Implementing Generic Interface in Java

Question

I have a Java generics question I was hoping someone could answer. Consider the following code:

public interface Event{}
public class AddressChanged implemen         


        

Answer 1

It isn't allowed because Java erases generic signatures during compilation. The interface method will actually have the signature

public void handle(Object event);

So you have two choices. Either implement separate Handlers for different events:

public class AddressChangedHandler implements Handles{ /* ... */ }
public class AddressDiscardedHandler implements Handles{ /* ... */ }

or implement one handler for all but check the type of the incoming event:

public void handle(Event e){
  if (e instanceof AddressChanged) {
     handleAdressChanged(e);
  }
  else if (e instanceof AddressDiscareded) {
     handleAdressDiscarded(e);
  }
}