public class A {

                void callme() {System.out.print("A");}

}

public class B extends A{

                void callme() {System.out.print("B");}

}

public class C extends B{

                void callme() {System.out.print("C");}

}

public class Extender {

                public static void main(String[] args) {

                                A a = new A();

                                B b = new B();

                                C c = new C();

                                A r = a;

                                r.callme();

                                r = b;

                                r.callme();

                                r = c;

                                r.callme();

                }

}