public Extent getExtent (Class pcClass, boolean includeSubclasses);

Extents are logical representations of all persistent instances of a given persistence-capable class, possibly including subclasses.

Extents are obtained through the PersistenceManager's getExtent method. This method takes two parameters: the class of objects the Extent contains, and a boolean indicating whether or not the Extent also contains subclass instances.

You cannot retrieve Extents for persistence-capable classes whose metadata specifies a value of false for the requires-extent attribute.