code: public List<ResourceType<L>> getResourceTypesBreadthFirst() {
          List<ResourceType<L>> result = new ArrayList<ResourceType<L>>();
          GraphIterator<ResourceType<L>, DefaultEdge> it = new BreadthFirstIterator<ResourceType<L>, DefaultEdge>(
                  this.resourceTypesGraph);
          while (it.hasNext()) {
              result.add(it.next());
          }
          return Collections.unmodifiableList(result);
      }
docs: Returns an immutable {@link List} of all {@link ResourceType}s contained in {@link #resourceTypesGraph} in
  breadth-first order.
  
  @return the list of all {@link ResourceType}s