001/* 002 * Copyright (C) 2016 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.graph; 018 019import com.google.common.annotations.Beta; 020import java.util.Collection; 021import java.util.Set; 022import javax.annotation.CheckForNull; 023 024/** 025 * An interface for <a 026 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, 027 * whose edges have associated non-unique values. 028 * 029 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes. 030 * 031 * <p>There are three primary interfaces provided to represent graphs. In order of increasing 032 * complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally 033 * prefer the simplest interface that satisfies your use case. See the <a 034 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type"> 035 * "Choosing the right graph type"</a> section of the Guava User Guide for more details. 036 * 037 * <h3>Capabilities</h3> 038 * 039 * <p>{@code ValueGraph} supports the following use cases (<a 040 * href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of 041 * terms</a>): 042 * 043 * <ul> 044 * <li>directed graphs 045 * <li>undirected graphs 046 * <li>graphs that do/don't allow self-loops 047 * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered 048 * <li>graphs whose edges have associated values 049 * </ul> 050 * 051 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges, 052 * and forbids implementations or extensions with parallel edges. If you need parallel edges, use 053 * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of 054 * edge multiplicity, but the {@code *degree()} and mutation methods will not reflect your 055 * interpretation of the edge value as its multiplicity.) 056 * 057 * <h3>Building a {@code ValueGraph}</h3> 058 * 059 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 060 * create an instance of one of the built-in implementations of {@code ValueGraph}, use the {@link 061 * ValueGraphBuilder} class: 062 * 063 * <pre>{@code 064 * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build(); 065 * }</pre> 066 * 067 * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a 068 * subtype of {@code ValueGraph} that provides methods for adding and removing nodes and edges. If 069 * you do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on 070 * the graph), you should use the non-mutating {@link ValueGraph} interface, or an {@link 071 * ImmutableValueGraph}. 072 * 073 * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link 074 * ImmutableValueGraph#copyOf(ValueGraph)}: 075 * 076 * <pre>{@code 077 * ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph); 078 * }</pre> 079 * 080 * <p>Instances of {@link ImmutableValueGraph} do not implement {@link MutableValueGraph} 081 * (obviously!) and are contractually guaranteed to be unmodifiable and thread-safe. 082 * 083 * <p>The Guava User Guide has <a 084 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 085 * information on (and examples of) building graphs</a>. 086 * 087 * <h3>Additional documentation</h3> 088 * 089 * <p>See the Guava User Guide for the {@code common.graph} package (<a 090 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 091 * additional documentation, including: 092 * 093 * <ul> 094 * <li><a 095 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 096 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 097 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 098 * Synchronization policy</a> 099 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 100 * for implementors</a> 101 * </ul> 102 * 103 * @author James Sexton 104 * @author Joshua O'Madadhain 105 * @param <N> Node parameter type 106 * @param <V> Value parameter type 107 * @since 20.0 108 */ 109@Beta 110@ElementTypesAreNonnullByDefault 111public interface ValueGraph<N, V> extends BaseGraph<N> { 112 // 113 // ValueGraph-level accessors 114 // 115 116 /** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */ 117 @Override 118 Set<N> nodes(); 119 120 /** Returns all edges in this graph. */ 121 @Override 122 Set<EndpointPair<N>> edges(); 123 124 /** 125 * Returns a live view of this graph as a {@link Graph}. The resulting {@link Graph} will have an 126 * edge connecting node A to node B if this {@link ValueGraph} has an edge connecting A to B. 127 */ 128 Graph<N> asGraph(); 129 130 // 131 // ValueGraph properties 132 // 133 134 /** 135 * Returns true if the edges in this graph are directed. Directed edges connect a {@link 136 * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while 137 * undirected edges connect a pair of nodes to each other. 138 */ 139 @Override 140 boolean isDirected(); 141 142 /** 143 * Returns true if this graph allows self-loops (edges that connect a node to itself). Attempting 144 * to add a self-loop to a graph that does not allow them will throw an {@link 145 * IllegalArgumentException}. 146 */ 147 @Override 148 boolean allowsSelfLoops(); 149 150 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 151 @Override 152 ElementOrder<N> nodeOrder(); 153 154 /** 155 * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of 156 * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link 157 * #successors(Object)} and {@link #incidentEdges(Object)}. 158 * 159 * @since 29.0 160 */ 161 @Override 162 ElementOrder<N> incidentEdgeOrder(); 163 164 // 165 // Element-level accessors 166 // 167 168 /** 169 * Returns the nodes which have an incident edge in common with {@code node} in this graph. 170 * 171 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 172 * 173 * @throws IllegalArgumentException if {@code node} is not an element of this graph 174 */ 175 @Override 176 Set<N> adjacentNodes(N node); 177 178 /** 179 * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing 180 * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 181 * 182 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 183 * 184 * @throws IllegalArgumentException if {@code node} is not an element of this graph 185 */ 186 @Override 187 Set<N> predecessors(N node); 188 189 /** 190 * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing 191 * {@code node}'s outgoing edges in the direction (if any) of the edge. 192 * 193 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 194 * 195 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 196 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 197 * 198 * @throws IllegalArgumentException if {@code node} is not an element of this graph 199 */ 200 @Override 201 Set<N> successors(N node); 202 203 /** 204 * Returns the edges in this graph whose endpoints include {@code node}. 205 * 206 * <p>This is equal to the union of incoming and outgoing edges. 207 * 208 * @throws IllegalArgumentException if {@code node} is not an element of this graph 209 * @since 24.0 210 */ 211 @Override 212 Set<EndpointPair<N>> incidentEdges(N node); 213 214 /** 215 * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently, 216 * the number of times an edge touches {@code node}). 217 * 218 * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}. 219 * 220 * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of 221 * self-loops incident to {@code node}). 222 * 223 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 224 * 225 * @throws IllegalArgumentException if {@code node} is not an element of this graph 226 */ 227 @Override 228 int degree(N node); 229 230 /** 231 * Returns the count of {@code node}'s incoming edges (equal to {@code predecessors(node).size()}) 232 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 233 * 234 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 235 * 236 * @throws IllegalArgumentException if {@code node} is not an element of this graph 237 */ 238 @Override 239 int inDegree(N node); 240 241 /** 242 * Returns the count of {@code node}'s outgoing edges (equal to {@code successors(node).size()}) 243 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 244 * 245 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 246 * 247 * @throws IllegalArgumentException if {@code node} is not an element of this graph 248 */ 249 @Override 250 int outDegree(N node); 251 252 /** 253 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 254 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}. 255 * 256 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 257 * 258 * @since 23.0 259 */ 260 @Override 261 boolean hasEdgeConnecting(N nodeU, N nodeV); 262 263 /** 264 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 265 * any, specified by {@code endpoints}). This is equivalent to {@code 266 * edges().contains(endpoints)}. 267 * 268 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 269 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 270 * consistency with the behavior of {@link Collection#contains(Object)} (which does not generally 271 * throw if the object cannot be present in the collection), and the desire to have this method's 272 * behavior be compatible with {@code edges().contains(endpoints)}. 273 * 274 * @since 27.1 275 */ 276 @Override 277 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 278 279 /** 280 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV}, if one is present; 281 * otherwise, returns {@code defaultValue}. 282 * 283 * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU, 284 * defaultValue)}. 285 * 286 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 287 * graph 288 */ 289 @CheckForNull 290 V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue); 291 292 /** 293 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 294 * by {@code endpoints}), if one is present; otherwise, returns {@code defaultValue}. 295 * 296 * <p>If this graph is directed, the endpoints must be ordered. 297 * 298 * @throws IllegalArgumentException if either endpoint is not an element of this graph 299 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 300 * @since 27.1 301 */ 302 @CheckForNull 303 V edgeValueOrDefault(EndpointPair<N> endpoints, @CheckForNull V defaultValue); 304 305 // 306 // ValueGraph identity 307 // 308 309 /** 310 * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and 311 * the same structural relationships as those in this graph. 312 * 313 * <p>Thus, two value graphs A and B are equal if <b>all</b> of the following are true: 314 * 315 * <ul> 316 * <li>A and B have equal {@link #isDirected() directedness}. 317 * <li>A and B have equal {@link #nodes() node sets}. 318 * <li>A and B have equal {@link #edges() edge sets}. 319 * <li>The {@link #edgeValue(Object, Object) value} of a given edge is the same in both A and B. 320 * </ul> 321 * 322 * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 323 * For example, two graphs may be considered equal even if one allows self-loops and the other 324 * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order 325 * in which they are iterated over, are irrelevant. 326 * 327 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}. 328 */ 329 @Override 330 boolean equals(@CheckForNull Object object); 331 332 /** 333 * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a 334 * map from each of its {@link #edges() edges} to the associated {@link #edgeValue(Object, Object) 335 * edge value}. 336 * 337 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}. 338 */ 339 @Override 340 int hashCode(); 341}