code: private void regenerate() {
  		try {
  			ArrayList list = new ArrayList();
  			for (int i=0;i<sprites.size();i++) {
  				list.add(sprites.elementAt(i));
  			}
  			
  			int b = ((Integer) border.getValue()).intValue();
  			Sheet sheet = pack.packImages(list, twidth, theight, b, null);
  			sheetPanel.setImage(sheet);
  		} catch (IOException e) {
  			// shouldn't happen 
  			e.printStackTrace();
  		}
  	}
docs: Regenerate the sprite sheet that is being displayed