观察者模式就是：
1、所有的观察者需要被通知，实现了一个接口，供主题调用
2、所有的主题都有一个观察者列表，主题通过调用观察者实现的接口通知观察者。
代码结构(inside代表使用java.util， self使用自定义的接口)：
interface DisplayElement:
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer;
/**
* Description :
* <br><br>Time : 2015/3/27 23:28
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public interface DisplayElement {
public void display();
}
interface subject:
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.self;
/**
* Description :
* <br><br>Time : 2015/3/27 23:25
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public interface Subject {
public void registerObserver(Observer o) ;
public void removeObserver(Observer o);
public void notifyObserver();
}
interface Observer:
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.self;
/**
* Description :
* <br><br>Time : 2015/3/27 23:26
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public interface Observer {
public void update(float temp, float humidity, float pressure);
}
WeatherData
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.self.impl;
import com.misuosi.dp.observer.self.Observer;
import com.misuosi.dp.observer.self.Subject;
import java.util.ArrayList;
/**
* Description :
* <br><br>Time : 2015/3/27 23:30
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public class WeatherData implements Subject {
private ArrayList observers;
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {
observers = new ArrayList();
}
@Override
public void registerObserver(Observer o) {
observers.add(o);
}
@Override
public void removeObserver(Observer o) {
int i = observers.indexOf(o);
if(i >= 0) {
observers.remove(i);
}
}
@Override
public void notifyObserver() {
for (int i = 0; i< observers.size(); i++) {
Observer observer = (Observer) observers.get(i);
observer.update(temperature, humidity, pressure);
}
}
public void measurementsChanged() {
notifyObserver();
}
public void setMeasurements(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
}
CurrentConditionsDisplay
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.self.impl;
import com.misuosi.dp.observer.DisplayElement;
import com.misuosi.dp.observer.self.Observer;
import com.misuosi.dp.observer.self.Subject;
/**
* Description :
* <br><br>Time : 2015/3/27 23:41
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public class CurrentConditionsDisplay implements Observer, DisplayElement {
private float temperature;
private float humidity;
private Subject weatherData;
public CurrentConditionsDisplay(Subject weatherData) {
this.weatherData = weatherData;
weatherData.registerObserver(this);
}
@Override
public void update(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
display();
}
@Override
public void display() {
System.out.println("Current conditions:" + temperature
+ "F degrees and "+ humidity + "% humidity");
}
}
使用jdk内置的观察者接口：
WeatherData
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.inside;
import java.util.Observable;
/**
* Description :
* <br><br>Time : 2015/3/28 8:03
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public class WeatherData extends Observable{
private float temperature;
private float humidity;
private float pressure;
public WeatherData() {}
public void measurementsChanged() {
setChanged();
notifyObservers();
}
public void setMeasurements(float temperature, float humidity, float pressure) {
this.temperature = temperature;
this.humidity = humidity;
this.pressure = pressure;
measurementsChanged();
}
public float getTemperature() {
return temperature;
}
public float getHumidity() {
return humidity;
}
public float getPressure() {
return pressure;
}
}
CurrentConditionsDisplay
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer.inside;
import com.misuosi.dp.observer.DisplayElement;
import java.util.Observable;
import java.util.Observer;
/**
* Description :
* <br><br>Time : 2015/3/28 8:15
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public class CurrentConditionsDisplay implements Observer, DisplayElement {
Observable observable;
private float temperature;
private float humidity;
public CurrentConditionsDisplay(Observable observable) {
this.observable = observable;
observable.addObserver(this);
}
@Override
public void update(Observable obs, Object arg) {
if(obs instanceof WeatherData){
WeatherData weatherData = (WeatherData) obs;
this.temperature = weatherData.getTemperature();
this.humidity = weatherData.getHumidity();
display();
}
}
@Override
public void display() {
System.out.println("Current conditions:" + temperature
+ "F degrees and " + humidity + "% humidity");
}
}
测试类：
WeatherStationSelf
/*
* Copyright (c) 2014
* 广州米所思信息科技有限公司(Guangzhou Mythos Information technology co., LTD)
* All rights reserved.
*/
package com.misuosi.dp.observer;
import com.misuosi.dp.observer.self.impl.CurrentConditionsDisplay;
import com.misuosi.dp.observer.self.impl.WeatherData;
import org.junit.Test;
/**
* Description :
* <br><br>Time : 2015/3/27 23:45
*
* @author ICE
* @version 1.0
* @since 1.0
*/
public class WeatherStationSelf {
@Test
public void test() {
WeatherData weatherData = new WeatherData();
CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(weatherData);
weatherData.setMeasurements(80, 65, 30.4f);
weatherData.setMeasurements(82, 70, 29.2f);
weatherData.setMeasurements(78, 90, 29.2f);
}
}
原文：http://www.cnblogs.com/yingbing/p/4373577.html