Review

class IndexModifier {
  /**
   * Make sure all changes are written to disk.
   * @throws CorruptIndexException if the index is corrupt
   * @throws LockObtainFailedException if another writer
   *  has this index open (<code>write.lock</code> could not
   *  be obtained)
   * @throws IOException if there is a low-level IO error
   */
  public void flush() throws CorruptIndexException, LockObtainFailedException, IOException {
    synchronized(directory) {
      assureOpen();
      if (indexWriter != null) {
        indexWriter.close();
        indexWriter = null;
        createIndexWriter();
      } else {
        indexReader.close();
        indexReader = null;
        createIndexReader();
      }
    }
  }

}