设计模式10：观察者模式

观察者模式所做的事情就是在解耦合，让耦合的双方都依赖于抽象，而不是依赖于具体。

这样各自的变化不会影响另一边的变化。

uml：

代码：

通知者：

package observer;

import java.util.ArrayList;
import java.util.List;

public class Subject {

	private List<Observer> observers = new ArrayList<>();
	private String state = null;

	public String getState() {
		return state;
	}

	public void setState(String state) {
		this.state = state;
	}
	
	public void attach(Observer observer) {
		observers.add(observer);
	}
		
	public void detach(Observer observer) {
		observers.remove(observer);
	}
	
	public void notifyAllObserver() {
		for(Observer observer : observers){
			observer.update();
		}
	}
}

package observer;


public class ConcreteSubject extends Subject {
	
	@Override
	public void notifyAllObserver() {
		System.out.println("老板回来啦！");
		super.notifyAllObserver();
	}
	
}

观察者：

package observer;

public abstract class Observer {
	
	protected Subject subject = null;
	
	public Observer(Subject subject) {
		this.subject = subject;
	}
	
	public abstract void update();
	
}

package observer;

public class ConcreteObserver extends Observer{

	private String name = null;
	private String state = null;
	
	public ConcreteObserver(String name, String state, Subject subject) {
		super(subject);
		this.name = name;
	}
	
	public String getState() {
		return state;
	}

	public void setState(String state) {
		this.state = state;
	}

	@Override
	public void update() {
		state = subject.getState();
		System.out.print(name + "的新状态是" + state);
		
	}
	
	
}

　　

DEMO：

package observer;

public class ObserverDemo {

	public static void main(String[] args) {
		Subject subject = new ConcreteSubject();
		ConcreteObserver observer = new ConcreteObserver("老王", "看电影", subject);
		subject.attach(observer);
		
		subject.setState("快工作！");
		subject.notifyAllObserver();
	}
	
}