Java事件監聽機制與觀察者設計模式

一. Java事件監聽機制

1. 事件監聽三要素： 事件源，事件對象，事件監聽器

2. 三要素之間的關系：事件源注冊事件監聽器后，當事件源上發生某個動作時，事件源就會調用事件監聽的一個方法，並將事件對象傳遞進去，開發者可以利用事件對象操作事件源。

 

3. 入門程序

/**
 * Created by IntelliJ IDEA.
 *
 * @Auther: ShaoHsiung
 * @Date: 2018/8/29 21:25
 * @Title: 事件監聽入門程序
 * @Description:
 */
public class Demo1 {
    public static void main(String[] args) {
        Frame frame = new Frame();
        frame.setSize(400, 500);
        frame.setVisible(true);
        // 為frame注冊一個事件監聽器
        frame.addWindowListener(new WindowListener() {
            @Override
            public void windowOpened(WindowEvent e) {

            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("再會~~~");
                // 通過事件對象獲取事件源
                Frame frame = (Frame) e.getSource();
                // 關閉窗口
                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. 設計一個能夠被其它類監聽的類（如何實現監聽機制）

其實就是觀察者模式

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("門打開了。。。");
    }

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

2. 事件監聽器

// 監聽器
interface DoorListener {
    public void doOpen(DoorEvent doorEvent);
    public void doClose(DoorEvent doorEvent);
}

3. 事件對象

// 事件對象
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. 測試

public class Demo2 {

    public static void main(String[] args) {
        // 門
        Door door = new Door();
        // 注冊監聽器
        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();
    }
}

完整代碼：

/**
 * Created by IntelliJ IDEA.
 *
 * @Auther: ShaoHsiung
 * @Date: 2018/8/29 21:45
 * @Title: 觀察者設計模式
 * @Description:
 */
public class Demo2 {

    public static void main(String[] args) {
        // 門
        Door door = new Door();
        // 注冊監聽器
        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("門打開了。。。");
    }

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

// 監聽器
interface DoorListener {
    public void doOpen(DoorEvent doorEvent);
    public void doClose(DoorEvent doorEvent);
}

// 事件對象
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;
    }
}