code: private void firePieceCompleted(Piece piece) throws IOException {
      for (PeerActivityListener listener : this.listeners) {
        listener.handlePieceCompleted(this, piece);
      }
    }
docs: Fire the piece completion event to all registered listeners.
  <p/>
  <p>
  The event contains the peer (this), and the piece number that was
  completed.
  </p>
  
  @param piece The completed piece.