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.base.Functions;
024import com.google.common.collect.ImmutableMap;
025import com.google.common.collect.Maps;
026import com.google.common.graph.GraphConstants.Presence;
027import com.google.errorprone.annotations.CanIgnoreReturnValue;
028import com.google.errorprone.annotations.Immutable;
029
030/**
031 * A {@link Graph} whose elements and structural relationships will never change. Instances of this
032 * class may be obtained with {@link #copyOf(Graph)}.
033 *
034 * <p>See the Guava User's Guide's <a
035 * href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
036 * of the {@code Immutable*} types</a> for more information on the properties and guarantees
037 * provided by this class.
038 *
039 * @author James Sexton
040 * @author Joshua O'Madadhain
041 * @author Omar Darwish
042 * @author Jens Nyman
043 * @param <N> Node parameter type
044 * @since 20.0
045 */
046@Beta
047@Immutable(containerOf = {"N"})
048public class ImmutableGraph<N> extends ForwardingGraph<N> {
049  @SuppressWarnings("Immutable") // The backing graph must be immutable.
050  private final BaseGraph<N> backingGraph;
051
052  ImmutableGraph(BaseGraph<N> backingGraph) {
053    this.backingGraph = backingGraph;
054  }
055
056  /** Returns an immutable copy of {@code graph}. */
057  public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) {
058    return (graph instanceof ImmutableGraph)
059        ? (ImmutableGraph<N>) graph
060        : new ImmutableGraph<N>(
061            new ConfigurableValueGraph<N, Presence>(
062                GraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size()));
063  }
064
065  /**
066   * Simply returns its argument.
067   *
068   * @deprecated no need to use this
069   */
070  @Deprecated
071  public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) {
072    return checkNotNull(graph);
073  }
074
075  private static <N> ImmutableMap<N, GraphConnections<N, Presence>> getNodeConnections(
076      Graph<N> graph) {
077    // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
078    // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
079    // input nodes are sorted.
080    ImmutableMap.Builder<N, GraphConnections<N, Presence>> nodeConnections = ImmutableMap.builder();
081    for (N node : graph.nodes()) {
082      nodeConnections.put(node, connectionsOf(graph, node));
083    }
084    return nodeConnections.build();
085  }
086
087  private static <N> GraphConnections<N, Presence> connectionsOf(Graph<N> graph, N node) {
088    Function<Object, Presence> edgeValueFn = Functions.constant(Presence.EDGE_EXISTS);
089    return graph.isDirected()
090        ? DirectedGraphConnections.ofImmutable(
091            graph.predecessors(node), Maps.asMap(graph.successors(node), edgeValueFn))
092        : UndirectedGraphConnections.ofImmutable(
093            Maps.asMap(graph.adjacentNodes(node), edgeValueFn));
094  }
095
096  @Override
097  protected BaseGraph<N> delegate() {
098    return backingGraph;
099  }
100
101  /**
102   * A builder for creating {@link ImmutableGraph} instances, especially {@code static final}
103   * graphs. Example:
104   *
105   * <pre>{@code
106   * static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH =
107   *     GraphBuilder.undirected()
108   *         .<Country>immutable()
109   *         .putEdge(FRANCE, GERMANY)
110   *         .putEdge(FRANCE, BELGIUM)
111   *         .putEdge(GERMANY, BELGIUM)
112   *         .addNode(ICELAND)
113   *         .build();
114   * }</pre>
115   *
116   * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
117   * multiple graphs in series. Each new graph contains all the elements of the ones created before
118   * it.
119   *
120   * @since 28.0
121   */
122  public static class Builder<N> {
123
124    private final MutableGraph<N> mutableGraph;
125
126    Builder(GraphBuilder<N> graphBuilder) {
127      this.mutableGraph = graphBuilder.build();
128    }
129
130    /**
131     * Adds {@code node} if it is not already present.
132     *
133     * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
134     *
135     * @return this {@code Builder} object
136     */
137    @CanIgnoreReturnValue
138    public Builder<N> addNode(N node) {
139      mutableGraph.addNode(node);
140      return this;
141    }
142
143    /**
144     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present.
145     *
146     * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
147     * undirected.
148     *
149     * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
150     * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
151     *
152     * @return this {@code Builder} object
153     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
154     *     #allowsSelfLoops()}
155     */
156    @CanIgnoreReturnValue
157    public Builder<N> putEdge(N nodeU, N nodeV) {
158      mutableGraph.putEdge(nodeU, nodeV);
159      return this;
160    }
161
162    /**
163     * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
164     * endpoints}) if one is not already present.
165     *
166     * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
167     * directed; if it is undirected, the added edge will be undirected.
168     *
169     * <p>If this graph is directed, {@code endpoints} must be ordered.
170     *
171     * <p>If either or both endpoints are not already present in this graph, this method will
172     * silently {@link #addNode(Object) add} each missing endpoint to the graph.
173     *
174     * @return this {@code Builder} object
175     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
176     *     #allowsSelfLoops()}
177     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
178     */
179    @CanIgnoreReturnValue
180    public Builder<N> putEdge(EndpointPair<N> endpoints) {
181      mutableGraph.putEdge(endpoints);
182      return this;
183    }
184
185    /**
186     * Returns a newly-created {@code ImmutableGraph} based on the contents of this {@code Builder}.
187     */
188    public ImmutableGraph<N> build() {
189      return ImmutableGraph.copyOf(mutableGraph);
190    }
191  }
192}