This example shows how to draw a mutable image on a Canvas.

 /*--------------------------------------------------
* MutableImage.java
*
* Draw mutable image on a canvas
*
* Example from the book:     Core J2ME Technology
* Copyright John W. Muchow   http://www.CoreJ2ME.com
* You may use/modify for any non-commercial purpose
*-------------------------------------------------*/  
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;

public class MutableImageWithCanvas extends MIDlet
{
  private Display  display;     // The display
  private ImageCanvas canvas;   // Canvas 
  public MutableImageWithCanvas()
  {
    display = Display.getDisplay(this);
    canvas  = new ImageCanvas(this);
  }
  protected void startApp()
  {
    display.setCurrent( canvas );
  }
  protected void pauseApp()
  { }

  protected void destroyApp( boolean unconditional )
  { }
  public void exitMIDlet()
  {
    destroyApp(true);
    notifyDestroyed();
  }
}

/*--------------------------------------------------
* Class ImageCanvas
*
* Draw mutable image
*-------------------------------------------------*/
class ImageCanvas extends Canvas implements CommandListener
{
  private Command cmExit;  // Exit midlet
  private MutableImage midlet;
  private Image im = null;
  private String message = "Core J2ME";
  public ImageCanvas(MutableImage midlet)
  {
    this.midlet = midlet;
    // Create exit command & listen for events
    cmExit = new Command("Exit", Command.EXIT, 1);
    addCommand(cmExit);
    setCommandListener(this);

    try
    {
      // Create mutable image
      im = Image.createImage(80, 20);

      // Get graphics object to draw onto the image        
      Graphics graphics = im.getGraphics();

      // Specify a font face, style and size
      Font font = Font.getFont(Font.FACE_SYSTEM, Font.STYLE_PLAIN, Font.SIZE_MEDIUM);
      graphics.setFont(font);

      // Draw a filled (black) rectangle
      graphics.setColor(0, 0, 0);
      graphics.fillRoundRect(0,0, im.getWidth()-1, im.getHeight()-1, 20, 20); 
      // Center text horizontally in the image. Draw text in white
      graphics.setColor(255, 255, 255);           
      graphics.drawString(message,
        (im.getWidth() / 2) - (font.stringWidth(message) / 2), 0, 
         Graphics.TOP | Graphics.LEFT);
    }
    catch (Exception e)
    {
      System.err.println("Error during image creation");
    }    
  } 

  /*--------------------------------------------------
  * Draw mutable image 
  *-------------------------------------------------*/
  protected void paint(Graphics g)
  {
    // Center the image on the display
    if (im != null) g.drawImage(im, getWidth() / 2, getHeight() / 2, Graphics.VCENTER | 
    Graphics.HCENTER);
  }

  public void commandAction(Command c, Displayable d)
  {
    if (c == cmExit)
      midlet.exitMIDlet();
  }
}