public Set<N> nodes() {
        return AbstractBaseGraph.this.nodes();
      }

      @Override
      public Set<EndpointPair<N>> edges() {
        return AbstractBaseGraph.this.edges();
      }

      @Override
      public Graph<N> asGraph() {
        if (AbstractBaseGraph.this instanceof Graph) {
          return (Graph<N>) AbstractBaseGraph.this;

 * class rather than implement {@link Graph} directly.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @since 20.0
 */
public abstract class AbstractGraph<N> extends AbstractBaseGraph<N> implements Graph<N> {
  /** Constructor for use by subclasses. */
  public AbstractGraph() {}

  @Override
  public final boolean equals(@Nullable Object obj) {
    if (obj == this) {
      return true;

 * more efficient implementation.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 * @since 20.0
 */
public abstract class AbstractValueGraph<N, V> extends AbstractBaseGraph<N>
    implements ValueGraph<N, V> {
  /** Constructor for use by subclasses. */
  public AbstractValueGraph() {}

  @Override
  public Graph<N> asGraph() {
    return new AbstractGraph<N>() {
      @Override