Java事件监听机制与观察者设计模式

Posted 2021-01-02 shaohsiung

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

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/8/29 21:25
 6  * @Title: 事件监听入门程序
 7  * @Description:
 8  */
 9 public class Demo1 {
10     public static void main(String[] args) {
11         Frame frame = new Frame();
12         frame.setSize(400, 500);
13         frame.setVisible(true);
14         // 为frame注册一个事件监听器
15         frame.addWindowListener(new WindowListener() {
16             @Override
17             public void windowOpened(WindowEvent e) {
18 
19             }
20 
21             @Override
22             public void windowClosing(WindowEvent e) {
23                 System.out.println("再会~~~");
24                 // 通过事件对象获取事件源
25                 Frame frame = (Frame) e.getSource();
26                 // 关闭窗口
27                 frame.dispose();
28             }
29 
30             @Override
31             public void windowClosed(WindowEvent e) {
32 
33             }
34 
35             @Override
36             public void windowIconified(WindowEvent e) {
37 
38             }
39 
40             @Override
41             public void windowDeiconified(WindowEvent e) {
42 
43             }
44 
45             @Override
46             public void windowActivated(WindowEvent e) {
47 
48             }
49 
50             @Override
51             public void windowDeactivated(WindowEvent e) {
52 
53             }
54         });
55     }
56 }

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

 1 // 事件源
 2 class Door {
 3 
 4     private DoorListener doorListener;
 5 
 6     public void addDoorListener(DoorListener doorListener) {
 7         this.doorListener = doorListener;
 8     }
 9 
10     public void open() {
11         if (doorListener != null) {
12             doorListener.doOpen(new DoorEvent(this));
13         }
14         System.out.println("门打开了。。。");
15     }
16 
17     public void close() {
18         if (doorListener != null) {
19             doorListener.doClose(new DoorEvent(this));
20         }
21         System.out.println("门关上了。。。");
22     }
23 }

2. 事件监听器

1 // 监听器
2 interface DoorListener {
3     public void doOpen(DoorEvent doorEvent);
4     public void doClose(DoorEvent doorEvent);
5 }

3. 事件对象

 1 // 事件对象
 2 class DoorEvent {
 3     // source
 4     private Door door;
 5     public DoorEvent() {}
 6     public DoorEvent(Door door) {
 7         this.door = door;
 8     }
 9 
10     public Door getDoor() {
11         return door;
12     }
13 
14     public void setDoor(Door door) {
15         this.door = door;
16     }
17 }

4. 测试

 1 public class Demo2 {
 2 
 3     public static void main(String[] args) {
 4         // 门
 5         Door door = new Door();
 6         // 注册监听器
 7         door.addDoorListener(new DoorListener() {
 8             @Override
 9             public void doOpen(DoorEvent doorEvent) {
10                 System.out.println(doorEvent + " bomb~~~");
11             }
12 
13             @Override
14             public void doClose(DoorEvent doorEvent) {
15                 System.out.println(doorEvent + " bomb2~~~");
16             }
17         });
18         door.open();
19         door.close();
20     }
21 }

完整代码：

 1 /**
 2  * Created by IntelliJ IDEA.
 3  *
 4  * @Auther: ShaoHsiung
 5  * @Date: 2018/8/29 21:45
 6  * @Title: 观察者设计模式
 7  * @Description:
 8  */
 9 public class Demo2 {
10 
11     public static void main(String[] args) {
12         // 门
13         Door door = new Door();
14         // 注册监听器
15         door.addDoorListener(new DoorListener() {
16             @Override
17             public void doOpen(DoorEvent doorEvent) {
18                 System.out.println(doorEvent + " bomb~~~");
19             }
20 
21             @Override
22             public void doClose(DoorEvent doorEvent) {
23                 System.out.println(doorEvent + " bomb2~~~");
24             }
25         });
26         door.open();
27         door.close();
28     }
29 }
30 
31 // 事件源
32 class Door {
33 
34     private DoorListener doorListener;
35 
36     public void addDoorListener(DoorListener doorListener) {
37         this.doorListener = doorListener;
38     }
39 
40     public void open() {
41         if (doorListener != null) {
42             doorListener.doOpen(new DoorEvent(this));
43         }
44         System.out.println("门打开了。。。");
45     }
46 
47     public void close() {
48         if (doorListener != null) {
49             doorListener.doClose(new DoorEvent(this));
50         }
51         System.out.println("门关上了。。。");
52     }
53 }
54 
55 // 监听器
56 interface DoorListener {
57     public void doOpen(DoorEvent doorEvent);
58     public void doClose(DoorEvent doorEvent);
59 }
60 
61 // 事件对象
62 class DoorEvent {
63     // source
64     private Door door;
65     public DoorEvent() {}
66     public DoorEvent(Door door) {
67         this.door = door;
68     }
69 
70     public Door getDoor() {
71         return door;
72     }
73 
74     public void setDoor(Door door) {
75         this.door = door;
76     }
77 }

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