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 javax.annotation.CheckForNull; 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") 106@ElementTypesAreNonnullByDefault 107public interface Network<N, E> extends SuccessorsFunction<N>, PredecessorsFunction<N> { 108 // 109 // Network-level accessors 110 // 111 112 /** Returns all nodes in this network, in the order specified by {@link #nodeOrder()}. */ 113 Set<N> nodes(); 114 115 /** Returns all edges in this network, in the order specified by {@link #edgeOrder()}. */ 116 Set<E> edges(); 117 118 /** 119 * Returns a live view of this network as a {@link Graph}. The resulting {@link Graph} will have 120 * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B. 121 * 122 * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be 123 * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node 124 * in the {@link Graph} view may be less than the degree of the same node in this {@link Network}. 125 */ 126 Graph<N> asGraph(); 127 128 // 129 // Network properties 130 // 131 132 /** 133 * Returns true if the edges in this network are directed. Directed edges connect a {@link 134 * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while 135 * undirected edges connect a pair of nodes to each other. 136 */ 137 boolean isDirected(); 138 139 /** 140 * Returns true if this network allows parallel edges. Attempting to add a parallel edge to a 141 * network that does not allow them will throw an {@link IllegalArgumentException}. 142 */ 143 boolean allowsParallelEdges(); 144 145 /** 146 * Returns true if this network allows self-loops (edges that connect a node to itself). 147 * Attempting to add a self-loop to a network that does not allow them will throw an {@link 148 * IllegalArgumentException}. 149 */ 150 boolean allowsSelfLoops(); 151 152 /** Returns the order of iteration for the elements of {@link #nodes()}. */ 153 ElementOrder<N> nodeOrder(); 154 155 /** Returns the order of iteration for the elements of {@link #edges()}. */ 156 ElementOrder<E> edgeOrder(); 157 158 // 159 // Element-level accessors 160 // 161 162 /** 163 * Returns the nodes which have an incident edge in common with {@code node} in this network. 164 * 165 * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}. 166 * 167 * @throws IllegalArgumentException if {@code node} is not an element of this network 168 */ 169 Set<N> adjacentNodes(N node); 170 171 /** 172 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 173 * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge. 174 * 175 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 176 * 177 * @throws IllegalArgumentException if {@code node} is not an element of this network 178 */ 179 @Override 180 Set<N> predecessors(N node); 181 182 /** 183 * Returns all nodes in this network adjacent to {@code node} which can be reached by traversing 184 * {@code node}'s outgoing edges in the direction (if any) of the edge. 185 * 186 * <p>In an undirected network, this is equivalent to {@link #adjacentNodes(Object)}. 187 * 188 * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing 189 * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}. 190 * 191 * @throws IllegalArgumentException if {@code node} is not an element of this network 192 */ 193 @Override 194 Set<N> successors(N node); 195 196 /** 197 * Returns the edges whose {@link #incidentNodes(Object) incident nodes} in this network include 198 * {@code node}. 199 * 200 * <p>This is equal to the union of {@link #inEdges(Object)} and {@link #outEdges(Object)}. 201 * 202 * @throws IllegalArgumentException if {@code node} is not an element of this network 203 */ 204 Set<E> incidentEdges(N node); 205 206 /** 207 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 208 * to end at {@code node}. 209 * 210 * <p>In a directed network, an incoming edge's {@link EndpointPair#target()} equals {@code node}. 211 * 212 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 213 * 214 * @throws IllegalArgumentException if {@code node} is not an element of this network 215 */ 216 Set<E> inEdges(N node); 217 218 /** 219 * Returns all edges in this network which can be traversed in the direction (if any) of the edge 220 * starting from {@code node}. 221 * 222 * <p>In a directed network, an outgoing edge's {@link EndpointPair#source()} equals {@code node}. 223 * 224 * <p>In an undirected network, this is equivalent to {@link #incidentEdges(Object)}. 225 * 226 * @throws IllegalArgumentException if {@code node} is not an element of this network 227 */ 228 Set<E> outEdges(N node); 229 230 /** 231 * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting 232 * self-loops twice (equivalently, the number of times an edge touches {@code node}). 233 * 234 * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}. 235 * 236 * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of 237 * self-loops incident to {@code node}). 238 * 239 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 240 * 241 * @throws IllegalArgumentException if {@code node} is not an element of this network 242 */ 243 int degree(N node); 244 245 /** 246 * Returns the count of {@code node}'s {@link #inEdges(Object) incoming edges} in a directed 247 * network. In an undirected network, returns the {@link #degree(Object)}. 248 * 249 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 250 * 251 * @throws IllegalArgumentException if {@code node} is not an element of this network 252 */ 253 int inDegree(N node); 254 255 /** 256 * Returns the count of {@code node}'s {@link #outEdges(Object) outgoing edges} in a directed 257 * network. In an undirected network, returns the {@link #degree(Object)}. 258 * 259 * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}. 260 * 261 * @throws IllegalArgumentException if {@code node} is not an element of this network 262 */ 263 int outDegree(N node); 264 265 /** 266 * Returns the nodes which are the endpoints of {@code edge} in this network. 267 * 268 * @throws IllegalArgumentException if {@code edge} is not an element of this network 269 */ 270 EndpointPair<N> incidentNodes(E edge); 271 272 /** 273 * Returns the edges which have an {@link #incidentNodes(Object) incident node} in common with 274 * {@code edge}. An edge is not considered adjacent to itself. 275 * 276 * @throws IllegalArgumentException if {@code edge} is not an element of this network 277 */ 278 Set<E> adjacentEdges(E edge); 279 280 /** 281 * Returns the set of edges that each directly connect {@code nodeU} to {@code nodeV}. 282 * 283 * <p>In an undirected network, this is equal to {@code edgesConnecting(nodeV, nodeU)}. 284 * 285 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 286 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 287 * edges}, the resulting set will contain at most one edge (equivalent to {@code 288 * edgeConnecting(nodeU, nodeV).asSet()}). 289 * 290 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 291 * network 292 */ 293 Set<E> edgesConnecting(N nodeU, N nodeV); 294 295 /** 296 * Returns the set of edges that each directly connect {@code endpoints} (in the order, if any, 297 * specified by {@code endpoints}). 298 * 299 * <p>The resulting set of edges will be parallel (i.e. have equal {@link 300 * #incidentNodes(Object)}). If this network does not {@link #allowsParallelEdges() allow parallel 301 * edges}, the resulting set will contain at most one edge (equivalent to {@code 302 * edgeConnecting(endpoints).asSet()}). 303 * 304 * <p>If this network is directed, {@code endpoints} must be ordered. 305 * 306 * @throws IllegalArgumentException if either endpoint is not an element of this network 307 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 308 * @since 27.1 309 */ 310 Set<E> edgesConnecting(EndpointPair<N> endpoints); 311 312 /** 313 * Returns the single edge that directly connects {@code nodeU} to {@code nodeV}, if one is 314 * present, or {@code null} if no such edge exists. 315 * 316 * <p>In an undirected network, this is equal to {@code edgeConnectingOrNull(nodeV, nodeU)}. 317 * 318 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 319 * to {@code nodeV} 320 * @throws IllegalArgumentException if {@code nodeU} or {@code nodeV} is not an element of this 321 * network 322 * @since 23.0 323 */ 324 @CheckForNull 325 E edgeConnectingOrNull(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 null} if no such edge exists. 330 * 331 * <p>If this graph is directed, the endpoints must be ordered. 332 * 333 * @throws IllegalArgumentException if there are multiple parallel edges connecting {@code nodeU} 334 * to {@code nodeV} 335 * @throws IllegalArgumentException if either endpoint is not an element of this network 336 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 337 * @since 27.1 338 */ 339 @CheckForNull 340 E edgeConnectingOrNull(EndpointPair<N> endpoints); 341 342 /** 343 * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is 344 * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}, and to 345 * {@code edgeConnectingOrNull(nodeU, nodeV) != null}. 346 * 347 * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}. 348 * 349 * @since 23.0 350 */ 351 boolean hasEdgeConnecting(N nodeU, N nodeV); 352 353 /** 354 * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if 355 * any, specified by {@code endpoints}). 356 * 357 * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the 358 * endpoints are unordered and the graph is directed; it simply returns {@code false}. This is for 359 * consistency with {@link Graph#hasEdgeConnecting(EndpointPair)} and {@link 360 * ValueGraph#hasEdgeConnecting(EndpointPair)}. 361 * 362 * @since 27.1 363 */ 364 boolean hasEdgeConnecting(EndpointPair<N> endpoints); 365 366 // 367 // Network identity 368 // 369 370 /** 371 * Returns {@code true} iff {@code object} is a {@link Network} that has the same elements and the 372 * same structural relationships as those in this network. 373 * 374 * <p>Thus, two networks A and B are equal if <b>all</b> of the following are true: 375 * 376 * <ul> 377 * <li>A and B have equal {@link #isDirected() directedness}. 378 * <li>A and B have equal {@link #nodes() node sets}. 379 * <li>A and B have equal {@link #edges() edge sets}. 380 * <li>Every edge in A and B connects the same nodes in the same direction (if any). 381 * </ul> 382 * 383 * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. 384 * For example, two networks may be considered equal even if one allows parallel edges and the 385 * other doesn't. Additionally, the order in which nodes or edges are added to the network, and 386 * the order in which they are iterated over, are irrelevant. 387 * 388 * <p>A reference implementation of this is provided by {@link AbstractNetwork#equals(Object)}. 389 */ 390 @Override 391 boolean equals(@CheckForNull Object object); 392 393 /** 394 * Returns the hash code for this network. The hash code of a network is defined as the hash code 395 * of a map from each of its {@link #edges() edges} to their {@link #incidentNodes(Object) 396 * incident nodes}. 397 * 398 * <p>A reference implementation of this is provided by {@link AbstractNetwork#hashCode()}. 399 */ 400 @Override 401 int hashCode(); 402}