Howdy,
Your entity bean is free to implement another
Java class.
EJB supports inheritance just as Java does, but EJB does *not* (at this time) support what they call "bean inheritance". Bean inheritance would give you the capability to inherit not just the things you'd inherit through the Java language, but also some of the 'beanness'. If you're familiar with non-enterprise Javabeans, they DO support bean inheritance (through things like BeanInfo). But EJB does not.
So, you can go ahead and have your bean inherit from another class. In EJB 1.1, it was not uncommon to subclass a bean-managed entity bean and make it container-managed, which is why the ejbCreate() method of a CMP bean has the same return type (the pk) even though the Container does not want or need you to return the PK from a CMP bean, and you are only supposed to return 'null' from a CMP bean.
If some form of bean inheritance were possible, it might mean, for example, that the deployment descriptor of the superclass bean would be picked up when you deploy the subclass bean, and then you might create only a *partial* DD for the subclass bean, perhaps putting in ONLY the parts of the DD that you want to be different from the superclass bean's behavior. There would be an awful lot of issues and complexities to work out, but bean inheritance might be really cool... but it's not supported now (and I don't believe in 2.1, either).
cheers,
Kathy