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;
    }
}