Review

class IndexModifier {
  /**
   * Make sure all changes are written to disk.
   * @throws IOException
   */
  public void flush() throws IOException {
    synchronized(directory) {
      assureOpen();
      if (indexWriter != null) {
        indexWriter.close();
        indexWriter = null;
        createIndexWriter();
      } else {
        indexReader.close();
        indexReader = null;
        createIndexReader();
      }
    }
  }

}