Java generics to enforce return type of abstract method

Question

I have the following situation :

abstract class X { abstract X someMethod (...) {...} }.

Now I want to constrain any implementation of X to

Answer 1

abstract class X> {
    protected X(Class implClazz) {
        if (!getClass().equals(implClazz)) {
            throw new IllegalArgumentException();
        }
    }

    abstract I someMethod();
}

Rationale: You can not refer to the dynamic type in type bounds, hence the indirect check in the constructor.