ImageIcon & Lazy image loading

Question

The whole day I'm fuzzing around with loading an ImageIcon lazily. I suppose you know what lazy means. I want to load my icons when they have to be painted on the screen, because I use thousands of them. I read the "How to Use Icons" tutorial (http://java.sun.com/docs/books/tutorial/uiswing/misc/icon.html). With its ArrowIcon implementation of Icon (http://www.iam.ubc.ca/guides/javatut99/uiswing/misc/example-swing/ArrowIcon.java) and its IconDemoApplet (http://java.sun.com/docs/books/tutorial/uiswing/misc/example-1dot4/IconDemoApplet.java). However, I'm still confused. I also took a look at the ImageIconProxy example of the proxy pattern (http://www.javaworld.com/javaworld/jw-02-2002/jw-0222-designpatterns.html). Finally I got the following code (the IconProperties part can be ignored). I'm afraid that this does not what I want. I have now only a few images, so I can't measure it directly. Does my class exactly the same as the ImageIcon class itself? Is there no postponing of instantiation because I subclass ImageIcon? Do I have to implement the interface Icon instead? Do I have to copy all the stuff in ImageIcon to my implementation in that case? Or is it better to extend the Image class to provide functions like described beneath (check upon existence).
And for completeness. I extend this LazyIcon object subsequently with a class named LayeredIcon to create combined icons.
* The class <code>LazyIcon</code> implements <code>ImageIcon</code>
* because their will be at least some calls like:
* <pre>
*   Icon icon = new ImageIcon(imageURL);
*     Image image = icon.getImage();
*     image = image.getScaledInstance(...);
*   Icon icon2 = new ImageIcon(image);
* </pre>
* Besides that I want to add a function <code>IconExists</code> and
* to add lazy image loading, and maybe also background loading.
* This doesn't work, so it seems like in the constructor of
* ImageIcon there is done more than only setImage(image).
* @author A.C. van Rossum
public class LazyIcon  extends ImageIcon {
  boolean isIconCreated = false;
  protected Image image;
  protected IconProperties properties;
   * The <code>LazyIcon</code> stores the <code>Image</code> until
   * the moment it has to be created. It has default icon properties.
  public LazyIcon(Image image) {
    this(image, IconProperties.DEFAULTICON);
  public LazyIcon(Image image, IconProperties properties) {
    this.image = image;
    setIconProperties(properties);
  //other constructors have to follow
   * The method <code>setIconProperties</code> enables the user
   * to change the properties of an icon, before calling the
   * method <code>paintIcon</code>.
   * @param properties A set of properties: dimension, etc.
  public void setIconProperties(IconProperties properties) {
    this.properties = properties;
  public int getIconHeight() {
    return isIconCreated ? super.getIconHeight() : properties.getHeight();
  public int getIconWidth() {
     return isIconCreated ? super.getIconWidth() : properties.getWidth();
   * The method <code>paintIcon</code> does only set the image of
   * the ImageIcon class lazily (when this function is called.)
  public void paintIcon(final Component c, Graphics g, int x, int y) {
    if(!isIconCreated) {
      setImage(image);
      isIconCreated = true;
    super.paintIcon(c, g, x, y);
  public Image getImage() {
    if (isIconCreated)
      return super.getImage();
    else return image;
}Is my problem formulation clear enough? Many thanks in advance if you want to give it a look.
Andy

Answer 1

I spent some more time looking at the programs today, and it seems that all of the students involved were using a graphics library called objectdraw (http://cortland.cs.williams.edu:16080/~cs134/eof/). As far as I can tell, the objectdraw source code isn't public, so I can't say which (if any) of the standard methods they were using.
After some work, I managed to produce a method with the same parameters as the objectdraw getImage method that used the AWT Toolkit. When I overrode the objectdraw version in the students' code, the bug (at least for the moment) seems to have gone away. So the problem may be in that other library.
Does anyone else have experience with objectdraw? Is this a known bug, or could this be something else...?