1 /*
2 * Copyright (C) 2014 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.graph;
18
19 import static com.google.common.base.Preconditions.checkNotNull;
20
21 import com.google.common.annotations.Beta;
22 import com.google.common.base.Function;
23 import com.google.common.collect.ImmutableMap;
24 import com.google.common.collect.Maps;
25 import com.google.errorprone.annotations.CanIgnoreReturnValue;
26 import com.google.errorprone.annotations.Immutable;
27 import java.util.Map;
28
29 /**
30 * A {@link Network} whose elements and structural relationships will never change. Instances of
31 * this class may be obtained with {@link #copyOf(Network)}.
32 *
33 * <p>See the Guava User's Guide's <a
34 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
35 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
36 * provided by this class.
37 *
38 * @author James Sexton
39 * @author Joshua O'Madadhain
40 * @author Omar Darwish
41 * @author Jens Nyman
42 * @param <N> Node parameter type
43 * @param <E> Edge parameter type
44 * @since 20.0
45 */
46 @Beta
47 @Immutable(containerOf = {"N", "E"})
48 @SuppressWarnings("Immutable") // Extends StandardNetwork but uses ImmutableMaps.
49 @ElementTypesAreNonnullByDefault
50 public final class ImmutableNetwork<N, E> extends StandardNetwork<N, E> {
51
52 private ImmutableNetwork(Network<N, E> network) {
53 super(
54 NetworkBuilder.from(network), getNodeConnections(network), getEdgeToReferenceNode(network));
55 }
56
57 /** Returns an immutable copy of {@code network}. */
58 public static <N, E> ImmutableNetwork<N, E> copyOf(Network<N, E> network) {
59 return (network instanceof ImmutableNetwork)
60 ? (ImmutableNetwork<N, E>) network
61 : new ImmutableNetwork<N, E>(network);
62 }
63
64 /**
65 * Simply returns its argument.
66 *
67 * @deprecated no need to use this
68 */
69 @Deprecated
70 public static <N, E> ImmutableNetwork<N, E> copyOf(ImmutableNetwork<N, E> network) {
71 return checkNotNull(network);
72 }
73
74 @Override
75 public ImmutableGraph<N> asGraph() {
76 return new ImmutableGraph<N>(super.asGraph()); // safe because the view is effectively immutable
77 }
78
79 private static <N, E> Map<N, NetworkConnections<N, E>> getNodeConnections(Network<N, E> network) {
80 // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
81 // whatever ordering the network's nodes do, so ImmutableSortedMap is unnecessary even if the
82 // input nodes are sorted.
83 ImmutableMap.Builder<N, NetworkConnections<N, E>> nodeConnections = ImmutableMap.builder();
84 for (N node : network.nodes()) {
85 nodeConnections.put(node, connectionsOf(network, node));
86 }
87 return nodeConnections.build();
88 }
89
90 private static <N, E> Map<E, N> getEdgeToReferenceNode(Network<N, E> network) {
91 // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
92 // whatever ordering the network's edges do, so ImmutableSortedMap is unnecessary even if the
93 // input edges are sorted.
94 ImmutableMap.Builder<E, N> edgeToReferenceNode = ImmutableMap.builder();
95 for (E edge : network.edges()) {
96 edgeToReferenceNode.put(edge, network.incidentNodes(edge).nodeU());
97 }
98 return edgeToReferenceNode.build();
99 }
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(final Network<N, E> network) {
119 return new Function<E, N>() {
120 @Override
121 public N apply(E edge) {
122 return network.incidentNodes(edge).source();
123 }
124 };
125 }
126
127 private static <N, E> Function<E, N> targetNodeFn(final Network<N, E> network) {
128 return new Function<E, N>() {
129 @Override
130 public N apply(E edge) {
131 return network.incidentNodes(edge).target();
132 }
133 };
134 }
135
136 private static <N, E> Function<E, N> adjacentNodeFn(final Network<N, E> network, final N node) {
137 return new Function<E, N>() {
138 @Override
139 public N apply(E edge) {
140 return network.incidentNodes(edge).adjacentNode(node);
141 }
142 };
143 }
144
145 /**
146 * A builder for creating {@link ImmutableNetwork} instances, especially {@code static final}
147 * networks. Example:
148 *
149 * <pre>{@code
150 * static final ImmutableNetwork<City, Train> TRAIN_NETWORK =
151 * NetworkBuilder.undirected()
152 * .allowsParallelEdges(true)
153 * .<City, Train>immutable()
154 * .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
155 * .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))
156 * .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333"))
157 * .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444"))
158 * .addNode(REYKJAVIK)
159 * .build();
160 * }</pre>
161 *
162 * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
163 * multiple networks in series. Each new network contains all the elements of the ones created
164 * before it.
165 *
166 * @since 28.0
167 */
168 public static class Builder<N, E> {
169
170 private final MutableNetwork<N, E> mutableNetwork;
171
172 Builder(NetworkBuilder<N, E> networkBuilder) {
173 this.mutableNetwork = networkBuilder.build();
174 }
175
176 /**
177 * Adds {@code node} if it is not already present.
178 *
179 * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
180 *
181 * @return this {@code Builder} object
182 */
183 @CanIgnoreReturnValue
184 public ImmutableNetwork.Builder<N, E> addNode(N node) {
185 mutableNetwork.addNode(node);
186 return this;
187 }
188
189 /**
190 * Adds {@code edge} connecting {@code nodeU} to {@code nodeV}.
191 *
192 * <p>If the network is directed, {@code edge} will be directed in this network; otherwise, it
193 * will be undirected.
194 *
195 * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It
196 * must also be non-null.
197 *
198 * <p>If {@code nodeU} and {@code nodeV} are not already present in this network, this method
199 * will silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the network.
200 *
201 * <p>If {@code edge} already connects {@code nodeU} to {@code nodeV} (in the specified order if
202 * this network {@link #isDirected()}, else in any order), then this method will have no effect.
203 *
204 * @return this {@code Builder} object
205 * @throws IllegalArgumentException if {@code edge} already exists in the network and does not
206 * connect {@code nodeU} to {@code nodeV}
207 * @throws IllegalArgumentException if the introduction of the edge would violate {@link
208 * #allowsParallelEdges()} or {@link #allowsSelfLoops()}
209 */
210 @CanIgnoreReturnValue
211 public ImmutableNetwork.Builder<N, E> addEdge(N nodeU, N nodeV, E edge) {
212 mutableNetwork.addEdge(nodeU, nodeV, edge);
213 return this;
214 }
215
216 /**
217 * Adds {@code edge} connecting {@code endpoints}. In an undirected network, {@code edge} will
218 * also connect {@code nodeV} to {@code nodeU}.
219 *
220 * <p>If this network is directed, {@code edge} will be directed in this network; if it is
221 * undirected, {@code edge} will be undirected in this network.
222 *
223 * <p>If this network is directed, {@code endpoints} must be ordered.
224 *
225 * <p><b>{@code edge} must be unique to this network</b>, just as a {@code Map} key must be. It
226 * must also be non-null.
227 *
228 * <p>If either or both endpoints are not already present in this network, this method will
229 * silently {@link #addNode(Object) add} each missing endpoint to the network.
230 *
231 * <p>If {@code edge} already connects an endpoint pair equal to {@code endpoints}, then this
232 * method will have no effect.
233 *
234 * @return this {@code Builder} object
235 * @throws IllegalArgumentException if {@code edge} already exists in the network and connects
236 * some other endpoint pair that is not equal to {@code endpoints}
237 * @throws IllegalArgumentException if the introduction of the edge would violate {@link
238 * #allowsParallelEdges()} or {@link #allowsSelfLoops()}
239 * @throws IllegalArgumentException if the endpoints are unordered and the network is directed
240 */
241 @CanIgnoreReturnValue
242 public ImmutableNetwork.Builder<N, E> addEdge(EndpointPair<N> endpoints, E edge) {
243 mutableNetwork.addEdge(endpoints, edge);
244 return this;
245 }
246
247 /**
248 * Returns a newly-created {@code ImmutableNetwork} based on the contents of this {@code
249 * Builder}.
250 */
251 public ImmutableNetwork<N, E> build() {
252 return ImmutableNetwork.copyOf(mutableNetwork);
253 }
254 }
255 }