001/* 002 * Copyright (C) 2014 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.errorprone.annotations.DoNotMock; 020import java.util.Optional; 021import java.util.Set; 022import org.jspecify.annotations.Nullable; 023 024/** 025 * An interface for <a 026 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, 027 * whose edges are <a 028 * href="https://github.com/google/guava/wiki/GraphsExplained#uniqueness">unique</a> objects. 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 * <h2>Capabilities</h2> 039 * 040 * <p>{@code Network} 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 parallel edges 048 * <li>graphs that do/don't allow self-loops 049 * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered 050 * <li>graphs whose edges are <a 051 * href="https://github.com/google/guava/wiki/GraphsExplained#uniqueness">unique</a> objects 052 * </ul> 053 * 054 * <h2>Building a {@code Network}</h2> 055 * 056 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 057 * create an instance of one of the built-in implementations of {@code Network}, use the {@link 058 * NetworkBuilder} class: 059 * 060 * {@snippet : 061 * MutableNetwork<Integer, MyEdge> network = NetworkBuilder.directed().build(); 062 * } 063 * 064 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a 065 * subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you 066 * do not need to mutate a network (e.g. if you write a method than runs a read-only algorithm on 067 * the network), you should use the non-mutating {@link Network} interface, or an {@link 068 * ImmutableNetwork}. 069 * 070 * <p>You can create an immutable copy of an existing {@code Network} using {@link 071 * ImmutableNetwork#copyOf(Network)}: 072 * 073 * {@snippet : 074 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(network); 075 * } 076 * 077 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and 078 * are contractually guaranteed to be unmodifiable and thread-safe. 079 * 080 * <p>The Guava User Guide has <a 081 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 082 * information on (and examples of) building graphs</a>. 083 * 084 * <h2>Additional documentation</h2> 085 * 086 * <p>See the Guava User Guide for the {@code common.graph} package (<a 087 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 088 * additional documentation, including: 089 * 090 * <ul> 091 * <li><a 092 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 093 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 094 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 095 * Synchronization policy</a> 096 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 097 * for implementors</a> 098 * </ul> 099 * 100 * @author James Sexton 101 * @author Joshua O'Madadhain 102 * @param <N> Node parameter type 103 * @param <E> Edge parameter type 104 * @since 20.0 105 */ 106@DoNotMock("Use NetworkBuilder to create a real instance") 107public interface Network<N, E> extends ArchetypeGraph<N> { 108 // 109 // Network-level accessors 110 // 111 112 /** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */ 113 Set<E> edges(); 114 115 /** 116 * Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have 117 * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B. 118 * 119 * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be 120 * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node 121 * in the {@link Graph} view may be less than the degree of the same node in this {@link Network}. 122 */ 123 Graph<N> asGraph(); 124 125 // 126 // Network properties 127 // 128 129 /** 130 * Returns true if this network allows parallel edges. Attempting to add a parallel edge to a 131 * network that does not allow them will throw an {@link IllegalArgumentException}. 132 */ 133 boolean allowsParallelEdges(); 134 135 /** Returns the order of iteration for the elements of {@link #edges()}. */ 136 ElementOrder<E> edgeOrder(); 137 138 // 139 // Element-level accessors 140 // 141 142 /** 143 * Returns a live view of the edges whose {@link #incidentNodes(Object) incident nodes} in this 144 * network include {@code node}. 145 * 146 * <p>This is equal to the union of {@link #inEdges(Object)} and {@link #outEdges(Object)}. 147 * 148 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 149 * {@code view} returned by this method will be invalidated, and will throw {@code 150 * IllegalStateException} if it is accessed in any way, with the following exceptions: 151 * 152 * <ul> 153 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 154 * expression involving {@code view} will throw) 155 * <li>{@code hashCode()} does not throw 156 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 157 * behavior is undefined 158 * </ul> 159 * 160 * @throws IllegalArgumentException if {@code node} is not an element of this network 161 * @since 24.0 162 */ 163 Set<E> incidentEdges(N node); 164 165 /** 166 * Returns a live view of all edges in this network which can be traversed in the direction (if 167 * any) of the edge to end at {@code node}. 168 * 169 * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}. 170 * 171 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 172 * 173 * <p>If {@code node} is removed from the network 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 network 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 network 186 */ 187 Set<E> inEdges(N node); 188 189 /** 190 * Returns a live view of all edges in this network which can be traversed in the direction (if 191 * any) of the edge starting from {@code node}. 192 * 193 * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}. 194 * 195 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 196 * 197 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 198 * {@code view} returned by this method will be invalidated, and will throw {@code 199 * IllegalStateException} if it is accessed in any way, with the following exceptions: 200 * 201 * <ul> 202 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 203 * expression involving {@code view} will throw) 204 * <li>{@code hashCode()} does not throw 205 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 206 * behavior is undefined 207 * </ul> 208 * 209 * @throws IllegalArgumentException if {@code node} is not an element of this network 210 */ 211 Set<E> outEdges(N node); 212 213 /** 214 * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting 215 * self-loops twice (equivalently, the number of times an edge touches {@code node}). 216 * 217 * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}. 218 * 219 * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of 220 * self-loops incident to {@code node}). 221 * 222 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 223 * 224 * @throws IllegalArgumentException if {@code node} is not an element of this network 225 */ 226 @Override 227 int degree(N node); 228 229 /** 230 * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed 231 * network. In an undirected network, returns the {@link #degree(Object)}. 232 * 233 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 234 * 235 * @throws IllegalArgumentException if {@code node} is not an element of this network 236 */ 237 @Override 238 int inDegree(N node); 239 240 /** 241 * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed 242 * network. In an undirected network, returns the {@link #degree(Object)}. 243 * 244 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 245 * 246 * @throws IllegalArgumentException if {@code node} is not an element of this network 247 */ 248 @Override 249 int outDegree(N node); 250 251 /** 252 * Returns the nodes which are the endpoints of {@code edge} in this network. 253 * 254 * @throws IllegalArgumentException if {@code edge} is not an element of this network 255 */ 256 EndpointPair<N> incidentNodes(E edge); 257 258 /** 259 * Returns a live view of the edges which have an {@link #incidentNodes(Object) incident node} in 260 * common with {@code edge}. An edge is not considered adjacent to itself. 261 * 262 * <p>If {@code edge} is removed from the network after this method is called, the {@code Set} 263 * {@code view} returned by this method will be invalidated, and will throw {@code 264 * IllegalStateException} if it is accessed in any way, with the following exceptions: 265 * 266 * <ul> 267 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 268 * expression involving {@code view} will throw) 269 * <li>{@code hashCode()} does not throw 270 * <li>if {@code edge} is re-added to the network after having been removed, {@code view}'s 271 * behavior is undefined 272 * </ul> 273 * 274 * @throws IllegalArgumentException if {@code edge} is not an element of this network 275 */ 276 Set<E> adjacentEdges(E edge); 277 278 /** 279 * Returns a live view of the set of edges that each directly connect {@code nodeU} to {@code 280 * nodeV}. 281 * 282 * <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}. 283 * 284 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 285 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 286 * edges}, the resulting set will contain at most one edge (equivalent to {@code 287 * edgeConnecting(nodeU, nodeV).asSet()}). 288 * 289 * <p>If either {@code nodeU} or {@code nodeV} are removed from the network after this method is 290 * called, the {@code Set} {@code view} returned by this method will be invalidated, and will 291 * throw {@code IllegalStateException} if it is accessed in any way, with the following 292 * exceptions: 293 * 294 * <ul> 295 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 296 * expression involving {@code view} will throw) 297 * <li>{@code hashCode()} does not throw 298 * <li>if {@code nodeU} or {@code nodeV} are re-added to the network after having been removed, 299 * {@code view}'s behavior is undefined 300 * </ul> 301 * 302 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 303 * network 304 */ 305 Set<E> edgesConnecting(N nodeU, N nodeV); 306 307 /** 308 * Returns a live view of the set of edges that each directly connect {@code endpoints} (in the 309 * order, if any, specified by {@code endpoints}). 310 * 311 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 312 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 313 * edges}, the resulting set will contain at most one edge (equivalent to {@code 314 * edgeConnecting(endpoints).asSet()}). 315 * 316 * <p>If this network is directed, {@code endpoints} must be ordered. 317 * 318 * <p>If either element of {@code endpoints} is removed from the network after this method is 319 * called, the {@code Set} {@code view} returned by this method will be invalidated, and will 320 * throw {@code IllegalStateException} if it is accessed in any way, with the following 321 * exceptions: 322 * 323 * <ul> 324 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other {@code equals()} 325 * expression involving {@code view} will throw) 326 * <li>{@code hashCode()} does not throw 327 * <li>if either endpoint is re-added to the network after having been removed, {@code view}'s 328 * behavior is undefined 329 * </ul> 330 * 331 * @throws IllegalArgumentException if either endpoint is not an element of this network 332 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 333 * @since 27.1 334 */ 335 Set<E> edgesConnecting(EndpointPair<N> endpoints); 336 337 /** 338 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 339 * present, or {@code Optional.empty()} if no such edge exists. 340 * 341 * <p>In an undirected network, this is equal to {@code edgeConnecting(nodeV, nodeU)}. 342 * 343 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 344 * to {@code nodeV} 345 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 346 * network 347 * @since 23.0 348 */ 349 Optional<E> edgeConnecting(N nodeU, N nodeV); 350 351 /** 352 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 353 * specified by {@code endpoints}), if one is present, or {@code Optional.empty()} if no such edge 354 * exists. 355 * 356 * <p>If this network is directed, the endpoints must be ordered. 357 * 358 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 359 * to {@code nodeV} 360 * @throws IllegalArgumentException if either endpoint is not an element of this network 361 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 362 * @since 27.1 363 */ 364 Optional<E> edgeConnecting(EndpointPair<N> endpoints); 365 366 /** 367 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 368 * present, or {@code null} if no such edge exists. 369 * 370 * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}. 371 * 372 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 373 * to {@code nodeV} 374 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 375 * network 376 * @since 23.0 377 */ 378 @Nullable E edgeConnectingOrNull(N nodeU, N nodeV); 379 380 /** 381 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 382 * specified by {@code endpoints}), if one is present, or {@code null} if no such edge exists. 383 * 384 * <p>If this network is directed, the endpoints must be ordered. 385 * 386 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 387 * to {@code nodeV} 388 * @throws IllegalArgumentException if either endpoint is not an element of this network 389 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 390 * @since 27.1 391 */ 392 @Nullable E edgeConnectingOrNull(EndpointPair<N> endpoints); 393 394 /** 395 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 396 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to 397 * {@code edgeConnectingOrNull(nodeU, nodeV) != null}. 398 * 399 * <p>In an undirected network, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 400 * 401 * @since 23.0 402 */ 403 @Override 404 boolean hasEdgeConnecting(N nodeU, N nodeV); 405 406 /** 407 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 408 * any, specified by {@code endpoints}). 409 * 410 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 411 * endpoints are unordered and the network is directed; it simply returns {@code false}. This is 412 * for consistency with {@link Graph#hasEdgeConnecting(EndpointPair)} and {@link 413 * ValueGraph#hasEdgeConnecting(EndpointPair)}. 414 * 415 * @since 27.1 416 */ 417 @Override 418 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 419 420 // 421 // Network identity 422 // 423 424 /** 425 * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the 426 * same structural relationships as those in this network. 427 * 428 * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true: 429 * 430 * <ul> 431 * <li>A and B have equal {@link #isDirected() directedness}. 432 * <li>A and B have equal {@link #nodes() node sets}. 433 * <li>A and B have equal {@link #edges() edge sets}. 434 * <li>Every edge in A and B connects the same nodes in the same direction (if any). 435 * </ul> 436 * 437 * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 438 * For example, two networks may be considered equal even if one allows parallel edges and the 439 * other doesn't. Additionally, the order in which nodes or edges are added to the network, and 440 * the order in which they are iterated over, are irrelevant. 441 * 442 * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}. 443 */ 444 @Override 445 boolean equals(@Nullable Object object); 446 447 /** 448 * Returns the hash code for this network. The hash code of a network is defined as the hash code 449 * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object) 450 * incident nodes}. 451 * 452 * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}. 453 */ 454 @Override 455 int hashCode(); 456}