JDO provides a means of transparent persistence of objects of user defined classes. With JDO there are actually 3 types of classes.

• Persistence Capable classes are classes whose instances can be persisted to a datastore. JDO provide the mechanism for persisting these instances, and they are core to JDO. These classes need to be enhanced according to a JDO Meta-Data specification before use within a JDO environment.

• Persistence Aware classes are classes that manipulate PersistenceCapable instances through direct attribute manipulation. These classes are typically enhanced with very minimal JDO Meta-Data. The enhancement process performs very little changes to these classes.

• Normal classes are classes that aren’t themselves persistable, and have no knowledge of persistence either. These classes are totally unchanged in JDO, and require no JDO Meta-Data whatsoever.

PersistenceCapable

Classes are defined as PersistenceCapable, either by XML MetaData, like this

<class name="MyClass">
    ...
</class>

or using Annotations, like this

@PersistenceCapable
public class MyClass
{
    ...
}

PersistenceAware

Classes are defined as PersistenceAware either by XML MetaData, like this

<class name="MyClass" persistence-modifier="persistence-aware"/>

or using Annotations, like this

@PersistenceAware
public class MyClass
{
    ...
}