class StatisticsMonitor {

  public void addListener(final StatisticsListener listener) {
    if (listener == null) {
      throw new NullPointerException("StatisticsListener is null");
    }
    synchronized (this.mutex) {
      if (!this.listeners.contains(listener)) {
        this.listeners.add(listener);
        getStatMonitorHandler().addMonitor(this);
      }
    }
  }

  public  StatisticsMonitor();

}