Using wildcard type in java generics

Question

I want to pass object of GameObject class which would also implement Collidable interface. How should it look like?

private boolean isCollision(GameObject<? extends Collidable> collid) {
}

How should it look like? collid must be instance of both GameObject and Collidable .

Answer 1

如果你想确保collid是一个GameObject 和 Collidable ，你可以使用这个语法：

private <T extends GameObject & Collidable> boolean isCollision(T collid)

Answer 2

It may be easier to define an interface that extends GameObject and Collidable . Then declare your parameter to be of that type.

public interface CollidableGameObject extends GameObject, Collidable {
}

Then your method might be:

private boolean isCollision(CollidableGameObject collid) {
}

Unless I'm missing something, generics don't appear to be needed. If GameObject is not already an interface, consider making it one?