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