一.事件机制基本概念

  java中的事件机制的参与者有3种角色：

  1.event object：事件状态对象，用于listener的相应的方法之中，作为参数，一般存在与listerner的方法之中

  2.event listener：对每个明确的事件的发生，都相应地定义一个明确的Java方法。这些方法都集中定义在事件监听者（EventListener）接口中，
   这个接口要继承 java.util.EventListener。 实现了事件监听者接口中一些或全部方法的类就是事件监听者。

  3.event source：具体的事件源，比如说，你点击一个button，那么button就是event source，要想使button对某些事件进行响应，你就需要注册特定的listener。

二.举例 Door1
   属性 name 和status 改变，被监管
  1.Door1

public class Door1 {
    private String state = "";
    private String name = "";
    private DoorStateListener stateListener;
    private DoorNameListener  nameListener;
    
    public void setState(String newValue) {
        if (state != newValue) {
            state = newValue;
            if (stateListener != null){
  //注意参数传递
                Door1Event event = new Door1Event(this, "state",newValue);
                stateListener.doorEvent(event);             
            }
        }        
    }
    
    public void setName(String newValue) {
        if (name != newValue) {
            name = newValue;
            if (nameListener != null){
                Door1Event event = new Door1Event(this,"name", newValue);
                nameListener.doorEvent(event);                 
            }
        }  
    }
 
    public void setStateListener(DoorStateListener stateListener) {
        this.stateListener = stateListener;
    }

    public void setNameListener(DoorNameListener nameListener) {
        this.nameListener = nameListener;
    }

    public String getState() {
        return state;
    }

    public String getName() {
        return name;
    }
}

2.数据传递对象  Door1Event

import java.util.EventObject;

public class Door1Event extends EventObject {
    private static final long serialVersionUID = 6496098798146410884L;
    
    private final String key ; 
    private final String value  ; 
    
    public Door1Event(Object source,String key , String value) {
        super(source);
        this.key = key;
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public String getKey() {
        return key;
    }
}

3.被监管对象

    Door1StateObserver

class DoorStateListener implements EventListener {
    public void doorEvent(Door1Event event) {
        if (event.getValue() != null && event.getValue().equals("open")) {
            System.out.println("门1打开");
        } else {
            System.out.println("门1关闭");
        }
    }
}

    Door1NameObserver

class DoorNameListener implements EventListener {
    public void doorEvent(Door1Event event) {
        Door1 door = (Door1) event.getSource();
        System.out.println("I got a new name,named \"" + door.getName() + "\"");
    }
}

4 .Door1Test

public class Door1Test {
    public static void main(String[] args) {

        Door1 door = new Door1();
        door.setStateListener(new DoorStateListener());   
        door.setNameListener (new DoorNameListener());    
        // 开门
        door.setState("open");
        System.out.println("我已经进来了");
        // 关门
        door.setState("close");

        // 改名

        door.setName("dengzy"); } }