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;
	}
	
	@Override
	public void registerObserver(Observer observer) {
		// TODO Auto-generated method stub
        if(!observers.contains(observer))
        	observers.add(observer);
	}
	@Override
	public void unRegisterObserver(Observer observer) {
		// TODO Auto-generated method stub
		if(observers.contains(observer))
        	observers.remove(observer);
	}
	@Override
	public void notifyAllObservers() {
		// TODO Auto-generated method stub
		for(Observer o:observers)
			o.update(this);
	}
	@Override
	public void notifyObserver(Observer observer) {
		// TODO Auto-generated method stub
		if(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;
	}
	@Override
	public void registerSubject(Subject subject) {
		// TODO Auto-generated method stub
		subject.registerObserver(this);
	}
	@Override
	public void unRegisterSubject(Subject subject) {
		// TODO Auto-generated method stub
		subject.unRegisterObserver(this);
	}
	@Override
	public void update(Subject subject) {
		// TODO Auto-generated method stub
		if(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 stub
		WeatherDataSubject 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();
	}
}