this.edgeCount = checkNonNegative(edgeCount);
  }

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

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

  @Override
  public boolean allowsSelfLoops() {
    return allowsSelfLoops;
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return nodeOrder;
  }

    return nodeConnections.unmodifiableKeySet();
  }

  @Override
  public Set<E> edges() {
    return edgeToReferenceNode.unmodifiableKeySet();
  }

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

  @Override
  public boolean allowsParallelEdges() {
    return allowsParallelEdges;
  }

  @Override
  public boolean allowsSelfLoops() {
    return allowsSelfLoops;

   * <p>The "queryable" properties are those that are exposed through the {@link Graph} interface,
   * such as {@link Graph#isDirected()}. Other properties, such as {@link #expectedNodeCount(int)},
   * are not set in the new builder.
   */
  public static <N> GraphBuilder<N> from(Graph<N> graph) {
    return new GraphBuilder<N>(graph.isDirected())
        .allowsSelfLoops(graph.allowsSelfLoops())
        .nodeOrder(graph.nodeOrder())

   * interface, such as {@link ValueGraph#isDirected()}. Other properties, such as {@link
   * #expectedNodeCount(int)}, are not set in the new builder.
   */
  public static <N, V> ValueGraphBuilder<N, V> from(ValueGraph<N, V> graph) {
    return new ValueGraphBuilder<N, V>(graph.isDirected())
        .allowsSelfLoops(graph.allowsSelfLoops())
        .nodeOrder(graph.nodeOrder())

   * such as {@link Network#isDirected()}. Other properties, such as {@link
   * #expectedNodeCount(int)}, are not set in the new builder.
   */
  public static <N, E> NetworkBuilder<N, E> from(Network<N, E> network) {
    return new NetworkBuilder<N, E>(network.isDirected())
        .allowsParallelEdges(network.allowsParallelEdges())