The primary key class can be specific to a particular entity bean class.
That is, each entity bean can define its own primary key class. Or multiple entity beans CAN share the same primary key class.
If two entity objects with the SAME home interface have the SAME primary key, they are considered IDENTICAL entity objects. If they have a different primary key, they are considered different entity objects.
There are 2 ways of comparing Entity Beans:
1. Using isIdentical(EJBObject obj) method of javax.ejb.EJBObject interface on bean's REMOTE interface, or isIdentical(EJBLocalObject obj) method of javax.ejb.EJBLocalObject interface on bean's LOCAL
2. Comparing primary keys of two entity object references (ONLY FROM THE SAME HOME INTERFACE !) :
More details here : http://java.boot.by/bcd-guide/ch08s02.html