Generics and Class.asSubclass

Question

I've always thought the following should work. I get an object which I know is a Class<X> where X extends some class Xyz. In order to make it type-safe I wanted to use Class.asSubclass like in the following method:

private Class<? extends Xyz> castToXyzClass(Object o) {
    final Class<?> resultClass = (Class<?>) o;
    final Class<? extends Xyz> result = Xyz.class.asSubclass(resultClass);
    return result;
}

However, in Eclipse it doesn't work, the only solution I see is an unchecked cast. I'd bet the above code must work, I've used something like this already... no idea what's wrong here.

Answer 1

asSubclass() operates on the object it's called on, not on its parameter - not what one is used to, but it reads quite well. You just have to do this:

final Class<? extends Xyz> result = resultClass.asSubclass(Xyz.class);