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) 2016 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 have associated non-unique values.

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


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

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



ValueGraph, as a subtype of Graph, explicitly does not support parallel edges, and forbids implementations or extensions with parallel edges. If you need parallel edges, use Network. (You can use a positive Integer edge value as a loose representation of edge multiplicity, but the *degree() and mutation methods will not reflect your interpretation of the edge value as its multiplicity.) 
Building a ValueGraph


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

MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build();



ValueGraphBuilder.build() returns an instance of MutableValueGraph, which is a subtype of ValueGraph 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 ValueGraph interface, or an ImmutableValueGraph. 
You can create an immutable copy of an existing ValueGraph using ImmutableValueGraph.copyOf(ValueGraph<Object,Object>): 

ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph);



Instances of ImmutableValueGraph do not implement MutableValueGraph (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
  • <V> – Value parameter type
Since:20.0
/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges have associated non-unique values.
 *
 * <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 ValueGraph} 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 self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges have associated values
 * </ul>
 *
 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges,
 * and forbids implementations or extensions with parallel edges. If you need parallel edges, use
 * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of
 * edge multiplicity, but the {@code *degree()} and mutation methods will not reflect your
 * interpretation of the edge value as its multiplicity.)
 *
 * <h3>Building a {@code ValueGraph}</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 ValueGraph}, use the {@link
 * ValueGraphBuilder} class:
 *
 * <pre>{@code
 * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build();
 * }</pre>
 *
 * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a
 * subtype of {@code ValueGraph} 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 ValueGraph} interface, or an {@link
 * ImmutableValueGraph}.
 *
 * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link
 * ImmutableValueGraph#copyOf(ValueGraph)}:
 *
 * <pre>{@code
 * ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph);
 * }</pre>
 *
 * <p>Instances of {@link ImmutableValueGraph} do not implement {@link MutableValueGraph}
 * (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 <V> Value parameter type
 * @since 20.0
 */
@Beta
public interface ValueGraph<N, V> extends BaseGraph<N> {
  //
  // ValueGraph-level accessors
  //

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

  
Returns all edges in this graph. 
/** Returns all edges in this graph. */
  @Override
  Set<EndpointPair<N>> edges();

  
Returns a live view of this graph as a Graph. The resulting Graph will have an edge connecting node A to node B if this ValueGraph has an edge connecting A to B. 
/**
   * Returns a live view of this graph as a {@link Graph}. The resulting {@link Graph} will have an
   * edge connecting node A to node B if this {@link ValueGraph} has an edge connecting A to B.
   */
  Graph<N> asGraph();

  //
  // ValueGraph properties
  //

  
Returns true if the edges in this graph 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 graph 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.
   */
  @Override
  boolean isDirected();

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

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

  //
  // Element-level accessors
  //

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

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

In an undirected graph, this is equivalent to adjacentNodes(Object). 
Throws:
/**
   * Returns all nodes in this graph 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 graph, this is equivalent to {@link #adjacentNodes(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  @Override
  Set<N> predecessors(N node);

  
Returns all nodes in this graph adjacent to node which can be reached by traversing node's outgoing edges in the direction (if any) of the edge. 
In an undirected graph, 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 graph 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 graph, 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 graph
   */
  @Override
  Set<N> successors(N node);

  
Returns the edges in this graph whose endpoints include node. 
Throws:
Since:24.0
/**
   * Returns the edges in this graph whose endpoints include {@code node}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   * @since 24.0
   */
  @Override
  Set<EndpointPair<N>> incidentEdges(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 graphs, this is equal to inDegree(node) + outDegree(node). 
For undirected graphs, 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 incident edges, counting self-loops twice (equivalently,
   * the number of times an edge touches {@code node}).
   *
   * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected graphs, 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 graph
   */
  @Override
  int degree(N node);

  
Returns the count of node's incoming edges (equal to predecessors(node).size()) in a directed graph. In an undirected graph, 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 incoming edges (equal to {@code predecessors(node).size()})
   * in a directed graph. In an undirected graph, 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 graph
   */
  @Override
  int inDegree(N node);

  
Returns the count of node's outgoing edges (equal to successors(node).size()) in a directed graph. In an undirected graph, 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 outgoing edges (equal to {@code successors(node).size()})
   * in a directed graph. In an undirected graph, 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 graph
   */
  @Override
  int outDegree(N node);

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

  
Returns the value of the edge connecting nodeU to nodeV, if one is present; otherwise, returns Optional.empty(). 
In an undirected graph, this is equal to edgeValue(nodeV, nodeU). 
Throws:
Since:23.0 (since 20.0 with return type V)
/**
   * Returns the value of the edge connecting {@code nodeU} to {@code nodeV}, if one is present;
   * otherwise, returns {@code Optional.empty()}.
   *
   * <p>In an undirected graph, this is equal to {@code edgeValue(nodeV, nodeU)}.
   *
   * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
   *     graph
   * @since 23.0 (since 20.0 with return type {@code V})
   */
  Optional<V> edgeValue(N nodeU, N nodeV);

  
Returns the value of the edge connecting nodeU to nodeV, if one is present; otherwise, returns defaultValue. 
In an undirected graph, this is equal to edgeValueOrDefault(nodeV, nodeU,
defaultValue). 
Throws:
/**
   * Returns the value of the edge connecting {@code nodeU} to {@code nodeV}, if one is present;
   * otherwise, returns {@code defaultValue}.
   *
   * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU,
   * defaultValue)}.
   *
   * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this
   *     graph
   */
  @Nullable
  V edgeValueOrDefault(N nodeU, N nodeV, @Nullable V defaultValue);

  //
  // ValueGraph identity
  //

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



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

A reference implementation of this is provided by AbstractValueGraph.equals(Object). 
/**
   * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and
   * the same structural relationships as those in this graph.
   *
   * <p>Thus, two value graphs 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>The {@link #edgeValue(Object, Object) value} of a given edge is the same in both A and B.
   * </ul>
   *
   * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality.
   * For example, two graphs may be considered equal even if one allows self-loops and the other
   * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order
   * in which they are iterated over, are irrelevant.
   *
   * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}.
   */
  @Override
  boolean equals(@Nullable Object object);

  
Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a map from each of its edges to the associated 
edge value. 
A reference implementation of this is provided by AbstractValueGraph.hashCode(). 
/**
   * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a
   * map from each of its {@link #edges() edges} to the associated {@link #edgeValue(Object, Object)
   * edge value}.
   *
   * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}.
   */
  @Override
  int hashCode();
}