code: public static String getImageFilename(String strFilename, String strSubDirectory)
     {
         if ((strFilename == null) || (strFilename.length() == 0))
             return null;    // A null will tell a JButton not to load an image
         if (strFilename.indexOf('.') == -1)
             strFilename += ".gif";
         strFilename = Util.getFullFilename(strFilename, strSubDirectory, Constant.IMAGE_LOCATION, true);
         return strFilename;
     }
docs: Get this image's full filename.
  @param filename The filename of this image (if no path, assumes images/buttons; if not ext assumes .gif).
  @param strSubDirectory The sub-directory.
  @return The full (relative) filename for this image.