SimpleGui3C.java

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();
}
}
class MyDrawPanel extends JPanel{
	public void paintComponent(Graphics g){
		Graphics2D g2d=(Graphics2D) g;

		int red=(int) (Math.random() *255);
		int green=(int) (Math.random()*255);
		int blue=(int)(Math.random()*255);
		Color startColor=new Color(red,green,blue);

		red=(int)(Math.random()*255);
		green=(int)(Math.random()*255);
		blue=(int)(Math.random()*255);
		Color endColor=new Color(red, green, blue);

		GradientPaint gradient=new GradientPaint(70,70, startColor,150,150,endColor);
		g2d.setPaint(gradient);
		g2d.fillOval(70,70,100,100);

	}
}