How to force generic argument superclass type when implementing Map?

Question

I have all kinds of GameObject s. I want to make basic collection definition for them all:

//Wrong number of type arguments; required 2. > expected
public interface GameObjectMap<T> extends Map<String, T extends GameObject> {

}

The collection will allways be mapped by string (because the data are loaded from JSON ). But the second generic type argument should be any instance of GameObject . I have no idea how to write the code above correctly.

Answer 1

You're almost right. Simply move the extends GameObject to the first generic definition:

public interface GameObjectMap<T extends GameObject> extends Map<String, T> {

}

Answer 2

The restriction comes on the first declaration of T , like

public interface GameObjectMap<T extends GameObject> extends Map<String, T> {

}