@Override
  public Set<N> nodes() {
    return delegate().nodes();
  }

  /**
   * Defer to {@link AbstractGraph#edges()} (based on {@link #successors(Object)}) for full edges()
   * implementation.
   */
  @Override
  protected long edgeCount() {
    return delegate().edges().size();
  }

  @Override
  public boolean isDirected() {
    return delegate().isDirected();
  }

  @Override

@ElementTypesAreNonnullByDefault
abstract class AbstractBaseGraph<N> implements BaseGraph<N> {

  /**
   * Returns the number of edges in this graph; used to calculate the size of {@link Graph#edges()}.
   * This implementation requires O(|N|) time. Classes extending this one may manually keep track of
   * the number of edges as the graph is updated, and override this method for better performance.
   */
  protected long edgeCount() {

  }

  @Override
  public N adjacentNode(E edge) {
    // Since the reference node is defined to be 'source' for directed graphs,
    // we can assume this edge lives in the set of outgoing edges.
    // (We're relying on callers to call this method only with an edge that's in the graph.)
    return requireNonNull(outEdgeMap.get(edge));
  }

  @Override
  public N removeInEdge(E edge, boolean isSelfLoop) {
    if (isSelfLoop) {

    assertThat(graph.nodes()).containsExactly("A");
    assertThat(graph.edges()).isEmpty();
  }

  @Test
  public void immutableGraphBuilder_putEdgeFromNodes() {
    ImmutableGraph<String> graph =
        GraphBuilder.directed().<String>immutable().putEdge("A", "B").build();

    assertThat(graph.nodes()).containsExactly("A", "B");
    assertThat(graph.edges()).containsExactly(EndpointPair.ordered("A", "B"));
  }

  @Test

    assertThat(graph.nodes()).containsExactly("A");
    assertThat(graph.edges()).isEmpty();
  }

  @Test
  public void immutableGraphBuilder_putEdgeFromNodes() {
    ImmutableGraph<String> graph =
        GraphBuilder.directed().<String>immutable().putEdge("A", "B").build();

    assertThat(graph.nodes()).containsExactly("A", "B");
    assertThat(graph.edges()).containsExactly(EndpointPair.ordered("A", "B"));
  }

  @Test

 *       locks---to each of the acquired locks, an edge from the soon-to-be-acquired lock is either
 *       verified or created.
 *   <li>If a new edge needs to be created, the outgoing edges of the acquired locks are traversed
 *       to check for a cycle that reaches the lock to be acquired. If no cycle is detected, a new
 *       "safe" edge is created.
 *   <li>If a cycle is detected, an "unsafe" (cyclic) edge is created to represent a potential

  static final String PARALLEL_EDGES_NOT_ALLOWED =
      "Nodes %s and %s are already connected by a different edge. To construct a graph "
          + "that allows parallel edges, call allowsParallelEdges(true) on the Builder.";
  static final String SELF_LOOPS_NOT_ALLOWED =
      "Cannot add self-loop edge on node %s, as self-loops are not allowed. To construct a graph "

  public Set<E> outEdges(N node) {
    return delegate().outEdges(node);
  }

  @Override
  public EndpointPair<N> incidentNodes(E edge) {
    return delegate().incidentNodes(edge);
  }

  @Override
  public Set<E> adjacentEdges(E edge) {
    return delegate().adjacentEdges(edge);
  }

  @Override
  public int degree(N node) {
    return delegate().degree(node);
  }

  @Override

    ImmutableMultimap.Builder<Character, Character> graphMapBuilder = ImmutableMultimap.builder();
    for (String edge : edges) {
      checkArgument(
          edge.length() == 2, "Expecting each edge to consist of 2 characters but got %s", edge);
      char node1 = edge.charAt(0);
      char node2 = edge.charAt(1);
      graphMapBuilder.put(node1, node2);

    ImmutableMultimap.Builder<Character, Character> graphMapBuilder = ImmutableMultimap.builder();
    for (String edge : edges) {
      checkArgument(
          edge.length() == 2, "Expecting each edge to consist of 2 characters but got %s", edge);
      char node1 = edge.charAt(0);
      char node2 = edge.charAt(1);
      graphMapBuilder.put(node1, node2);