四种监听器（自身类，外部类，内部类，匿名类）

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

public class ThisClassEvent extends JFrame implements ActionListener{
    public ThisClassEvent(){
        setLayout(new FlowLayout());
        JButton btn=new JButton("ok");
        add(btn);
        btn.addActionListener(this);
    }
    public void actionPerformed (ActionEvent e){
     System.out.println("The OK button is clicked");
    }
    public static void main(String args[]){
     ThisClassEvent frame = new ThisClassEvent();
        frame.setTitle("自身类作为事件监听器");
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(280, 100);
        frame.setVisible(true);
        new ThisClassEvent();
    }
}

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

public class OuterClassEvent extends JFrame{
    public OuterClassEvent(){
     setLayout(new FlowLayout());
        JButton btn=new JButton("ok");
        add(btn);
        OuterClass btListener=new OuterClass();
        btn.addActionListener(btListener);
    }
    public static void main(String args[]){
     OuterClassEvent frame = new OuterClassEvent();
        frame.setTitle("外部类作为事件监听器");
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(280, 100);
        frame.setVisible(true);
        new ThisClassEvent();
    }
}
class OuterClass implements ActionListener{
    public void actionPerformed(ActionEvent e){
     System.out.println("The OK button is clicked");
    }
}

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

class InnerClassEvent extends JFrame{
    public InnerClassEvent(){
     setLayout(new FlowLayout());
        JButton btn=new JButton("ok");
        add(btn);
        OuterClass btListener=new OuterClass();
        btn.addActionListener(btListener);
    }
    class InnerClass implements ActionListener{
        public void actionPerformed (ActionEvent e){
         System.out.println("The OK button is clicked");
        }
    }
    public static void main(String args[]){
     InnerClassEvent frame = new InnerClassEvent();
        frame.setTitle("内部类作为事件监听器");
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(280, 100);
        frame.setVisible(true);
        new ThisClassEvent();
    }

}

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

class AnonymousEvent extends JFrame{
    public AnonymousEvent(){
     setLayout(new FlowLayout());
        JButton btn=new JButton("ok");
        add(btn);
        btn.addActionListener(
            new ActionListener(){   //匿名内部类作为参数，new 一个lisenter实际上是创建了一个实现了这个listener的类
                public void actionPerformed(ActionEvent e){
                 System.out.println("The OK button is clicked");
                }
            }
        );
    }
    public static void main(String args[]){
     AnonymousEvent frame = new AnonymousEvent();
        frame.setTitle("匿名内部类作为事件监听器");
        frame.setLocationRelativeTo(null); // Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(280, 100);
        frame.setVisible(true);
        new ThisClassEvent();
    }
}