/**
 * 披着面向对象外衣的面向过程
 */

public class Main1 {
    public static void main(String[] args) {
        boolean cry = false;

        while(!cry) {
            //进行处理
        }
    }
}

版本二：面向对象式地傻等

抽象出一个Child类来，提供一个wakeUp()方法和一个cry属性。本质上同版本一没区别，只不过用了面向对象的思想。

/**
 * 面向对象的傻等
 */

class Child {
    private boolean cry = false;

    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        System.out.println("Waked Up! Crying wuwuwuwu...");
        cry = true;
    }
}

public class Main {
    public static void main(String[] args) {
        Child child = new Child();
        while(!child.isCry()) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("observing...");
        }

    }
}

版本三：加入观察者

加入观察者Dad。当Child的wakeUp()了之后就调用Dad的feed()方法

/**
 * 加入观察者
 */

class Child {
    private boolean cry = false;
    private Dad d = new Dad();

    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;
        d.feed();
    }
}

class Dad {
    public void feed() {
        System.out.println("dad feeding...");
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

版本四：加入多个观察者

/**
 * 加入多个观察者
 */

class Child {
    private boolean cry = false;
    private Dad dad = new Dad();
    private Mum mum = new Mum();
    private Dog dog = new Dog();


    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;
        dad.feed();
        dog.wang();
        mum.hug();
    }
}

class Dad {
    public void feed() {
        System.out.println("dad feeding...");
    }
}

class Mum {
    public void hug() {
        System.out.println("mum hugging...");
    }
}

class Dog {
    public void wang() {
        System.out.println("dog wang...");
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

版本五：分离观察者与被观察者

定义一个观察者接口Observer，提供一个actionOnWakeUp()方法供观察者实现。

/**
 * 分离观察者与被观察者
 */

class Child {
    private boolean cry = false;
    private List<Observer> observers = new ArrayList<>();

    {
        observers.add(new Dad());
        observers.add(new Mum());
        observers.add(new Dog());
    }


    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;
        for(Observer o : observers) {
            o.actionOnWakeUp();
        }
    }
}

interface Observer {
    void actionOnWakeUp();
}

class Dad implements Observer {
    public void feed() {
        System.out.println("dad feeding...");
    }

    @Override
    public void actionOnWakeUp() {
        feed();
    }
}

class Mum implements Observer {
    public void hug() {
        System.out.println("mum hugging...");
    }

    @Override
    public void actionOnWakeUp() {
        hug();
    }
}

class Dog implements Observer {
    public void wang() {
        System.out.println("dog wang...");
    }

    @Override
    public void actionOnWakeUp() {
        wang();
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

版本六：观察者根据事件来作出处理

有很多时候，观察者需要根据事件的具体情况来进行处理。

①Source--事件源对象

②Observer--观察者（监听者）

③Event--事件对象

事件源对象Source会发出一些事件Event，Observer观察者观察到这些事件后作出一系列的反应。

比如键盘监听对象MyKeyListener extends KeyAdapter，事件源对象就是窗口Frame，事件对象是KeyEvent，观察者（监听器）是MykeyListener。

Observer观察者设计模式_后台编程_02

import java.util.ArrayList;
import java.util.List;

/**
 * 有很多时候，观察者需要根据事件的具体情况来进行处理
 */

class Child {
    private boolean cry = false;
    private List<Observer> observers = new ArrayList<>();

    {
        observers.add(new Dad());
        observers.add(new Mum());
        observers.add(new Dog());
    }


    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;

        wakeUpEvent event = new wakeUpEvent(System.currentTimeMillis(), "bed");

        for(Observer o : observers) {
            o.actionOnWakeUp(event);
        }
    }
}

//事件类 fire Event
class wakeUpEvent{
    long timestamp;
    String loc;

    public wakeUpEvent(long timestamp, String loc) {
        this.timestamp = timestamp;
        this.loc = loc;
    }
}

interface Observer {
    void actionOnWakeUp(wakeUpEvent event);
}

class Dad implements Observer {
    public void feed() {
        System.out.println("dad feeding...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        feed();
    }
}

class Mum implements Observer {
    public void hug() {
        System.out.println("mum hugging...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        hug();
    }
}

class Dog implements Observer {
    public void wang() {
        System.out.println("dog wang...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        wang();
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

版本七：处理事件需要事件源对象

* 有很多时候，观察者需要根据事件的具体情况来进行处理
* 大多数时候，我们处理事件的时候，需要事件源对象

import java.util.ArrayList;
import java.util.List;

/**
 * 有很多时候，观察者需要根据事件的具体情况来进行处理
 * 大多数时候，我们处理事件的时候，需要事件源对象
 */

class Child {
    private boolean cry = false;
    private List<Observer> observers = new ArrayList<>();

    {
        observers.add(new Dad());
        observers.add(new Mum());
        observers.add(new Dog());
    }


    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;

        wakeUpEvent event = new wakeUpEvent(System.currentTimeMillis(), "bed", this);

        for(Observer o : observers) {
            o.actionOnWakeUp(event);
        }
    }
}

class wakeUpEvent{
    long timestamp;
    String loc;
    Child source;

    public wakeUpEvent(long timestamp, String loc, Child source) {
        this.timestamp = timestamp;
        this.loc = loc;
        this.source = source;
    }
}

interface Observer {
    void actionOnWakeUp(wakeUpEvent event);
}

class Dad implements Observer {
    public void feed() {
        System.out.println("dad feeding...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        feed();
    }
}

class Mum implements Observer {
    public void hug() {
        System.out.println("mum hugging...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        hug();
    }
}

class Dog implements Observer {
    public void wang() {
        System.out.println("dog wang...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        wang();
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

版本八：事件形成继承体系

* 有很多时候，观察者需要根据事件的具体情况来进行处理
* 大多数时候，我们处理事件的时候，需要事件源对象
* 事件也可以形成继承体系

import java.util.ArrayList;
import java.util.List;

/**
 * 有很多时候，观察者需要根据事件的具体情况来进行处理
 * 大多数时候，我们处理事件的时候，需要事件源对象
 * 事件也可以形成继承体系
 */

class Child {
    private boolean cry = false;
    private List<Observer> observers = new ArrayList<>();

    {
        observers.add(new Dad());
        observers.add(new Mum());
        observers.add(new Dog());
    }


    public boolean isCry() {
        return cry;
    }

    public void wakeUp() {
        cry = true;

        wakeUpEvent event = new wakeUpEvent(System.currentTimeMillis(), "bed", this);

        for(Observer o : observers) {
            o.actionOnWakeUp(event);
        }
    }
}

abstract class Event<T> {
    abstract T getSource();
}

class wakeUpEvent extends Event<Child>{
    long timestamp;
    String loc;
    Child source;

    public wakeUpEvent(long timestamp, String loc, Child source) {
        this.timestamp = timestamp;
        this.loc = loc;
        this.source = source;
    }

    @Override
    Child getSource() {
        return source;
    }
}

interface Observer {
    void actionOnWakeUp(wakeUpEvent event);
}

class Dad implements Observer {
    public void feed() {
        System.out.println("dad feeding...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        feed();
    }
}

class Mum implements Observer {
    public void hug() {
        System.out.println("mum hugging...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        hug();
    }
}

class Dog implements Observer {
    public void wang() {
        System.out.println("dog wang...");
    }

    @Override
    public void actionOnWakeUp(wakeUpEvent event) {
        wang();
    }
}

public class Main {
    public static void main(String[] args) {
        Child c = new Child();
        //do sth
        c.wakeUp();
    }
}

java.awt.Frame类应用观察者模式

import java.awt.Button;
import java.awt.Frame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class TestFrame extends Frame {
	public void launch() {
		Button b = new Button("press me");
		b.addActionListener(new MyActionListener());
		b.addActionListener(new MyActionListener2());
		this.add(b);
		this.pack();
		
		this.addWindowListener(new WindowAdapter(){

			@Override
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
			
		});
		this.setLocation(400, 400);
		this.setVisible(true);
	}
	
	public static void main(String[] args) {
		new TestFrame().launch();
	}
	
	private class MyActionListener implements ActionListener { //Observer

		public void actionPerformed(ActionEvent e) {
			((Button)e.getSource()).setLabel("press me again!");
			System.out.println("button pressed!");
		}
		
	}
	
	private class MyActionListener2 implements ActionListener {

		public void actionPerformed(ActionEvent e) {
			System.out.println("button pressed 2!");
		}
		
	}
}