private static void processReferences(ScrollbarStyleListener toAdd, ScrollbarStyleListener toRemove, List<? super ScrollbarStyleListener> list) {
    synchronized (ourStyleListeners) {
      Iterator<Reference<ScrollbarStyleListener>> iterator = ourStyleListeners.iterator();
      while (iterator.hasNext()) {
        Reference<ScrollbarStyleListener> reference = iterator.next();
        ScrollbarStyleListener ui = reference.get();
        if (ui == null || ui == toRemove) {
          iterator.remove();
        }
        else if (list != null) {
          list.add(ui);
        }
      }
      if (toAdd != null) {
        ourStyleListeners.add(new WeakReference<>(toAdd));
      }
    }
  }
private static void processReferences(ScrollbarStyleListener toAdd, ScrollbarStyleListener toRemove, List<? super ScrollbarStyleListener> list)