Question

I have classes A, B with B extends A
I have interface defined as

public interface MyProcessor<EVENT> {
     void processEvent(EVENT event);
}

I have two implementations

public class EventAProcessor implements EventProcessor<A> {
    @Override
    public void processEvent(A a) {
}
public class EventBProcessor implements EventProcessor<B> {
    @Override
    public void processEvent(B b) {
}

there is common processing so I decided to extend BProcessor from Aprocessor

public class EventBProcessor extends EventAProcessor implements EventProcessor<B> {

    }

This is where it fails with the message

 MyProcessor cannot be inherited with different arguments: <A> and <B>

I have other solutions to workaround my problem, but just wondering, how to get this working.

Answer 1

You should introduce an abstract generic class:

public abstract class AbstractEventProcessor<EVENT> 
  implements EventProcessor<EVENT> {

  // Put your common logic here
}

Your other classes will then inherit common functionality as such:

public class EventAProcessor extends AbstractEventProcessor<A> {}
public class EventBProcessor extends AbstractEventProcessor<B> {}

This doesn’t necessarily have to do with generics. It’s a general way to approch polymorphism in object-oriented programming.