public static void main(String[] args) {
   Callee1 c1 = new Callee1();
   Callee2 c2 = new Callee2();
   MyIncrement.f(c2);
   Caller caller1 = new Caller(c1);
   Caller caller2 = new Caller(c2.getCallbackReference());
   caller1.go();
   caller1.go();
   caller2.go();
   caller2.go();
 }
 public void increment() {
   super.increment();
   i++;
   print(i);
 }
 static void f(MyIncrement mi) {
   mi.increment();
 }