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.Optional; 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 a live view of the nodes which have an incident edge in common with {@code node} in 170 * this graph. 171 * 172 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 173 * 174 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 175 * {@code view} returned by this method will be invalidated, and will throw {@code 176 * IllegalStateException} if it is accessed in any way, with the following exceptions: 177 * 178 * <ul> 179 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 180 * expression involving {@code view} will throw) 181 * <li>{@code hashCode()} does not throw 182 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 183 * behavior is undefined 184 * </ul> 185 * 186 * @throws IllegalArgumentException if {@code node} is not an element of this graph 187 */ 188 @Override 189 Set<N> adjacentNodes(N node); 190 191 /** 192 * Returns a live view of all nodes in this graph adjacent to {@code node} which can be reached by 193 * traversing {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 194 * 195 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 196 * 197 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 198 * returned by this method will be invalidated, and will throw {@code IllegalStateException} if it 199 * is accessed in any way. 200 * 201 * @throws IllegalArgumentException if {@code node} is not an element of this graph 202 */ 203 @Override 204 Set<N> predecessors(N node); 205 206 /** 207 * Returns a live view of all nodes in this graph adjacent to {@code node} which can be reached by 208 * traversing {@code node}'s outgoing edges in the direction (if any) of the edge. 209 * 210 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 211 * 212 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 213 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 214 * 215 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 216 * {@code view} returned by this method will be invalidated, and will throw {@code 217 * IllegalStateException} if it is accessed in any way, with the following exceptions: 218 * 219 * <ul> 220 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 221 * expression involving {@code view} will throw) 222 * <li>{@code hashCode()} does not throw 223 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 224 * behavior is undefined 225 * </ul> 226 * 227 * @throws IllegalArgumentException if {@code node} is not an element of this graph 228 */ 229 @Override 230 Set<N> successors(N node); 231 232 /** 233 * Returns a live view of the edges in this graph whose endpoints include {@code node}. 234 * 235 * <p>This is equal to the union of incoming and outgoing edges. 236 * 237 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 238 * {@code view} returned by this method will be invalidated, and will throw {@code 239 * IllegalStateException} if it is accessed in any way, with the following exceptions: 240 * 241 * <ul> 242 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 243 * expression involving {@code view} will throw) 244 * <li>{@code hashCode()} does not throw 245 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 246 * behavior is undefined 247 * </ul> 248 * 249 * @throws IllegalArgumentException if {@code node} is not an element of this graph 250 * @since 24.0 251 */ 252 @Override 253 Set<EndpointPair<N>> incidentEdges(N node); 254 255 /** 256 * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently, 257 * the number of times an edge touches {@code node}). 258 * 259 * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}. 260 * 261 * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of 262 * self-loops incident to {@code node}). 263 * 264 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 265 * 266 * @throws IllegalArgumentException if {@code node} is not an element of this graph 267 */ 268 @Override 269 int degree(N node); 270 271 /** 272 * Returns the count of {@code node}'s incoming edges (equal to {@code predecessors(node).size()}) 273 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 274 * 275 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 276 * 277 * @throws IllegalArgumentException if {@code node} is not an element of this graph 278 */ 279 @Override 280 int inDegree(N node); 281 282 /** 283 * Returns the count of {@code node}'s outgoing edges (equal to {@code successors(node).size()}) 284 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 285 * 286 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 287 * 288 * @throws IllegalArgumentException if {@code node} is not an element of this graph 289 */ 290 @Override 291 int outDegree(N node); 292 293 /** 294 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 295 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}. 296 * 297 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 298 * 299 * @since 23.0 300 */ 301 @Override 302 boolean hasEdgeConnecting(N nodeU, N nodeV); 303 304 /** 305 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 306 * any, specified by {@code endpoints}). This is equivalent to {@code 307 * edges().contains(endpoints)}. 308 * 309 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 310 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 311 * consistency with the behavior of {@link Collection#contains(Object)} (which does not generally 312 * throw if the object cannot be present in the collection), and the desire to have this method's 313 * behavior be compatible with {@code edges().contains(endpoints)}. 314 * 315 * @since 27.1 316 */ 317 @Override 318 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 319 320 /** 321 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV} (in the order, if 322 * any, specified by {@code endpoints}), if one is present; otherwise, returns {@code 323 * Optional.empty()}. 324 * 325 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 326 * graph 327 * @since 23.0 (since 20.0 with return type {@code V}) 328 */ 329 Optional<V> edgeValue(N nodeU, N nodeV); 330 331 /** 332 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 333 * by {@code endpoints}), if one is present; otherwise, returns {@code Optional.empty()}. 334 * 335 * <p>If this graph is directed, the endpoints must be ordered. 336 * 337 * @throws IllegalArgumentException if either endpoint is not an element of this graph 338 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 339 * @since 27.1 340 */ 341 Optional<V> edgeValue(EndpointPair<N> endpoints); 342 343 /** 344 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV}, if one is present; 345 * otherwise, returns {@code defaultValue}. 346 * 347 * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU, 348 * defaultValue)}. 349 * 350 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 351 * graph 352 */ 353 @CheckForNull 354 V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue); 355 356 /** 357 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 358 * by {@code endpoints}), if one is present; otherwise, returns {@code defaultValue}. 359 * 360 * <p>If this graph is directed, the endpoints must be ordered. 361 * 362 * @throws IllegalArgumentException if either endpoint is not an element of this graph 363 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 364 * @since 27.1 365 */ 366 @CheckForNull 367 V edgeValueOrDefault(EndpointPair<N> endpoints, @CheckForNull V defaultValue); 368 369 // 370 // ValueGraph identity 371 // 372 373 /** 374 * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and 375 * the same structural relationships as those in this graph. 376 * 377 * <p>Thus, two value graphs A and B are equal if <b>all</b> of the following are true: 378 * 379 * <ul> 380 * <li>A and B have equal {@link #isDirected() directedness}. 381 * <li>A and B have equal {@link #nodes() node sets}. 382 * <li>A and B have equal {@link #edges() edge sets}. 383 * <li>The {@link #edgeValue(N, N) value} of a given edge is the same in both A and B. 384 * </ul> 385 * 386 * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 387 * For example, two graphs may be considered equal even if one allows self-loops and the other 388 * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order 389 * in which they are iterated over, are irrelevant. 390 * 391 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}. 392 */ 393 @Override 394 boolean equals(@CheckForNull Object object); 395 396 /** 397 * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a 398 * map from each of its {@link #edges() edges} to the associated {@link #edgeValue(N, N) edge 399 * value}. 400 * 401 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}. 402 */ 403 @Override 404 int hashCode(); 405}