java 23 种设计模式-20-java 观察者模式（Observer Pattern）

目录

观察者模式

当对象间存在一对多关系时，则使用观察者模式（Observer Pattern）。

比如，当一个对象被修改时，则会自动通知它的依赖对象。观察者模式属于行为型模式。

实际案例

类信息概览：

定义

• Bee.java

package com.ryo.design.pattern.note.observer;import java.util.Observable;
import java.util.Observer;/*** @author houbinbin* @version 1.0* @on 17/3/14* @see Flower* @since 1.7*/
public class Bee {
    /*** 小蜜蜂的名字*/private String name;private Observer openObserver = new OpenObserver();private Observer closeObserver = new CloseObserver();public Bee(String name) {this.name = name;}// An inner class for observing openings:private class OpenObserver implements Observer {
    @Overridepublic void update(Observable ob, Object a) {System.out.println("Bee " + name+ "'s breakfast time!");}}// Another inner class for closings:private class CloseObserver implements Observer {
    @Overridepublic void update(Observable ob, Object a) {System.out.println("Bee " + name+ "'s bed time!");}}public Observer getOpenObserver() {return openObserver;}public Observer getCloseObserver() {return closeObserver;}
}

• Flower.java

package com.ryo.design.pattern.note.observer;import java.util.Observable;/*** @author houbinbin* @version 1.0* @on 17/3/14* @since 1.7*/
public class Flower {
    /*** 标志当前花是否开放*/private boolean isOpen;private OpenNotifier openNotifier = new OpenNotifier();private CloseNotifier closeNotifier = new CloseNotifier();/*** 默认花不开*/public Flower() {isOpen = false;}public Observable getOpenNotifier() {return openNotifier;}public Observable getCloseNotifier() {return closeNotifier;}/*** 花开*/public void open() {isOpen = true;openNotifier.notifyObservers(); //通知所有观察者， 花开了。closeNotifier.open();   //重置状态}/*** 花落*/public void close() {isOpen = false;closeNotifier.notifyObservers();openNotifier.close();   //重置状态}/*** 花开通知器*/private class OpenNotifier extends Observable {
    private boolean alreadyOpen = false;//从花未开变成了花开@Overridepublic void notifyObservers() {if (isOpen && !alreadyOpen) {setChanged();super.notifyObservers();alreadyOpen = true;}}public void close() {alreadyOpen = false;}}/*** 花落通知器*/private class CloseNotifier extends Observable {
    private boolean alreadyClosed = false;/*** 从花落变成了花开*/@Overridepublic void notifyObservers() {if (!isOpen && !alreadyClosed) {setChanged();super.notifyObservers();alreadyClosed = true;}}public void open() {alreadyClosed = false;}}}

• HummingBird.java

package com.ryo.design.pattern.note.observer;import java.util.Observable;
import java.util.Observer;/*** @author houbinbin* @version 1.0* @on 17/3/14* @see Flower* @since 1.7*/
public class HummingBird {
    /*** 蜂鸟的名字*/private String name;private Observer openObserver = new OpenObserver();private Observer closeObserver = new CloseObserver();public HummingBird(String name) {this.name = name;}/*** An inner class for observing openings:*/private class OpenObserver implements Observer {
    @Overridepublic void update(Observable ob, Object a) {System.out.println("HummingBird " + name+ "'s breakfast time!");}}/*** Another inner class for closings:*/private class CloseObserver implements Observer {
    @Overridepublic void update(Observable ob, Object a) {System.out.println("HummingBird " + name+ "'s bed time!");}}public Observer getOpenObserver() {return openObserver;}public Observer getCloseObserver() {return closeObserver;}
}

测试

• Main.java

/** DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.* Copyright (c) 2012-2018. houbinbini Inc.* design-pattern All rights reserved.*/package com.ryo.design.pattern.note.observer;/*** <p> </p>** <pre> Created: 2018/5/23 下午8:57 </pre>* <pre> Project: design-pattern </pre>** @author houbinbin* @version 1.0* @since JDK 1.7*/
public class Main {
    public static void main(String[] args) {Flower flower = new Flower();Bee bee = new Bee("Bee A");HummingBird hummingBird = new HummingBird("HummingBird A");flower.getOpenNotifier().addObserver(bee.getOpenObserver());flower.getCloseNotifier().addObserver(bee.getCloseObserver());flower.getOpenNotifier().addObserver(hummingBird.getOpenObserver());System.out.println("-- flower start open");flower.open();System.out.println("-- flower end open");System.out.println("-- flower start close");flower.close();System.out.println("-- flower end close");}}

• 测试结果

-- flower start open
HummingBird HummingBird A's breakfast time!
Bee Bee A's breakfast time!
-- flower end open
-- flower start close
Bee Bee A's bed time!
-- flower end close

实现方式

UML & Code

UML

UML 图示如下

Code

代码地址

观察者模式

系列导航

系列导航