* @since 20.0
 */
@Beta
public final class ValueGraphBuilder<N, V> extends AbstractGraphBuilder<N> {

  /** Creates a new instance with the specified edge directionality. */
  private ValueGraphBuilder(boolean directed) {
    super(directed);
  }

  /** Returns a {@link ValueGraphBuilder} for building directed graphs. */
  public static ValueGraphBuilder<Object, Object> directed() {
    return new ValueGraphBuilder<>(true);

 * @since 20.0
 */
@Beta
public final class ValueGraphBuilder<N, V> extends AbstractGraphBuilder<N> {

  /** Creates a new instance with the specified edge directionality. */
  private ValueGraphBuilder(boolean directed) {
    super(directed);
  }

  /** Returns a {@link ValueGraphBuilder} for building directed graphs. */
  public static ValueGraphBuilder<Object, Object> directed() {
    return new ValueGraphBuilder<>(true);

@SuppressWarnings("Immutable") // Extends StandardValueGraph but uses ImmutableMaps.
public final class ImmutableValueGraph<N, V> extends StandardValueGraph<N, V> {

  private ImmutableValueGraph(ValueGraph<N, V> graph) {
    super(ValueGraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size());
  }

  /** Returns an immutable copy of {@code graph}. */
  public static <N, V> ImmutableValueGraph<N, V> copyOf(ValueGraph<N, V> graph) {

      ValueGraph<N, V> graph, Iterable<? extends N> nodes) {
    MutableValueGraph<N, V> subgraph =
        (nodes instanceof Collection)
            ? ValueGraphBuilder.from(graph).expectedNodeCount(((Collection) nodes).size()).build()
            : ValueGraphBuilder.from(graph).build();
    for (N node : nodes) {
      subgraph.addNode(node);
    }
    for (N node : subgraph.nodes()) {

      ValueGraph<N, V> graph, Iterable<? extends N> nodes) {
    MutableValueGraph<N, V> subgraph =
        (nodes instanceof Collection)
            ? ValueGraphBuilder.from(graph).expectedNodeCount(((Collection) nodes).size()).build()
            : ValueGraphBuilder.from(graph).build();
    for (N node : nodes) {
      subgraph.addNode(node);
    }
    for (N node : subgraph.nodes()) {

    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.directed().build();
    valueGraph.putEdgeValue("a", "b", 11);

    Traverser.forTree(valueGraph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedValueGraph_throws() throws Exception {
    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.undirected().build();
    valueGraph.putEdgeValue("a", "b", 11);

    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.directed().build();
    valueGraph.putEdgeValue("a", "b", 11);

    Traverser.forTree(valueGraph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedValueGraph_throws() throws Exception {
    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.undirected().build();
    valueGraph.putEdgeValue("a", "b", 11);