Draw Rectangle to Canvas ?

Question

I am finding that working with drawing shape in Java is a bit hard to understand. I am hoping someone can help me out. I have wanting to draw a simple Rectangle to a Canvas. I am hoping that will give the user the look that a Rectangle has been drawn to the screen and not inside of a JFrame or anything like that.
Here is my code that does not seam to work.
Canvas can;
Graphics g2;
Rectangle r;
public void drawShape()
       can = createCanvas();
       g2 = can.getGraphics();
       g2.drawRect(0, 0, 640, 480);
//create canvas that I call from another class
public Canvas createCanvas( )
          r.width = java.awt.Toolkit.getDefaultToolkit().getScreenSize().width;
          r.height = java.awt.Toolkit.getDefaultToolkit().getScreenSize().height;
          r.x = 0;
          r.y = 0;
          if(box == null)
               box = new Canvas();
               box.setBounds(r);
          return box;
     }

Answer 1

simple demo, might start you off
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Testing
  public void buildGUI()
    JPanel p = new JPanel(){
      public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawString("alt-F4 to close",400,300);
        g.drawRect(300,200,300,200);
    p.setBackground(Color.WHITE);
    JFrame f = new JFrame();
    f.getContentPane().add(p);
    f.setUndecorated(true);
    GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice().setFullScreenWindow(f);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
  public static void main(String[] args)
    SwingUtilities.invokeLater(new Runnable(){
      public void run(){
        new Testing().buildGUI();
}more reading here
[http://java.sun.com/docs/books/tutorial/uiswing/painting/index.html]
and this
can.getGraphics();is generally a very bad way to do it