All you need to do is add a MouseListener to the component in which you
are drawing the image.

If you're drawing the image in the applet itself, just add a
MouseListener to the applet. If you're using a Canvas, add a mouse
listener to the canvas.

For example:

  public class ImageCanvas extends Canvas
         implements MouseListener {

    public ImageCanvas() {
      addMouseListener(this);
    }

    public void paint(Graphics g) {
      // draw image
    }

    public void mousePressed(MouseEvent e) {
      // handle mouse being pressed
    }

    public void mouseReleased(MouseEvent e) {
      // handle mouse being released
    }

    // other methods in MouseListener

How about some thing like this... using a canvas. Use a special Canvas
to preload 2 GIFs, and using a MouseListener simply toggle the image.

[JDK1.1]

import java.awt.*;
import java.awt.event.*;
import java.net.*;

public class ToggleGifCanvas extends Canvas
  implements MouseListener {
  Image img1, img2;
  int     index = 0;
  MediaTracker tracker;

  public ToggleGifCanvas(URL n1, URL n2) {
    tracker = new MediaTracker(this);
    try {
      img1 = Toolkit.getDefaultToolkit().getImage(n1);
      img2 = Toolkit.getDefaultToolkit().getImage(n2);
      tracker.addImage(img1,0);
      tracker.addImage(img2,1);
      tracker.waitForAll();
      addMouseListener(this);
      }
    catch (Exception e) {
      e.printStackTrace();
      }
    }

  public void paint(Graphics g) {
    if (img1 != null) {
       if (index == 0) {
          g.drawImage(img1,0,0,this);
          index++;
          }
       else {
          g.drawImage(img2,0,0,this);
          index--;
          }
       }
     }

  public Dimension getPreferredSize (){
    return new Dimension
      (img1.getHeight(this), img2.getWidth(this));
    }

  public void mouseClicked(MouseEvent e) {}
  public void mousePressed(MouseEvent e) {}
  public void mouseReleased(MouseEvent e) {}
  public void mouseEntered(MouseEvent e) {
    index = 1; repaint();
    }
  public void mouseExited(MouseEvent e) {
    index = 0; repaint();
     }
}

To use such Canvas, try something like this. This example needs our
Gumby GIFs ( and ).

import java.applet.*;
import java.awt.*;
import java.net.*;

public class tcanvas extends Applet {
  ToggleGifCanvas tgc;

  public void init() {
     try {
       tgc = new ToggleGifCanvas
           (new URL(getDocumentBase(),"gumby.gif"),
            new URL(getDocumentBase(),"gumby2.gif"));
       add(tgc);
       }
     catch (Exception e) {
       e.printStackTrace();
       }
    }
  }

Look at some code that uses it such as
http://mindprod.com/products1.html#BIO

fro ResizingImageViewer see
http://mindprod.com/products1.html#NETWORKCAM
for sample code that uses it.

   Would this code correct support PNG's alpha transparency? (e.g.
semi-transparent buttons) I assume it would, because Sun's library supports
PNG's alpha transparency elsewhere, but I don't have an image editing
program handy to test this out on this machine.

   - Oliver