java小程序设计，设计一个窗口程序

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;
public class FrameTest {
private JFrame jf;
private JButton yellow,blue,green;
private JPanel panel1;
public FrameTest(){
jf = new JFrame("Frame");
yellow = new JButton("yellow");
blue = new JButton("blue");
green = new JButton("green");
panel1 = new JPanel();
panel1.setLayout(new FlowLayout());
jf.add(panel1,BorderLayout.CENTER);
jf.setVisible(true);
jf.setSize(500,600);
jf.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e){
System.exit(0);
}
}
);
blue.setForeground(Color.blue);
panel1.add(blue);
blue.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
panel1.setBackground(Color.blue);
}
});
yellow.setForeground(Color.yellow);
panel1.add(yellow);
yellow.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
panel1.setBackground(Color.yellow);
}
});
green.setForeground(Color.green);
panel1.add(green);
green.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
panel1.setBackground(Color.green);
}
});

}
public static void main(String args[]){
FrameTest ft = new FrameTest();
}
}

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