Review

class IndexReader {
  /** Deletes the document numbered <code>docNum</code>.  Once a document is
   * deleted it will not appear in TermDocs or TermPostitions enumerations.
   * Attempts to read its field with the {@link #document}
   * method will result in an error.  The presence of this document may still be
   * reflected in the {@link #docFreq} statistic, though
   * this will be corrected eventually as the index is further modified.
   *
   * @throws StaleReaderException if the index has changed
   * since this reader was opened
   * @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 synchronized void deleteDocument(int docNum) throws StaleReaderException, CorruptIndexException, LockObtainFailedException, IOException {
    ensureOpen();
    acquireWriteLock();
    hasChanges = true;
    doDelete(docNum);
  }

}