edgeToReferenceNode.put(edge, nodeU);
    return true;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean addEdge(EndpointPair<N> endpoints, E edge) {
    validateEndpoints(endpoints);
    return addEdge(endpoints.nodeU(), endpoints.nodeV(), edge);
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeNode(N node) {
    checkNotNull(node, "node");

    return networkBuilder.build();
  }

  @Override
  void addNode(Integer n) {
    networkBuilder.addNode(n);
    network = networkBuilder.build();
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkBuilder.addEdge(n1, n2, e);
    network = networkBuilder.build();
  }

    return networkBuilder.build();
  }

  @Override
  void addNode(Integer n) {
    networkBuilder.addNode(n);
    network = networkBuilder.build();
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkBuilder.addEdge(n1, n2, e);
    network = networkBuilder.build();
  }

        .edgeOrder(edgeOrder)
        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

      ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.
        assertThat(
                network.addEdge(
                    getRandomElement(nodeList, gen), getRandomElement(nodeList, gen), new Object()))
            .isTrue();
      }
      ArrayList<Object> edgeList = new ArrayList<>(network.edges());

   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsParallelEdges()} or {@link #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  boolean addEdge(N nodeU, N nodeV, E edge);

  /**
   * Adds {@code edge} connecting {@code endpoints}. In an undirected network, {@code edge} will
   * also connect {@code nodeV} to {@code nodeU}.
   *

      ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.
        assertThat(
                network.addEdge(
                    getRandomElement(nodeList, gen), getRandomElement(nodeList, gen), new Object()))
            .isTrue();
      }
      ArrayList<Object> edgeList = new ArrayList<>(network.edges());

        {
            ArtifactMetadata md = node.getMd();
            MetadataGraphEdge e =
                    new MetadataGraphEdge(md.version, md.resolved, md.artifactScope, md.artifactUri, depth, pomOrder);
            addEdge(parentVertex, vertex, e);
        } else {
            entry = vertex;
        }

        MetadataTreeNode[] kids = node.getChildren();
        if (kids == null || kids.length < 1) {
            return;

    public Collection<Vertex> getVertices() {
        return vertices.values();
    }

    Vertex addVertex(String label) {
        return vertices.computeIfAbsent(label, Vertex::new);
    }

    void addEdge(Vertex from, Vertex to) throws CycleDetectedException {
        from.children.add(to);
        to.parents.add(from);
        List<String> cycle = findCycle(to);
        if (cycle != null) {

import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

class Graph {

    final Map<String, Set<String>> graph = new LinkedHashMap<>();

    synchronized void addEdge(String from, String to) throws CycleDetectedException {
        if (graph.computeIfAbsent(from, l -> new HashSet<>()).add(to)) {