按下按钮圆圈可以改变颜色

import javax.swing.*;
import java.awt.*;
public class MyDrawPanel extends JPanel
{
public void paintComponent(Graphics g)
{
Graphics2D g2d=(Graphics2D)g;
int red=(int)(Math.random()*255);
int blue=(int)(Math.random()*255);
int green=(int)(Math.random()*255);
Color startColor=new Color(red,green,blue);
red=(int)(Math.random()*255);
blue=(int)(Math.random()*255);
green=(int)(Math.random()*255);
Color endColor=new Color(red,green,blue);
GradientPaint gradient=new GradientPaint(70,70,startColor,100,100,endColor);
g2d.setPaint(gradient);
g2d.fillOval(70,70,100,100);
}
}

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class SimpleGui3C implements ActionListener
{
JFrame frame;
public static void main(String [] args)
{
SimpleGui3C gui=new SimpleGui3C();
gui.go();
}
public void go()
{
frame =new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton button=new JButton("Change colors");
button.addActionListener(this);
MyDrawPanel drawPanel=new MyDrawPanel();
frame.getContentPane().add(BorderLayout.SOUTH,button);
frame.getContentPane().add(BorderLayout.CENTER,drawPanel);
frame.setSize(300,300);
frame.setVisible(true);
}
public void actionPerformed(ActionEvent event)
{
frame.repaint();
}
}