Observer Pattern(观察者模式)

观察者模式应用比较广泛，写一个简单的示例，扩展了一下Head First上面例子的应用范围，进一步降低Observer与Subject之间的耦合度。

简单例子，直接给代码：

package test;public interface Subject {public void registerObserver(Observer observer);public void unRegisterObserver(Observer observer);public void notifyAllObservers();public void notifyObserver(Observer observer);}package test;public interface Observer {public void registerSubject(Subject subject);public void unRegisterSubject(Subject subject);public void update(Subject subject);} package test;import java.util.ArrayList;import java.util.List;public class WeatherDataSubject implements Subject {List<Observer> observers = new ArrayList<Observer>();private float temperature;private float humidity;private float pressure;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 getPressure() {return pressure;}public void setPressure(float pressure) {this.pressure = pressure;}@Overridepublic void registerObserver(Observer observer) {// TODO Auto-generated method stub if(!observers.contains(observer)) observers.add(observer);}@Overridepublic void unRegisterObserver(Observer observer) {// TODO Auto-generated method stubif(observers.contains(observer)) observers.remove(observer);}@Overridepublic void notifyAllObservers() {// TODO Auto-generated method stubfor(Observer o:observers)o.update(this);}@Overridepublic void notifyObserver(Observer observer) {// TODO Auto-generated method stubif(observers.contains(observer)) observer.update(this);}public void setWeatherDataParameters(float temperature,float humidity,float pressure){this.setTemperature(temperature);this.setHumidity(humidity);this.setPressure(pressure);this.notifyAllObservers();}} package test;public class DisplayPanel implements Observer {private float temperature;private float humidity;private float pressure;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 getPressure() {return pressure;}public void setPressure(float pressure) {this.pressure = pressure;}@Overridepublic void registerSubject(Subject subject) {// TODO Auto-generated method stubsubject.registerObserver(this);}@Overridepublic void unRegisterSubject(Subject subject) {// TODO Auto-generated method stubsubject.unRegisterObserver(this);}@Overridepublic void update(Subject subject) {// TODO Auto-generated method stubif(subject instanceof WeatherDataSubject){WeatherDataSubject s = (WeatherDataSubject)subject;this.setTemperature(s.getTemperature());this.setHumidity(s.getHumidity());this.setPressure(s.getPressure());}this.display();}public void display() {System.out.println("Temperature:"+this.getTemperature());System.out.println("Humidity:"+this.getHumidity());System.out.println("Pressure:"+this.getPressure());}} package test;public class Driver {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubWeatherDataSubject subject1=new WeatherDataSubject();WeatherDataSubject subject2=new WeatherDataSubject();Observer panel1 = new DisplayPanel();Observer panel2 = new DisplayPanel();panel1.registerSubject(subject1);panel1.registerSubject(subject2);panel2.registerSubject(subject2);subject1.setWeatherDataParameters(15.0f, 0.32f, 1076.23f);subject2.setWeatherDataParameters(13.5f, 0.42f, 1087.11f);System.out.println("Subject1:======================");subject1.notifyAllObservers();System.out.println("Subject2:======================");subject2.notifyAllObservers();}}