import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.EventObject;
public class ButtonTest2
{
    public static void main(String[] args)
    {
        ButtonFrame frame=new ButtonFrame();
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        frame.show();
    }
}
class ButtonFrame2 extends JFrame
{
    public ButtonFrame2()
    {
        setTitle("ButtonTest");
        this.setSize(WIDTH,HEIGHT);
        ButtonPanel2 panel=new ButtonPanel2();
        Container contentpanel=this.getContentPane();
        contentpanel.add(panel);
    }
    public final int WIDTH=300;
    public final int HEIGHT=200;
}

class ButtonPanel2 extends JPanel implements ActionListener
{
    public ButtonPanel2()
    {
        //create button
        JButton yellowButton=new JButton("yellow");
        JButton blueButton=new JButton("blue");
        JButton redButton=new JButton("red");
        //add button
        this.add(yellowButton);
        this.add(blueButton);
        this.add(redButton);
        yellowButton.addActionListener(this);
        blueButton.addActionListener(this);
        redButton.addActionListener(this);
    }
    public void actionPerformed(ActionEvent e)
    {
        Object source;
        EventObject event=new EventObject(source);
        Object ce=event.getSource();
        if (ce=yellowButton) this.setBackground(Color.yellow);
        else if (e=blueButton) this.setBackground(Color.blue);
        else if (e=redButton) this.setBackground(Color.red);
    }

}


最后总说yellowButton,blueButton,redButton找不到？不知道为什么。

修订程序如下》：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class ButtonPanel extends JPanel
{
public ButtonPanel()
{
JButton yellowButton=new JButton("yellow");
JButton blueButton=new JButton("blue");
JButton redButton=new JButton("red");


add(yellowButton);
add(blueButton);
add(redButton);

ColorAction yellowAction=new ColorAction(Color.yellow);
ColorAction blueAction=new ColorAction(Color.blue);
ColorAction redAction=new ColorAction(Color.red);

yellowButton.addActionListener(yellowAction);
blueButton.addActionListener(blueAction);
redButton.addActionListener(redAction);
}

private class ColorAction implements ActionListener{
public ColorAction(Color c)
{
backgroundColor=c;
}
public void actionPerformed(ActionEvent event)
{
setBackground(backgroundColor);
repaint();
}

private Color backgroundColor;
}
}

class ButtonFrame extends JFrame
{
public ButtonFrame()
{
setTitle("ButtonTest");
setSize(WIDTH,HEIGHT);

ButtonPanel panel=new ButtonPanel();
Container contentPanel=getContentPane();
contentPanel.add(panel);
}
public static final int WIDTH=300;
public static final int HEIGHT=500;
}

public class ButtonTest
{
public static void main(String[] args)
{
ButtonFrame frame=new ButtonFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}

frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);这句怎么报错？？

Container contentpanel=this.getContentPane(); 是什么意思，哪位给解释一下。