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.Set; 021import javax.annotation.CheckForNull; 022 023/** 024 * An interface for <a 025 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, 026 * whose edges have associated non-unique values. 027 * 028 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes. 029 * 030 * <p>There are three primary interfaces provided to represent graphs. In order of increasing 031 * complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally 032 * prefer the simplest interface that satisfies your use case. See the <a 033 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type"> 034 * "Choosing the right graph type"</a> section of the Guava User Guide for more details. 035 * 036 * <h3>Capabilities</h3> 037 * 038 * <p>{@code ValueGraph} supports the following use cases (<a 039 * href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of 040 * terms</a>): 041 * 042 * <ul> 043 * <li>directed graphs 044 * <li>undirected graphs 045 * <li>graphs that do/don't allow self-loops 046 * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered 047 * <li>graphs whose edges have associated values 048 * </ul> 049 * 050 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges, 051 * and forbids implementations or extensions with parallel edges. If you need parallel edges, use 052 * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of 053 * edge multiplicity, but the {@code *degree()} and mutation methods will not reflect your 054 * interpretation of the edge value as its multiplicity.) 055 * 056 * <h3>Building a {@code ValueGraph}</h3> 057 * 058 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 059 * create an instance of one of the built-in implementations of {@code ValueGraph}, use the {@link 060 * ValueGraphBuilder} class: 061 * 062 * <pre>{@code 063 * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build(); 064 * }</pre> 065 * 066 * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a 067 * subtype of {@code ValueGraph} that provides methods for adding and removing nodes and edges. If 068 * you do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on 069 * the graph), you should use the non-mutating {@link ValueGraph} interface, or an {@link 070 * ImmutableValueGraph}. 071 * 072 * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link 073 * ImmutableValueGraph#copyOf(ValueGraph)}: 074 * 075 * <pre>{@code 076 * ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph); 077 * }</pre> 078 * 079 * <p>Instances of {@link ImmutableValueGraph} do not implement {@link MutableValueGraph} 080 * (obviously!) and are contractually guaranteed to be unmodifiable and thread-safe. 081 * 082 * <p>The Guava User Guide has <a 083 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 084 * information on (and examples of) building graphs</a>. 085 * 086 * <h3>Additional documentation</h3> 087 * 088 * <p>See the Guava User Guide for the {@code common.graph} package (<a 089 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 090 * additional documentation, including: 091 * 092 * <ul> 093 * <li><a 094 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 095 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 096 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 097 * Synchronization policy</a> 098 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 099 * for implementors</a> 100 * </ul> 101 * 102 * @author James Sexton 103 * @author Joshua O'Madadhain 104 * @param <N> Node parameter type 105 * @param <V> Value parameter type 106 * @since 20.0 107 */ 108@Beta 109@ElementTypesAreNonnullByDefault 110public interface ValueGraph<N, V> extends BaseGraph<N> { 111 // 112 // ValueGraph-level accessors 113 // 114 115 /** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */ 116 @Override 117 Set<N> nodes(); 118 119 /** Returns all edges in this graph. */ 120 @Override 121 Set<EndpointPair<N>> edges(); 122 123 /** 124 * Returns a live view of this graph as a {@link Graph}. The resulting {@link Graph} will have an 125 * edge connecting node A to node B if this {@link ValueGraph} has an edge connecting A to B. 126 */ 127 Graph<N> asGraph(); 128 129 // 130 // ValueGraph properties 131 // 132 133 /** 134 * Returns true if the edges in this graph are directed. Directed edges connect a {@link 135 * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while 136 * undirected edges connect a pair of nodes to each other. 137 */ 138 @Override 139 boolean isDirected(); 140 141 /** 142 * Returns true if this graph allows self-loops (edges that connect a node to itself). Attempting 143 * to add a self-loop to a graph that does not allow them will throw an {@link 144 * IllegalArgumentException}. 145 */ 146 @Override 147 boolean allowsSelfLoops(); 148 149 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 150 @Override 151 ElementOrder<N> nodeOrder(); 152 153 /** 154 * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of 155 * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link 156 * #successors(Object)} and {@link #incidentEdges(Object)}. 157 * 158 * @since 29.0 159 */ 160 @Override 161 ElementOrder<N> incidentEdgeOrder(); 162 163 // 164 // Element-level accessors 165 // 166 167 /** 168 * Returns a live view of the nodes which have an incident edge in common with {@code node} in 169 * this graph. 170 * 171 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 172 * 173 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 174 * {@code view} returned by this method will be invalidated, and will throw {@code 175 * IllegalStateException} if it is accessed in any way, with the following exceptions: 176 * 177 * <ul> 178 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 179 * expression involving {@code view} will throw) 180 * <li>{@code hashCode()} does not throw 181 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 182 * behavior is undefined 183 * </ul> 184 * 185 * @throws IllegalArgumentException if {@code node} is not an element of this graph 186 */ 187 @Override 188 Set<N> adjacentNodes(N node); 189 190 /** 191 * Returns a live view of all nodes in this graph adjacent to {@code node} which can be reached by 192 * traversing {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 193 * 194 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 195 * 196 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 197 * returned by this method will be invalidated, and will throw {@code IllegalStateException} if it 198 * is accessed in any way. 199 * 200 * @throws IllegalArgumentException if {@code node} is not an element of this graph 201 */ 202 @Override 203 Set<N> predecessors(N node); 204 205 /** 206 * Returns a live view of all nodes in this graph adjacent to {@code node} which can be reached by 207 * traversing {@code node}'s outgoing edges in the direction (if any) of the edge. 208 * 209 * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}. 210 * 211 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 212 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 213 * 214 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 215 * {@code view} returned by this method will be invalidated, and will throw {@code 216 * IllegalStateException} if it is accessed in any way, with the following exceptions: 217 * 218 * <ul> 219 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 220 * expression involving {@code view} will throw) 221 * <li>{@code hashCode()} does not throw 222 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 223 * behavior is undefined 224 * </ul> 225 * 226 * @throws IllegalArgumentException if {@code node} is not an element of this graph 227 */ 228 @Override 229 Set<N> successors(N node); 230 231 /** 232 * Returns a live view of the edges in this graph whose endpoints include {@code node}. 233 * 234 * <p>This is equal to the union of incoming and outgoing edges. 235 * 236 * <p>If {@code node} is removed from the graph after this method is called, the {@code Set} 237 * {@code view} returned by this method will be invalidated, and will throw {@code 238 * IllegalStateException} if it is accessed in any way, with the following exceptions: 239 * 240 * <ul> 241 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 242 * expression involving {@code view} will throw) 243 * <li>{@code hashCode()} does not throw 244 * <li>if {@code node} is re-added to the graph after having been removed, {@code view}'s 245 * behavior is undefined 246 * </ul> 247 * 248 * @throws IllegalArgumentException if {@code node} is not an element of this graph 249 * @since 24.0 250 */ 251 @Override 252 Set<EndpointPair<N>> incidentEdges(N node); 253 254 /** 255 * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently, 256 * the number of times an edge touches {@code node}). 257 * 258 * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}. 259 * 260 * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of 261 * self-loops incident to {@code node}). 262 * 263 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 264 * 265 * @throws IllegalArgumentException if {@code node} is not an element of this graph 266 */ 267 @Override 268 int degree(N node); 269 270 /** 271 * Returns the count of {@code node}'s incoming edges (equal to {@code predecessors(node).size()}) 272 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 273 * 274 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 275 * 276 * @throws IllegalArgumentException if {@code node} is not an element of this graph 277 */ 278 @Override 279 int inDegree(N node); 280 281 /** 282 * Returns the count of {@code node}'s outgoing edges (equal to {@code successors(node).size()}) 283 * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}. 284 * 285 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 286 * 287 * @throws IllegalArgumentException if {@code node} is not an element of this graph 288 */ 289 @Override 290 int outDegree(N node); 291 292 /** 293 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 294 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}. 295 * 296 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 297 * 298 * @since 23.0 299 */ 300 @Override 301 boolean hasEdgeConnecting(N nodeU, N nodeV); 302 303 /** 304 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 305 * any, specified by {@code endpoints}). This is equivalent to {@code 306 * edges().contains(endpoints)}. 307 * 308 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 309 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 310 * consistency with the behavior of {@link Collection#contains(Object)} (which does not generally 311 * throw if the object cannot be present in the collection), and the desire to have this method's 312 * behavior be compatible with {@code edges().contains(endpoints)}. 313 * 314 * @since 27.1 315 */ 316 @Override 317 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 318 319 /** 320 * Returns the value of the edge that connects {@code nodeU} to {@code nodeV}, if one is present; 321 * otherwise, returns {@code defaultValue}. 322 * 323 * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU, 324 * defaultValue)}. 325 * 326 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 327 * graph 328 */ 329 @CheckForNull 330 V edgeValueOrDefault(N nodeU, N nodeV, @CheckForNull V defaultValue); 331 332 /** 333 * Returns the value of the edge that connects {@code endpoints} (in the order, if any, specified 334 * by {@code endpoints}), if one is present; otherwise, returns {@code defaultValue}. 335 * 336 * <p>If this graph is directed, the endpoints must be ordered. 337 * 338 * @throws IllegalArgumentException if either endpoint is not an element of this graph 339 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 340 * @since 27.1 341 */ 342 @CheckForNull 343 V edgeValueOrDefault(EndpointPair<N> endpoints, @CheckForNull V defaultValue); 344 345 // 346 // ValueGraph identity 347 // 348 349 /** 350 * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and 351 * the same structural relationships as those in this graph. 352 * 353 * <p>Thus, two value graphs A and B are equal if <b>all</b> of the following are true: 354 * 355 * <ul> 356 * <li>A and B have equal {@link #isDirected() directedness}. 357 * <li>A and B have equal {@link #nodes() node sets}. 358 * <li>A and B have equal {@link #edges() edge sets}. 359 * <li>The {@link #edgeValueOrDefault(N, N, V) value} of a given edge is the same in both A and 360 * B. 361 * </ul> 362 * 363 * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 364 * For example, two graphs may be considered equal even if one allows self-loops and the other 365 * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order 366 * in which they are iterated over, are irrelevant. 367 * 368 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#equals(Object)}. 369 */ 370 @Override 371 boolean equals(@CheckForNull Object object); 372 373 /** 374 * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a 375 * map from each of its {@link #edges() edges} to the associated {@link #edgeValueOrDefault(N, N, 376 * V) edge value}. 377 * 378 * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}. 379 */ 380 @Override 381 int hashCode(); 382}