import java.util.Collections;
import java.util.Map;
import java.util.Set;

/**
 * An implementation of {@link NetworkConnections} for directed networks.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
@ElementTypesAreNonnullByDefault
final class DirectedNetworkConnections<N, E> extends AbstractDirectedNetworkConnections<N, E> {

import java.util.Set;

/**
 * A class to allow {@link Graph} implementations to be backed by a {@link BaseGraph}. This is not
 * currently planned to be released as a general-purpose forwarding class.
 *
 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
abstract class ForwardingGraph<N> extends AbstractGraph<N> {

  abstract BaseGraph<N> delegate();

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

import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for representing and manipulating an origin node's adjacent nodes and edge values in
 * a {@link Graph}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
@ElementTypesAreNonnullByDefault
interface GraphConnections<N, V> {

  Set<N> adjacentNodes();

  Set<N> predecessors();

/**
 * A class to allow {@link Network} implementations to be backed by a provided delegate. This is not
 * currently planned to be released as a general-purpose forwarding class.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 */
@ElementTypesAreNonnullByDefault
abstract class ForwardingNetwork<N, E> extends AbstractNetwork<N, E> {

  abstract Network<N, E> delegate();

  @Override

 *
 * <p>Time complexities for mutation methods are all O(1) except for {@code removeNode(N node)},
 * which is in O(d_node) where d_node is the degree of {@code node}.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
@ElementTypesAreNonnullByDefault

 * {@link EndpointPair} of an undirected edge is an unordered pair of nodes ({@link #nodeU()} and
 * {@link #nodeV()}).
 *
 * <p>The edge is a self-loop if, and only if, the two endpoints are equal.
 *
 * @author James Sexton
 * @since 20.0
 */
@Beta
@Immutable(containerOf = {"N"})
@ElementTypesAreNonnullByDefault
public abstract class EndpointPair<N> implements Iterable<N> {
  private final N nodeU;
  private final N nodeV;

import javax.annotation.CheckForNull;

/**
 * This class provides a skeletal implementation of {@link Graph}. It is recommended to extend this
 * class rather than implement {@link Graph} directly.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @since 20.0
 */
@Beta
@ElementTypesAreNonnullByDefault
public abstract class AbstractGraph<N> extends AbstractBaseGraph<N> implements Graph<N> {

  @Override

import java.util.Collections;
import java.util.Map;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * A base implementation of {@link NetworkConnections} for undirected networks.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
@ElementTypesAreNonnullByDefault
abstract class AbstractUndirectedNetworkConnections<N, E> implements NetworkConnections<N, E> {

/**
 * A {@link MapIteratorCache} that adds additional caching. In addition to the caching provided by
 * {@link MapIteratorCache}, this structure caches values for the two most recently retrieved keys.
 *
 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
final class MapRetrievalCache<K, V> extends MapIteratorCache<K, V> {
  // See the note about volatile in the superclass.

/**
 * A subinterface of {@link Graph} which adds mutation methods. When mutation is not required, users
 * should prefer the {@link Graph} interface.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @param <N> Node parameter type
 * @since 20.0
 */
@Beta
@ElementTypesAreNonnullByDefault
public interface MutableGraph<N> extends Graph<N> {

  /**