Hi!

  I'm building a component with a JList that lists the JPG files
in a directory as thumbnails. The problem is that I have to
resize them and this is very slow, cpu and memory consuming. This is
the code for the listcellrenderer I'm using:

public class ThumbnaiListCellRenderer extends JLabel implements
ListCellRenderer {

private Hashtable thumbnails;

public ThumbnaiListCellRenderer() {
    setOpaque(true);
    setVerticalTextPosition(JLabel.BOTTOM);
    setHorizontalTextPosition(JLabel.CENTER);
    setHorizontalAlignment(CENTER);
    setVerticalAlignment(CENTER);
    thumbnails = new Hashtable();
}

public Component getListCellRendererComponent(
    JList list,
    Object value,            // value to display
    int index,               // cell index
    boolean isSelected,      // is the cell selected
    boolean cellHasFocus)    // the list and the cell have the focus
{                    

        if (value instanceof File) {

      File file = (File)value;
      setText(file.getName());
      Thumbnail thumbnail = (Thumbnail)thumbnails.get(value);
      if (thumbnail == null) {
        thumbnail = new Thumbnail(file);
             thumbnails.put(value,thumbnail);
      }       
      setIcon(thumbnail);
      setEnabled(list.isEnabled());
      setFont(list.getFont());
           setOpaque(true);

        }
        return this;

}

}

----
The code for the Thumbnail class:
----

public class Thumbnail implements Icon {
   
private Image image = null;
private int width = 0;
private int height = 0;
   
public Thumbnail(File file) {       
    URL imageURL = null;
           
    try {
      if (file.isDirectory()) {
         File folder = new File("folder.jpg");
         imageURL = folder.toURL();
      } else {
         imageURL = file.toURL();
      }
    } catch (MalformedURLException e) {
      e.printStackTrace();
    }

    if (imageURL == null) {
      System.err.println("Resource not found: " + file);
    } else {
           
           Image source = Toolkit.getDefaultToolkit().getImage(imageURL);
           MediaTracker mediaTracker = new MediaTracker(new Container());
      mediaTracker.addImage(source, 0);
      try {
         mediaTracker.waitForID(0);
      } catch (InterruptedException e) {
         e.printStackTrace();
      }
      // determine thumbnail size from WIDTH and HEIGHT
           int thumbWidth = 100;
      int thumbHeight = 100;
      double thumbRatio = (double)thumbWidth / (double)thumbHeight;
           int imageWidth = source.getWidth(null);
           int imageHeight = source.getHeight(null);
      double imageRatio = (double)imageWidth / (double)imageHeight;
      if (thumbRatio < imageRatio) {
         thumbHeight = (int)(thumbWidth / imageRatio);
           } else {
         thumbWidth = (int)(thumbHeight * imageRatio);
      }
      Image target = source.getScaledInstance(thumbWidth, thumbHeight,
Image.SCALE_FAST);
      this.image = target;
      this.width = thumbWidth;
      this.height = thumbHeight;
      source.flush();
    }             
}
   
public int getIconHeight() {
    return height;
}

public int getIconWidth() {
    return width;
}

public void paintIcon(Component c, Graphics g, int x, int y) {
    Graphics2D graphics2D = (Graphics2D)g;
    graphics2D.drawImage(image, 0, 0, getIconWidth(),
             getIconHeight(), null);
}

---
Is there any way to improve the performance of this code ? I mean,
the thumbnail view in windows explorer is way faster than this
and consumes less resources.

Regards

--
Abs