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.Optional; 022import java.util.Set; 023import javax.annotation.CheckForNull; 024 025/** 026 * An interface for <a 027 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, 028 * whose edges have associated non-unique values. 029 * 030 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes. 031 * 032 * <p>There are three primary interfaces provided to represent graphs. In order of increasing 033 * complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally 034 * prefer the simplest interface that satisfies your use case. See the <a 035 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type"> 036 * "Choosing the right graph type"</a> section of the Guava User Guide for more details. 037 * 038 * <h3>Capabilities</h3> 039 * 040 * <p>{@code ValueGraph} supports the following use cases (<a 041 * href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of 042 * terms</a>): 043 * 044 * <ul> 045 * <li>directed graphs 046 * <li>undirected graphs 047 * <li>graphs that do/don't allow self-loops 048 * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered 049 * <li>graphs whose edges have associated values 050 * </ul> 051 * 052 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges, 053 * and forbids implementations or extensions with parallel edges. If you need parallel edges, use 054 * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of 055 * edge multiplicity, but the {@code *degree()} and mutation methods will not reflect your 056 * interpretation of the edge value as its multiplicity.) 057 * 058 * <h3>Building a {@code ValueGraph}</h3> 059 * 060 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 061 * create an instance of one of the built-in implementations of {@code ValueGraph}, use the {@link 062 * ValueGraphBuilder} class: 063 * 064 * <pre>{@code 065 * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build(); 066 * }</pre> 067 * 068 * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a 069 * subtype of {@code ValueGraph} that provides methods for adding and removing nodes and edges. If 070 * you do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on 071 * the graph), you should use the non-mutating {@link ValueGraph} interface, or an {@link 072 * ImmutableValueGraph}. 073 * 074 * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link 075 * ImmutableValueGraph#copyOf(ValueGraph)}: 076 * 077 * <pre>{@code 078 * ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph); 079 * }</pre> 080 * 081 * <p>Instances of {@link ImmutableValueGraph} do not implement {@link MutableValueGraph} 082 * (obviously!) and are contractually guaranteed to be unmodifiable and thread-safe. 083 * 084 * <p>The Guava User Guide has <a 085 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 086 * information on (and examples of) building graphs</a>. 087 * 088 * <h3>Additional documentation</h3> 089 * 090 * <p>See the Guava User Guide for the {@code common.graph} package (<a 091 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 092 * additional documentation, including: 093 * 094 * <ul> 095 * <li><a 096 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 097 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 098 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 099 * Synchronization policy</a> 100 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 101 * for implementors</a> 102 * </ul> 103 * 104 * @author James Sexton 105 * @author Joshua O'Madadhain 106 * @param <N> Node parameter type 107 * @param <V> Value parameter type 108 * @since 20.0 109 */ 110@Beta 111@ElementTypesAreNonnullByDefault 112public interface ValueGraph<N, V> extends BaseGraph<N> { 113 // 114 // ValueGraph-level accessors 115 // 116 117 /** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */ 118 @Override 119 Set<N> nodes(); 120 121 /** Returns all edges in this graph. */ 122 @Override 123 Set<EndpointPair<N>> edges(); 124 125 /** 126 * Returns a live view of this graph as a {@link Graph}. The resulting {@link Graph} will have an 127 * edge connecting node A to node B if this {@link ValueGraph} has an edge connecting A to B. 128 */ 129 Graph<N> asGraph(); 130 131 // 132 // ValueGraph properties 133 // 134 135 /** 136 * Returns true if the edges in this graph are directed. Directed edges connect a {@link 137 * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while 138 * undirected edges connect a pair of nodes to each other. 139 */ 140 @Override 141 boolean isDirected(); 142 143 /** 144 * Returns true if this graph allows self-loops (edges that connect a node to itself). Attempting 145 * to add a self-loop to a graph that does not allow them will throw an {@link 146 * IllegalArgumentException}. 147 */ 148 @Override 149 boolean allowsSelfLoops(); 150 151 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 152 @Override 153 ElementOrder<N> nodeOrder(); 154 155 /** 156 * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of 157 * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link 158 * #successors(Object)} and {@link #incidentEdges(Object)}. 159 * 160 * @since 29.0 161 */ 162 @Override 163 ElementOrder<N> incidentEdgeOrder(); 164 165 // 166 // Element-level accessors 167 // 168 169 /** 170 * Returns the nodes which have an incident edge in common with {@code node} in this graph. 171 * 172 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 173 * 174 * @throws IllegalArgumentException if {@code node} is not an element of this graph 175 */ 176 @Override 177 Set<N> adjacentNodes(N node); 178 179 /** 180 * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing 181 * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 182 * 183 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 184 * 185 * @throws IllegalArgumentException if {@code node} is not an element of this graph 186 */ 187 @Override 188 Set<N> predecessors(N node); 189 190 /** 191 * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing 192 * {@code node}'s outgoing edges in the direction (if any) of the edge. 193 * 194 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 195 * 196 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 197 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 198 * 199 * @throws IllegalArgumentException if {@code node} is not an element of this graph 200 */ 201 @Override 202 Set<N> successors(N node); 203 204 /** 205 * Returns the edges in this graph whose endpoints include {@code node}. 206 * 207 * <p>This is equal to the union of incoming and outgoing edges. 208 * 209 * @throws IllegalArgumentException if {@code node} is not an element of this graph 210 * @since 24.0 211 */ 212 @Override 213 Set<EndpointPair<N>> incidentEdges(N node); 214 215 /** 216 * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently, 217 * the number of times an edge touches {@code node}). 218 * 219 * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}. 220 * 221 * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of 222 * self-loops incident to {@code node}). 223 * 224 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 225 * 226 * @throws IllegalArgumentException if {@code node} is not an element of this graph 227 */ 228 @Override 229 int degree(N node); 230 231 /** 232 * Returns the count of {@code node}'s incoming edges (equal to {@code predecessors(node).size()}) 233 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 234 * 235 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 236 * 237 * @throws IllegalArgumentException if {@code node} is not an element of this graph 238 */ 239 @Override 240 int inDegree(N node); 241 242 /** 243 * Returns the count of {@code node}'s outgoing edges (equal to {@code successors(node).size()}) 244 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 245 * 246 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 247 * 248 * @throws IllegalArgumentException if {@code node} is not an element of this graph 249 */ 250 @Override 251 int outDegree(N node); 252 253 /** 254 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 255 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}. 256 * 257 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 258 * 259 * @since 23.0 260 */ 261 @Override 262 boolean hasEdgeConnecting(N nodeU, N nodeV); 263 264 /** 265 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 266 * any, specified by {@code endpoints}). This is equivalent to {@code 267 * edges().contains(endpoints)}. 268 * 269 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 270 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 271 * consistency with the behavior of {@link Collection#contains(Object)} (which does not generally 272 * throw if the object cannot be present in the collection), and the desire to have this method's 273 * behavior be compatible with {@code edges().contains(endpoints)}. 274 * 275 * @since 27.1 276 */ 277 @Override 278 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 279 280 /** 281 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV} (in the order, if 282 * any, specified by {@code endpoints}), if one is present; otherwise, returns {@code 283 * Optional.empty()}. 284 * 285 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 286 * graph 287 * @since 23.0 (since 20.0 with return type {@code V}) 288 */ 289 Optional<V> edgeValue(N nodeU, N nodeV); 290 291 /** 292 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 293 * by {@code endpoints}), if one is present; otherwise, returns {@code Optional.empty()}. 294 * 295 * <p>If this graph is directed, the endpoints must be ordered. 296 * 297 * @throws IllegalArgumentException if either endpoint is not an element of this graph 298 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 299 * @since 27.1 300 */ 301 Optional<V> edgeValue(EndpointPair<N> endpoints); 302 303 /** 304 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV}, if one is present; 305 * otherwise, returns {@code defaultValue}. 306 * 307 * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU, 308 * defaultValue)}. 309 * 310 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 311 * graph 312 */ 313 @CheckForNull 314 V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue); 315 316 /** 317 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 318 * by {@code endpoints}), if one is present; otherwise, returns {@code defaultValue}. 319 * 320 * <p>If this graph is directed, the endpoints must be ordered. 321 * 322 * @throws IllegalArgumentException if either endpoint is not an element of this graph 323 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 324 * @since 27.1 325 */ 326 @CheckForNull 327 V edgeValueOrDefault(EndpointPair<N> endpoints, @CheckForNull V defaultValue); 328 329 // 330 // ValueGraph identity 331 // 332 333 /** 334 * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and 335 * the same structural relationships as those in this graph. 336 * 337 * <p>Thus, two value graphs A and B are equal if <b>all</b> of the following are true: 338 * 339 * <ul> 340 * <li>A and B have equal {@link #isDirected() directedness}. 341 * <li>A and B have equal {@link #nodes() node sets}. 342 * <li>A and B have equal {@link #edges() edge sets}. 343 * <li>The {@link #edgeValue(Object, Object) value} of a given edge is the same in both A and B. 344 * </ul> 345 * 346 * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 347 * For example, two graphs may be considered equal even if one allows self-loops and the other 348 * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order 349 * in which they are iterated over, are irrelevant. 350 * 351 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}. 352 */ 353 @Override 354 boolean equals(@CheckForNull Object object); 355 356 /** 357 * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a 358 * map from each of its {@link #edges() edges} to the associated {@link #edgeValue(Object, Object) 359 * edge value}. 360 * 361 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}. 362 */ 363 @Override 364 int hashCode(); 365}