What should be done that ERD Generated Java (hibernate) superclass to be declared abstract?

Hello,
I need to design a DB and generate Java code from the ERD for the following situation:

A User has a list of Advertisements, where the User is a real entity and Advertisement should be an abstract class implemented by more specific P_Advertisement, S_Advertisement and V_Advertisement classes like in attached file.
The problem is that when I generate the Java (Hibernate) classes from this erd I get a concrete class for Advertise entity. What I need is an abstract class for Advertise and concrete classes for the subtypes.
What should I do to produce the right java code from the erd?
schema.png