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.common.annotations.Beta; 020import com.google.errorprone.annotations.DoNotMock; 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 are unique 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 * <h3>Capabilities</h3> 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 unique objects 051 * </ul> 052 * 053 * <h3>Building a {@code Network}</h3> 054 * 055 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 056 * create an instance of one of the built-in implementations of {@code Network}, use the {@link 057 * NetworkBuilder} class: 058 * 059 * <pre>{@code 060 * MutableNetwork<Integer, MyEdge> network = NetworkBuilder.directed().build(); 061 * }</pre> 062 * 063 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a 064 * subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you 065 * do not need to mutate a network (e.g. if you write a method than runs a read-only algorithm on 066 * the network), you should use the non-mutating {@link Network} interface, or an {@link 067 * ImmutableNetwork}. 068 * 069 * <p>You can create an immutable copy of an existing {@code Network} using {@link 070 * ImmutableNetwork#copyOf(Network)}: 071 * 072 * <pre>{@code 073 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(network); 074 * }</pre> 075 * 076 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and 077 * are contractually guaranteed to be unmodifiable and thread-safe. 078 * 079 * <p>The Guava User Guide has <a 080 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 081 * information on (and examples of) building graphs</a>. 082 * 083 * <h3>Additional documentation</h3> 084 * 085 * <p>See the Guava User Guide for the {@code common.graph} package (<a 086 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 087 * additional documentation, including: 088 * 089 * <ul> 090 * <li><a 091 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 092 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 093 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 094 * Synchronization policy</a> 095 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 096 * for implementors</a> 097 * </ul> 098 * 099 * @author James Sexton 100 * @author Joshua O'Madadhain 101 * @param <N> Node parameter type 102 * @param <E> Edge parameter type 103 * @since 20.0 104 */ 105@Beta 106@DoNotMock("Use NetworkBuilder to create a real instance") 107@ElementTypesAreNonnullByDefault 108public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> { 109 // 110 // Network-level accessors 111 // 112 113 /** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */ 114 Set<N> nodes(); 115 116 /** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */ 117 Set<E> edges(); 118 119 /** 120 * Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have 121 * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B. 122 * 123 * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be 124 * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node 125 * in the {@link Graph} view may be less than the degree of the same node in this {@link Network}. 126 */ 127 Graph<N> asGraph(); 128 129 // 130 // Network properties 131 // 132 133 /** 134 * Returns true if the edges in this network 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 boolean isDirected(); 139 140 /** 141 * Returns true if this network allows parallel edges. Attempting to add a parallel edge to a 142 * network that does not allow them will throw an {@link IllegalArgumentException}. 143 */ 144 boolean allowsParallelEdges(); 145 146 /** 147 * Returns true if this network allows self-loops (edges that connect a node to itself). 148 * Attempting to add a self-loop to a network that does not allow them will throw an {@link 149 * IllegalArgumentException}. 150 */ 151 boolean allowsSelfLoops(); 152 153 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 154 ElementOrder<N> nodeOrder(); 155 156 /** Returns the order of iteration for the elements of {@link #edges()}. */ 157 ElementOrder<E> edgeOrder(); 158 159 // 160 // Element-level accessors 161 // 162 163 /** 164 * Returns a live view of the nodes which have an incident edge in common with {@code node} in 165 * this graph. 166 * 167 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 168 * 169 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 170 * {@code view} returned by this method will be invalidated, and will throw {@code 171 * IllegalStateException} if it is accessed in any way, with the following exceptions: 172 * 173 * <ul> 174 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 175 * involving {@code view} will throw) 176 * <li>{@code hashCode()} does not throw 177 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 178 * behavior is undefined 179 * </ul> 180 * 181 * @throws IllegalArgumentException if {@code node} is not an element of this network 182 */ 183 Set<N> adjacentNodes(N node); 184 185 /** 186 * Returns a live view of all nodes in this network adjacent to {@code node} which can be reached 187 * by traversing {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 188 * 189 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 190 * 191 * <p>If {@code node} is removed from the network after this method is called, the `Set` returned 192 * by this method will be invalidated, and will throw `IllegalStateException` if it is accessed in 193 * any way. 194 * 195 * @throws IllegalArgumentException if {@code node} is not an element of this network 196 */ 197 @Override 198 Set<N> predecessors(N node); 199 200 /** 201 * Returns a live view of all nodes in this network adjacent to {@code node} which can be reached 202 * by traversing {@code node}'s outgoing edges in the direction (if any) of the edge. 203 * 204 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 205 * 206 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 207 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 208 * 209 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 210 * {@code view} returned by this method will be invalidated, and will throw {@code 211 * IllegalStateException} if it is accessed in any way, with the following exceptions: 212 * 213 * <ul> 214 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 215 * involving {@code view} will throw) 216 * <li>{@code hashCode()} does not throw 217 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 218 * behavior is undefined 219 * </ul> 220 * 221 * @throws IllegalArgumentException if {@code node} is not an element of this network 222 */ 223 @Override 224 Set<N> successors(N node); 225 226 /** 227 * Returns a live view of the edges whose {@link #incidentNodes(Object) incident nodes} in this 228 * network include {@code node}. 229 * 230 * <p>This is equal to the union of {@link #inEdges(Object)} and {@link #outEdges(Object)}. 231 * 232 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 233 * {@code view} returned by this method will be invalidated, and will throw {@code 234 * IllegalStateException} if it is accessed in any way, with the following exceptions: 235 * 236 * <ul> 237 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 238 * involving {@code view} will throw) 239 * <li>{@code hashCode()} does not throw 240 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 241 * behavior is undefined 242 * </ul> 243 * 244 * @throws IllegalArgumentException if {@code node} is not an element of this network 245 * @since 24.0 246 */ 247 Set<E> incidentEdges(N node); 248 249 /** 250 * Returns a live view of all edges in this network which can be traversed in the direction (if 251 * any) of the edge to end at {@code node}. 252 * 253 * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}. 254 * 255 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 256 * 257 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 258 * {@code view} returned by this method will be invalidated, and will throw {@code 259 * IllegalStateException} if it is accessed in any way, with the following exceptions: 260 * 261 * <ul> 262 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 263 * involving {@code view} will throw) 264 * <li>{@code hashCode()} does not throw 265 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 266 * behavior is undefined 267 * </ul> 268 * 269 * @throws IllegalArgumentException if {@code node} is not an element of this network 270 */ 271 Set<E> inEdges(N node); 272 273 /** 274 * Returns a live view of all edges in this network which can be traversed in the direction (if 275 * any) of the edge starting from {@code node}. 276 * 277 * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}. 278 * 279 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 280 * 281 * <p>If {@code node} is removed from the network after this method is called, the {@code Set} 282 * {@code view} returned by this method will be invalidated, and will throw {@code 283 * IllegalStateException} if it is accessed in any way, with the following exceptions: 284 * 285 * <ul> 286 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 287 * involving {@code view} will throw) 288 * <li>{@code hashCode()} does not throw 289 * <li>if {@code node} is re-added to the network after having been removed, {@code view}'s 290 * behavior is undefined 291 * </ul> 292 * 293 * @throws IllegalArgumentException if {@code node} is not an element of this network 294 */ 295 Set<E> outEdges(N node); 296 297 /** 298 * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting 299 * self-loops twice (equivalently, the number of times an edge touches {@code node}). 300 * 301 * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}. 302 * 303 * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of 304 * self-loops incident to {@code node}). 305 * 306 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 307 * 308 * @throws IllegalArgumentException if {@code node} is not an element of this network 309 */ 310 int degree(N node); 311 312 /** 313 * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed 314 * network. In an undirected network, returns the {@link #degree(Object)}. 315 * 316 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 317 * 318 * @throws IllegalArgumentException if {@code node} is not an element of this network 319 */ 320 int inDegree(N node); 321 322 /** 323 * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed 324 * network. In an undirected network, returns the {@link #degree(Object)}. 325 * 326 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 327 * 328 * @throws IllegalArgumentException if {@code node} is not an element of this network 329 */ 330 int outDegree(N node); 331 332 /** 333 * Returns the nodes which are the endpoints of {@code edge} in this network. 334 * 335 * @throws IllegalArgumentException if {@code edge} is not an element of this network 336 */ 337 EndpointPair<N> incidentNodes(E edge); 338 339 /** 340 * Returns a live view of the edges which have an {@link #incidentNodes(Object) incident node} in 341 * common with {@code edge}. An edge is not considered adjacent to itself. 342 * 343 * <p>If {@code edge} is removed from the network after this method is called, the {@code Set} 344 * {@code view} returned by this method will be invalidated, and will throw {@code 345 * IllegalStateException} if it is accessed in any way, with the following exceptions: 346 * 347 * <ul> 348 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 349 * involving {@code view} will throw) 350 * <li>{@code hashCode()} does not throw 351 * <li>if {@code edge} is re-added to the network after having been removed, {@code view}'s 352 * behavior is undefined 353 * </ul> 354 * 355 * @throws IllegalArgumentException if {@code edge} is not an element of this network 356 */ 357 Set<E> adjacentEdges(E edge); 358 359 /** 360 * Returns a live view of the set of edges that each directly connect {@code nodeU} to {@code 361 * nodeV}. 362 * 363 * <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}. 364 * 365 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 366 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 367 * edges}, the resulting set will contain at most one edge (equivalent to {@code 368 * edgeConnecting(nodeU, nodeV).asSet()}). 369 * 370 * <p>If either {@code nodeU} or {@code nodeV} are removed from the network after this method is 371 * called, the {@code Set} {@code view} returned by this method will be invalidated, and will 372 * throw {@code IllegalStateException} if it is accessed in any way, with the following 373 * exceptions: 374 * 375 * <ul> 376 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 377 * involving {@code view} will throw) 378 * <li>{@code hashCode()} does not throw 379 * <li>if {@code nodeU} or {@code nodeV} are re-added to the network after having been removed, 380 * {@code view}'s behavior is undefined 381 * </ul> 382 * 383 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 384 * network 385 */ 386 Set<E> edgesConnecting(N nodeU, N nodeV); 387 388 /** 389 * Returns a live view of the set of edges that each directly connect {@code endpoints} (in the 390 * order, if any, specified by {@code endpoints}). 391 * 392 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 393 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 394 * edges}, the resulting set will contain at most one edge (equivalent to {@code 395 * edgeConnecting(endpoints).asSet()}). 396 * 397 * <p>If this network is directed, {@code endpoints} must be ordered. 398 * 399 * <p>If either element of {@code endpoints} is removed from the network after this method is 400 * called, the {@code Set} {@code view} returned by this method will be invalidated, and will 401 * throw {@code IllegalStateException} if it is accessed in any way, with the following 402 * exceptions: 403 * 404 * <ul> 405 * <li>{@code view.equals(view)} evaluates to {@code true} (but any other `equals()` expression 406 * involving {@code view} will throw) 407 * <li>{@code hashCode()} does not throw 408 * <li>if either endpoint is re-added to the network after having been removed, {@code view}'s 409 * behavior is undefined 410 * </ul> 411 * 412 * @throws IllegalArgumentException if either endpoint is not an element of this network 413 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 414 * @since 27.1 415 */ 416 Set<E> edgesConnecting(EndpointPair<N> endpoints); 417 418 /** 419 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 420 * present, or {@code Optional.empty()} if no such edge exists. 421 * 422 * <p>In an undirected network, this is equal to {@code edgeConnecting(nodeV, nodeU)}. 423 * 424 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 425 * to {@code nodeV} 426 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 427 * network 428 * @since 23.0 429 */ 430 Optional<E> edgeConnecting(N nodeU, N nodeV); 431 432 /** 433 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 434 * specified by {@code endpoints}), if one is present, or {@code Optional.empty()} if no such edge 435 * exists. 436 * 437 * <p>If this network is directed, the endpoints must be ordered. 438 * 439 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 440 * to {@code nodeV} 441 * @throws IllegalArgumentException if either endpoint is not an element of this network 442 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 443 * @since 27.1 444 */ 445 Optional<E> edgeConnecting(EndpointPair<N> endpoints); 446 447 /** 448 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 449 * present, or {@code null} if no such edge exists. 450 * 451 * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}. 452 * 453 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 454 * to {@code nodeV} 455 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 456 * network 457 * @since 23.0 458 */ 459 @CheckForNull 460 E edgeConnectingOrNull(N nodeU, N nodeV); 461 462 /** 463 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 464 * specified by {@code endpoints}), if one is present, or {@code null} if no such edge exists. 465 * 466 * <p>If this network is directed, the endpoints must be ordered. 467 * 468 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 469 * to {@code nodeV} 470 * @throws IllegalArgumentException if either endpoint is not an element of this network 471 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 472 * @since 27.1 473 */ 474 @CheckForNull 475 E edgeConnectingOrNull(EndpointPair<N> endpoints); 476 477 /** 478 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 479 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to 480 * {@code edgeConnectingOrNull(nodeU, nodeV) != null}. 481 * 482 * <p>In an undirected network, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 483 * 484 * @since 23.0 485 */ 486 boolean hasEdgeConnecting(N nodeU, N nodeV); 487 488 /** 489 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 490 * any, specified by {@code endpoints}). 491 * 492 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 493 * endpoints are unordered and the network is directed; it simply returns {@code false}. This is 494 * for consistency with {@link Graph#hasEdgeConnecting(EndpointPair)} and {@link 495 * ValueGraph#hasEdgeConnecting(EndpointPair)}. 496 * 497 * @since 27.1 498 */ 499 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 500 501 // 502 // Network identity 503 // 504 505 /** 506 * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the 507 * same structural relationships as those in this network. 508 * 509 * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true: 510 * 511 * <ul> 512 * <li>A and B have equal {@link #isDirected() directedness}. 513 * <li>A and B have equal {@link #nodes() node sets}. 514 * <li>A and B have equal {@link #edges() edge sets}. 515 * <li>Every edge in A and B connects the same nodes in the same direction (if any). 516 * </ul> 517 * 518 * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 519 * For example, two networks may be considered equal even if one allows parallel edges and the 520 * other doesn't. Additionally, the order in which nodes or edges are added to the network, and 521 * the order in which they are iterated over, are irrelevant. 522 * 523 * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}. 524 */ 525 @Override 526 boolean equals(@CheckForNull Object object); 527 528 /** 529 * Returns the hash code for this network. The hash code of a network is defined as the hash code 530 * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object) 531 * incident nodes}. 532 * 533 * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}. 534 */ 535 @Override 536 int hashCode(); 537}