void playPrevious() {
   if (playStack.size() < 2) return;
   System.out.println("------------");
   for (PlaylistAndTrack pnt : playStack) {
     System.out.println(pnt.track.getTitle());
   }
   playStack.removeFirst();
   PlaylistAndTrack prevPlaylistAndTrack = playStack.removeFirst();
   playlistsView.getSelectionModel().select(prevPlaylistAndTrack.playlist);
   tracksView.getSelectionModel().select(prevPlaylistAndTrack.track);
   tracksView.scrollTo(tracksView.getSelectionModel().getSelectedIndex());
   playTrack(prevPlaylistAndTrack.track);
 }
 void pushToPlayStack(Playlist p, Track t) {
   if (playStack.size() > 10000) {
     playStack.removeLast();
   }
   playStack.push(new PlaylistAndTrack(p, t));
 }