unchecked changes to the mutable object would compromise security or other important properties, you will need to do something different. Returning a new copy of the object is better approach in many situations.

EI: May expose internal representation by returning a buffer sharing non-public data (EI_EXPOSE_BUF)

Returning a reference to a buffer (java.nio.*Buffer) which wraps an array stored in one of the object’s fields exposes the internal representation of the array elements because the buffer only stores a reference to the array instead of copying its content. Similarly, returning a shallow-copy of such a buffer (using its duplicate() method) stored in one of the object’s fields also exposes the internal representation of the buffer. If instances are accessed by untrusted code, and unchecked changes to the array would compromise security or other important properties, you will need to do something different. Returning a read-only buffer (using its asReadOnly() method) or copying the array to a new buffer (using its put() method) is a better approach in many situations.

EI2: May expose internal representation by incorporating reference to mutable object (EI_EXPOSE_REP2)

This code stores a reference to an externally mutable object into the internal representation of the object. If instances are accessed by untrusted code, and unchecked changes to the mutable object would compromise security or other important properties, you will need to do something different. Storing a copy of the object is better approach in many situations.

MS: May expose internal static state by storing a mutable object into a static field (EI_EXPOSE_STATIC_REP2)

This code stores a reference to an externally mutable object into a static field. If unchecked changes to the mutable object would compromise security or other important properties, you will need to do something different. Storing a copy of the object is better approach in many situations.

EI2: May expose internal representation by creating a buffer which incorporates reference to array (EI_EXPOSE_BUF2)

This code creates a buffer which stores a reference to an external array or the array of an external buffer into the internal representation of the object. If instances are accessed by untrusted code, and unchecked changes to the array would compromise security or other important properties, you will need to do something different. Storing a copy of the array is a better approach in many situations.

MS: May expose internal static state by creating a buffer which stores an external array into a static field (EI_EXPOSE_STATIC_BUF2)

This code creates a buffer which stores a reference to an external array or the array of an external buffer into a static field. If unchecked changes to the array would compromise security or other important properties, you will need to do something different. Storing a copy of the array is a better approach in many situations.

MS: Field should be moved out of an interface and made package protected (MS_OOI_PKGPROTECT)

A final static field that is defined in an interface references a mutable object such as an array or hashtable. This mutable object could be changed by malicious code or by accident from another package. To solve this, the field needs to be moved to a class and made package protected to avoid this vulnerability.

MS: Field should be both final and package protected (MS_FINAL_PKGPROTECT)

A mutable static field could be changed by malicious code or by accident from another package. The field could be made package protected and/or made final to avoid this vulnerability.

MS: Field isn’t final but should be (MS_SHOULD_BE_FINAL)

This public static or protected static field is not final, and could be changed by malicious code or by accident from another package. The field could be made final to avoid this vulnerability.

MS: Field isn’t final but should be refactored to be so (MS_SHOULD_BE_REFACTORED_TO_BE_FINAL)

This public static or protected static field is not final, and could be changed by malicious code or by accident from another package. The field could be made final to avoid this vulnerability. However, the static initializer contains more than one write to the field, so doing so will require some refactoring.

MS: Field should be package protected (MS_PKGPROTECT)

A mutable static field could be changed by malicious code or by accident. The field could be made package protected to avoid this vulnerability.

MS: Field is a mutable Hashtable (MS_MUTABLE_HASHTABLE)

A final static field references a Hashtable and can be accessed by malicious code or by accident from another package. This code can freely modify the contents of the Hashtable.

MS: Field is a mutable array (MS_MUTABLE_ARRAY)

A final static field references an array and can be accessed by malicious code or by accident from another package. This code can freely modify the contents of the array.

MS: Field is a mutable collection (MS_MUTABLE_COLLECTION)

A mutable collection instance is assigned to a final static field, thus can be changed by malicious code or by accident from another package. Consider wrapping this field into Collections.unmodifiableSet/List/Map/etc. to avoid this vulnerability.

MS: Field is a mutable collection which should be package protected (MS_MUTABLE_COLLECTION_PKGPROTECT)

A mutable collection instance is assigned to a final static field, thus can be changed by malicious code or by accident from another package. The field could be made package protected to avoid this vulnerability. Alternatively you may wrap this field into Collections.unmodifiableSet/List/Map/etc. to avoid this vulnerability.

MS: Field isn’t final and cannot be protected from malicious code (MS_CANNOT_BE_FINAL)

A mutable static field could be changed by malicious code or by accident from another package. Unfortunately, the way the field is used doesn’t allow any easy fix to this problem.

REFLC: Public method uses reflection to create a class it gets in its parameter which could increase the accessibility of any class (REFLC_REFLECTION_MAY_INCREASE_ACCESSIBILITY_OF_CLASS)

SEI CERT SEC05-J rule forbids the use of reflection to increase accessibility of classes, methods or fields. If a class in a package provides a public method which takes an instance of java.lang.Class as its parameter and calls its newInstance() method then it increases accessibility of classes in the same package without public constructors. An attacker code may call this method and pass such class to create an instance of it. This should be avoided by either making the method non-public or by checking for package access permission on the package. A third possibility is to use the java.beans.Beans.instantiate() method instead of java.lang.Class.newInstance() which checks whether the Class object being received has any public constructors.

REFLF: Public method uses reflection to modify a field it gets in its parameter which could increase the accessibility of any class (REFLF_REFLECTION_MAY_INCREASE_ACCESSIBILITY_OF_FIELD)

SEI CERT SEC05-J rule forbids the use of reflection to increase accessibility of classes, methods or fields. If a class in a package provides a public method which takes an instance of java.lang.reflect.Field as its parameter and calls a setter (or setAccessible()) method then it increases accessibility of fields in the same package which are private, protected or package private. An attacker code may call this method and pass such field to change it. This should be avoided by either making the method non-public or by checking for package access permission on the package.

MC: An overridable method is called from a constructor (MC_OVERRIDABLE_METHOD_CALL_IN_CONSTRUCTOR)

Calling an overridable method during in a constructor may result in the use of uninitialized data. It may also leak the this reference of the partially constructed object. Only static, final or private methods should be invoked from a constructor.

See SEI CERT rule MET05-J. Ensure that constructors do not call overridable methods.

MC: An overridable method is called from the clone() method. (MC_OVERRIDABLE_METHOD_CALL_IN_CLONE)

Calling overridable methods from the clone() method is insecure because a subclass could override the method, affecting the behavior of clone(). It can also observe or modify the clone object in a partially initialized state. Only static, final or private methods should be invoked from the clone() method.

See SEI CERT rule MET06-J. Do not invoke overridable methods in clone().

MC: An overridable method is called from the readObject method. (MC_OVERRIDABLE_METHOD_CALL_IN_READ_OBJECT)

The readObject() method must not call any overridable methods. Invoking overridable methods from the readObject() method can provide the overriding method with access to the object’s state before it is fully initialized. This premature access is possible because, in deserialization, readObject plays the role of object constructor and therefore object initialization is not complete until readObject exits.

See SEI CERT rule SER09-J. Do not invoke overridable methods from the readObject() method.

PERM: Custom class loader does not call its superclass’s getPermissions() (PERM_SUPER_NOT_CALLED_IN_GETPERMISSIONS)

SEI CERT rule SEC07-J requires that custom class loaders must always call their superclass’s getPermissions() method in their own getPermissions() method to initialize the object they return at the end. Omitting it means that a class defined using this custom class loader has permissions that are completely independent of those specified in the systemwide policy file. In effect, the class’s permissions override them.

USC: Potential security check based on untrusted source. (USC_POTENTIAL_SECURITY_CHECK_BASED_ON_UNTRUSTED_SOURCE)

A public method of a public class may be called from outside the package which means that untrusted data may be passed to it. Calling a method before the doPrivileged to check its return value and then calling the same method inside the class is dangerous if the method or its enclosing class is not final. An attacker may pass an instance of a malicious descendant of the class instead of an instance of the expected one where this method is overridden in a way that it returns different values upon different invocations. For example, a method returning a file path may return a harmless path to check before entering the doPrivileged block and then a sensitive file upon the call inside the doPrivileged block. To avoid such scenario defensively copy the object received in the parameter, e.g. by using the copy constructor of the class used as the type of the formal parameter. This ensures that the method behaves exactly as expected.

See SEI CERT rule SEC02-J. Do not base security checks on untrusted sources.

VSC: Non-Private and non-final security check methods are vulnerable (VSC_VULNERABLE_SECURITY_CHECK_METHODS)

Methods that perform security checks should be prevented from being overridden, so they must be declared as private or final. Otherwise, these methods can be compromised when a malicious subclass overrides them and omits the checks.

See SEI CERT rule MET03-J. Methods that perform a security check must be declared private or final.

Multithreaded correctness (MT_CORRECTNESS)

Code flaws having to do with threads, locks, and volatiles

AT: Sequence of calls to concurrent abstraction may not be atomic (AT_OPERATION_SEQUENCE_ON_CONCURRENT_ABSTRACTION)

This code contains a sequence of calls to a concurrent abstraction (such as a concurrent hash map). These calls will not be executed atomically.

STCAL: Static Calendar field (STCAL_STATIC_CALENDAR_INSTANCE)

Even though the JavaDoc does not contain a hint about it, Calendars are inherently unsafe for multithreaded use. Sharing a single instance across thread boundaries without proper synchronization will result in erratic behavior of the application. Under 1.4 problems seem to surface less often than under Java 5 where you will probably see random ArrayIndexOutOfBoundsExceptions or IndexOutOfBoundsExceptions in sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate().

You may also experience serialization problems.

Using an instance field is recommended.

For more information on this see JDK Bug #6231579 and JDK Bug #6178997.

STCAL: Static DateFormat (STCAL_STATIC_SIMPLE_DATE_FORMAT_INSTANCE)

As the JavaDoc states, DateFormats are inherently unsafe for multithreaded use. Sharing a single instance across thread boundaries without proper synchronization will result in erratic behavior of the application.

You may also experience serialization problems.

Using an instance field is recommended.

For more information on this see JDK Bug #6231579 and JDK Bug #6178997.

STCAL: Call to static Calendar (STCAL_INVOKE_ON_STATIC_CALENDAR_INSTANCE)

Even though the JavaDoc does not contain a hint about it, Calendars are inherently unsafe for multithreaded use. The detector has found a call to an instance of Calendar that has been obtained via a static field. This looks suspicious.

For more information on this see JDK Bug #6231579 and JDK Bug #6178997.

STCAL: Call to static DateFormat (STCAL_INVOKE_ON_STATIC_DATE_FORMAT_INSTANCE)

As the JavaDoc states, DateFormats are inherently unsafe for multithreaded use. The detector has found a call to an instance of DateFormat that has been obtained via a static field. This looks suspicious.

For more information on this see JDK Bug #6231579 and JDK Bug #6178997.

NP: Synchronize and null check on the same field. (NP_SYNC_AND_NULL_CHECK_FIELD)

Since the field is synchronized on, it seems not likely to be null. If it is null and then synchronized on a NullPointerException will be thrown and the check would be pointless. Better to synchronize on another field.

VO: A volatile reference to an array doesn’t treat the array elements as volatile (VO_VOLATILE_REFERENCE_TO_ARRAY)

This declares a volatile reference to an array, which might not be what you want. With a volatile reference to an array, reads and writes of the reference to the array are treated as volatile, but the array elements are non-volatile. To get volatile array elements, you will need to use one of the atomic array classes in java.util.concurrent (provided in Java 5.0).

VO: An increment to a volatile field isn’t atomic (VO_VOLATILE_INCREMENT)

This code increments/decrements a volatile field. Increments/Decrements of volatile fields aren’t atomic. If more than one thread is incrementing/decrementing the field at the same time, increments/decrements could be lost.

Dm: Monitor wait() called on Condition (DM_MONITOR_WAIT_ON_CONDITION)

This method calls wait() on a java.util.concurrent.locks.Condition object. Waiting for a Condition should be done using one of the await() methods defined by the Condition interface.

Dm: A thread was created using the default empty run method (DM_USELESS_THREAD)

This method creates a thread without specifying a run method either by deriving from the Thread class, or by passing a Runnable object. This thread, then, does nothing but waste time.

DC: Possible double-check of field (DC_DOUBLECHECK)

This method may contain an instance of double-checked locking. This idiom is not correct according to the semantics of the Java memory model. For more information, see the web page http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html.

DC: Possible exposure of partially initialized object (DC_PARTIALLY_CONSTRUCTED)

Looks like this method uses lazy field initialization with double-checked locking. While the field is correctly declared as volatile, it’s possible that the internal structure of the object is changed after the field assignment, thus another thread may see the partially initialized object.

To fix this problem consider storing the object into the local variable first and save it to the volatile field only after it’s fully constructed.

DL: Synchronization on String literal (DL_SYNCHRONIZATION_ON_SHARED_CONSTANT)

The code synchronizes on String literal.

private static String LOCK = "LOCK";
...
synchronized(LOCK) {
    ...
}
...

Constant Strings are interned and shared across all other classes loaded by the JVM. Thus, this code is locking on something that other code might also be locking. This could result in very strange and hard to diagnose blocking and deadlock behavior. See http://www.javalobby.org/java/forums/t96352.html and http://jira.codehaus.org/browse/JETTY-352.

See CERT LCK01-J. Do not synchronize on objects that may be reused for more information.

DL: Synchronization on Boolean (DL_SYNCHRONIZATION_ON_BOOLEAN)

The code synchronizes on a boxed primitive constant, such as a Boolean.

private static Boolean inited = Boolean.FALSE;
...
synchronized(inited) {
    if (!inited) {
        init();
        inited = Boolean.TRUE;
    }
}
...

Since there normally exist only two Boolean objects, this code could be synchronizing on the same object as other, unrelated code, leading to unresponsiveness and possible deadlock.

See CERT LCK01-J. Do not synchronize on objects that may be reused for more information.

DL: Synchronization on boxed primitive (DL_SYNCHRONIZATION_ON_BOXED_PRIMITIVE)

The code synchronizes on a boxed primitive constant, such as an Integer.

private static Integer count = 0;
...
synchronized(count) {
    count++;
}
...

Since Integer objects can be cached and shared, this code could be synchronizing on the same object as other, unrelated code, leading to unresponsiveness and possible deadlock.

See CERT LCK01-J. Do not synchronize on objects that may be reused for more information.

DL: Synchronization on boxed primitive values (DL_SYNCHRONIZATION_ON_UNSHARED_BOXED_PRIMITIVE)

The code synchronizes on an apparently unshared boxed primitive, such as an Integer.

private static final Integer fileLock = new Integer(1);
...
synchronized(fileLock) {
    .. do something ..
}
...

It would be much better, in this code, to redeclare fileLock as

private static final Object fileLock = new Object();

The existing code might be OK, but it is confusing and a future refactoring, such as the “Remove Boxing” refactoring in IntelliJ, might replace this with the use of an interned Integer object shared throughout the JVM, leading to very confusing behavior and potential deadlock.

DL: Synchronization on interned String (DL_SYNCHRONIZATION_ON_INTERNED_STRING)

The code synchronizes on interned String.

private static String LOCK = new String("LOCK").intern();
...
synchronized(LOCK) {
    ...
}
...

Constant Strings are interned and shared across all other classes loaded by the JVM. Thus, this code is locking on something that other code might also be locking. This could result in very strange and hard to diagnose blocking and deadlock behavior. See http://www.javalobby.org/java/forums/t96352.html and http://jira.codehaus.org/browse/JETTY-352.

See CERT LCK01-J. Do not synchronize on objects that may be reused for more information.

WL: Synchronization on getClass rather than class literal (WL_USING_GETCLASS_RATHER_THAN_CLASS_LITERAL)

This instance method synchronizes on this.getClass(). If this class is subclassed, subclasses will synchronize on the class object for the subclass, which isn’t likely what was intended. For example, consider this code from java.awt.Label:

private static final String base = "label";
private static int nameCounter = 0;
String constructComponentName() {
    synchronized (getClass()) {
        return base + nameCounter++;
    }
}

Subclasses of Label won’t synchronize on the same subclass, giving rise to a datarace. Instead, this code should be synchronizing on Label.class.

private static final String base = "label";
private static int nameCounter = 0;
String constructComponentName() {
    synchronized (Label.class) {
        return base + nameCounter++;
    }
}

Bug pattern contributed by Jason Mehrens.

ESync: Empty synchronized block (ESync_EMPTY_SYNC)

The code contains an empty synchronized block:

synchronized() {
}

Empty synchronized blocks are far more subtle and hard to use correctly than most people recognize, and empty synchronized blocks are almost never a better solution than less contrived solutions.

MSF: Mutable servlet field (MSF_MUTABLE_SERVLET_FIELD)

A web server generally only creates one instance of servlet or JSP class (i.e., treats the class as a Singleton), and will have multiple threads invoke methods on that instance to service multiple simultaneous requests. Thus, having a mutable instance field generally creates race conditions.

IS: Inconsistent synchronization (IS2_INCONSISTENT_SYNC)

The fields of this class appear to be accessed inconsistently with respect to synchronization. This bug report indicates that the bug pattern detector judged that

• The class contains a mix of locked and unlocked accesses,
• The class is not annotated as javax.annotation.concurrent.NotThreadSafe,
• At least one locked access was performed by one of the class’s own methods, and
• The number of unsynchronized field accesses (reads and writes) was no more than one third of all accesses, with writes being weighed twice as high as reads

A typical bug matching this bug pattern is forgetting to synchronize one of the methods in a class that is intended to be thread-safe.

You can select the nodes labeled “Unsynchronized access” to show the code locations where the detector believed that a field was accessed without synchronization.

Note that there are various sources of inaccuracy in this detector; for example, the detector cannot statically detect all situations in which a lock is held. Also, even when the detector is accurate in distinguishing locked vs. unlocked accesses, the code in question may still be correct.

NN: Naked notify (NN_NAKED_NOTIFY)

A call to notify() or notifyAll() was made without any (apparent) accompanying modification to mutable object state. In general, calling a notify method on a monitor is done because some condition another thread is waiting for has become true. However, for the condition to be meaningful, it must involve a heap object that is visible to both threads.

This bug does not necessarily indicate an error, since the change to mutable object state may have taken place in a method which then called the method containing the notification.

Ru: Invokes run on a thread (did you mean to start it instead?) (RU_INVOKE_RUN)

This method explicitly invokes run() on an object. In general, classes implement the Runnable interface because they are going to have their run() method invoked in a new thread, in which case Thread.start() is the right method to call.

SP: Method spins on field (SP_SPIN_ON_FIELD)

This method spins in a loop which reads a field. The compiler may legally hoist the read out of the loop, turning the code into an infinite loop. The class should be changed so it uses proper synchronization (including wait and notify calls).

TLW: Wait with two locks held (TLW_TWO_LOCK_WAIT)

Waiting on a monitor while two locks are held may cause deadlock. Performing a wait only releases the lock on the object being waited on, not any other locks. This not necessarily a bug, but is worth examining closely.

UW: Unconditional wait (UW_UNCOND_WAIT)

This method contains a call to java.lang.Object.wait() which is not guarded by conditional control flow. The code should verify that condition it intends to wait for is not already satisfied before calling wait; any previous notifications will be ignored.

UG: Unsynchronized get method, synchronized set method (UG_SYNC_SET_UNSYNC_GET)

This class contains similarly-named get and set methods where the set method is synchronized and the get method is not. This may result in incorrect behavior at runtime, as callers of the get method will not necessarily see a consistent state for the object. The get method should be made synchronized.

IS: Field not guarded against concurrent access (IS_FIELD_NOT_GUARDED)

This field is annotated with net.jcip.annotations.GuardedBy or javax.annotation.concurrent.GuardedBy, but can be accessed in a way that seems to violate those annotations.

ML: Synchronization on field in futile attempt to guard that field (ML_SYNC_ON_FIELD_TO_GUARD_CHANGING_THAT_FIELD)

This method synchronizes on a field in what appears to be an attempt to guard against simultaneous updates to that field. But guarding a field gets a lock on the referenced object, not on the field. This may not provide the mutual exclusion you need, and other threads might be obtaining locks on the referenced objects (for other purposes). An example of this pattern would be:

private Long myNtfSeqNbrCounter = new Long(0);
private Long getNotificationSequenceNumber() {
     Long result = null;
     synchronized(myNtfSeqNbrCounter) {
         result = new Long(myNtfSeqNbrCounter.longValue() + 1);
         myNtfSeqNbrCounter = new Long(result.longValue());
     }
     return result;
}

ML: Method synchronizes on an updated field (ML_SYNC_ON_UPDATED_FIELD)

This method synchronizes on an object referenced from a mutable field. This is unlikely to have useful semantics, since different threads may be synchronizing on different objects.

WS: Class’s writeObject() method is synchronized but nothing else is (WS_WRITEOBJECT_SYNC)

This class has a writeObject() method which is synchronized; however, no other method of the class is synchronized.

RS: Class’s readObject() method is synchronized (RS_READOBJECT_SYNC)

This serializable class defines a readObject() which is synchronized. By definition, an object created by deserialization is only reachable by one thread, and thus there is no need for readObject() to be synchronized. If the readObject() method itself is causing the object to become visible to another thread, that is an example of very dubious coding style.

SC: Constructor invokes Thread.start() (SC_START_IN_CTOR)

The constructor starts a thread. This is likely to be wrong if the class is ever extended/subclassed, since the thread will be started before the subclass constructor is started.

Wa: Wait not in loop (WA_NOT_IN_LOOP)

This method contains a call to java.lang.Object.wait() which is not in a loop. If the monitor is used for multiple conditions, the condition the caller intended to wait for might not be the one that actually occurred.

Wa: Condition.await() not in loop (WA_AWAIT_NOT_IN_LOOP)

This method contains a call to java.util.concurrent.await() (or variants) which is not in a loop. If the object is used for multiple conditions, the condition the caller intended to wait for might not be the one that actually occurred.

No: Using notify() rather than notifyAll() (NO_NOTIFY_NOT_NOTIFYALL)

This method calls notify() rather than notifyAll(). Java monitors are often used for multiple conditions. Calling notify() only wakes up one thread, meaning that the thread woken up might not be the one waiting for the condition that the caller just satisfied.

UL: Method does not release lock on all paths (UL_UNRELEASED_LOCK)

This method acquires a JSR-166 (java.util.concurrent) lock, but does not release it on all paths out of the method. In general, the correct idiom for using a JSR-166 lock is:

Lock l = ...;
l.lock();
try {
    // do something
} finally {
    l.unlock();
}

UL: Method does not release lock on all exception paths (UL_UNRELEASED_LOCK_EXCEPTION_PATH)

This method acquires a JSR-166 (java.util.concurrent) lock, but does not release it on all exception paths out of the method. In general, the correct idiom for using a JSR-166 lock is:

Lock l = ...;
l.lock();
try {
    // do something
} finally {
    l.unlock();
}

MWN: Mismatched wait() (MWN_MISMATCHED_WAIT)

This method calls Object.wait() without obviously holding a lock on the object. Calling wait() without a lock held will result in an IllegalMonitorStateException being thrown.

MWN: Mismatched notify() (MWN_MISMATCHED_NOTIFY)

This method calls Object.notify() or Object.notifyAll() without obviously holding a lock on the object. Calling notify() or notifyAll() without a lock held will result in an IllegalMonitorStateException being thrown.

LI: Incorrect lazy initialization of static field (LI_LAZY_INIT_STATIC)

This method contains an unsynchronized lazy initialization of a non-volatile static field. Because the compiler or processor may reorder instructions, threads are not guaranteed to see a completely initialized object, if the method can be called by multiple threads. You can make the field volatile to correct the problem. For more information, see the Java Memory Model web site.

LI: Incorrect lazy initialization and update of static field (LI_LAZY_INIT_UPDATE_STATIC)

This method contains an unsynchronized lazy initialization of a static field. After the field is set, the object stored into that location is further updated or accessed. The setting of the field is visible to other threads as soon as it is set. If the further accesses in the method that set the field serve to initialize the object, then you have a very serious multithreading bug, unless something else prevents any other thread from accessing the stored object until it is fully initialized.

Even if you feel confident that the method is never called by multiple threads, it might be better to not set the static field until the value you are setting it to is fully populated/initialized.

JLM: Synchronization performed on util.concurrent instance (JLM_JSR166_UTILCONCURRENT_MONITORENTER)

This method performs synchronization on an object that is an instance of a class from the java.util.concurrent package (or its subclasses). Instances of these classes have their own concurrency control mechanisms that are orthogonal to the synchronization provided by the Java keyword synchronized. For example, synchronizing on an AtomicBoolean will not prevent other threads from modifying the AtomicBoolean.

Such code may be correct, but should be carefully reviewed and documented, and may confuse people who have to maintain the code at a later date.

JLM: Using monitor style wait methods on util.concurrent abstraction (JML_JSR166_CALLING_WAIT_RATHER_THAN_AWAIT)

This method calls wait(), notify() or notifyAll() on an object that also provides an await(), signal(), signalAll() method (such as util.concurrent Condition objects). This probably isn’t what you want, and even if you do want it, you should consider changing your design, as other developers will find it exceptionally confusing.

JLM: Synchronization performed on Lock (JLM_JSR166_LOCK_MONITORENTER)

This method performs synchronization on an object that implements java.util.concurrent.locks.Lock. Such an object is locked/unlocked using acquire()/release() rather than using the synchronized (...) construct.

SWL: Method calls Thread.sleep() with a lock held (SWL_SLEEP_WITH_LOCK_HELD)

This method calls Thread.sleep() with a lock held. This may result in very poor performance and scalability, or a deadlock, since other threads may be waiting to acquire the lock. It is a much better idea to call wait() on the lock, which releases the lock and allows other threads to run.

RV: Return value of putIfAbsent ignored, value passed to putIfAbsent reused (RV_RETURN_VALUE_OF_PUTIFABSENT_IGNORED)

The putIfAbsent method is typically used to ensure that a single value is associated with a given key (the first value for which put if absent succeeds). If you ignore the return value and retain a reference to the value passed in, you run the risk of retaining a value that is not the one that is associated with the key in the map. If it matters which one you use and you use the one that isn’t stored in the map, your program will behave incorrectly.

SSD: Instance level lock was used on a shared static data (SSD_DO_NOT_USE_INSTANCE_LOCK_ON_SHARED_STATIC_DATA)

If the lock or the synchronized method is not static, that modifies the static field, that could leave the shared static data unprotected against concurrent access. This could occur in two ways, if a synchronization method uses a non-static lock object, or a synchronized method is declared as non-static. Both ways are ineffective. Best solution is to use a private static final lock object to secure the shared static data.

See SEI CERT rule LCK06-J. Do not use an instance lock to protect shared static data.

Bogus random noise (NOISE)

Bogus random noise: intended to be useful as a control in data mining experiments, not in finding actual bugs in software

NOISE: Bogus warning about a null pointer dereference (NOISE_NULL_DEREFERENCE)

Bogus warning.

NOISE: Bogus warning about a method call (NOISE_METHOD_CALL)

Bogus warning.

NOISE: Bogus warning about a field reference (NOISE_FIELD_REFERENCE)

Bogus warning.

NOISE: Bogus warning about an operation (NOISE_OPERATION)

Bogus warning.

Performance (PERFORMANCE)

Code that is not necessarily incorrect but may be inefficient

HSC: Huge string constants is duplicated across multiple class files (HSC_HUGE_SHARED_STRING_CONSTANT)

A large String constant is duplicated across multiple class files. This is likely because a final field is initialized to a String constant, and the Java language mandates that all references to a final field from other classes be inlined into that classfile. See JDK bug 6447475 for a description of an occurrence of this bug in the JDK and how resolving it reduced the size of the JDK by 1 megabyte.

Dm: The equals and hashCode methods of URL are blocking (DMI_BLOCKING_METHODS_ON_URL)

The equals and hashCode method of URL perform domain name resolution, this can result in a big performance hit. See http://michaelscharf.blogspot.com/2006/11/javaneturlequals-and-hashcode-make.html for more information. Consider using java.net.URI instead.

Dm: Maps and sets of URLs can be performance hogs (DMI_COLLECTION_OF_URLS)

This method or field is or uses a Map or Set of URLs. Since both the equals and hashCode method of URL perform domain name resolution, this can result in a big performance hit. See http://michaelscharf.blogspot.com/2006/11/javaneturlequals-and-hashcode-make.html for more information. Consider using java.net.URI instead.

Dm: Method invokes inefficient new String(String) constructor (DM_STRING_CTOR)

Using the java.lang.String(String) constructor wastes memory because the object so constructed will be functionally indistinguishable from the String passed as a parameter. Just use the argument String directly.

Dm: Method invokes inefficient new String() constructor (DM_STRING_VOID_CTOR)

Creating a new java.lang.String object using the no-argument constructor wastes memory because the object so created will be functionally indistinguishable from the empty string constant "". Java guarantees that identical string constants will be represented by the same String object. Therefore, you should just use the empty string constant directly.

Dm: Method invokes toString() method on a String (DM_STRING_TOSTRING)

Calling String.toString() is a redundant operation. Just use the String.

Dm: Explicit garbage collection; extremely dubious except in benchmarking code (DM_GC)

Code explicitly invokes garbage collection. Except for specific use in benchmarking, this is very dubious.

In the past, situations where people have explicitly invoked the garbage collector in routines such as close or finalize methods has led to huge performance black holes. Garbage collection can be expensive. Any situation that forces hundreds or thousands of garbage collections will bring the machine to a crawl.

Dm: Method invokes inefficient Boolean constructor; use Boolean.valueOf(…) instead (DM_BOOLEAN_CTOR)

Creating new instances of java.lang.Boolean wastes memory, since Boolean objects are immutable and there are only two useful values of this type. Use the Boolean.valueOf() method (or Java 5 autoboxing) to create Boolean objects instead.

Bx: Method invokes inefficient Number constructor; use static valueOf instead (DM_NUMBER_CTOR)

Using new Integer(int) is guaranteed to always result in a new object whereas Integer.valueOf(int) allows caching of values to be done by the compiler, class library, or JVM. Using of cached values avoids object allocation and the code will be faster.

Values between -128 and 127 are guaranteed to have corresponding cached instances and using valueOf is approximately 3.5 times faster than using constructor. For values outside the constant range the performance of both styles is the same.

Unless the class must be compatible with JVMs predating Java 5, use either autoboxing or the valueOf() method when creating instances of Long, Integer, Short, Character, and Byte.

Bx: Method invokes inefficient floating-point Number constructor; use static valueOf instead (DM_FP_NUMBER_CTOR)

Using new Double(double) is guaranteed to always result in a new object whereas Double.valueOf(double) allows caching of values to be done by the compiler, class library, or JVM. Using of cached values avoids object allocation and the code will be faster.

Unless the class must be compatible with JVMs predating Java 5, use either autoboxing or the valueOf() method when creating instances of Double and Float.

Bx: Method allocates a boxed primitive just to call toString (DM_BOXED_PRIMITIVE_TOSTRING)

A boxed primitive is allocated just to call toString(). It is more effective to just use the static form of toString which takes the primitive value. So,

Bx: Boxing/unboxing to parse a primitive (DM_BOXED_PRIMITIVE_FOR_PARSING)

A boxed primitive is created from a String, just to extract the unboxed primitive value. It is more efficient to just call the static parseXXX method.

Bx: Boxing a primitive to compare (DM_BOXED_PRIMITIVE_FOR_COMPARE)

A boxed primitive is created just to call compareTo() method. It’s more efficient to use static compare method (for double and float since Java 1.4, for other primitive types since Java 7) which works on primitives directly.

Bx: Primitive value is unboxed and coerced for ternary operator (BX_UNBOXED_AND_COERCED_FOR_TERNARY_OPERATOR)

A wrapped primitive value is unboxed and converted to another primitive type as part of the evaluation of a conditional ternary operator (the b ? e1 : e2 operator). The semantics of Java mandate that if e1 and e2 are wrapped numeric values, the values are unboxed and converted/coerced to their common type (e.g, if e1 is of type Integer and e2 is of type Float, then e1 is unboxed, converted to a floating point value, and boxed. See JLS Section 15.25.

Bx: Boxed value is unboxed and then immediately reboxed (BX_UNBOXING_IMMEDIATELY_REBOXED)

A boxed value is unboxed and then immediately reboxed.

Bx: Primitive value is boxed and then immediately unboxed (BX_BOXING_IMMEDIATELY_UNBOXED)

A primitive is boxed, and then immediately unboxed. This probably is due to a manual boxing in a place where an unboxed value is required, thus forcing the compiler to immediately undo the work of the boxing.

Bx: Primitive value is boxed then unboxed to perform primitive coercion (BX_BOXING_IMMEDIATELY_UNBOXED_TO_PERFORM_COERCION)

A primitive boxed value constructed and then immediately converted into a different primitive type (e.g., new Double(d).intValue()). Just perform direct primitive coercion (e.g., (int) d).

Dm: Method allocates an object, only to get the class object (DM_NEW_FOR_GETCLASS)

This method allocates an object just to call getClass() on it, in order to retrieve the Class object for it. It is simpler to just access the .class property of the class.

Dm: Use the nextInt method of Random rather than nextDouble to generate a random integer (DM_NEXTINT_VIA_NEXTDOUBLE)

If r is a java.util.Random, you can generate a random number from 0 to n-1 using r.nextInt(n), rather than using (int)(r.nextDouble() * n).

The argument to nextInt must be positive. If, for example, you want to generate a random value from -99 to 0, use -r.nextInt(100).

SS: Unread field: should this field be static? (SS_SHOULD_BE_STATIC)

This class contains an instance final field that is initialized to a compile-time static value. Consider making the field static.

UuF: Unused field (UUF_UNUSED_FIELD)

This field is never used. Consider removing it from the class.

UrF: Unread field (URF_UNREAD_FIELD)

This field is never read. Consider removing it from the class.

SIC: Should be a static inner class (SIC_INNER_SHOULD_BE_STATIC)

This class is an inner class, but does not use its embedded reference to the object which created it. This reference makes the instances of the class larger, and may keep the reference to the creator object alive longer than necessary. If possible, the class should be made static.

SIC: Could be refactored into a static inner class (SIC_INNER_SHOULD_BE_STATIC_NEEDS_THIS)

This class is an inner class, but does not use its embedded reference to the object which created it except during construction of the inner object. This reference makes the instances of the class larger, and may keep the reference to the creator object alive longer than necessary. If possible, the class should be made into a static inner class. Since the reference to the outer object is required during construction of the inner instance, the inner class will need to be refactored so as to pass a reference to the outer instance to the constructor for the inner class.

SIC: Could be refactored into a named static inner class (SIC_INNER_SHOULD_BE_STATIC_ANON)

This class is an inner class, but does not use its embedded reference to the object which created it. This reference makes the instances of the class larger, and may keep the reference to the creator object alive longer than necessary. If possible, the class should be made into a static inner class. Since anonymous inner classes cannot be marked as static, doing this will require refactoring the inner class so that it is a named inner class.

UPM: Private method is never called (UPM_UNCALLED_PRIVATE_METHOD)

This private method is never called. Although it is possible that the method will be invoked through reflection, it is more likely that the method is never used, and should be removed.

SBSC: Method concatenates strings using + in a loop (SBSC_USE_STRINGBUFFER_CONCATENATION)

The method seems to be building a String using concatenation in a loop. In each iteration, the String is converted to a StringBuffer/StringBuilder, appended to, and converted back to a String. This can lead to a cost quadratic in the number of iterations, as the growing string is recopied in each iteration.

Better performance can be obtained by using a StringBuffer (or StringBuilder in Java 5) explicitly.

For example:

// This is bad
String s = "";
for (int i = 0; i < field.length; ++i) {
    s = s + field[i];
}
// This is better
StringBuffer buf = new StringBuffer();
for (int i = 0; i < field.length; ++i) {
    buf.append(field[i]);
}
String s = buf.toString();

IIL: NodeList.getLength() called in a loop (IIL_ELEMENTS_GET_LENGTH_IN_LOOP)

The method calls NodeList.getLength() inside the loop and NodeList was produced by getElementsByTagName call. This NodeList doesn’t store its length, but computes it every time in not very optimal way. Consider storing the length to the variable before the loop.

IIL: Method calls prepareStatement in a loop (IIL_PREPARE_STATEMENT_IN_LOOP)

The method calls Connection.prepareStatement inside the loop passing the constant arguments. If the PreparedStatement should be executed several times there’s no reason to recreate it for each loop iteration. Move this call outside of the loop.

IIL: Method calls Pattern.compile in a loop (IIL_PATTERN_COMPILE_IN_LOOP)

The method calls Pattern.compile inside the loop passing the constant arguments. If the Pattern should be used several times there’s no reason to compile it for each loop iteration. Move this call outside of the loop or even into static final field.

IIL: Method compiles the regular expression in a loop (IIL_PATTERN_COMPILE_IN_LOOP_INDIRECT)

The method creates the same regular expression inside the loop, so it will be compiled every iteration. It would be more optimal to precompile this regular expression using Pattern.compile outside of the loop.

IIO: Inefficient use of String.indexOf(String) (IIO_INEFFICIENT_INDEX_OF)

This code passes a constant string of length 1 to String.indexOf(). It is more efficient to use the integer implementations of String.indexOf(). f. e. call myString.indexOf('.') instead of myString.indexOf(".")

IIO: Inefficient use of String.lastIndexOf(String) (IIO_INEFFICIENT_LAST_INDEX_OF)

This code passes a constant string of length 1 to String.lastIndexOf(). It is more efficient to use the integer implementations of String.lastIndexOf(). f. e. call myString.lastIndexOf('.') instead of myString.lastIndexOf(".")

ITA: Method uses toArray() with zero-length array argument (ITA_INEFFICIENT_TO_ARRAY)

This method uses the toArray() method of a collection derived class, and passes in a zero-length prototype array argument. It is more efficient to use myCollection.toArray(new Foo[myCollection.size()]) If the array passed in is big enough to store all of the elements of the collection, then it is populated and returned directly. This avoids the need to create a second array (by reflection) to return as the result.

WMI: Inefficient use of keySet iterator instead of entrySet iterator (WMI_WRONG_MAP_ITERATOR)

This method accesses the value of a Map entry, using a key that was retrieved from a keySet iterator. It is more efficient to use an iterator on the entrySet of the map, to avoid the Map.get(key) lookup.

UM: Method calls static Math class method on a constant value (UM_UNNECESSARY_MATH)

This method uses a static method from java.lang.Math on a constant value. This method’s result in this case, can be determined statically, and is faster and sometimes more accurate to just use the constant. Methods detected are:

IMA: Method accesses a private member variable of owning class (IMA_INEFFICIENT_MEMBER_ACCESS)

This method of an inner class reads from or writes to a private member variable of the owning class, or calls a private method of the owning class. The compiler must generate a special method to access this private member, causing this to be less efficient. Relaxing the protection of the member variable or method will allow the compiler to treat this as a normal access.

Security (SECURITY)

A use of untrusted input in a way that could create a remotely exploitable security vulnerability.

XSS: Servlet reflected cross site scripting vulnerability in error page (XSS_REQUEST_PARAMETER_TO_SEND_ERROR)

This code directly writes an HTTP parameter to a Server error page (using HttpServletResponse.sendError). Echoing this untrusted input allows for a reflected cross site scripting vulnerability. See http://en.wikipedia.org/wiki/Cross-site_scripting for more information.

SpotBugs looks only for the most blatant, obvious cases of cross site scripting. If SpotBugs found any, you almost certainly have more cross site scripting vulnerabilities that SpotBugs doesn’t report. If you are concerned about cross site scripting, you should seriously consider using a commercial static analysis or pen-testing tool.

XSS: Servlet reflected cross site scripting vulnerability (XSS_REQUEST_PARAMETER_TO_SERVLET_WRITER)

This code directly writes an HTTP parameter to Servlet output, which allows for a reflected cross site scripting vulnerability. See http://en.wikipedia.org/wiki/Cross-site_scripting for more information.

SpotBugs looks only for the most blatant, obvious cases of cross site scripting. If SpotBugs found any, you almost certainly have more cross site scripting vulnerabilities that SpotBugs doesn’t report. If you are concerned about cross site scripting, you should seriously consider using a commercial static analysis or pen-testing tool.

XSS: JSP reflected cross site scripting vulnerability (XSS_REQUEST_PARAMETER_TO_JSP_WRITER)

This code directly writes an HTTP parameter to JSP output, which allows for a cross site scripting vulnerability. See http://en.wikipedia.org/wiki/Cross-site_scripting for more information.

SpotBugs looks only for the most blatant, obvious cases of cross site scripting. If SpotBugs found any, you almost certainly have more cross site scripting vulnerabilities that SpotBugs doesn’t report. If you are concerned about cross site scripting, you should seriously consider using a commercial static analysis or pen-testing tool.

HRS: HTTP cookie formed from untrusted input (HRS_REQUEST_PARAMETER_TO_COOKIE)

This code constructs an HTTP Cookie using an untrusted HTTP parameter. If this cookie is added to an HTTP response, it will allow an HTTP response splitting vulnerability. See http://en.wikipedia.org/wiki/HTTP_response_splitting for more information.

SpotBugs looks only for the most blatant, obvious cases of HTTP response splitting. If SpotBugs found any, you almost certainly have more vulnerabilities that SpotBugs doesn’t report. If you are concerned about HTTP response splitting, you should seriously consider using a commercial static analysis or pen-testing tool.

PT: Absolute path traversal in servlet (PT_ABSOLUTE_PATH_TRAVERSAL)

The software uses an HTTP request parameter to construct a pathname that should be within a restricted directory, but it does not properly neutralize absolute path sequences such as “/abs/path” that can resolve to a location that is outside of that directory. See http://cwe.mitre.org/data/definitions/36.html for more information.

SpotBugs looks only for the most blatant, obvious cases of absolute path traversal. If SpotBugs found any, you almost certainly have more vulnerabilities that SpotBugs doesn’t report. If you are concerned about absolute path traversal, you should seriously consider using a commercial static analysis or pen-testing tool.

PT: Relative path traversal in servlet (PT_RELATIVE_PATH_TRAVERSAL)

The software uses an HTTP request parameter to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as “..” that can resolve to a location that is outside of that directory. See http://cwe.mitre.org/data/definitions/23.html for more information.

SpotBugs looks only for the most blatant, obvious cases of relative path traversal. If SpotBugs found any, you almost certainly have more vulnerabilities that SpotBugs doesn’t report. If you are concerned about relative path traversal, you should seriously consider using a commercial static analysis or pen-testing tool.

Dm: Hardcoded constant database password (DMI_CONSTANT_DB_PASSWORD)

This code creates a database connect using a hardcoded, constant password. Anyone with access to either the source code or the compiled code can easily learn the password.

Dm: Empty database password (DMI_EMPTY_DB_PASSWORD)

This code creates a database connect using a blank or empty password. This indicates that the database is not protected by a password.

SQL: Nonconstant string passed to execute or addBatch method on an SQL statement (SQL_NONCONSTANT_STRING_PASSED_TO_EXECUTE)

The method invokes the execute or addBatch method on an SQL statement with a String that seems to be dynamically generated. Consider using a prepared statement instead. It is more efficient and less vulnerable to SQL injection attacks.

SQL: A prepared statement is generated from a nonconstant String (SQL_PREPARED_STATEMENT_GENERATED_FROM_NONCONSTANT_STRING)

The code creates an SQL prepared statement from a nonconstant String. If unchecked, tainted data from a user is used in building this String, SQL injection could be used to make the prepared statement do something unexpected and undesirable.

ASE: Expression in assertion may produce a side effect (ASE_ASSERTION_WITH_SIDE_EFFECT)

Expressions used in assertions must not produce side effects.

See SEI CERT Rule EXP06 for more information.

ASE: Method invoked in assertion may produce a side effect (ASE_ASSERTION_WITH_SIDE_EFFECT_METHOD)

Expressions used in assertions must not produce side effects.

See SEI CERT Rule EXP06 for more information.

Dodgy code (STYLE)

Code that is confusing, anomalous, or written in a way that leads itself to errors. Examples include dead local stores, switch fall through, unconfirmed casts, and redundant null check of value known to be null. More false positives accepted. In previous versions of SpotBugs, this category was known as Style.

CAA: Covariant array assignment to a field (CAA_COVARIANT_ARRAY_FIELD)

Array of covariant type is assigned to a field. This is confusing and may lead to ArrayStoreException at runtime if the reference of some other type will be stored in this array later like in the following code:

Number[] arr = new Integer[10];
arr[0] = 1.0;

Consider changing the type of created array or the field type.

CAA: Covariant array is returned from the method (CAA_COVARIANT_ARRAY_RETURN)

Array of covariant type is returned from the method. This is confusing and may lead to ArrayStoreException at runtime if the calling code will try to store the reference of some other type in the returned array.

Consider changing the type of created array or the method return type.

CAA: Covariant array assignment to a local variable (CAA_COVARIANT_ARRAY_LOCAL)

Array of covariant type is assigned to a local variable. This is confusing and may lead to ArrayStoreException at runtime if the reference of some other type will be stored in this array later like in the following code:

Number[] arr = new Integer[10];
arr[0] = 1.0;

Consider changing the type of created array or the local variable type.

Dm: Call to unsupported method (DMI_UNSUPPORTED_METHOD)

All targets of this method invocation throw an UnsupportedOperationException.

Dm: Thread passed where Runnable expected (DMI_THREAD_PASSED_WHERE_RUNNABLE_EXPECTED)

A Thread object is passed as a parameter to a method where a Runnable is expected. This is rather unusual, and may indicate a logic error or cause unexpected behavior.

NP: Dereference of the result of readLine() without nullcheck (NP_DEREFERENCE_OF_READLINE_VALUE)

The result of invoking readLine() is dereferenced without checking to see if the result is null. If there are no more lines of text to read, readLine() will return null and dereferencing that will generate a null pointer exception.

NP: Immediate dereference of the result of readLine() (NP_IMMEDIATE_DEREFERENCE_OF_READLINE)

The result of invoking readLine() is immediately dereferenced. If there are no more lines of text to read, readLine() will return null and dereferencing that will generate a null pointer exception.

RV: Remainder of 32-bit signed random integer (RV_REM_OF_RANDOM_INT)

This code generates a random signed integer and then computes the remainder of that value modulo another value. Since the random number can be negative, the result of the remainder operation can also be negative. Be sure this is intended, and strongly consider using the Random.nextInt(int) method instead.

RV: Remainder of hashCode could be negative (RV_REM_OF_HASHCODE)

This code computes a hashCode, and then computes the remainder of that value modulo another value. Since the hashCode can be negative, the result of the remainder operation can also be negative.

Assuming you want to ensure that the result of your computation is nonnegative, you may need to change your code. If you know the divisor is a power of 2, you can use a bitwise and operator instead (i.e., instead of using x.hashCode()%n, use x.hashCode()&(n-1)). This is probably faster than computing the remainder as well. If you don’t know that the divisor is a power of 2, take the absolute value of the result of the remainder operation (i.e., use Math.abs(x.hashCode()%n)).

Eq: Unusual equals method (EQ_UNUSUAL)

This class doesn’t do any of the patterns we recognize for checking that the type of the argument is compatible with the type of the this object. There might not be anything wrong with this code, but it is worth reviewing.

Eq: Class doesn’t override equals in superclass (EQ_DOESNT_OVERRIDE_EQUALS)

This class extends a class that defines an equals method and adds fields, but doesn’t define an equals method itself. Thus, equality on instances of this class will ignore the identity of the subclass and the added fields. Be sure this is what is intended, and that you don’t need to override the equals method. Even if you don’t need to override the equals method, consider overriding it anyway to document the fact that the equals method for the subclass just return the result of invoking super.equals(o).

NS: Questionable use of non-short-circuit logic (NS_NON_SHORT_CIRCUIT)

This code seems to be using non-short-circuit logic (e.g., & or |) rather than short-circuit logic (&& or ||). Non-short-circuit logic causes both sides of the expression to be evaluated even when the result can be inferred from knowing the left-hand side. This can be less efficient and can result in errors if the left-hand side guards cases when evaluating the right-hand side can generate an error.

See the Java Language Specification for details.

NS: Potentially dangerous use of non-short-circuit logic (NS_DANGEROUS_NON_SHORT_CIRCUIT)

This code seems to be using non-short-circuit logic (e.g., & or |) rather than short-circuit logic (&& or ||). In addition, it seems possible that, depending on the value of the left hand side, you might not want to evaluate the right hand side (because it would have side effects, could cause an exception or could be expensive.

Non-short-circuit logic causes both sides of the expression to be evaluated even when the result can be inferred from knowing the left-hand side. This can be less efficient and can result in errors if the left-hand side guards cases when evaluating the right-hand side can generate an error.

See the Java Language Specification for details.

IC: Initialization circularity (IC_INIT_CIRCULARITY)

A circularity was detected in the static initializers of the two classes referenced by the bug instance. Many kinds of unexpected behavior may arise from such circularity.

IA: Potentially ambiguous invocation of either an inherited or outer method (IA_AMBIGUOUS_INVOCATION_OF_INHERITED_OR_OUTER_METHOD)

An inner class is invoking a method that could be resolved to either an inherited method or a method defined in an outer class. For example, you invoke foo(17), which is defined in both a superclass and in an outer method. By the Java semantics, it will be resolved to invoke the inherited method, but this may not be what you intend.

If you really intend to invoke the inherited method, invoke it by invoking the method on super (e.g., invoke super.foo(17)), and thus it will be clear to other readers of your code and to SpotBugs that you want to invoke the inherited method, not the method in the outer class.

If you call this.foo(17), then the inherited method will be invoked. However, since SpotBugs only looks at classfiles, it cannot tell the difference between an invocation of this.foo(17) and foo(17), it will still complain about a potential ambiguous invocation.

Se: Private readResolve method not inherited by subclasses (SE_PRIVATE_READ_RESOLVE_NOT_INHERITED)

This class defines a private readResolve method. Since it is private, it won’t be inherited by subclasses. This might be intentional and OK, but should be reviewed to ensure it is what is intended.

Se: Transient field of class that isn’t Serializable. (SE_TRANSIENT_FIELD_OF_NONSERIALIZABLE_CLASS)

The field is marked as transient, but the class isn’t Serializable, so marking it as transient has absolutely no effect. This may be leftover marking from a previous version of the code in which the class was Serializable, or it may indicate a misunderstanding of how serialization works.

This bug is reported only if special option reportTransientFieldOfNonSerializableClass is set.

SF: Switch statement found where one case falls through to the next case (SF_SWITCH_FALLTHROUGH)

This method contains a switch statement where one case branch will fall through to the next case. Usually you need to end this case with a break or return.

SF: Switch statement found where default case is missing (SF_SWITCH_NO_DEFAULT)

This method contains a switch statement where default case is missing. Usually you need to provide a default case.

Because the analysis only looks at the generated bytecode, this warning can be incorrect triggered if the default case is at the end of the switch statement and the switch statement doesn’t contain break statements for other cases.

UuF: Unused public or protected field (UUF_UNUSED_PUBLIC_OR_PROTECTED_FIELD)

This field is never used. The field is public or protected, so perhaps it is intended to be used with classes not seen as part of the analysis. If not, consider removing it from the class.

UrF: Unread public/protected field (URF_UNREAD_PUBLIC_OR_PROTECTED_FIELD)

This field is never read. The field is public or protected, so perhaps it is intended to be used with classes not seen as part of the analysis. If not, consider removing it from the class.

QF: Complicated, subtle or wrong increment in for-loop (QF_QUESTIONABLE_FOR_LOOP)

Are you sure this for loop is incrementing/decrementing the correct variable? It appears that another variable is being initialized and checked by the for loop.

NP: Read of unwritten public or protected field (NP_UNWRITTEN_PUBLIC_OR_PROTECTED_FIELD)

The program is dereferencing a public or protected field that does not seem to ever have a non-null value written to it. Unless the field is initialized via some mechanism not seen by the analysis, dereferencing this value will generate a null pointer exception.

UwF: Field not initialized in constructor but dereferenced without null check (UWF_FIELD_NOT_INITIALIZED_IN_CONSTRUCTOR)

This field is never initialized within any constructor, and is therefore could be null after the object is constructed. Elsewhere, it is loaded and dereferenced without a null check. This could be either an error or a questionable design, since it means a null pointer exception will be generated if that field is dereferenced before being initialized.

UwF: Unwritten public or protected field (UWF_UNWRITTEN_PUBLIC_OR_PROTECTED_FIELD)

No writes were seen to this public/protected field. All reads of it will return the default value. Check for errors (should it have been initialized?), or remove it if it is useless.

UC: Useless non-empty void method (UC_USELESS_VOID_METHOD)

Our analysis shows that this non-empty void method does not actually perform any useful work. Please check it: probably there’s a mistake in its code or its body can be fully removed.

We are trying to reduce the false positives as much as possible, but in some cases this warning might be wrong. Common false-positive cases include:

• The method is intended to trigger loading of some class which may have a side effect.
• The method is intended to implicitly throw some obscure exception.

UC: Condition has no effect (UC_USELESS_CONDITION)

This condition always produces the same result as the value of the involved variable that was narrowed before. Probably something else was meant or the condition can be removed.

UC: Condition has no effect due to the variable type (UC_USELESS_CONDITION_TYPE)

This condition always produces the same result due to the type range of the involved variable. Probably something else was meant or the condition can be removed.

UC: Useless object created (UC_USELESS_OBJECT)

Our analysis shows that this object is useless. It’s created and modified, but its value never go outside of the method or produce any side-effect. Either there is a mistake and object was intended to be used or it can be removed.

This analysis rarely produces false-positives. Common false-positive cases include:

- This object used to implicitly throw some obscure exception.

- This object used as a stub to generalize the code.

- This object used to hold strong references to weak/soft-referenced objects.

UC: Useless object created on stack (UC_USELESS_OBJECT_STACK)

This object is created just to perform some modifications which don’t have any side-effect. Probably something else was meant or the object can be removed.

RV: Method ignores return value, is this OK? (RV_RETURN_VALUE_IGNORED_INFERRED)

This code calls a method and ignores the return value. The return value is the same type as the type the method is invoked on, and from our analysis it looks like the return value might be important (e.g., like ignoring the return value of String.toLowerCase()).

We are guessing that ignoring the return value might be a bad idea just from a simple analysis of the body of the method. You can use a @CheckReturnValue annotation to instruct SpotBugs as to whether ignoring the return value of this method is important or acceptable.

Please investigate this closely to decide whether it is OK to ignore the return value.

RV: Return value of method without side effect is ignored (RV_RETURN_VALUE_IGNORED_NO_SIDE_EFFECT)

This code calls a method and ignores the return value. However, our analysis shows that the method (including its implementations in subclasses if any) does not produce any effect other than return value. Thus, this call can be removed.

We are trying to reduce the false positives as much as possible, but in some cases this warning might be wrong. Common false-positive cases include:

- The method is designed to be overridden and produce a side effect in other projects which are out of the scope of the analysis.

- The method is called to trigger the class loading which may have a side effect.

- The method is called just to get some exception.

If you feel that our assumption is incorrect, you can use a @CheckReturnValue annotation to instruct SpotBugs that ignoring the return value of this method is acceptable.

RV: Method checks to see if result of String.indexOf is positive (RV_CHECK_FOR_POSITIVE_INDEXOF)

The method invokes String.indexOf and checks to see if the result is positive or non-positive. It is much more typical to check to see if the result is negative or non-negative. It is positive only if the substring checked for occurs at some place other than at the beginning of the String.

RV: Method discards result of readLine after checking if it is non-null (RV_DONT_JUST_NULL_CHECK_READLINE)

The value returned by readLine is discarded after checking to see if the return value is non-null. In almost all situations, if the result is non-null, you will want to use that non-null value. Calling readLine again will give you a different line.

NP: Parameter must be non-null but is marked as nullable (NP_PARAMETER_MUST_BE_NONNULL_BUT_MARKED_AS_NULLABLE)

This parameter is always used in a way that requires it to be non-null, but the parameter is explicitly annotated as being Nullable. Either the use of the parameter or the annotation is wrong.

NP: Possible null pointer dereference due to return value of called method (NP_NULL_ON_SOME_PATH_FROM_RETURN_VALUE)

The return value from a method is dereferenced without a null check, and the return value of that method is one that should generally be checked for null. This may lead to a NullPointerException when the code is executed.

NP: Possible null pointer dereference on branch that might be infeasible (NP_NULL_ON_SOME_PATH_MIGHT_BE_INFEASIBLE)

There is a branch of statement that, if executed, guarantees that a null value will be dereferenced, which would generate a NullPointerException when the code is executed. Of course, the problem might be that the branch or statement is infeasible and that the null pointer exception cannot ever be executed; deciding that is beyond the ability of SpotBugs. Due to the fact that this value had been previously tested for nullness, this is a definite possibility.

NP: Load of known null value (NP_LOAD_OF_KNOWN_NULL_VALUE)

The variable referenced at this point is known to be null due to an earlier check against null. Although this is valid, it might be a mistake (perhaps you intended to refer to a different variable, or perhaps the earlier check to see if the variable is null should have been a check to see if it was non-null).

PZLA: Consider returning a zero length array rather than null (PZLA_PREFER_ZERO_LENGTH_ARRAYS)

It is often a better design to return a length zero array rather than a null reference to indicate that there are no results (i.e., an empty list of results). This way, no explicit check for null is needed by clients of the method.

On the other hand, using null to indicate “there is no answer to this question” is probably appropriate. For example, File.listFiles() returns an empty list if given a directory containing no files, and returns null if the file is not a directory.

UCF: Useless control flow (UCF_USELESS_CONTROL_FLOW)

This method contains a useless control flow statement, where control flow continues onto the same place regardless of whether or not the branch is taken. For example, this is caused by having an empty statement block for an if statement:

if (argv.length == 0) {
    // TODO: handle this case
}

UCF: Useless control flow to next line (UCF_USELESS_CONTROL_FLOW_NEXT_LINE)

This method contains a useless control flow statement in which control flow follows to the same or following line regardless of whether or not the branch is taken. Often, this is caused by inadvertently using an empty statement as the body of an if statement, e.g.:

if (argv.length == 1);
    System.out.println("Hello, " + argv[0]);

RCN: Redundant nullcheck of value known to be null (RCN_REDUNDANT_NULLCHECK_OF_NULL_VALUE)

This method contains a redundant check of a known null value against the constant null.

RCN: Redundant nullcheck of value known to be non-null (RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE)

This method contains a redundant check of a known non-null value against the constant null.

RCN: Redundant comparison of two null values (RCN_REDUNDANT_COMPARISON_TWO_NULL_VALUES)

This method contains a redundant comparison of two references known to both be definitely null.

RCN: Redundant comparison of non-null value to null (RCN_REDUNDANT_COMPARISON_OF_NULL_AND_NONNULL_VALUE)

This method contains a reference known to be non-null with another reference known to be null.

SA: Self assignment of local variable (SA_LOCAL_SELF_ASSIGNMENT)

This method contains a self assignment of a local variable; e.g.

public void foo() {
    int x = 3;
    x = x;
}

Such assignments are useless, and may indicate a logic error or typo.

INT: Integer remainder modulo 1 (INT_BAD_REM_BY_1)

Any expression (exp % 1) is guaranteed to always return zero. Did you mean (exp & 1) or (exp % 2) instead?

INT: Vacuous comparison of integer value (INT_VACUOUS_COMPARISON)

There is an integer comparison that always returns the same value (e.g., x <= Integer.MAX_VALUE).

INT: Vacuous bit mask operation on integer value (INT_VACUOUS_BIT_OPERATION)

This is an integer bit operation (and, or, or exclusive or) that doesn’t do any useful work (e.g., v & 0xffffffff).

SA: Double assignment of local variable (SA_LOCAL_DOUBLE_ASSIGNMENT)

This method contains a double assignment of a local variable; e.g.

public void foo() {
    int x,y;
    x = x = 17;
}

Assigning the same value to a variable twice is useless, and may indicate a logic error or typo.

SA: Double assignment of field (SA_FIELD_DOUBLE_ASSIGNMENT)

This method contains a double assignment of a field; e.g.

int x,y;
public void foo() {
    x = x = 17;
}

Assigning to a field twice is useless, and may indicate a logic error or typo.

DLS: Useless assignment in return statement (DLS_DEAD_LOCAL_STORE_IN_RETURN)

This statement assigns to a local variable in a return statement. This assignment has no effect. Please verify that this statement does the right thing.

DLS: Dead store to local variable (DLS_DEAD_LOCAL_STORE)

This instruction assigns a value to a local variable, but the value is not read or used in any subsequent instruction. Often, this indicates an error, because the value computed is never used.

Note that Sun’s javac compiler often generates dead stores for final local variables. Because SpotBugs is a bytecode-based tool, there is no easy way to eliminate these false positives.

DLS: Dead store to local variable that shadows field (DLS_DEAD_LOCAL_STORE_SHADOWS_FIELD)

This instruction assigns a value to a local variable, but the value is not read or used in any subsequent instruction. Often, this indicates an error, because the value computed is never used. There is a field with the same name as the local variable. Did you mean to assign to that variable instead?

DLS: Dead store of null to local variable (DLS_DEAD_LOCAL_STORE_OF_NULL)

The code stores null into a local variable, and the stored value is not read. This store may have been introduced to assist the garbage collector, but as of Java SE 6.0, this is no longer needed or useful.

REC: Exception is caught when Exception is not thrown (REC_CATCH_EXCEPTION)

This method uses a try-catch block that catches Exception objects, but Exception is not thrown within the try block, and RuntimeException is not explicitly caught. It is a common bug pattern to say try { … } catch (Exception e) { something } as a shorthand for catching a number of types of exception each of whose catch blocks is identical, but this construct also accidentally catches RuntimeException as well, masking potential bugs.

A better approach is to either explicitly catch the specific exceptions that are thrown, or to explicitly catch RuntimeException exception, rethrow it, and then catch all non-Runtime Exceptions, as shown below:

try {
    ...
} catch (RuntimeException e) {
    throw e;
} catch (Exception e) {
    ... deal with all non-runtime exceptions ...
}

DCN: NullPointerException caught (DCN_NULLPOINTER_EXCEPTION)

According to SEI Cert rule ERR08-J NullPointerException should not be caught. Handling NullPointerException is considered an inferior alternative to null-checking.

This non-compliant code catches a NullPointerException to see if an incoming parameter is null:

boolean hasSpace(String m) {
  try {
    String ms[] = m.split(" ");
    return names.length != 1;
  } catch (NullPointerException e) {
    return false;
  }
}

A compliant solution would use a null-check as in the following example:

boolean hasSpace(String m) {
    if (m == null) return false;
    String ms[] = m.split(" ");
    return names.length != 1;
}

FE: Test for floating point equality (FE_FLOATING_POINT_EQUALITY)

This operation compares two floating point values for equality. Because floating point calculations may involve rounding, calculated float and double values may not be accurate. For values that must be precise, such as monetary values, consider using a fixed-precision type such as BigDecimal. For values that need not be precise, consider comparing for equality within some range, for example: if ( Math.abs(x - y) < .0000001 ). See the Java Language Specification, section 4.2.4.

CD: Test for circular dependencies among classes (CD_CIRCULAR_DEPENDENCY)

This class has a circular dependency with other classes. This makes building these classes difficult, as each is dependent on the other to build correctly. Consider using interfaces to break the hard dependency.

RI: Class implements same interface as superclass (RI_REDUNDANT_INTERFACES)

This class declares that it implements an interface that is also implemented by a superclass. This is redundant because once a superclass implements an interface, all subclasses by default also implement this interface. It may point out that the inheritance hierarchy has changed since this class was created, and consideration should be given to the ownership of the interface’s implementation.

MTIA: Class extends Struts Action class and uses instance variables (MTIA_SUSPECT_STRUTS_INSTANCE_FIELD)

This class extends from a Struts Action class, and uses an instance member variable. Since only one instance of a struts Action class is created by the Struts framework, and used in a multithreaded way, this paradigm is highly discouraged and most likely problematic. Consider only using method local variables. Only instance fields that are written outside of a monitor are reported.

MTIA: Class extends Servlet class and uses instance variables (MTIA_SUSPECT_SERVLET_INSTANCE_FIELD)

This class extends from a Servlet class, and uses an instance member variable. Since only one instance of a Servlet class is created by the J2EE framework, and used in a multithreaded way, this paradigm is highly discouraged and most likely problematic. Consider only using method local variables.

PS: Class exposes synchronization and semaphores in its public interface (PS_PUBLIC_SEMAPHORES)

This class uses synchronization along with wait(), notify() or notifyAll() on itself (the this reference). Client classes that use this class, may, in addition, use an instance of this class as a synchronizing object. Because two classes are using the same object for synchronization, Multithread correctness is suspect. You should not synchronize nor call semaphore methods on a public reference. Consider using an internal private member variable to control synchronization.

ICAST: Result of integer multiplication cast to long (ICAST_INTEGER_MULTIPLY_CAST_TO_LONG)

This code performs integer multiply and then converts the result to a long, as in:

long convertDaysToMilliseconds(int days) { return 1000*3600*24*days; }

If the multiplication is done using long arithmetic, you can avoid the possibility that the result will overflow. For example, you could fix the above code to:

long convertDaysToMilliseconds(int days) { return 1000L*3600*24*days; }

or

static final long MILLISECONDS_PER_DAY = 24L*3600*1000;
long convertDaysToMilliseconds(int days) { return days * MILLISECONDS_PER_DAY; }

ICAST: Integral division result cast to double or float (ICAST_IDIV_CAST_TO_DOUBLE)

This code casts the result of an integral division (e.g., int or long division) operation to double or float. Doing division on integers truncates the result to the integer value closest to zero. The fact that the result was cast to double suggests that this precision should have been retained. What was probably meant was to cast one or both of the operands to double before performing the division. Here is an example:

int x = 2;
int y = 5;
// Wrong: yields result 0.0
double value1 = x / y;
// Right: yields result 0.4
double value2 = x / (double) y;

BC: Questionable cast to concrete collection (BC_BAD_CAST_TO_CONCRETE_COLLECTION)

This code casts an abstract collection (such as a Collection, List, or Set) to a specific concrete implementation (such as an ArrayList or HashSet). This might not be correct, and it may make your code fragile, since it makes it harder to switch to other concrete implementations at a future point. Unless you have a particular reason to do so, just use the abstract collection class.

BC: Unchecked/unconfirmed cast (BC_UNCONFIRMED_CAST)

This cast is unchecked, and not all instances of the type cast from can be cast to the type it is being cast to. Check that your program logic ensures that this cast will not fail.

BC: Unchecked/unconfirmed cast of return value from method (BC_UNCONFIRMED_CAST_OF_RETURN_VALUE)

This code performs an unchecked cast of the return value of a method. The code might be calling the method in such a way that the cast is guaranteed to be safe, but SpotBugs is unable to verify that the cast is safe. Check that your program logic ensures that this cast will not fail.

BC: instanceof will always return true (BC_VACUOUS_INSTANCEOF)

This instanceof test will always return true (unless the value being tested is null). Although this is safe, make sure it isn’t an indication of some misunderstanding or some other logic error. If you really want to test the value for being null, perhaps it would be clearer to do better to do a null test rather than an instanceof test.

BC: Questionable cast to abstract collection (BC_BAD_CAST_TO_ABSTRACT_COLLECTION)

This code casts a Collection to an abstract collection (such as List, Set, or Map). Ensure that you are guaranteed that the object is of the type you are casting to. If all you need is to be able to iterate through a collection, you don’t need to cast it to a Set or List.

IM: Check for oddness that won’t work for negative numbers (IM_BAD_CHECK_FOR_ODD)

The code uses x % 2 == 1 to check to see if a value is odd, but this won’t work for negative numbers (e.g., (-5) % 2 == -1). If this code is intending to check for oddness, consider using (x & 1) == 1, or x % 2 != 0.

IM: Computation of average could overflow (IM_AVERAGE_COMPUTATION_COULD_OVERFLOW)

The code computes the average of two integers using either division or signed right shift, and then uses the result as the index of an array. If the values being averaged are very large, this can overflow (resulting in the computation of a negative average). Assuming that the result is intended to be nonnegative, you can use an unsigned right shift instead. In other words, rather that using (low+high)/2, use (low+high) >>> 1

This bug exists in many earlier implementations of binary search and merge sort. Martin Buchholz found and fixed it in the JDK libraries, and Joshua Bloch widely publicized the bug pattern.

BSHIFT: Unsigned right shift cast to short/byte (ICAST_QUESTIONABLE_UNSIGNED_RIGHT_SHIFT)

The code performs an unsigned right shift, whose result is then cast to a short or byte, which discards the upper bits of the result. Since the upper bits are discarded, there may be no difference between a signed and unsigned right shift (depending upon the size of the shift).

DMI: Code contains a hard coded reference to an absolute pathname (DMI_HARDCODED_ABSOLUTE_FILENAME)

This code constructs a File object using a hard coded to an absolute pathname (e.g., new File("/home/dannyc/workspace/j2ee/src/share/com/sun/enterprise/deployment");

DMI: Invocation of substring(0), which returns the original value (DMI_USELESS_SUBSTRING)

This code invokes substring(0) on a String, which returns the original value.

ST: Write to static field from instance method (ST_WRITE_TO_STATIC_FROM_INSTANCE_METHOD)

This instance method writes to a static field. This is tricky to get correct if multiple instances are being manipulated, and generally bad practice.

DMI: Non serializable object written to ObjectOutput (DMI_NONSERIALIZABLE_OBJECT_WRITTEN)

This code seems to be passing a non-serializable object to the ObjectOutput.writeObject method. If the object is, indeed, non-serializable, an error will result.

DB: Method uses the same code for two branches (DB_DUPLICATE_BRANCHES)

This method uses the same code to implement two branches of a conditional branch. Check to ensure that this isn’t a coding mistake.

DB: Method uses the same code for two switch clauses (DB_DUPLICATE_SWITCH_CLAUSES)

This method uses the same code to implement two clauses of a switch statement. This could be a case of duplicate code, but it might also indicate a coding mistake.

XFB: Method directly allocates a specific implementation of xml interfaces (XFB_XML_FACTORY_BYPASS)

This method allocates a specific implementation of an xml interface. It is preferable to use the supplied factory classes to create these objects so that the implementation can be changed at runtime. See

• javax.xml.parsers.DocumentBuilderFactory
• javax.xml.parsers.SAXParserFactory
• javax.xml.transform.TransformerFactory
• org.w3c.dom.Document.createXXXX

for details.

USM: Method superfluously delegates to parent class method (USM_USELESS_SUBCLASS_METHOD)

This derived method merely calls the same superclass method passing in the exact parameters received. This method can be removed, as it provides no additional value.

USM: Abstract Method is already defined in implemented interface (USM_USELESS_ABSTRACT_METHOD)

This abstract method is already defined in an interface that is implemented by this abstract class. This method can be removed, as it provides no additional value.

CI: Class is final but declares protected field (CI_CONFUSED_INHERITANCE)

This class is declared to be final, but declares fields to be protected. Since the class is final, it cannot be derived from, and the use of protected is confusing. The access modifier for the field should be changed to private or public to represent the true use for the field.

TQ: Value required to not have type qualifier, but marked as unknown (TQ_EXPLICIT_UNKNOWN_SOURCE_VALUE_REACHES_NEVER_SINK)

A value is used in a way that requires it to be never be a value denoted by a type qualifier, but there is an explicit annotation stating that it is not known where the value is prohibited from having that type qualifier. Either the usage or the annotation is incorrect.

TQ: Value required to have type qualifier, but marked as unknown (TQ_EXPLICIT_UNKNOWN_SOURCE_VALUE_REACHES_ALWAYS_SINK)

A value is used in a way that requires it to be always be a value denoted by a type qualifier, but there is an explicit annotation stating that it is not known where the value is required to have that type qualifier. Either the usage or the annotation is incorrect.

NP: Method relaxes nullness annotation on return value (NP_METHOD_RETURN_RELAXING_ANNOTATION)

A method should always implement the contract of a method it overrides. Thus, if a method takes is annotated as returning a @Nonnull value, you shouldn’t override that method in a subclass with a method annotated as returning a @Nullable or @CheckForNull value. Doing so violates the contract that the method shouldn’t return null.

NP: Method tightens nullness annotation on parameter (NP_METHOD_PARAMETER_TIGHTENS_ANNOTATION)

A method should always implement the contract of a method it overrides. Thus, if a method takes a parameter that is marked as @Nullable, you shouldn’t override that method in a subclass with a method where that parameter is @Nonnull. Doing so violates the contract that the method should handle a null parameter.