https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import com.google.common.annotations.Beta;
import java.util.Optional;
import java.util.Set;
import org.checkerframework.checker.nullness.qual.Nullable;


An interface for graph-structured data,
whose edges are unique objects.

A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.

There are three primary interfaces provided to represent graphs. In order of increasing complexity they are: Graph, ValueGraph, and Network. You should generally prefer the simplest interface that satisfies your use case. See the 
"Choosing the right graph type" section of the Guava User Guide for more details.

Capabilities


Network supports the following use cases (definitions of
terms):

    
  
  • directed graphs
  
  • undirected graphs
  
  • graphs that do/don't allow parallel edges
  
  • graphs that do/don't allow self-loops
  
  • graphs whose nodes/edges are insertion-ordered, sorted, or unordered
  
  • graphs whose edges are unique objects



Building a Network


The implementation classes that common.graph provides are not public, by design. To create an instance of one of the built-in implementations of Network, use the NetworkBuilder class: 

MutableNetwork<Integer, MyEdge> graph = NetworkBuilder.directed().build();



NetworkBuilder.build() returns an instance of MutableNetwork, which is a subtype of Network that provides methods for adding and removing nodes and edges. If you do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on the graph), you should use the non-mutating Network interface, or an ImmutableNetwork. 
You can create an immutable copy of an existing Network using ImmutableNetwork.copyOf(Network<Object,Object>): 

ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(graph);



Instances of ImmutableNetwork do not implement MutableNetwork (obviously!) and are contractually guaranteed to be unmodifiable and thread-safe. 
The Guava User Guide has more
information on (and examples of) building graphs.

Additional documentation


See the Guava User Guide for the common.graph package ("Graphs Explained") for
additional documentation, including:



Author:James Sexton, Joshua O'Madadhain
Type parameters:
  • <N> – Node parameter type
  • <E> – Edge parameter type
Since:20.0
/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges are unique objects.
 *
 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
 *
 * <p>There are three primary interfaces provided to represent graphs. In order of increasing
 * complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally
 * prefer the simplest interface that satisfies your use case. See the <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type">
 * "Choosing the right graph type"</a> section of the Guava User Guide for more details.
 *
 * <h3>Capabilities</h3>
 *
 * <p>{@code Network} supports the following use cases (<a
 * href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of
 * terms</a>):
 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow parallel edges
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges are unique objects
 * </ul>
 *
 * <h3>Building a {@code Network}</h3>
 *
 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To
 * create an instance of one of the built-in implementations of {@code Network}, use the {@link
 * NetworkBuilder} class:
 *
 * <pre>{@code
 * MutableNetwork<Integer, MyEdge> graph = NetworkBuilder.directed().build();
 * }</pre>
 *
 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a
 * subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you
 * do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on the
 * graph), you should use the non-mutating {@link Network} interface, or an {@link
 * ImmutableNetwork}.
 *
 * <p>You can create an immutable copy of an existing {@code Network} using {@link
 * ImmutableNetwork#copyOf(Network)}:
 *
 * <pre>{@code
 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(graph);
 * }</pre>
 *
 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and
 * are contractually guaranteed to be unmodifiable and thread-safe.
 *
 * <p>The Guava User Guide has <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more
 * information on (and examples of) building graphs</a>.
 *
 * <h3>Additional documentation</h3>
 *
 * <p>See the Guava User Guide for the {@code common.graph} package (<a
 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for
 * additional documentation, including:
 *
 * <ul>
 *   <li><a
 *       href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence">
 *       {@code equals()}, {@code hashCode()}, and graph equivalence</a>
 *   <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization">
 *       Synchronization policy</a>
 *   <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes
 *       for implementors</a>
 * </ul>
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 * @since 20.0
 */
@Beta
public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
  //
  // Network-level accessors
  //

  
Returns all nodes in this network, in the order specified by nodeOrder(). 
/** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */
  Set<N> nodes();

  
Returns all edges in this network, in the order specified by edgeOrder(). 
/** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */
  Set<E> edges();

  
Returns a live view of this network as a Graph. The resulting Graph will have an edge connecting node A to node B if this Network has an edge connecting A to B. 
If this network allows parallel edges, parallel edges will be treated as if collapsed into a single edge. For example, the degree(Object) of a node in the Graph view may be less than the degree of the same node in this Network. 
/**
   * Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have
   * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B.
   *
   * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be
   * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node
   * in the {@link Graph} view may be less than the degree of the same node in this {@link Network}.
   */
  Graph<N> asGraph();

  //
  // Network properties
  //

  
Returns true if the edges in this network are directed. Directed edges connect a source node to a target node, while undirected edges connect a pair of nodes to each other. 
/**
   * Returns true if the edges in this network are directed. Directed edges connect a {@link
   * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while
   * undirected edges connect a pair of nodes to each other.
   */
  boolean isDirected();

  
Returns true if this network allows parallel edges. Attempting to add a parallel edge to a network that does not allow them will throw an IllegalArgumentException. 
/**
   * Returns true if this network allows parallel edges. Attempting to add a parallel edge to a
   * network that does not allow them will throw an {@link IllegalArgumentException}.
   */
  boolean allowsParallelEdges();

  
Returns true if this network allows self-loops (edges that connect a node to itself). Attempting to add a self-loop to a network that does not allow them will throw an IllegalArgumentException. 
/**
   * Returns true if this network allows self-loops (edges that connect a node to itself).
   * Attempting to add a self-loop to a network that does not allow them will throw an {@link
   * IllegalArgumentException}.
   */
  boolean allowsSelfLoops();

  
Returns the order of iteration for the elements of nodes(). 
/** Returns the order of iteration for the elements of {@link #nodes()}. */
  ElementOrder<N> nodeOrder();

  
Returns the order of iteration for the elements of edges(). 
/** Returns the order of iteration for the elements of {@link #edges()}. */
  ElementOrder<E> edgeOrder();

  //
  // Element-level accessors
  //

  
Returns the nodes which have an incident edge in common with node in this network. 
Throws:
/**
   * Returns the nodes which have an incident edge in common with {@code node} in this network.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  Set<N> adjacentNodes(N node);

  
Returns all nodes in this network adjacent to node which can be reached by traversing node's incoming edges against the direction (if any) of the edge.

In an undirected network, this is equivalent to adjacentNodes(Object). 
Throws:
/**
   * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing
   * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge.
   *
   * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  @Override
  Set<N> predecessors(N node);

  
Returns all nodes in this network adjacent to node which can be reached by traversing node's outgoing edges in the direction (if any) of the edge. 
In an undirected network, this is equivalent to adjacentNodes(Object). 
This is not the same as "all nodes reachable from node by following outgoing edges". For that functionality, see Graphs.reachableNodes(Graph<Object>, Object). 
Throws:
/**
   * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing
   * {@code node}'s outgoing edges in the direction (if any) of the edge.
   *
   * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}.
   *
   * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing
   * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  @Override
  Set<N> successors(N node);

  
Returns the edges whose incident nodes in this network include node. 
Throws:
/**
   * Returns the edges whose {@link #incidentNodes(Object) incident nodes} in this network include
   * {@code node}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  Set<E> incidentEdges(N node);

  
Returns all edges in this network which can be traversed in the direction (if any) of the edge to end at node. 
In a directed network, an incoming edge's EndpointPair.target() equals node. 
In an undirected network, this is equivalent to incidentEdges(Object). 
Throws:
/**
   * Returns all edges in this network which can be traversed in the direction (if any) of the edge
   * to end at {@code node}.
   *
   * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}.
   *
   * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  Set<E> inEdges(N node);

  
Returns all edges in this network which can be traversed in the direction (if any) of the edge starting from node. 
In a directed network, an outgoing edge's EndpointPair.source() equals node. 
In an undirected network, this is equivalent to incidentEdges(Object). 
Throws:
/**
   * Returns all edges in this network which can be traversed in the direction (if any) of the edge
   * starting from {@code node}.
   *
   * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}.
   *
   * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  Set<E> outEdges(N node);

  
Returns the count of node's incident edges, counting self-loops twice (equivalently, the number of times an edge touches node). 
For directed networks, this is equal to inDegree(node) + outDegree(node). 
For undirected networks, this is equal to incidentEdges(node).size() + (number of self-loops incident to node). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting
   * self-loops twice (equivalently, the number of times an edge touches {@code node}).
   *
   * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of
   * self-loops incident to {@code node}).
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  int degree(N node);

  
Returns the count of node's incoming edges in a directed network. In an undirected network, returns the degree(Object). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed
   * network. In an undirected network, returns the {@link #degree(Object)}.
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  int inDegree(N node);

  
Returns the count of node's outgoing edges in a directed network. In an undirected network, returns the degree(Object). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed
   * network. In an undirected network, returns the {@link #degree(Object)}.
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this network
   */
  int outDegree(N node);

  
Returns the nodes which are the endpoints of edge in this network. 
Throws:
/**
   * Returns the nodes which are the endpoints of {@code edge} in this network.
   *
   * @throws IllegalArgumentException if {@code edge} is not an element of this network
   */
  EndpointPair<N> incidentNodes(E edge);

  
Returns the edges which have an incident node in common with edge. An edge is not considered adjacent to itself. 
Throws:
/**
   * Returns the edges which have an {@link #incidentNodes(Object) incident node} in common with
   * {@code edge}. An edge is not considered adjacent to itself.
   *
   * @throws IllegalArgumentException if {@code edge} is not an element of this network
   */
  Set<E> adjacentEdges(E edge);

  
Returns the set of edges directly connecting nodeU to nodeV. 
In an undirected network, this is equal to edgesConnecting(nodeV, nodeU). 
The resulting set of edges will be parallel (i.e. have equal incidentNodes(Object). If this network does not allow parallel edges, the resulting set will contain at most one edge (equivalent to edgeConnecting(nodeU, nodeV).asSet()). 
Throws:
/**
   * Returns the set of edges directly connecting {@code nodeU} to {@code nodeV}.
   *
   * <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}.
   *
   * <p>The resulting set of edges will be parallel (i.e. have equal {@link #incidentNodes(Object)}.
   * If this network does not {@link #allowsParallelEdges() allow parallel edges}, the resulting set
   * will contain at most one edge (equivalent to {@code edgeConnecting(nodeU, nodeV).asSet()}).
   *
   * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
   *     network
   */
  Set<E> edgesConnecting(N nodeU, N nodeV);

  
Returns the single edge directly connecting nodeU to nodeV, if one is present, or Optional.empty() if no such edge exists. 
In an undirected network, this is equal to edgeConnecting(nodeV, nodeU). 
Throws:
Since:23.0
/**
   * Returns the single edge directly connecting {@code nodeU} to {@code nodeV}, if one is present,
   * or {@code Optional.empty()} if no such edge exists.
   *
   * <p>In an undirected network, this is equal to {@code edgeConnecting(nodeV, nodeU)}.
   *
   * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU}
   *     to {@code nodeV}
   * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
   *     network
   * @since 23.0
   */
  Optional<E> edgeConnecting(N nodeU, N nodeV);

  
Returns the single edge directly connecting nodeU to nodeV, if one is present, or null if no such edge exists. 
In an undirected network, this is equal to edgeConnectingOrNull(nodeV, nodeU). 
Throws:
Since:23.0
/**
   * Returns the single edge directly connecting {@code nodeU} to {@code nodeV}, if one is present,
   * or {@code null} if no such edge exists.
   *
   * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}.
   *
   * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU}
   *     to {@code nodeV}
   * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
   *     network
   * @since 23.0
   */
  @Nullable
  E edgeConnectingOrNull(N nodeU, N nodeV);

  
Returns true if there is an edge directly connecting nodeU to nodeV. This is equivalent to nodes().contains(nodeU) && successors(nodeU).contains(nodeV), and to edgeConnectingOrNull(nodeU, nodeV) != null. 
In an undirected graph, this is equal to hasEdgeConnecting(nodeV, nodeU). 
Since:23.0
/**
   * Returns true if there is an edge directly connecting {@code nodeU} to {@code nodeV}. This is
   * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to
   * {@code edgeConnectingOrNull(nodeU, nodeV) != null}.
   *
   * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}.
   *
   * @since 23.0
   */
  boolean hasEdgeConnecting(N nodeU, N nodeV);

  //
  // Network identity
  //

  
Returns true iff object is a Network that has the same elements and the same structural relationships as those in this network. 
Thus, two networks A and B are equal if all of the following are true:

    
  
  • A and B have equal directedness. 
  • A and B have equal node sets. 
  • A and B have equal edge sets. 
  • Every edge in A and B connects the same nodes in the same direction (if any).



Network properties besides directedness do not affect equality.
For example, two networks may be considered equal even if one allows parallel edges and the
other doesn't. Additionally, the order in which nodes or edges are added to the network, and
the order in which they are iterated over, are irrelevant.

A reference implementation of this is provided by AbstractNetwork.equals(Object). 
/**
   * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the
   * same structural relationships as those in this network.
   *
   * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true:
   *
   * <ul>
   *   <li>A and B have equal {@link #isDirected() directedness}.
   *   <li>A and B have equal {@link #nodes() node sets}.
   *   <li>A and B have equal {@link #edges() edge sets}.
   *   <li>Every edge in A and B connects the same nodes in the same direction (if any).
   * </ul>
   *
   * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality.
   * For example, two networks may be considered equal even if one allows parallel edges and the
   * other doesn't. Additionally, the order in which nodes or edges are added to the network, and
   * the order in which they are iterated over, are irrelevant.
   *
   * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  
Returns the hash code for this network. The hash code of a network is defined as the hash code of a map from each of its edges to their 
incident nodes. 
A reference implementation of this is provided by AbstractNetwork.hashCode(). 
/**
   * Returns the hash code for this network. The hash code of a network is defined as the hash code
   * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object)
   * incident nodes}.
   *
   * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}.
   */
  @Override
  int hashCode();
}