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> graph = 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 graph (e.g. if you write a method than runs a read-only algorithm on the 066 * graph), 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(graph); 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 the nodes which have an incident edge in common with {@code node} in this network. 165 * 166 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 167 * 168 * @throws IllegalArgumentException if {@code node} is not an element of this network 169 */ 170 Set<N> adjacentNodes(N node); 171 172 /** 173 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 174 * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 175 * 176 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 177 * 178 * @throws IllegalArgumentException if {@code node} is not an element of this network 179 */ 180 @Override 181 Set<N> predecessors(N node); 182 183 /** 184 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 185 * {@code node}'s outgoing edges in the direction (if any) of the edge. 186 * 187 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 188 * 189 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 190 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 191 * 192 * @throws IllegalArgumentException if {@code node} is not an element of this network 193 */ 194 @Override 195 Set<N> successors(N node); 196 197 /** 198 * Returns the edges whose {@link #incidentNodes(Object) incident nodes} in this network include 199 * {@code node}. 200 * 201 * <p>This is equal to the union of {@link #inEdges(Object)} and {@link #outEdges(Object)}. 202 * 203 * @throws IllegalArgumentException if {@code node} is not an element of this network 204 */ 205 Set<E> incidentEdges(N node); 206 207 /** 208 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 209 * to end at {@code node}. 210 * 211 * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}. 212 * 213 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 214 * 215 * @throws IllegalArgumentException if {@code node} is not an element of this network 216 */ 217 Set<E> inEdges(N node); 218 219 /** 220 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 221 * starting from {@code node}. 222 * 223 * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}. 224 * 225 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 226 * 227 * @throws IllegalArgumentException if {@code node} is not an element of this network 228 */ 229 Set<E> outEdges(N node); 230 231 /** 232 * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting 233 * self-loops twice (equivalently, the number of times an edge touches {@code node}). 234 * 235 * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}. 236 * 237 * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of 238 * self-loops incident to {@code node}). 239 * 240 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 241 * 242 * @throws IllegalArgumentException if {@code node} is not an element of this network 243 */ 244 int degree(N node); 245 246 /** 247 * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed 248 * network. In an undirected network, returns the {@link #degree(Object)}. 249 * 250 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 251 * 252 * @throws IllegalArgumentException if {@code node} is not an element of this network 253 */ 254 int inDegree(N node); 255 256 /** 257 * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed 258 * network. In an undirected network, returns the {@link #degree(Object)}. 259 * 260 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 261 * 262 * @throws IllegalArgumentException if {@code node} is not an element of this network 263 */ 264 int outDegree(N node); 265 266 /** 267 * Returns the nodes which are the endpoints of {@code edge} in this network. 268 * 269 * @throws IllegalArgumentException if {@code edge} is not an element of this network 270 */ 271 EndpointPair<N> incidentNodes(E edge); 272 273 /** 274 * Returns the edges which have an {@link #incidentNodes(Object) incident node} in common with 275 * {@code edge}. An edge is not considered adjacent to itself. 276 * 277 * @throws IllegalArgumentException if {@code edge} is not an element of this network 278 */ 279 Set<E> adjacentEdges(E edge); 280 281 /** 282 * Returns the set of edges that each directly connect {@code nodeU} to {@code nodeV}. 283 * 284 * <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}. 285 * 286 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 287 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 288 * edges}, the resulting set will contain at most one edge (equivalent to {@code 289 * edgeConnecting(nodeU, nodeV).asSet()}). 290 * 291 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 292 * network 293 */ 294 Set<E> edgesConnecting(N nodeU, N nodeV); 295 296 /** 297 * Returns the set of edges that each directly connect {@code endpoints} (in the order, if any, 298 * specified by {@code endpoints}). 299 * 300 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 301 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 302 * edges}, the resulting set will contain at most one edge (equivalent to {@code 303 * edgeConnecting(endpoints).asSet()}). 304 * 305 * <p>If this network is directed, {@code endpoints} must be ordered. 306 * 307 * @throws IllegalArgumentException if either endpoint is not an element of this network 308 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 309 * @since 27.1 310 */ 311 Set<E> edgesConnecting(EndpointPair<N> endpoints); 312 313 /** 314 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 315 * present, or {@code Optional.empty()} if no such edge exists. 316 * 317 * <p>In an undirected network, this is equal to {@code edgeConnecting(nodeV, nodeU)}. 318 * 319 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 320 * to {@code nodeV} 321 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 322 * network 323 * @since 23.0 324 */ 325 Optional<E> edgeConnecting(N nodeU, N nodeV); 326 327 /** 328 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 329 * specified by {@code endpoints}), if one is present, or {@code Optional.empty()} if no such edge 330 * exists. 331 * 332 * <p>If this graph is directed, the endpoints must be ordered. 333 * 334 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 335 * to {@code nodeV} 336 * @throws IllegalArgumentException if either endpoint is not an element of this network 337 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 338 * @since 27.1 339 */ 340 Optional<E> edgeConnecting(EndpointPair<N> endpoints); 341 342 /** 343 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 344 * present, or {@code null} if no such edge exists. 345 * 346 * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}. 347 * 348 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 349 * to {@code nodeV} 350 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 351 * network 352 * @since 23.0 353 */ 354 @CheckForNull 355 E edgeConnectingOrNull(N nodeU, N nodeV); 356 357 /** 358 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 359 * specified by {@code endpoints}), if one is present, or {@code null} if no such edge exists. 360 * 361 * <p>If this graph is directed, the endpoints must be ordered. 362 * 363 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 364 * to {@code nodeV} 365 * @throws IllegalArgumentException if either endpoint is not an element of this network 366 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 367 * @since 27.1 368 */ 369 @CheckForNull 370 E edgeConnectingOrNull(EndpointPair<N> endpoints); 371 372 /** 373 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 374 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to 375 * {@code edgeConnectingOrNull(nodeU, nodeV) != null}. 376 * 377 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 378 * 379 * @since 23.0 380 */ 381 boolean hasEdgeConnecting(N nodeU, N nodeV); 382 383 /** 384 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 385 * any, specified by {@code endpoints}). 386 * 387 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 388 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 389 * consistency with {@link Graph#hasEdgeConnecting(EndpointPair)} and {@link 390 * ValueGraph#hasEdgeConnecting(EndpointPair)}. 391 * 392 * @since 27.1 393 */ 394 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 395 396 // 397 // Network identity 398 // 399 400 /** 401 * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the 402 * same structural relationships as those in this network. 403 * 404 * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true: 405 * 406 * <ul> 407 * <li>A and B have equal {@link #isDirected() directedness}. 408 * <li>A and B have equal {@link #nodes() node sets}. 409 * <li>A and B have equal {@link #edges() edge sets}. 410 * <li>Every edge in A and B connects the same nodes in the same direction (if any). 411 * </ul> 412 * 413 * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 414 * For example, two networks may be considered equal even if one allows parallel edges and the 415 * other doesn't. Additionally, the order in which nodes or edges are added to the network, and 416 * the order in which they are iterated over, are irrelevant. 417 * 418 * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}. 419 */ 420 @Override 421 boolean equals(@CheckForNull Object object); 422 423 /** 424 * Returns the hash code for this network. The hash code of a network is defined as the hash code 425 * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object) 426 * incident nodes}. 427 * 428 * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}. 429 */ 430 @Override 431 int hashCode(); 432}