Java override abstract generic method

Question

I have the following code

public abstract class Event {
    public void fire(Object... args) {
        // tell the event handler that if there are free resources it should call 
        // doEventStuff(args)
    }

    // this is not correct, but I basically want to be able to define a generic 
    // return type and be able to pass generic arguments. (T... args) would also 
    // be ok
    public abstract <T, V> V doEventStuff(T args);
}

public class A extends Event {
   // This is what I want to do
   @Overide
   public String doEventStuff(String str) {
      if(str == "foo") { 
         return "bar";
      } else {
         return "fail";
      }
   }
}

somewhere() {
  EventHandler eh = new EventHandler();
  Event a = new A();
  eh.add(a);
  System.out.println(a.fire("foo")); //output is bar
}

However I don't know how to do this, as I cannot override doEventStuff with something specific.

Does anyone know how to do this?

Answer 1

It's not really clear what you're trying to do, but perhaps you just need to make Event itself generic:

public abstract class Event<T, V>
{
    public abstract V doEventStuff(T args);
}

public class A extends Event<String, String>
{
    @Override public String doEventStuff(String str)
    {
        ...
    }
}

Answer 2

You're using generics but you are not providing a binding.

public abstract class Event<I, O> { // <-- I is input O is Output
  public abstract O doEventStuff(I args);
}

public class A extends Event<String, String> { // <-- binding in the impl.
  @Override
    public String doEventStuff(String str) {
  }
}

Or simpler with only one generic binding...

public abstract class Event<T> { // <-- only one provided
  public abstract T doEventStuff(T args);
}

public class A extends Event<String> { // <-- binding the impl.

  @Override
    public String doEventStuff(String str) {
  }
}

Answer 3

This is still not working for me. I have the following code:

public interface Container<T extends MyEntity> {
...
}


public class MyConcreteContainer implements Container<MyContreteEntity> {
   ...
}

public abstract class MyAbstractClass<T extends MyEntity> {

  public abstract String doStuff(Container<T> container);
}

public class MyConcreteEntity implements MyEntity {
   ...
}

public class MyConcreteImplementedClass extends MyAbstractClass<MyContreteEntity> {
  
  @Override
  public String doStuff(MyConcreteContainer container) {
    ...
  }
}

Since MyConcreteContainer IS AN implementation of the generic Container , why is my comppiler not recognising that I have Overridden the doStuff method correctly?