Assign a subclass of a Generic class to a super class of this class

Question

I have couple of supplied interfaces

public interface Finder,T extends Item> {
    public S find(S s, int a);
}

public interf         


        

Answer 1

The problem is that obviously Stack is not S extends Stack. Java is strongly typed and won't let you do such things.

You can either cast to Stack, in which case you will still get a warning about unchecked conversion. This means this conversion is unsafe.

public class SimpleFinder, T extends Item> implements Finder {

    @Override
    public S find(S s, int a) {
        Stack stack = s.getCopy();
        return (S) stack;
    }

}

or simply use Stack instead of S extends Stack, which is my recommendation:

public class SimpleFinder implements Finder, T> {

    @Override
    public Stack find(Stack s, int a) {
        Stack stack = s.getCopy();
        return stack;
    }

}