if (ref != null) sb.append('#').append(ref);
  protected String toExternalForm (URL url)  {    String file = url.getFile();    // return "jar:" + file;    // Performance!!:     //  Do the concatenation manually to avoid resize StringBuffer's     //  internal buffer.    StringBuffer sb = new StringBuffer (file.length() + 5);    sb.append ("jar:");    sb.append (file);    return sb.toString();  }