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：
| 类名 | 说明 |
|---|---|
| Main.java | 方法的总入口 |
| Bee.java | 蜜蜂 |
| Flower.java | 花朵 |
| HummingBird.java | 蜂鸟 |
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 {
@Override
public void update(Observable ob, Object a) {
System.out.println("Bee " + name
+ "'s breakfast time!");
}
}
// Another inner class for closings:
private class CloseObserver implements Observer {
@Override
public 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
@Override
public 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
*/
@Override
public 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 {
@Override
public void update(Observable ob, Object a) {
System.out.println("HummingBird " + name
+ "'s breakfast time!");
}
}
/**
* Another inner class for closings:
*/
private class CloseObserver implements Observer {
@Override
public 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
