public String diff() throws IOException {
  try {
    String reference=readReference();
    return diff(reference,m_Output.toString());
  }
 catch (  FileNotFoundException fnf) {
    writeAsReference();
    return null;
  }
}

public String diff ( ) throws IOException { try { String reference = readReference ( ) ; return diff ( reference , m_Output . toString ( ) ) ; } catch ( FileNotFoundException fnf ) { writeAsReference ( ) ; return null ; } }
returns the difference between the current output and the reference version .
