javac must reject this test case:

class T {
    static abstract class A<T> {
        abstract void f(T t);
        public int f(Integer t) { return 3; }
    }
    static abstract class B extends A<Integer> {
        // error: A<Integer>.f(Integer) returning int can't implement
        // A<Integer>.f(Integer) returning void.
    }
    static class C extends B {}
}