com.google.common.graph.ImmutableGraph.java Source code

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Here is the source code for com.google.common.graph.ImmutableGraph.java

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/*
 * 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.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.collect.ImmutableMap;
import com.google.common.graph.DirectedNodeAdjacencies.Adjacency;

import java.util.Set;

/**
 * A {@link Graph} whose relationships are constant. Instances of this class may be obtained
 * with {@link #copyOf(Graph)}.
 *
 * <p>The time complexity of {@code edgesConnecting(node1, node2)} is O(min(outD_node1, inD_node2)).
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @author Omar Darwish
 * @param <N> Node parameter type
 */
public final class ImmutableGraph<N> extends AbstractConfigurableGraph<N> {

    private ImmutableGraph(Graph<N> graph) {
        super(GraphBuilder.from(graph), getNodeConnections(graph));
    }

    /**
     * Returns an immutable copy of {@code graph}.
     */
    public static <N> ImmutableGraph<N> copyOf(Graph<N> graph) {
        // TODO(b/28087289): we can remove this restriction when Graph supports parallel edges
        checkArgument(!(graph instanceof Network), "Input must not implement common.graph.Network");
        return (graph instanceof ImmutableGraph) ? (ImmutableGraph<N>) graph : new ImmutableGraph<N>(graph);
    }

    /**
     * Simply returns its argument.
     *
     * @deprecated no need to use this
     */
    @Deprecated
    public static <N> ImmutableGraph<N> copyOf(ImmutableGraph<N> graph) {
        return checkNotNull(graph);
    }

    private static <N> ImmutableMap<N, NodeAdjacencies<N>> getNodeConnections(Graph<N> graph) {
        ImmutableMap.Builder<N, NodeAdjacencies<N>> nodeConnections = ImmutableMap.builder();
        for (N node : graph.nodes()) {
            nodeConnections.put(node, nodeConnectionsOf(graph, node));
        }
        return nodeConnections.build();
    }

    private static <N> NodeAdjacencies<N> nodeConnectionsOf(Graph<N> graph, N node) {
        return graph.isDirected()
                ? DirectedNodeAdjacencies.ofImmutable(createAdjacencyMap(graph, node),
                        graph.predecessors(node).size(), graph.successors(node).size())
                : UndirectedNodeAdjacencies.ofImmutable(graph.adjacentNodes(node));
    }

    private static <N> ImmutableMap<N, Adjacency> createAdjacencyMap(Graph<N> graph, N node) {
        Set<N> predecessors = graph.predecessors(node);
        Set<N> successors = graph.successors(node);
        ImmutableMap.Builder<N, Adjacency> nodeAdjacencies = ImmutableMap.builder();
        for (N adjacentNode : graph.adjacentNodes(node)) {
            nodeAdjacencies.put(adjacentNode,
                    getAdjacency(predecessors.contains(adjacentNode), successors.contains(adjacentNode)));
        }
        return nodeAdjacencies.build();
    }

    private static Adjacency getAdjacency(boolean isPredecessor, boolean isSuccesor) {
        if (isPredecessor && isSuccesor) {
            return Adjacency.BOTH;
        } else if (isPredecessor) {
            return Adjacency.PRED;
        } else if (isSuccesor) {
            return Adjacency.SUCC;
        } else {
            throw new IllegalStateException();
        }
    }
}