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

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

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/*
 * Copyright (C) 2016 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 com.google.common.annotations.Beta;
import com.google.common.base.Optional;

import java.util.Comparator;

/**
 * A builder for constructing instances of {@link Graph} with user-defined properties.
 *
 * <p>A graph built by this class will have the following properties by default:
 * <ul>
 * <li>does not allow parallel edges
 * <li>allows self-loops
 * </ul>
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @since 20.0
 */
// TODO(b/24620028): Add support for sorted nodes/edges. Use the same pattern as CacheBuilder
// to narrow the generic type when Comparators are provided.
@Beta
public final class GraphBuilder<N> {
    final boolean directed;
    boolean allowsSelfLoops = true;
    Comparator<N> nodeComparator = null;
    Optional<Integer> expectedNodeCount = Optional.absent();

    /**
     * Creates a new instance with the specified edge directionality.
     *
     * @param directed if true, creates an instance for graphs whose edges are each directed;
     *      if false, creates an instance for graphs whose edges are each undirected.
     */
    private GraphBuilder(boolean directed) {
        this.directed = directed;
    }

    /**
     * Returns a {@link GraphBuilder} for building directed graphs.
     */
    public static GraphBuilder<Object> directed() {
        return new GraphBuilder<Object>(true);
    }

    /**
     * Returns a {@link GraphBuilder} for building undirected graphs.
     */
    public static GraphBuilder<Object> undirected() {
        return new GraphBuilder<Object>(false);
    }

    /**
     * Returns a {@link GraphBuilder} initialized with all properties queryable from {@code graph}.
     *
     * <p>The "queryable" properties are those that are exposed through the {@link Graph} interface,
     * such as {@link Graph#isDirected()}. Other properties, such as {@link #expectedNodeCount(int)},
     * are not set in the new builder.
     */
    public static <N> GraphBuilder<N> from(Graph<N> graph) {
        // TODO(b/28087289): add allowsParallelEdges() once we support them
        return new GraphBuilder<N>(graph.isDirected()).allowsSelfLoops(graph.allowsSelfLoops());
    }

    /**
     * Specifies whether the graph will allow self-loops (edges that connect a node to itself).
     * Attempting to add a self-loop to a graph that does not allow them will throw an
     * {@link UnsupportedOperationException}.
     */
    public GraphBuilder<N> allowsSelfLoops(boolean allowsSelfLoops) {
        this.allowsSelfLoops = allowsSelfLoops;
        return this;
    }

    /**
     * Specifies the expected number of nodes in the graph.
     *
     * @throws IllegalArgumentException if {@code expectedNodeCount} is negative
     */
    public GraphBuilder<N> expectedNodeCount(int expectedNodeCount) {
        checkArgument(expectedNodeCount >= 0, "The expected number of nodes can't be negative: %s",
                expectedNodeCount);
        this.expectedNodeCount = Optional.of(expectedNodeCount);
        return this;
    }

    /**
     * Returns an empty {@link MutableGraph} with the properties of this {@link GraphBuilder}.
     */
    public <N1 extends N> MutableGraph<N1> build() {
        return new ConfigurableMutableGraph<N1>(this);
    }
}