观察者模式Observer

//Purpose.  Observer design pattern

//1. Model the "independent" functionality with a "subject" abstraction
//2. Model the "dependent" functionality with "observer" hierarchy
//3. The Subject is coupled only to the Observer base class
//4. Observers register themselves with the Subject
//5. The Subject broadcasts events to all registered Observers
//6. Observers "pull" the information they need from the Subject
//7. Client configures the number and type of Observers

class Subject { // 1. The "independent" abs
	private Observer[] observers = new Observer[9]; // 3. Coupled to base class
	private int totalObs = 0;
	private int state;

	public void attach(Observer o) {
		observers[totalObs++] = o;
	} // 3. Coupled

	public int getState() {
		return state;
	}

	public void setState(int in) {
		state = in;
		notifyObservers();
	}

	private void notifyObservers() {
		for (int i = 0; i < totalObs; i++)
			observers[i].update(); // 3. Coupled to base class
	}
} // 5. Broadcast events to observers

abstract class Observer { // 2. Root of the "dependent" hierarchy
	protected Subject subj;

	public abstract void update();
}

class HexObserver extends Observer { // 2. Concrete class of the "dependent"
	public HexObserver(Subject s) { // hierarchy
		subj = s;
		subj.attach(this);
	} // 4. Observers register themselves

	public void update() {
		System.out.print("  " + Integer.toHexString(subj.getState()));
	}
} // 6. Observers "pull" information

class OctObserver extends Observer {
	public OctObserver(Subject s) {
		subj = s;
		subj.attach(this);
	} // 4. Observers register themselves

	public void update() {
		System.out.print("  " + Integer.toOctalString(subj.getState()));
	}
} // 6. Observers "pull" information

class BinObserver extends Observer {
	public BinObserver(Subject s) {
		subj = s;
		subj.attach(this);
	} // 4. Observers register themselves

	public void update() {
		System.out.print("  " + Integer.toBinaryString(subj.getState()));
	}
} // 6. Observers "pull" information

public class ObserverDemo {
	public static void main(String[] args) {
		Subject sub = new Subject();
		// 7. Client configures the number and type of Observers
		new HexObserver(sub);
		new OctObserver(sub);
		new BinObserver(sub);
		
		InputStreamReader is = new InputStreamReader(System.in);
		while (true) {
			System.out.print("\nEnter a number: ");
			try {
				sub.setState(is.read());
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}finally{
				if(is!=null){
					try {
						is.close();
					} catch (IOException e) {
						e.printStackTrace();
					}
				}
				
			}
		}
	}
}