每天一个设计模式之观察者模式

观察者模式

观察者模式定义了对象之间的一对多依赖关系，这样一来。当一个对象改变状态时，他的所有依赖的对象都会收到通知和更新

简要的来说就是当一个对象改变，在这个对象里面通知其他对象

现在我们用小明的妈妈给她儿子零花钱这个例子来演示这个例子

//主题的抽象接口
public interface Subject{
public void registerObserver(Oberver o);
public void removeObserver(Observer o);
public void notifyObservers();
}

//观察者抽象接口
public interface Oberver{
public void update(int price);
}

//妈妈主题 妈妈实现抽象接口
public class MomSuject implements Subject{
private ArrayList obervers;

public MomSuject(){
obervers = new ArrayList();
}

public void registerObserver(Oberver o){
obervers.add(o);
}

public void removeObserver(Oberver o){
obervers.remove(o);
}

public void notifyObservers(){
for (int i = 0; i < obervers.size() -1; i++) {
System.out.println(obervers.get(i));
}
}

public void setPrice(int price){
for (int i = 0; i < obervers.size() -1; i++) {
obervers.get(i).setPrice(price)
}
}
}

//儿子抽象观察者实现类，
public class SonObserver implements Observer{
private int price;

private MomSuject monSubject;

public SonObserver(MomSuject monSubject){
this.monSubject = monSubject;
monSubject.registerObserver(this);
}

public void display(){
System.out.println(price)
}
}

//妈妈给孩子们零花钱，孩子将零花钱打印出来
public class ObserverTest{
Subject monSubject = new MomSuject();
Obrver bigSon = new SonObserver(monSubject);
Oberver twoSon = new SonObserver(monSubject);
Oberver threaSon = new SonObserver(monSubject);

monSubject.setPrice(100);
monSubject.setPrice(300);
monSubject.setPrice(400);
}

在Java中有很多地方都 会用到观察者模式，例如Swingjianting 中事件监听

import java.awt.;
import java.awt.event.;
import javax.swing.;
import javax.swing.event.;

public class SwingObserverExample {
JFrame frame;

public static void main(String[] args) {
SwingObserverExample example = new SwingObserverExample();
example.go();
}

public void go() {
frame = new JFrame();

JButton button = new JButton("Should I do it?");
button.addActionListener(new AngelListener());
button.addActionListener(new DevilListener());
frame.getContentPane().add(BorderLayout.CENTER, button);

// Set frame properties
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(BorderLayout.CENTER, button);
frame.setSize(300,300);
frame.setVisible(true);
}

class AngelListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
System.out.println("Don't do it, you might regret it!");
}
}

class DevilListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
System.out.println("Come on, do it!");
}
}
}