行為型-觀察者模式

package observer;
import java.util.ArrayList;
/**
 * @author jiq
 * 型別：Behavioral
 * 定義： 觀察者模式定義了物件之間一對多的依賴，這樣一來，當一個物件狀態改變時，
 * 		它所有的依賴者都會受到通知並自動更新。
 *
 *	這個模式很好滴遵循了OO設計的三個原則：
 * (1) 將變化的部分和不變的部分分離
 * (2) 針對介面程式設計，不針對實現程式設計
 * (3) 多用組合，少用繼承
 * 
 *  java中用到的觀察者模式：
 *  (1) Java Swing中為JButton註冊一個ActionListener時間監聽器。
 *  (2) Java中有一個Observable類提供了觀察者模式程式設計API，但是可擴充性不是很好。
 */
/* 主題 */
interface Subject{
	public void registerObserver(Observer o);
	public void removeObserver(Observer o);
	public void notifyObservers();
}

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

/* 顯示皮膚 */
interface Disply{
	public void disply();
}

/******
 * 為了方便天氣資料擴充，所以將其作為一個資料類定義出來
 * */
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;
	}
}

/****
 * 天氣資料類，繼承自主題(被觀察者)
 * */
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);
	}
	
	/* 主題狀態改變 */
	public void measurementsChanged(){
		notifyObservers();
	}
	
	public void setWeatherAttrib(WeatherAttrib wb){
		this.wb = wb;
		measurementsChanged();
	}
}

/****
 *  觀察者(繼承自觀察者介面)
 * */
class CurrentConditionDisplay implements Observer, Disply{
	private WeatherAttrib wb;
	private Subject weatherData;	//組合主題
	
	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();	//更新顯示
	}
	
	public void cancelObserve(){
		weatherData.removeObserver(this);
	}

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

/**
 * 氣象站測試
 * */
public class WeatherORama {
	public static void main(String[] args) {
		/*
		 *  建立主題 
		 *  */
		WeatherData weatherData = new WeatherData();
		
		/*
		 * 建立觀察者
		 * */
		CurrentConditionDisplay cd_observer = new CurrentConditionDisplay(weatherData);
		ForecastDisplay fd_observer = new ForecastDisplay(weatherData);
		
		/*
		 * 更改主題狀態
		 * */
		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(); //不再關注主題
		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
*/