public interface InterestingEvent {
 // 这只是一个普通的方法，可以接收参数、也可以返回值
 public void interestingEvent();
}

class EventNotifier {
 private InterestingEvent ie;
 private boolean somethingHappened;

 public EventNotifier(InterestingEvent event) {
  ie = event;
  somethingHappened = false;
  }
public void doWork() {
        if (somethingHappened) {
            // 事件发生时，通过调用接口的这个方法来通知
            ie.interestingEvent();
        }       
    }
}

public class CallMe implements InterestingEvent {
 private EventNotifier en;

 public CallMe() {
  // 新建一个事件通知者对象，并把自己传递给它
  en = new EventNotifier(this);
 }

 // 实现事件发生时，实际处理事件的方法
 public void interestingEvent() {
  // 这个事件发生了，进行处理
 }
}

interface InterestingEvent {
 public void interestingEvent(String event);
}

class CallMe implements InterestingEvent {
 private String name;
 public CallMe(String name){
  this.name = name;
 } 
 public void interestingEvent(String event) {
  System.out.println(name + ":[" +event + "] happened");
 }
}

class EventNotifier {
 private List<CallMe> callMes = new ArrayList<CallMe>();
 
 public void regist(CallMe callMe){
  callMes.add(callMe);
 }
 
 public void doWork(){
  for(CallMe callMe: callMes) {
   callMe.interestingEvent("sample event");
  }
 } 
}

public class CallMeTest {
 public static void main(String[] args) {
  EventNotifier ren = new EventNotifier();
  CallMe a = new CallMe("CallMe A");
  CallMe b = new CallMe("CallMe B");

  // regiest
  ren.regist(a);
  ren.regist(b);
  
  // test
  ren.doWork();  
 }
}