观察者模式 定义了对象之间的一对多的依赖，这样一来，当一个对象状态改变时，他的
多有依赖都会受到通知并自动更新。
本例为一个温度基站，和三个终端。温度基站为广播类WeatherData，三个终端监听者类分别为：TVDispaly，FactoryDisplay，MobileDisplay
其中，Observable为广播类父类，含有基本的方法。
Observer类为监听者接口，监听者需实现updata方法。
Display为显示接口，需实现display方法。
ObserverDemo为测试类。
下面直接上代码，注释很清晰。基本上很容易理解。
Observable.java
package observer;
/*
* @author trojan
* 广播类的父类
*
*/
public class Observable {
protected boolean change = false;
public void setChanged() {
change = true;
}
public void notifyObservers(Object arg) {}
public void notifyObservers(){ notifyObservers(null);}
public void addObserver(Observer observer){}
}
WeatherData.java
package observer;
/*
* @author trojan
* 该类为广播类
*/
import java.util.ArrayList;
public class WeatherData extends Observable {
//温度
private float temperature;
//湿度
private float humidity;
//污染指数
private float pollution_index;
ArrayList<Observer> observers = new ArrayList<Observer>();
public WeatherData(){ }
//增加监听者
public void addObserver(Observer observer){
observers.add(observer);
}
//将更改广播给所有监听者
public void notifyObservers(Object arg) {
if(change){
for(Observer observer : observers){
observer.update(this,arg);
}
}
change = false;
}
public void notifyObservers() { notifyObservers(null);}
public void stateChange() {
//调用notifyObservers之前应调用状态改变标志函数
setChanged();
notifyObservers();
}
//设置状态后，将调用stateChange函数，通知监听者
public void setState(float temperature, float humidity, float pollution_index) {
this.temperature = temperature;
this.humidity = humidity;
this.pollution_index = pollution_index;
stateChange();
}
public float getTemperature() {
return temperature;
}
public void setTemperature(float temperature) {
this.temperature = temperature;
}
public float getHumidity() {
return humidity;
}
public void setHumidity(float humidity) {
this.humidity = humidity;
}
public float getPollution_index() {
return pollution_index;
}
public void setPollution_index(float pollution_index) {
this.pollution_index = pollution_index;
}
}
Display.java
package observer;
/*
* @author
* 显示接口
*/
public interface Display {
public void display();
}
Observer.java
package observer;
/*
* @author trojan
* 这是一个监听者的接口，需要实现updata方法
* 该方法可以被广播者调用，向监听者广播数据，或者说是一种推的方式
* 监听者可以可以调用该方法主动更新数据，就像是一种拉的方式
* 当然，对于每一个实现的监听者可能会有不同的数据需求
* 所以，他们可以实现对自己感兴趣的那部分数据更新
*
*/
public interface Observer {
public void update(Object obj,Object arg);;
}
TVDisplay.java
package observer;
/*
* @author trojan
* 对于电视台来说可能需要的气象数据要比其他的设备多
* 所以updata需要更新更多的数据
*/
public class TVDisplay implements Observer, Display{
Observable observable;
private float temperature;
private float humidity;
private float pollution_index;
//变成一个监听者
public void becomeOberser(Observable observable) {
this.observable = observable;
observable.addObserver(this);;
}
@Override
public void update(Object obj, Object arg) {
if(obj instanceof WeatherData){
WeatherData weatherData = (WeatherData)obj;
this.temperature = weatherData.getTemperature();
this.humidity = weatherData.getHumidity();
this.pollution_index = weatherData.getPollution_index();
}
}
@Override
public void display() {
System.out.println("WeatherData:\n"
+ "temperature: "+temperature +"\n"
+"humidity"+humidity+"\n"
+"pollution_index:"+pollution_index);
}
}
FactoryDisplay.java
package observer;
/*
* @author torjan
* 工厂显示平台所需要的广播数据
*
*/
public class FactoryDisplay implements Observer, Display{
Observable observable;
private float temperature;
private float pollution_index;
//变成一个监听者
public void becomeOberser(Observable observable) {
this.observable = observable;
observable.addObserver(this);;
}
@Override
public void update(Object obj, Object arg) {
if(obj instanceof WeatherData){
WeatherData weatherData = (WeatherData)obj;
this.temperature = weatherData.getTemperature();
this.pollution_index = weatherData.getPollution_index();
}
}
@Override
public void display() {
System.out.println("WeatherData:\n"
+ "temperature: "+temperature +"\n"
+"pollution_index"+pollution_index);
}
}
MobileDisplay.java
package observer;
/*
* @author
* 手机平台所需要的广播数据
*
*/
public class MobileDisplay implements Observer, Display {
Observable observable;
private float temperature;
private float humidity;
//变成一个监听者
public void becomeOberser(Observable observable) {
this.observable = observable;
observable.addObserver(this);;
}
@Override
public void update(Object obj, Object arg) {
if(obj instanceof WeatherData){
WeatherData weatherData = (WeatherData)obj;
this.temperature = weatherData.getTemperature();
this.humidity = weatherData.getHumidity();
}
}
@Override
public void display() {
System.out.println("WeatherData:\n"
+ "temperature: "+temperature +"\n"
+"humidity"+humidity);
}
}
测试类：
ObserverDemo.java
package observer;
public class ObserverDemo {
public static void main(String[] args) {
WeatherData weatherData = new WeatherData();
FactoryDisplay factoryDisplay = new FactoryDisplay();
MobileDisplay mobileDisplay = new MobileDisplay();
TVDisplay tvDisplay = new TVDisplay();
weatherData.addObserver(factoryDisplay);
weatherData.addObserver(mobileDisplay);;
tvDisplay.becomeOberser(weatherData);
weatherData.setState(23, 70, 120);
factoryDisplay.display();
mobileDisplay.display();
tvDisplay.display();
}
}
测试结果：
WeatherData: temperature: 23.0 pollution_index120.0 WeatherData: temperature: 23.0 humidity70.0 WeatherData: temperature: 23.0 humidity70.0 pollution_index:120.0
总结:
设计原则：找出程序中会变化的方面，然后根据其和固定不变的方面相分离
在观察者模式中，会改变的是主题的状态，以及观察者的数目和种类。用这个模式，可以改变依赖于主题状态的对象，却不必改变主题。
设计原则：针对接口编程，不针对实现编程
设计原则：多用组合，少用继承
时间： 2024-08-01 10:30:39