无法将ActionListener添加到JPanel？

Question

I've been trying for over a hour to test a simple program to change the color of a ball on click , when I try myPanel.addActionListener(new BallListener()) , i get one error during compile time

Please help me spot the error?

myPanel.addActionListener(new BallListener());
       ^
  symbol:   method addActionListener(Ball.BallListener)
  location: variable myPanel of type MyPanel
1 error





//first Java Program on the new VM
    import java.awt.*;
    import javax.swing.*;
    import java.awt.event.*;
    import java.awt.geom.*;
    import java.util.*;

    public class Ball{

    private MyFrame myFrame;
    private MyPanel myPanel;

    public static void main(String[] args)
    {
    Ball ball=new Ball();
    ball.go();

    }//main ends

    public class BallListener implements ActionListener{

    public void actionPerformed(ActionEvent e)
    {
    myFrame.repaint();
    }

    }//listener ends

    public void go()
    {

    myPanel=new MyPanel();
    //myPanel.addActionListener(new BallListener());
    myFrame=new MyFrame();
    myFrame.add(BorderLayout.CENTER,myPanel);
    myFrame.setVisible(true);
    }

    }//class ends



    //ball panel
    class MyPanel extends JPanel
    {
    public void paintComponent(Graphics g)
    {
    Graphics2D g2d=(Graphics2D)g;
    Ellipse2D ellipse=new Ellipse2D.Double(200,200,400,400);
    int r=(int)Math.random()*256;
    int b=(int)Math.random()*256;
    int g1=(int)Math.random()*256;
    Color color=new Color(r,g1,b);
    g2d.setPaint(color);
    g2d.fill(ellipse);
    }
    }//Class ends

    //a simple JFrame
    class MyFrame extends JFrame{

    public MyFrame()
    {
    setSize(600,600);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setResizable(false);
    }
    }//class ends

Answer 1

JPanel s don't support ActionListener s because they don't have a natural action. For buttons, the natural action is clicking on them, so it makes sense to have an ActionListener that fires when they are clicked. JPanel s are not buttons.

If you want to detect clicks on a JPanel , you need to add a MouseListener , not an ActionListener .

Answer 2

对于面板事件，您可以使用WindowListener覆盖WindowsClosing方法等，ActionListener不用于框架或面板等。