Java设计模式之观察者模式

[color=red]OBSERVER[/color] （Object Behavioral）
[color=red]Purpose[/color]
Lets one or more objects be notified of state changes in other
objects within the system.
[color=red]Use When[/color]
1 State changes in one or more objects should trigger behavior
in other objects
2 Broadcasting capabilities are required.
3 An understanding exists that objects will be blind to the
expense of notification.
[color=red]Example[/color]
This pattern can be found in almost every GUI environment.
When buttons, text, and other fields are placed in applications
the application typically registers as a listener for those controls.
When a user triggers an event, such as clicking a button, the
control iterates through its registered observers and sends a
notification to each.

package javaPattern.observer;

import java.util.ArrayList;

public interface Observer {
	public void update();
}
class ConcreteObserver implements Observer{

	@Override
	public void update() {
		System.out.println("update...");

	}

}
interface Subject{
	public void attach(Observer o);
	public void detach(Observer o);
	public void notifyObserver();
}
class ConreteSubject implements Subject{
	private ArrayList<Observer> observers = new ArrayList<Observer>();
	@Override
	public void attach(Observer o) {
		observers.add(o);

	}

	@Override
	public void detach(Observer o) {
		observers.remove(o);

	}

	@Override
	public void notifyObserver() {
		for(Observer o : observers){
			o.update();
		}

	}

}
class Client{
	public static void main(String[] args) {
		Subject subject = new ConreteSubject();
		Observer observer1 = new ConcreteObserver();
		Observer observer2 = new ConcreteObserver();
		Observer observer3 = new ConcreteObserver();
		subject.attach(observer1);
		subject.attach(observer2);
		subject.attach(observer3);
		subject.notifyObserver();

	}
}