目錄

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問題

程序模擬?

版本一：while死循環(huán)

版本二：面向?qū)ο笫降厣档?

版本三：加入觀察者

版本四：加入多個觀察者

版本五：分離觀察者與被觀察者

版本六：觀察者根據(jù)事件來作出處理

版本七：處理事件需要事件源對象

版本八：事件形成繼承體系

java.awt.Frame類應用觀察者模式

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reactor模型的本質(zhì)就是觀察者模式。

問題

首先來看一個問題：

程序模擬?

版本一：while死循環(huán)

程序模擬小孩哭：一個死循環(huán)等著，當cry為true時就執(zhí)行。類似于面向過程式地傻等

/*** 披著面向?qū)ο笸庖碌拿嫦蜻^程*/public class Main1 {public static void main(String[] args) {boolean cry = false;while(!cry) {//進行處理}} }

版本二：面向?qū)ο笫降厣档?

抽象出一個Child類來，提供一個wakeUp()方法和一個cry屬性。本質(zhì)上同版本一沒區(qū)別，只不過用了面向?qū)ο蟮乃枷搿?/p> /*** 面向?qū)ο蟮纳档?/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：加入觀察者

加入觀察者Dad。當Child的wakeUp()了之后就調(diào)用Dad的feed()方法

/*** 加入觀察者*/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 sthc.wakeUp();} }

版本四：加入多個觀察者

/*** 加入多個觀察者*/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 sthc.wakeUp();} }

版本五：分離觀察者與被觀察者

定義一個觀察者接口Observer，提供一個actionOnWakeUp()方法供觀察者實現(xiàn)。

/*** 分離觀察者與被觀察者*/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...");}@Overridepublic void actionOnWakeUp() {feed();} }class Mum implements Observer {public void hug() {System.out.println("mum hugging...");}@Overridepublic void actionOnWakeUp() {hug();} }class Dog implements Observer {public void wang() {System.out.println("dog wang...");}@Overridepublic void actionOnWakeUp() {wang();} }public class Main {public static void main(String[] args) {Child c = new Child();//do sthc.wakeUp();} }

版本六：觀察者根據(jù)事件來作出處理

有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理。

①Source--事件源對象

②Observer--觀察者（監(jiān)聽者）

③Event--事件對象

事件源對象Source會發(fā)出一些事件Event，Observer觀察者觀察到這些事件后作出一系列的反應。

比如鍵盤監(jiān)聽對象MyKeyListener extends KeyAdapter，事件源對象就是窗口Frame，事件對象是KeyEvent，觀察者（監(jiān)聽器）是MykeyListener。

import java.util.ArrayList; import java.util.List;/*** 有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理*/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);}} }//事件類 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...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {feed();} }class Mum implements Observer {public void hug() {System.out.println("mum hugging...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {hug();} }class Dog implements Observer {public void wang() {System.out.println("dog wang...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {wang();} }public class Main {public static void main(String[] args) {Child c = new Child();//do sthc.wakeUp();} }

版本七：處理事件需要事件源對象

?* 有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理
?* 大多數(shù)時候，我們處理事件的時候，需要事件源對象

import java.util.ArrayList; import java.util.List;/*** 有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理* 大多數(shù)時候，我們處理事件的時候，需要事件源對象*/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...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {feed();} }class Mum implements Observer {public void hug() {System.out.println("mum hugging...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {hug();} }class Dog implements Observer {public void wang() {System.out.println("dog wang...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {wang();} }public class Main {public static void main(String[] args) {Child c = new Child();//do sthc.wakeUp();} }

版本八：事件形成繼承體系

?* 有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理
?* 大多數(shù)時候，我們處理事件的時候，需要事件源對象
?* 事件也可以形成繼承體系

import java.util.ArrayList; import java.util.List;/*** 有很多時候，觀察者需要根據(jù)事件的具體情況來進行處理* 大多數(shù)時候，我們處理事件的時候，需要事件源對象* 事件也可以形成繼承體系*/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;}@OverrideChild getSource() {return source;} }interface Observer {void actionOnWakeUp(wakeUpEvent event); }class Dad implements Observer {public void feed() {System.out.println("dad feeding...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {feed();} }class Mum implements Observer {public void hug() {System.out.println("mum hugging...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {hug();} }class Dog implements Observer {public void wang() {System.out.println("dog wang...");}@Overridepublic void actionOnWakeUp(wakeUpEvent event) {wang();} }public class Main {public static void main(String[] args) {Child c = new Child();//do sthc.wakeUp();} }

java.awt.Frame類應用觀察者模式

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(){@Overridepublic 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 { //Observerpublic 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!");}} }

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