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I should start out by saying that I am fairly new to Java EE and that I do not have a strong theoretical background in Java yet. I'm having trouble grasping how to use JPA together with interfaces in Java. To illustrate what I find hard I created a very simple example. If I have two simple interfaces Person and Pet : public interface Person { public Pet getPet(); public void setPet(Pet pet); } public interface Pet { public String getName(); } And an Entity PersonEntity which implements Person as well as a PetEntity which implements Pet : @Entity public class PersonEntity implements Person { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private PetEntity pet; @Override public void setPet(Pet pet) { /* How do i solve this? */ } } @Entity public class PetEntity implements Pet { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private String name; /* Getters and Setters omitted */ } How do I properly handle the case in the setPet method in which I want to persist the relationships between the two entities above? The main reason I want to use interfaces is because I want to keep dependencies between modules/layers to the public interfaces. How else do I avoid getting a dependency from e.g. my ManagedBean directly to an Entity? If someone recommends against using interfaces on entities, then please explain what alternatives methods or patterns there are.

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