ImmutableGraph.java
/*
* Copyright (C) 2014 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.graph;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.base.Function;
import com.google.common.base.Functions;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Maps;
import com.google.common.graph.GraphConstants.Presence;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.Immutable;
/**
* A {@link Graph} whose elements and structural relationships will never change. Instances of this
* class may be obtained with {@link #copyOf(Graph)}.
*
* <p>See the Guava User's Guide's <a
* href="https://github.com/google/guava/wiki/GraphsExplained#immutable-implementations">discussion
* of the {@code Immutable*} types</a> for more information on the properties and guarantees
* provided by this class.
*
* @author James Sexton
* @author Joshua O'Madadhain
* @author Omar Darwish
* @author Jens Nyman
* @param <N> Node parameter type
* @since 20.0
*/
@Beta
@Immutable(containerOf = {"N"})
@ElementTypesAreNonnullByDefault
public class ImmutableGraph<N> extends ForwardingGraph<N> {
@SuppressWarnings("Immutable") // The backing graph must be immutable.
private final BaseGraph<N> backingGraph;
ImmutableGraph(BaseGraph<N> backingGraph) {
this.backingGraph = backingGraph;
}
/** Returns an immutable copy of {@code graph}. */
public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) {
return (graph instanceof ImmutableGraph)
? (ImmutableGraph<N>) graph
: new ImmutableGraph<N>(
new StandardValueGraph<N, Presence>(
GraphBuilder.from(graph), getNodeConnections(graph), graph.edges().size()));
}
/**
* Simply returns its argument.
*
* @deprecated no need to use this
*/
@Deprecated
public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) {
return checkNotNull(graph);
}
@Override
public ElementOrder<N> incidentEdgeOrder() {
return ElementOrder.stable();
}
private static <N> ImmutableMap<N, GraphConnections<N, Presence>> getNodeConnections(
Graph<N> graph) {
// ImmutableMap.Builder maintains the order of the elements as inserted, so the map will have
// whatever ordering the graph's nodes do, so ImmutableSortedMap is unnecessary even if the
// input nodes are sorted.
ImmutableMap.Builder<N, GraphConnections<N, Presence>> nodeConnections = ImmutableMap.builder();
for (N node : graph.nodes()) {
nodeConnections.put(node, connectionsOf(graph, node));
}
return nodeConnections.build();
}
@SuppressWarnings("unchecked")
private static <N> GraphConnections<N, Presence> connectionsOf(Graph<N> graph, N node) {
Function<N, Presence> edgeValueFn =
(Function<N, Presence>) Functions.constant(Presence.EDGE_EXISTS);
return graph.isDirected()
? DirectedGraphConnections.ofImmutable(node, graph.incidentEdges(node), edgeValueFn)
: UndirectedGraphConnections.ofImmutable(
Maps.asMap(graph.adjacentNodes(node), edgeValueFn));
}
@Override
BaseGraph<N> delegate() {
return backingGraph;
}
/**
* A builder for creating {@link ImmutableGraph} instances, especially {@code static final}
* graphs. Example:
*
* <pre>{@code
* static final ImmutableGraph<Country> COUNTRY_ADJACENCY_GRAPH =
* GraphBuilder.undirected()
* .<Country>immutable()
* .putEdge(FRANCE, GERMANY)
* .putEdge(FRANCE, BELGIUM)
* .putEdge(GERMANY, BELGIUM)
* .addNode(ICELAND)
* .build();
* }</pre>
*
* <p>Builder instances can be reused; it is safe to call {@link #build} multiple times to build
* multiple graphs in series. Each new graph contains all the elements of the ones created before
* it.
*
* @since 28.0
*/
public static class Builder<N> {
private final MutableGraph<N> mutableGraph;
Builder(GraphBuilder<N> graphBuilder) {
// The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
// modify this builder, so we make a copy instead.
this.mutableGraph = graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
}
/**
* Adds {@code node} if it is not already present.
*
* <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
*
* @return this {@code Builder} object
*/
@CanIgnoreReturnValue
public Builder<N> addNode(N node) {
mutableGraph.addNode(node);
return this;
}
/**
* Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present.
*
* <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
* undirected.
*
* <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
* silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
*
* @return this {@code Builder} object
* @throws IllegalArgumentException if the introduction of the edge would violate {@link
* #allowsSelfLoops()}
*/
@CanIgnoreReturnValue
public Builder<N> putEdge(N nodeU, N nodeV) {
mutableGraph.putEdge(nodeU, nodeV);
return this;
}
/**
* Adds an edge connecting {@code endpoints} (in the order, if any, specified by {@code
* endpoints}) if one is not already present.
*
* <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
* directed; if it is undirected, the added edge will be undirected.
*
* <p>If this graph is directed, {@code endpoints} must be ordered.
*
* <p>If either or both endpoints are not already present in this graph, this method will
* silently {@link #addNode(Object) add} each missing endpoint to the graph.
*
* @return this {@code Builder} object
* @throws IllegalArgumentException if the introduction of the edge would violate {@link
* #allowsSelfLoops()}
* @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
*/
@CanIgnoreReturnValue
public Builder<N> putEdge(EndpointPair<N> endpoints) {
mutableGraph.putEdge(endpoints);
return this;
}
/**
* Returns a newly-created {@code ImmutableGraph} based on the contents of this {@code Builder}.
*/
public ImmutableGraph<N> build() {
return ImmutableGraph.copyOf(mutableGraph);
}
}
}