sclass JThumbnailButton > JToggleButton {
  ThumbnailCache thumbnailCache;
  gettable File imageFile;
  
  *(ThumbnailCache *thumbnailCache, File *imageFile) {
    toolTip(this, fileInfo(imageFile));
    setButtonImage(this, whiteImage(thumbnailCache.thumbnailSize()));
    thumbnailCache.get(imageFile, img -> {
      setButtonImage(this, centerImageOnBackground(Color.gray, thumbnailCache.thumbnailSize(), img));
    });
  }
}