Review

class IndexWriter {
  private final void prepareCommit(Map commitUserData, boolean internal) throws CorruptIndexException, IOException {

    if (hitOOM) {
      throw new IllegalStateException("this writer hit an OutOfMemoryError; cannot commit");
    }

    if (autoCommit && !internal)
      throw new IllegalStateException("this method can only be used when autoCommit is false");

    if (!autoCommit && pendingCommit != null)
      throw new IllegalStateException("prepareCommit was already called with no corresponding call to commit");

    if (infoStream != null)
      message("prepareCommit: flush");

    flush(true, true, true);

    startCommit(0, commitUserData);
  }

}