public static void printNodes(String title, Collection<? extends SceneGraphNode> l) {
   System.out.println(title + " -----------------------------");
   for (SceneGraphNode g : l) {
     System.out.println(g.getName());
   }
   System.out.println("----------------------------------------");
 }
 public static <T extends SceneGraphNode> void printNameMap(HashMap<T, String> map) {
   System.out.println("Names ----------------------------------");
   for (SceneGraphNode c : map.keySet()) {
     System.out.println(c.getName() + " -> " + map.get(c));
   }
   System.out.println("----------------------------------------");
 }