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.Set; 022import org.checkerframework.checker.nullness.compatqual.NullableDecl; 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 unique objects. 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 Network} 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 parallel edges 047 * <li>graphs that do/don't allow self-loops 048 * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered 049 * <li>graphs whose edges are unique objects 050 * </ul> 051 * 052 * <h3>Building a {@code Network}</h3> 053 * 054 * <p>The implementation classes that {@code common.graph} provides are not public, by design. To 055 * create an instance of one of the built-in implementations of {@code Network}, use the {@link 056 * NetworkBuilder} class: 057 * 058 * <pre>{@code 059 * MutableNetwork<Integer, MyEdge> graph = NetworkBuilder.directed().build(); 060 * }</pre> 061 * 062 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a 063 * subtype of {@code Network} that provides methods for adding and removing nodes and edges. If you 064 * do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on the 065 * graph), you should use the non-mutating {@link Network} interface, or an {@link 066 * ImmutableNetwork}. 067 * 068 * <p>You can create an immutable copy of an existing {@code Network} using {@link 069 * ImmutableNetwork#copyOf(Network)}: 070 * 071 * <pre>{@code 072 * ImmutableNetwork<Integer, MyEdge> immutableGraph = ImmutableNetwork.copyOf(graph); 073 * }</pre> 074 * 075 * <p>Instances of {@link ImmutableNetwork} do not implement {@link MutableNetwork} (obviously!) and 076 * are contractually guaranteed to be unmodifiable and thread-safe. 077 * 078 * <p>The Guava User Guide has <a 079 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more 080 * information on (and examples of) building graphs</a>. 081 * 082 * <h3>Additional documentation</h3> 083 * 084 * <p>See the Guava User Guide for the {@code common.graph} package (<a 085 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for 086 * additional documentation, including: 087 * 088 * <ul> 089 * <li><a 090 * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> 091 * {@code equals()}, {@code hashCode()}, and graph equivalence</a> 092 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> 093 * Synchronization policy</a> 094 * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes 095 * for implementors</a> 096 * </ul> 097 * 098 * @author James Sexton 099 * @author Joshua O'Madadhain 100 * @param <N> Node parameter type 101 * @param <E> Edge parameter type 102 * @since 20.0 103 */ 104@Beta 105@DoNotMock("Use NetworkBuilder to create a real instance") 106public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> { 107 // 108 // Network-level accessors 109 // 110 111 /** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */ 112 Set<N> nodes(); 113 114 /** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */ 115 Set<E> edges(); 116 117 /** 118 * Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have 119 * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B. 120 * 121 * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be 122 * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node 123 * in the {@link Graph} view may be less than the degree of the same node in this {@link Network}. 124 */ 125 Graph<N> asGraph(); 126 127 // 128 // Network properties 129 // 130 131 /** 132 * Returns true if the edges in this network are directed. Directed edges connect a {@link 133 * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while 134 * undirected edges connect a pair of nodes to each other. 135 */ 136 boolean isDirected(); 137 138 /** 139 * Returns true if this network allows parallel edges. Attempting to add a parallel edge to a 140 * network that does not allow them will throw an {@link IllegalArgumentException}. 141 */ 142 boolean allowsParallelEdges(); 143 144 /** 145 * Returns true if this network allows self-loops (edges that connect a node to itself). 146 * Attempting to add a self-loop to a network that does not allow them will throw an {@link 147 * IllegalArgumentException}. 148 */ 149 boolean allowsSelfLoops(); 150 151 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 152 ElementOrder<N> nodeOrder(); 153 154 /** Returns the order of iteration for the elements of {@link #edges()}. */ 155 ElementOrder<E> edgeOrder(); 156 157 // 158 // Element-level accessors 159 // 160 161 /** 162 * Returns the nodes which have an incident edge in common with {@code node} in this network. 163 * 164 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 165 * 166 * @throws IllegalArgumentException if {@code node} is not an element of this network 167 */ 168 Set<N> adjacentNodes(N node); 169 170 /** 171 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 172 * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 173 * 174 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 175 * 176 * @throws IllegalArgumentException if {@code node} is not an element of this network 177 */ 178 @Override 179 Set<N> predecessors(N node); 180 181 /** 182 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 183 * {@code node}'s outgoing edges in the direction (if any) of the edge. 184 * 185 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 186 * 187 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 188 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 189 * 190 * @throws IllegalArgumentException if {@code node} is not an element of this network 191 */ 192 @Override 193 Set<N> successors(N node); 194 195 /** 196 * Returns the edges whose {@link #incidentNodes(Object) incident nodes} in this network include 197 * {@code node}. 198 * 199 * <p>This is equal to the union of {@link #inEdges(Object)} and {@link #outEdges(Object)}. 200 * 201 * @throws IllegalArgumentException if {@code node} is not an element of this network 202 */ 203 Set<E> incidentEdges(N node); 204 205 /** 206 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 207 * to end at {@code node}. 208 * 209 * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}. 210 * 211 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 212 * 213 * @throws IllegalArgumentException if {@code node} is not an element of this network 214 */ 215 Set<E> inEdges(N node); 216 217 /** 218 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 219 * starting from {@code node}. 220 * 221 * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}. 222 * 223 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 224 * 225 * @throws IllegalArgumentException if {@code node} is not an element of this network 226 */ 227 Set<E> outEdges(N node); 228 229 /** 230 * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting 231 * self-loops twice (equivalently, the number of times an edge touches {@code node}). 232 * 233 * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}. 234 * 235 * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of 236 * self-loops incident to {@code node}). 237 * 238 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 239 * 240 * @throws IllegalArgumentException if {@code node} is not an element of this network 241 */ 242 int degree(N node); 243 244 /** 245 * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed 246 * network. In an undirected network, returns the {@link #degree(Object)}. 247 * 248 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 249 * 250 * @throws IllegalArgumentException if {@code node} is not an element of this network 251 */ 252 int inDegree(N node); 253 254 /** 255 * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed 256 * network. In an undirected network, returns the {@link #degree(Object)}. 257 * 258 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 259 * 260 * @throws IllegalArgumentException if {@code node} is not an element of this network 261 */ 262 int outDegree(N node); 263 264 /** 265 * Returns the nodes which are the endpoints of {@code edge} in this network. 266 * 267 * @throws IllegalArgumentException if {@code edge} is not an element of this network 268 */ 269 EndpointPair<N> incidentNodes(E edge); 270 271 /** 272 * Returns the edges which have an {@link #incidentNodes(Object) incident node} in common with 273 * {@code edge}. An edge is not considered adjacent to itself. 274 * 275 * @throws IllegalArgumentException if {@code edge} is not an element of this network 276 */ 277 Set<E> adjacentEdges(E edge); 278 279 /** 280 * Returns the set of edges that each directly connect {@code nodeU} to {@code 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 #incidentNodes(Object)}. 285 * If this network does not {@link #allowsParallelEdges() allow parallel edges}, the resulting set 286 * will contain at most one edge (equivalent to {@code edgeConnecting(nodeU, nodeV).asSet()}). 287 * 288 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 289 * network 290 */ 291 Set<E> edgesConnecting(N nodeU, N nodeV); 292 293 /** 294 * Returns the set of edges that each directly connect {@code endpoints} (in the order, if any, 295 * specified by {@code endpoints}). 296 * 297 * <p>The resulting set of edges will be parallel (i.e. have equal {@link #incidentNodes(Object)}. 298 * If this network does not {@link #allowsParallelEdges() allow parallel edges}, the resulting set 299 * will contain at most one edge (equivalent to {@code edgeConnecting(endpoints).asSet()}). 300 * 301 * <p>If this network is directed, {@code endpoints} must be ordered. 302 * 303 * @throws IllegalArgumentException if either endpoint is not an element of this network 304 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 305 * @since 27.1 306 */ 307 Set<E> edgesConnecting(EndpointPair<N> endpoints); 308 309 /** 310 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 311 * present, or {@code null} if no such edge exists. 312 * 313 * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}. 314 * 315 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 316 * to {@code nodeV} 317 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 318 * network 319 * @since 23.0 320 */ 321 @NullableDecl 322 E edgeConnectingOrNull(N nodeU, N nodeV); 323 324 /** 325 * Returns the single edge that directly connects {@code endpoints} (in the order, if any, 326 * specified by {@code endpoints}), if one is present, or {@code null} if no such edge exists. 327 * 328 * <p>If this graph is directed, the endpoints must be ordered. 329 * 330 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 331 * to {@code nodeV} 332 * @throws IllegalArgumentException if either endpoint is not an element of this network 333 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 334 * @since 27.1 335 */ 336 @NullableDecl 337 E edgeConnectingOrNull(EndpointPair<N> endpoints); 338 339 /** 340 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 341 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to 342 * {@code edgeConnectingOrNull(nodeU, nodeV) != null}. 343 * 344 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 345 * 346 * @since 23.0 347 */ 348 boolean hasEdgeConnecting(N nodeU, N nodeV); 349 350 /** 351 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 352 * any, specified by {@code endpoints}). 353 * 354 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 355 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 356 * consistency with {@link Graph#hasEdgeConnecting(EndpointPair)} and {@link 357 * ValueGraph#hasEdgeConnecting(EndpointPair)}. 358 * 359 * @since 27.1 360 */ 361 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 362 363 // 364 // Network identity 365 // 366 367 /** 368 * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the 369 * same structural relationships as those in this network. 370 * 371 * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true: 372 * 373 * <ul> 374 * <li>A and B have equal {@link #isDirected() directedness}. 375 * <li>A and B have equal {@link #nodes() node sets}. 376 * <li>A and B have equal {@link #edges() edge sets}. 377 * <li>Every edge in A and B connects the same nodes in the same direction (if any). 378 * </ul> 379 * 380 * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 381 * For example, two networks may be considered equal even if one allows parallel edges and the 382 * other doesn't. Additionally, the order in which nodes or edges are added to the network, and 383 * the order in which they are iterated over, are irrelevant. 384 * 385 * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}. 386 */ 387 @Override 388 boolean equals(@NullableDecl Object object); 389 390 /** 391 * Returns the hash code for this network. The hash code of a network is defined as the hash code 392 * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object) 393 * incident nodes}. 394 * 395 * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}. 396 */ 397 @Override 398 int hashCode(); 399}