觀察者模式： 定義了對(duì)象之間的一對(duì)多依賴，這樣一來，當(dāng)一個(gè)對(duì)象改變狀態(tài)時(shí)，他的所有依賴者都會(huì)受到通知并自動(dòng)更新。

1，定義事件源接口

package com.pattern.observer;public interface Subject {public void registerObserver(Observer o);public void removeObserver(Observer o);public void notifyObserver(); }

2，定義事件源

package com.pattern.observer;import java.util.ArrayList;/*** 事件源*/ public class WeatherData implements Subject {private ArrayList observers;private float temperature;private float humidity;private float pressure;public WeatherData() {observers = new ArrayList();}/*** @see com.pattern.observer.Subject#registerObserver(com.pattern.observer.Observer)*/@Overridepublic void registerObserver(Observer o) {observers.add(o);}/*** @see com.pattern.observer.Subject#removeObserver(com.pattern.observer.Observer)*/@Overridepublic void removeObserver(Observer o) {int i = observers.indexOf(o);if (i >= 0) {observers.remove(i);}}/*** @see com.pattern.observer.Subject#notifyObserver()*/@Overridepublic 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();}}

3，定義觀察者接口

package com.pattern.observer;public interface Observer {public void update(float temp,float humidity,float pressure);}

4，定義顯示接口

package com.pattern.observer;public interface DisplayElement {public void display();}

5，觀察者實(shí)現(xiàn)類

package com.pattern.observer;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);}/** * @see com.pattern.observer.DisplayElement#display()*/@Overridepublic void display() {System.out.println("Current conditions: "+temperature +"F degrees and "+humidity+"% humidity");}/** * @see com.pattern.observer.Observer#update(float, float, float)*/@Overridepublic void update(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;display();}}

6,測(cè)試

package com.pattern.observer;public class WeatherStation {public static void main(String[] args){WeatherData weatherData = new WeatherData();CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);weatherData.setMeasurements(80, 65, 30.4f);} }

類圖如下所示：

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轉(zhuǎn)載于:https://www.cnblogs.com/mengjianzhou/p/5986821.html

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