Observer观察者模式

模拟按钮的点击事件处理过程

 

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


public class Test {
    public static void main(String[] args) {
        Button b = new Button();
        b.addActionListener(new MyActionListener());
        b.addActionListener(new MyActionListener2());
        b.buttonPressed();
    }
}

class Button {
    
    private List<ActionListener> actionListeners = new ArrayList<ActionListener>();
    
    public void buttonPressed() {
        ActionEvent e = new ActionEvent(System.currentTimeMillis(),this);
        for(int i=0; i<actionListeners.size(); i++) {
            ActionListener l = actionListeners.get(i);
            l.actionPerformed(e);
        }
    }
    
    public void addActionListener(ActionListener l) {
        actionListeners.add(l);
    }
}

interface ActionListener {
    public void actionPerformed(ActionEvent e);
}

class MyActionListener implements ActionListener {

    public void actionPerformed(ActionEvent e) {
        System.out.println("button pressed!");
    }
    
}

class MyActionListener2 implements ActionListener {

    public void actionPerformed(ActionEvent e) {
        System.out.println("button pressed 2!");
    }
    
}

class ActionEvent {
    
    long when;//事件发生的时间
    Object source;//事件源，这里就是被点击的那个Button
    
    public ActionEvent(long when, Object source) {
        super();
        this.when = when;
        this.source = source;
    }
    
    
    public long getWhen() {
        return when;
    }

    public Object getSource() {
        return source;
    }
    
}