Problem with Graphics and JPanel...

Question

I would like to draw a rectangle on a JPanel. Here is my code:
JPanel panel = new JPanel();
Graphics g = panel.getGraphics();
g.drawRect(20,20,20,20);
When I run my program, I have a NullPointerException...
Do you any suggestions to fix the problem??
thanks
Pete

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import javax.swing.*;
public class pete extends JFrame {
  public pete() {
    JPanel panel = new JPanel() {
      public void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int midx = getSize().width / 2;
        int midy = getSize().height / 2;
        g2.draw(new Rectangle2D.Double(midx/2, midy/2, midx, midy));
    getContentPane().add(panel, "Center");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(400,300);
    setLocation(300,100);
    setVisible(true);
  public static void main(String[] args) {
    new pete();
}