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"}) 048@ElementTypesAreNonnullByDefault 049public class ImmutableGraph<N> extends ForwardingGraph<N> { 050 @SuppressWarnings("Immutable") // The backing graph must be immutable. 051 private final BaseGraph<N> backingGraph; 052 053 ImmutableGraph(BaseGraph<N> backingGraph) { 054 this.backingGraph = backingGraph; 055 } 056 057 /** Returns an immutable copy of {@code graph}. */ 058 public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) { 059 return (graph instanceof ImmutableGraph) 060 ? (ImmutableGraph<N>) graph 061 : new ImmutableGraph<N>( 062 new StandardValueGraph<N, Presence>( 063 GraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size())); 064 } 065 066 /** 067 * Simply returns its argument. 068 * 069 * @deprecated no need to use this 070 */ 071 @Deprecated 072 public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) { 073 return checkNotNull(graph); 074 } 075 076 @Override 077 public ElementOrder<N> incidentEdgeOrder() { 078 return ElementOrder.stable(); 079 } 080 081 private static <N> ImmutableMap<N, GraphConnections<N, Presence>> getNodeConnections( 082 Graph<N> graph) { 083 // ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have 084 // whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the 085 // input nodes are sorted. 086 ImmutableMap.Builder<N, GraphConnections<N, Presence>> nodeConnections = ImmutableMap.builder(); 087 for (N node : graph.nodes()) { 088 nodeConnections.put(node, connectionsOf(graph, node)); 089 } 090 return nodeConnections.buildOrThrow(); 091 } 092 093 @SuppressWarnings("unchecked") 094 private static <N> GraphConnections<N, Presence> connectionsOf(Graph<N> graph, N node) { 095 Function<N, Presence> edgeValueFn = 096 (Function<N, Presence>) Functions.constant(Presence.EDGE_EXISTS); 097 return graph.isDirected() 098 ? DirectedGraphConnections.ofImmutable(node, graph.incidentEdges(node), edgeValueFn) 099 : UndirectedGraphConnections.ofImmutable( 100 Maps.asMap(graph.adjacentNodes(node), edgeValueFn)); 101 } 102 103 @Override 104 BaseGraph<N> delegate() { 105 return backingGraph; 106 } 107 108 /** 109 * A builder for creating {@link ImmutableGraph} instances, especially {@code static final} 110 * graphs. Example: 111 * 112 * <pre>{@code 113 * static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH = 114 * GraphBuilder.undirected() 115 * .<Country>immutable() 116 * .putEdge(FRANCE, GERMANY) 117 * .putEdge(FRANCE, BELGIUM) 118 * .putEdge(GERMANY, BELGIUM) 119 * .addNode(ICELAND) 120 * .build(); 121 * }</pre> 122 * 123 * <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build 124 * multiple graphs in series. Each new graph contains all the elements of the ones created before 125 * it. 126 * 127 * @since 28.0 128 */ 129 public static class Builder<N> { 130 131 private final MutableGraph<N> mutableGraph; 132 133 Builder(GraphBuilder<N> graphBuilder) { 134 // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to 135 // modify this builder, so we make a copy instead. 136 this.mutableGraph = graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build(); 137 } 138 139 /** 140 * Adds {@code node} if it is not already present. 141 * 142 * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null. 143 * 144 * @return this {@code Builder} object 145 */ 146 @CanIgnoreReturnValue 147 public Builder<N> addNode(N node) { 148 mutableGraph.addNode(node); 149 return this; 150 } 151 152 /** 153 * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present. 154 * 155 * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be 156 * undirected. 157 * 158 * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will 159 * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph. 160 * 161 * @return this {@code Builder} object 162 * @throws IllegalArgumentException if the introduction of the edge would violate {@link 163 * #allowsSelfLoops()} 164 */ 165 @CanIgnoreReturnValue 166 public Builder<N> putEdge(N nodeU, N nodeV) { 167 mutableGraph.putEdge(nodeU, nodeV); 168 return this; 169 } 170 171 /** 172 * Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code 173 * endpoints}) if one is not already present. 174 * 175 * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be 176 * directed; if it is undirected, the added edge will be undirected. 177 * 178 * <p>If this graph is directed, {@code endpoints} must be ordered. 179 * 180 * <p>If either or both endpoints are not already present in this graph, this method will 181 * silently {@link #addNode(Object) add} each missing endpoint to the graph. 182 * 183 * @return this {@code Builder} object 184 * @throws IllegalArgumentException if the introduction of the edge would violate {@link 185 * #allowsSelfLoops()} 186 * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed 187 */ 188 @CanIgnoreReturnValue 189 public Builder<N> putEdge(EndpointPair<N> endpoints) { 190 mutableGraph.putEdge(endpoints); 191 return this; 192 } 193 194 /** 195 * Returns a newly-created {@code ImmutableGraph} based on the contents of this {@code Builder}. 196 */ 197 public ImmutableGraph<N> build() { 198 return ImmutableGraph.copyOf(mutableGraph); 199 } 200 } 201}