Question

Sorry I had the wrong code before…

So I have an interface that looks like:

public interface Player { 
    void setPartner(Player partner); 
}

And I have an implementation of that interface that looks something like this:

public class Human implements Player
{
    private Human partner;

    public void setPartner(Human partner)
    {
        this.partner = partner;
    }
}

So the compiler says that I am not implementing every method from Player which indicates to me that I have to match the parameter type of the setPartner method exactly, even though the a Human, is a Player. Is there any good way of getting around this or implementing this differently?

Answer 1

You cannot have covariant parameters (what happens if you manipulate your Human instance through the Player interface?), however you can use generics.

public interface Player<T extends Player<T>> {
    void setPartner(T partner);
}

public class Human implements Player<Human> {
    private Human partner;

    public void setPartner(Human partner) {
        this.partner = partner;
    }
}

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However, you can’t force the implementing class to actually use its own type as the type parameter of Player.