java

public class A { protected int num; public A(int n) { num = n; } public int getNum() { return num; }

public boolean f(A a)
{
    System.out.println("F in A");
    return num == a.num * 2;
}

}// end of class A

public class B extends A { public B(int n) { super(n); } public boolean f(B b) { System.out.println("F in B"); return num == b.num; } }// end of class B

public class C extends A { public C (int n) { super(n); System.out.println("F in C"); } public boolean f(A a) { return a instanceof C && num == a.num; } } //end of class C

public class Driver { public static void main(String[] args) { A y1 = new B(10); B y2 = new B(10); A z1 = new C(10); C z2 = new C(10); (****) } }