Java事件监听机制与观察者设计模式

一. Java事件监听机制

1. 事件监听三要素： 事件源，事件对象，事件监听器

2. 三要素之间的关系：事件源注册事件监听器后，当事件源上发生某个动作时，事件源就会调用事件监听的一个方法，并将事件对象传递进去，开发者可以利用事件对象操作事件源。

3. 入门程序

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/8/29 21:25
  * @Title: 事件监听入门程序
  * @Description:
  */
 public class Demo1 {
     public static void main(String[] args) {
         Frame frame = new Frame();
         frame.setSize(400, 500);
         frame.setVisible(true);
         // 为frame注册一个事件监听器
         frame.addWindowListener(new WindowListener() {
             @Override
             public void windowOpened(WindowEvent e) {

             }

             @Override
             public void windowClosing(WindowEvent e) {
                 System.out.println("再会~~~");
                 // 通过事件对象获取事件源
                 Frame frame = (Frame) e.getSource();
                 // 关闭窗口
                 frame.dispose();
             }

             @Override
             public void windowClosed(WindowEvent e) {

             }

             @Override
             public void windowIconified(WindowEvent e) {

             }

             @Override
             public void windowDeiconified(WindowEvent e) {

             }

             @Override
             public void windowActivated(WindowEvent e) {

             }

             @Override
             public void windowDeactivated(WindowEvent e) {

             }
         });
     }
 }

二. 设计一个能够被其它类监听的类（如何实现监听机制）

其实就是观察者模式

1. 事件源

 // 事件源
 class Door {

     private DoorListener doorListener;

     public void addDoorListener(DoorListener doorListener) {
         this.doorListener = doorListener;
     }

     public void open() {
         if (doorListener != null) {
             doorListener.doOpen(new DoorEvent(this));
         }
         System.out.println("门打开了。。。");
     }

     public void close() {
         if (doorListener != null) {
             doorListener.doClose(new DoorEvent(this));
         }
         System.out.println("门关上了。。。");
     }
 }

2. 事件监听器

 // 监听器
 interface DoorListener {
     public void doOpen(DoorEvent doorEvent);
     public void doClose(DoorEvent doorEvent);
 }

3. 事件对象

 // 事件对象
 class DoorEvent {
     // source
     private Door door;
     public DoorEvent() {}
     public DoorEvent(Door door) {
         this.door = door;
     }

     public Door getDoor() {
         return door;
     }

     public void setDoor(Door door) {
         this.door = door;
     }
 }

4. 测试

 public class Demo2 {

     public static void main(String[] args) {
         // 门
         Door door = new Door();
         // 注册监听器
         door.addDoorListener(new DoorListener() {
             @Override
             public void doOpen(DoorEvent doorEvent) {
                 System.out.println(doorEvent + " bomb~~~");
             }

             @Override
             public void doClose(DoorEvent doorEvent) {
                 System.out.println(doorEvent + " bomb2~~~");
             }
         });
         door.open();
         door.close();
     }
 }

完整代码：

 /**
  * Created by IntelliJ IDEA.
  *
  * @Auther: ShaoHsiung
  * @Date: 2018/8/29 21:45
  * @Title: 观察者设计模式
  * @Description:
  */
 public class Demo2 {

     public static void main(String[] args) {
         // 门
         Door door = new Door();
         // 注册监听器
         door.addDoorListener(new DoorListener() {
             @Override
             public void doOpen(DoorEvent doorEvent) {
                 System.out.println(doorEvent + " bomb~~~");
             }

             @Override
             public void doClose(DoorEvent doorEvent) {
                 System.out.println(doorEvent + " bomb2~~~");
             }
         });
         door.open();
         door.close();
     }
 }

 // 事件源
 class Door {

     private DoorListener doorListener;

     public void addDoorListener(DoorListener doorListener) {
         this.doorListener = doorListener;
     }

     public void open() {
         if (doorListener != null) {
             doorListener.doOpen(new DoorEvent(this));
         }
         System.out.println("门打开了。。。");
     }

     public void close() {
         if (doorListener != null) {
             doorListener.doClose(new DoorEvent(this));
         }
         System.out.println("门关上了。。。");
     }
 }

 // 监听器
 interface DoorListener {
     public void doOpen(DoorEvent doorEvent);
     public void doClose(DoorEvent doorEvent);
 }

 // 事件对象
 class DoorEvent {
     // source
     private Door door;
     public DoorEvent() {}
     public DoorEvent(Door door) {
         this.door = door;
     }

     public Door getDoor() {
         return door;
     }

     public void setDoor(Door door) {
         this.door = door;
     }
 }