Question

For example

public interface X{
    public void foo(X i);
}

public class Y implements X{//error: doesn't implement foo(X i)...
    public void foo(Y i){
        fooBar(foo);
    }
    ....
}

Why can’t I do that? And how can I change it so this is possible? What can I do to declare foo in X with a parameter, and then be able to use Y as the parameter type in Y?

Answer 1

Additionally to what Don Boyle said, you can’t change it without hinting the compiler of the intention. You do this by introducing Generics to the interface, like so:

public interface X<T> {
    public void foo(T i);
}

public class Y implements X<Y> {
    public void foo(Y i){
        fooBar(foo);
    }
}