Incremental Painting in Swing

Question

Hello All!
How can I achieve incremental painting in a JPanel or in general JComponents.. By "incremental painting" I mean I do not want to lose my previous drawings on the panel aka. I want to update the drawing by adding more drawings.
An example would help this is the code:
import java.awt.*;
import javax.swing.*;
public class CustomPanel extends JPanel{
public final static int CIRCLE = 1, SQUARE = 2;
private int shape;
public void paintComponent(Graphics g){
super.paintComponent(g);
if(shape == CIRCLE)
g.fillOval(50,10,60,60);
else if(shape == SQUARE)
g.fillRect(150,110,60,60);
public void draw(int s){
shape = s;
repaint();
This class is used by the following class:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class CustomPanelTest extends JFrame{
private JPanel buttonPanel;
private CustomPanel myPanel;
private JButton circle, square;
public CustomPanelTest()
super("Custom Panel Test");
myPanel = new CustomPanel();
myPanel.setBackground(Color.green);
square = new JButton("Square");
square.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e)
myPanel.draw(CustomPanel.SQUARE);
circle = new JButton("Circle");
circle.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e)
myPanel.draw(CustomPanel.CIRCLE);
buttonPanel = new JPanel();
buttonPanel.setLayout(new GridLayout(1,2) );
buttonPanel.add(circle);
buttonPanel.add(square);
Container c = getContentPane();
c.add(myPanel, BorderLayout.CENTER);
c.add(buttonPanel, BorderLayout.SOUTH);
setSize(300,150);
show();
public static void main ( String args[] )
CustomPanelTest app = new CustomPanelTest();
app.addWindowListener(
new WindowAdapter() {
public void windowClosing (WindowEvent e )
System.exit(0);
While executing, either a circle or square is drawn by erasing the previous drawing. What I want to achieve is for example drawing a series of circles and/or squares without losing the previous drawings.
Thank you!!!!

Answer 1

This will do it. I added a bufferedimage.
import java.awt.*;
import javax.swing.*;
import java.awt.image.BufferedImage;
public class CustomPanel  extends JPanel
     public final static int CIRCLE = 1, SQUARE = 2;
     private int           shape;
     private BufferedImage I = null;
     private Graphics      G;
public void paintComponent(Graphics g)
     if (I == null)
          I = new BufferedImage(getWidth(),getHeight(),BufferedImage.TYPE_INT_ARGB);     
          G = I.getGraphics();
          G.setColor(Color.white);
          G.fillRect(0,0,getWidth(),getHeight());
     super.paintComponent(g);
     G.setColor(Color.red);
     if(shape == CIRCLE) G.fillOval(50,10,60,60);
     if(shape == SQUARE) G.fillRect(150,110,60,60);
     g.drawImage(I,0,0,null);
public void draw(int s)
     shape = s;
     repaint();
}Noah