学步园

package observer;
import java.util.ArrayList;
/**
 * @author jiq
 * 类型：Behavioral
 * 定义： 观察者模式定义了对象之间一对多的依赖，这样一来，当一个对象状态改变时，
 * 		它所有的依赖者都会受到通知并自动更新。
 *
 *	这个模式很好滴遵循了OO设计的三个原则：
 * (1) 将变化的部分和不变的部分分离
 * (2) 针对接口编程，不针对实现编程
 * (3) 多用组合，少用继承
 * 
 *  java中用到的观察者模式：
 *  (1) Java Swing中为JButton注册一个ActionListener时间监听器。
 *  (2) Java中有一个Observable类提供了观察者模式编程API，但是可拓展性不是很好。
 */
/* 主题 */
interface Subject{
	public void registerObserver(Observer o);
	public void removeObserver(Observer o);
	public void notifyObservers();
}

/* 观察者 */
interface Observer{
	public void update(WeatherAttrib wb);
}

/* 显示面板 */
interface Disply{
	public void disply();
}

/******
 * 为了方便天气数据拓展，所以将其作为一个数据类定义出来
 * */
class WeatherAttrib{
	float temperature;
	float humidity;
	float pressure;
	
	public WeatherAttrib(float temperature,	float humidity,	float pressure){
		this.temperature = temperature;
		this.humidity = humidity;
		this.temperature = pressure;
	}
}

/****
 * 天气数据类，继承自主题(被观察者)
 * */
class WeatherData implements Subject{
	private ArrayList<Observer> observers = new ArrayList<Observer>();
	private WeatherAttrib wb;
	
	public void registerObserver(Observer o) {
		observers.add(o);
	}

	public void notifyObservers() {
		for(int i=0;i<observers.size();i++){
			Observer observer = observers.get(i);
			observer.update(wb);
		}
	}

	public void removeObserver(Observer o) {
		int i = observers.indexOf(o);
		if(i >= 0) observers.remove(i);
	}
	
	/* 主题状态改变 */
	public void measurementsChanged(){
		notifyObservers();
	}
	
	public void setWeatherAttrib(WeatherAttrib wb){
		this.wb = wb;
		measurementsChanged();
	}
}

/****
 *  观察者(继承自观察者接口)
 * */
class CurrentConditionDisplay implements Observer, Disply{
	private WeatherAttrib wb;
	private Subject weatherData;	//组合主题
	
	public CurrentConditionDisplay(Subject weatherData){
		this.weatherData = weatherData;
		weatherData.registerObserver(this);
	}
	
	public void update(WeatherAttrib wb) {
		this.wb = wb;
		disply();
	}
	
	public void cancelObserve(){
		weatherData.removeObserver(this);
	}

	public void disply() {
		System.out.println("Current Condition: "+ wb.humidity+","
				+wb.temperature+""+wb.pressure);	
	}	
}

class ForecastDisplay implements Observer, Disply{
	private WeatherAttrib wb;
	private Subject weatherData;
	
	public ForecastDisplay(Subject weatherData){
		this.weatherData = weatherData;
		weatherData.registerObserver(this);
	}
	
	public void update(WeatherAttrib wb) {
		this.wb = wb;
		disply();	//更新显示
	}
	
	public void cancelObserve(){
		weatherData.removeObserver(this);
	}

	public void disply() {
		System.out.println("ForeCatst Disp: "+ wb.humidity+","+wb.temperature+""+wb.pressure);
		
	}	
}

/**
 * 气象站测试
 * */
public class WeatherORama {
	public static void main(String[] args) {
		/*
		 *  创建主题 
		 *  */
		WeatherData weatherData = new WeatherData();
		
		/*
		 * 创建观察者
		 * */
		CurrentConditionDisplay cd_observer = new CurrentConditionDisplay(weatherData);
		ForecastDisplay fd_observer = new ForecastDisplay(weatherData);
		
		/*
		 * 更改主题状态
		 * */
		System.out.println("###WeatherData change:");
		weatherData.setWeatherAttrib(new WeatherAttrib(80, 65, 30.4f));			
		System.out.println("###WeatherData change:");
		weatherData.setWeatherAttrib(new WeatherAttrib(82, 67, 29.4f));		
		fd_observer.cancelObserve(); //不再关注主题
		System.out.println("###WeatherData change:");
		weatherData.setWeatherAttrib(new WeatherAttrib(85, 63, 30.1f));
	}
}/** output
###WeatherData change:
Current Condition: 65.0,30.40.0
ForeCatst Disp: 65.0,30.40.0
###WeatherData change:
Current Condition: 67.0,29.40.0
ForeCatst Disp: 67.0,29.40.0
###WeatherData change:
Current Condition: 63.0,30.10.0
*/