}
    },
    SyncHM {
      @Override
      Map<Element, Element> create(Collection<Element> keys) {
        return Collections.synchronizedMap(Hash.create(keys));
      }
    },
    Tree {
      @Override
      Map<Element, Element> create(Collection<Element> keys) {
        Map<Element, Element> map = Maps.newTreeMap();
        for (Element element : keys) {
          map.put(element, element);
        }

   * {@link #ignoreClasses} to exclude generated classes, such as the {@code AutoValue_Foo} classes
   * generated by <a href="https://github.com/google/auto/tree/master/value">AutoValue</a>.
   *
   * @since 19.0
   */
  public static final Predicate<Class<?>> UNDERSCORE_IN_NAME =
      (Class<?> c) -> c.getSimpleName().contains("_");

   *       </ul>
   *   <li>another java.util.Set delegate implementation. In most modern JDKs, normal java.util hash
   *       collections intelligently fall back to a binary search tree if hash table collisions are
   *       detected. Rather than going to all the trouble of reimplementing this ourselves, we
   *       simply switch over to use the JDK implementation wholesale if probable hash flooding is

   *       </ul>
   *   <li>another java.util.Map delegate implementation. In most modern JDKs, normal java.util hash
   *       collections intelligently fall back to a binary search tree if hash table collisions are
   *       detected. Rather than going to all the trouble of reimplementing this ourselves, we
   *       simply switch over to use the JDK implementation wholesale if probable hash flooding is

  static final Tree c = new Tree('c');
  static final Tree d = new Tree('d', a, b, c);
  static final Tree e = new Tree('e');
  static final Tree f = new Tree('f');
  static final Tree g = new Tree('g', f);
  static final Tree h = new Tree('h', d, e, g);

  static String iterationOrder(Iterable<? extends Node> iterable) {
    StringBuilder builder = new StringBuilder();
    for (Node t : iterable) {

    tree.put("tree", 3);
    assertThat(tree.keySet()).containsExactly("tree", "google").inOrder();
    assertThat(tree.get("google")).containsExactly(6, 2).inOrder();

    TreeMultimap<String, Integer> copy = TreeMultimap.create(tree);
    assertEquals(tree, copy);
    assertThat(copy.keySet()).containsExactly("google", "tree").inOrder();
    assertThat(copy.get("google")).containsExactly(2, 6).inOrder();

  @Test
  public void forGraph_breadthFirst_tree() throws Exception {
    Traverser<Character> traverser = Traverser.forGraph(TREE);

    assertEqualCharNodes(traverser.breadthFirst('h'), "hdegabcf");
    assertEqualCharNodes(traverser.breadthFirst('d'), "dabc");
    assertEqualCharNodes(traverser.breadthFirst('a'), "a");
  }

  @Test
  public void forGraph_breadthFirstIterable_tree() throws Exception {

          root = Optional.of(new BinaryNode(rng.nextInt(), Optional.<BinaryNode>absent(), root));
        }
        return root;
      }
    },
    RANDOM {
      /**
       * Generates a tree with topology selected uniformly at random from the topologies of binary
       * trees of the specified size.
       */
      @Override
      Optional<BinaryNode> createTree(int size, Random rng) {

day!  Why, I haven't had a wink of sleep these three weeks!'

  `I'm very sorry you've been annoyed,' said Alice, who was
beginning to see its meaning.

  `And just as I'd taken the highest tree in the wood,' continued
the Pigeon, raising its voice to a shriek, `and just as I was
thinking I should be free of them at last, they must needs come
wriggling down from the sky!  Ugh, Serpent!'

        if (result == 0) {
          return count(getElement());
        } else {
          return result;
        }
      }
    };
  }

  /** Returns the first node in the tree that is in range. */
  @CheckForNull
  private AvlNode<E> firstNode() {
    AvlNode<E> root = rootReference.get();
    if (root == null) {
      return null;
    }
    AvlNode<E> node;