code: public boolean refresh()
          throws IOException {
          if (this.file != null &&
              this.file.lastModified() != this.lastModified) {
              return load(this.file);
          } else {
              return true;
          }
      }
docs: Reloads the gridmap from a file only if the gridmap
  was initially loaded using the {@link #load(File)
  load} or {@link #load(String) load} functions.
  The file will only be reloaded if it has changed
  since the last time.
  
  @exception IOException in case of I/O error or
  when there are parsing errors in the file (only when errors
  are not ignored).
  @return <tt>true</tt> if the file was parsed and refreshed successfully.
  <tt>False</tt> otherwise.