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 static com.google.common.base.Preconditions.checkNotNull; 020 021import com.google.common.annotations.Beta; 022import com.google.common.base.Function; 023import com.google.common.collect.ImmutableMap; 024import com.google.common.collect.Maps; 025import com.google.errorprone.annotations.CanIgnoreReturnValue; 026import com.google.errorprone.annotations.Immutable; 027import java.util.Map; 028 029/** 030 * A {@link Network} whose elements and structural relationships will never change. Instances of 031 * this class may be obtained with {@link #copyOf(Network)}. 032 * 033 * <p>See the Guava User's Guide's <a 034 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion 035 * of the {@code Immutable*} types</a> for more information on the properties and guarantees 036 * provided by this class. 037 * 038 * @author James Sexton 039 * @author Joshua O'Madadhain 040 * @author Omar Darwish 041 * @author Jens Nyman 042 * @param <N> Node parameter type 043 * @param <E> Edge parameter type 044 * @since 20.0 045 */ 046@Beta 047@Immutable(containerOf = {"N", "E"}) 048@SuppressWarnings("Immutable") // Extends StandardNetwork but uses ImmutableMaps. 049@ElementTypesAreNonnullByDefault 050public final class ImmutableNetwork<N, E> extends StandardNetwork<N, E> { 051 052 private ImmutableNetwork(Network<N, E> network) { 053 super( 054 NetworkBuilder.from(network), getNodeConnections(network), getEdgeToReferenceNode(network)); 055 } 056 057 /** Returns an immutable copy of {@code network}. */ 058 public static <N, E> ImmutableNetwork<N, E> copyOf(Network<N, E> network) { 059 return (network instanceof ImmutableNetwork) 060 ? (ImmutableNetwork<N, E>) network 061 : new ImmutableNetwork<N, E>(network); 062 } 063 064 /** 065 * Simply returns its argument. 066 * 067 * @deprecated no need to use this 068 */ 069 @Deprecated 070 public static <N, E> ImmutableNetwork<N, E> copyOf(ImmutableNetwork<N, E> network) { 071 return checkNotNull(network); 072 } 073 074 @Override 075 public ImmutableGraph<N> asGraph() { 076 return new ImmutableGraph<>(super.asGraph()); // safe because the view is effectively immutable 077 } 078 079 private static <N, E> Map<N, NetworkConnections<N, E>> getNodeConnections(Network<N, E> network) { 080 // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have 081 // whatever ordering the network's nodes do, so ImmutableSortedMap is unnecessary even if the 082 // input nodes are sorted. 083 ImmutableMap.Builder<N, NetworkConnections<N, E>> nodeConnections = ImmutableMap.builder(); 084 for (N node : network.nodes()) { 085 nodeConnections.put(node, connectionsOf(network, node)); 086 } 087 return nodeConnections.buildOrThrow(); 088 } 089 090 private static <N, E> Map<E, N> getEdgeToReferenceNode(Network<N, E> network) { 091 // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have 092 // whatever ordering the network's edges do, so ImmutableSortedMap is unnecessary even if the 093 // input edges are sorted. 094 ImmutableMap.Builder<E, N> edgeToReferenceNode = ImmutableMap.builder(); 095 for (E edge : network.edges()) { 096 edgeToReferenceNode.put(edge, network.incidentNodes(edge).nodeU()); 097 } 098 return edgeToReferenceNode.buildOrThrow(); 099 } 100 101 private static <N, E> NetworkConnections<N, E> connectionsOf(Network<N, E> network, N node) { 102 if (network.isDirected()) { 103 Map<E, N> inEdgeMap = Maps.asMap(network.inEdges(node), sourceNodeFn(network)); 104 Map<E, N> outEdgeMap = Maps.asMap(network.outEdges(node), targetNodeFn(network)); 105 int selfLoopCount = network.edgesConnecting(node, node).size(); 106 return network.allowsParallelEdges() 107 ? DirectedMultiNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount) 108 : DirectedNetworkConnections.ofImmutable(inEdgeMap, outEdgeMap, selfLoopCount); 109 } else { 110 Map<E, N> incidentEdgeMap = 111 Maps.asMap(network.incidentEdges(node), adjacentNodeFn(network, node)); 112 return network.allowsParallelEdges() 113 ? UndirectedMultiNetworkConnections.ofImmutable(incidentEdgeMap) 114 : UndirectedNetworkConnections.ofImmutable(incidentEdgeMap); 115 } 116 } 117 118 private static <N, E> Function<E, N> sourceNodeFn(Network<N, E> network) { 119 return (E edge) -> network.incidentNodes(edge).source(); 120 } 121 122 private static <N, E> Function<E, N> targetNodeFn(Network<N, E> network) { 123 return (E edge) -> network.incidentNodes(edge).target(); 124 } 125 126 private static <N, E> Function<E, N> adjacentNodeFn(Network<N, E> network, N node) { 127 return (E edge) -> network.incidentNodes(edge).adjacentNode(node); 128 } 129 130 /** 131 * A builder for creating {@link ImmutableNetwork} instances, especially {@code static final} 132 * networks. Example: 133 * 134 * <pre>{@code 135 * static final ImmutableNetwork<City, Train> TRAIN_NETWORK = 136 * NetworkBuilder.undirected() 137 * .allowsParallelEdges(true) 138 * .<City, Train>immutable() 139 * .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111")) 140 * .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222")) 141 * .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333")) 142 * .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444")) 143 * .addNode(REYKJAVIK) 144 * .build(); 145 * }</pre> 146 * 147 * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build 148 * multiple networks in series. Each new network contains all the elements of the ones created 149 * before it. 150 * 151 * @since 28.0 152 */ 153 public static class Builder<N, E> { 154 155 private final MutableNetwork<N, E> mutableNetwork; 156 157 Builder(NetworkBuilder<N, E> networkBuilder) { 158 this.mutableNetwork = networkBuilder.build(); 159 } 160 161 /** 162 * Adds {@code node} if it is not already present. 163 * 164 * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null. 165 * 166 * @return this {@code Builder} object 167 */ 168 @CanIgnoreReturnValue 169 public ImmutableNetwork.Builder<N, E> addNode(N node) { 170 mutableNetwork.addNode(node); 171 return this; 172 } 173 174 /** 175 * Adds {@code edge} connecting {@code nodeU} to {@code nodeV}. 176 * 177 * <p>If the network is directed, {@code edge} will be directed in this network; otherwise, it 178 * will be undirected. 179 * 180 * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It 181 * must also be non-null. 182 * 183 * <p>If {@code nodeU} and {@code nodeV} are not already present in this network, this method 184 * will silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the network. 185 * 186 * <p>If {@code edge} already connects {@code nodeU} to {@code nodeV} (in the specified order if 187 * this network {@link #isDirected()}, else in any order), then this method will have no effect. 188 * 189 * @return this {@code Builder} object 190 * @throws IllegalArgumentException if {@code edge} already exists in the network and does not 191 * connect {@code nodeU} to {@code nodeV} 192 * @throws IllegalArgumentException if the introduction of the edge would violate {@link 193 * #allowsParallelEdges()} or {@link #allowsSelfLoops()} 194 */ 195 @CanIgnoreReturnValue 196 public ImmutableNetwork.Builder<N, E> addEdge(N nodeU, N nodeV, E edge) { 197 mutableNetwork.addEdge(nodeU, nodeV, edge); 198 return this; 199 } 200 201 /** 202 * Adds {@code edge} connecting {@code endpoints}. In an undirected network, {@code edge} will 203 * also connect {@code nodeV} to {@code nodeU}. 204 * 205 * <p>If this network is directed, {@code edge} will be directed in this network; if it is 206 * undirected, {@code edge} will be undirected in this network. 207 * 208 * <p>If this network is directed, {@code endpoints} must be ordered. 209 * 210 * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It 211 * must also be non-null. 212 * 213 * <p>If either or both endpoints are not already present in this network, this method will 214 * silently {@link #addNode(Object) add} each missing endpoint to the network. 215 * 216 * <p>If {@code edge} already connects an endpoint pair equal to {@code endpoints}, then this 217 * method will have no effect. 218 * 219 * @return this {@code Builder} object 220 * @throws IllegalArgumentException if {@code edge} already exists in the network and connects 221 * some other endpoint pair that is not equal to {@code endpoints} 222 * @throws IllegalArgumentException if the introduction of the edge would violate {@link 223 * #allowsParallelEdges()} or {@link #allowsSelfLoops()} 224 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed 225 */ 226 @CanIgnoreReturnValue 227 public ImmutableNetwork.Builder<N, E> addEdge(EndpointPair<N> endpoints, E edge) { 228 mutableNetwork.addEdge(endpoints, edge); 229 return this; 230 } 231 232 /** 233 * Returns a newly-created {@code ImmutableNetwork} based on the contents of this {@code 234 * Builder}. 235 */ 236 public ImmutableNetwork<N, E> build() { 237 return ImmutableNetwork.copyOf(mutableNetwork); 238 } 239 } 240}