001/*
002 * Copyright (C) 2016 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;
020import static com.google.common.graph.Graphs.checkNonNegative;
021
022import com.google.common.annotations.Beta;
023import com.google.common.base.Optional;
024
025/**
026 * A builder for constructing instances of {@link MutableGraph} with user-defined properties.
027 *
028 * <p>A graph built by this class will have the following properties by default:
029 *
030 * <ul>
031 * <li>does not allow self-loops
032 * <li>orders {@link Graph#nodes()} in the order in which the elements were added
033 * </ul>
034 *
035 * <p>Example of use:
036 *
037 * <pre>{@code
038 * MutableGraph<String> graph = GraphBuilder.undirected().allowsSelfLoops(true).build();
039 * graph.putEdge("bread", "bread");
040 * graph.putEdge("chocolate", "peanut butter");
041 * graph.putEdge("peanut butter", "jelly");
042 * }</pre>
043 *
044 * @author James Sexton
045 * @author Joshua O'Madadhain
046 * @since 20.0
047 */
048@Beta
049public final class GraphBuilder<N> extends AbstractGraphBuilder<N> {
050
051  /** Creates a new instance with the specified edge directionality. */
052  private GraphBuilder(boolean directed) {
053    super(directed);
054  }
055
056  /** Returns a {@link GraphBuilder} for building directed graphs. */
057  public static GraphBuilder<Object> directed() {
058    return new GraphBuilder<>(true);
059  }
060
061  /** Returns a {@link GraphBuilder} for building undirected graphs. */
062  public static GraphBuilder<Object> undirected() {
063    return new GraphBuilder<>(false);
064  }
065
066  /**
067   * Returns a {@link GraphBuilder} initialized with all properties queryable from {@code graph}.
068   *
069   * <p>The "queryable" properties are those that are exposed through the {@link Graph} interface,
070   * such as {@link Graph#isDirected()}. Other properties, such as {@link #expectedNodeCount(int)},
071   * are not set in the new builder.
072   */
073  public static <N> GraphBuilder<N> from(Graph<N> graph) {
074    return new GraphBuilder<N>(graph.isDirected())
075        .allowsSelfLoops(graph.allowsSelfLoops())
076        .nodeOrder(graph.nodeOrder());
077  }
078
079  /**
080   * Specifies whether the graph will allow self-loops (edges that connect a node to itself).
081   * Attempting to add a self-loop to a graph that does not allow them will throw an {@link
082   * UnsupportedOperationException}.
083   */
084  public GraphBuilder<N> allowsSelfLoops(boolean allowsSelfLoops) {
085    this.allowsSelfLoops = allowsSelfLoops;
086    return this;
087  }
088
089  /**
090   * Specifies the expected number of nodes in the graph.
091   *
092   * @throws IllegalArgumentException if {@code expectedNodeCount} is negative
093   */
094  public GraphBuilder<N> expectedNodeCount(int expectedNodeCount) {
095    this.expectedNodeCount = Optional.of(checkNonNegative(expectedNodeCount));
096    return this;
097  }
098
099  /** Specifies the order of iteration for the elements of {@link Graph#nodes()}. */
100  public <N1 extends N> GraphBuilder<N1> nodeOrder(ElementOrder<N1> nodeOrder) {
101    GraphBuilder<N1> newBuilder = cast();
102    newBuilder.nodeOrder = checkNotNull(nodeOrder);
103    return newBuilder;
104  }
105
106  /** Returns an empty {@link MutableGraph} with the properties of this {@link GraphBuilder}. */
107  public <N1 extends N> MutableGraph<N1> build() {
108    return new ConfigurableMutableGraph<N1>(this);
109  }
110
111  @SuppressWarnings("unchecked")
112  private <N1 extends N> GraphBuilder<N1> cast() {
113    return (GraphBuilder<N1>) this;
114  }
115}