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.checkArgument;
020import static com.google.common.base.Preconditions.checkNotNull;
021import static com.google.common.graph.Graphs.checkNonNegative;
022
023import com.google.errorprone.annotations.CanIgnoreReturnValue;
024import com.google.errorprone.annotations.DoNotMock;
025
026/**
027 * A builder for constructing instances of {@link MutableGraph} or {@link ImmutableGraph} with
028 * user-defined properties.
029 *
030 * <p>A {@code Graph} built by this class has the following default properties:
031 *
032 * <ul>
033 *   <li>does not allow self-loops
034 *   <li>orders {@link Graph#nodes()} in the order in which the elements were added (insertion
035 *       order)
036 * </ul>
037 *
038 * <p>{@code Graph}s built by this class also guarantee that each collection-returning accessor
039 * returns a <b>(live) unmodifiable view</b>; see <a
040 * href="https://github.com/google/guava/wiki/GraphsExplained#accessor-behavior">the external
041 * documentation</a> for details.
042 *
043 * <p>Examples of use:
044 *
045 * {@snippet :
046 * // Building a mutable graph
047 * MutableGraph<String> graph = GraphBuilder.undirected().allowsSelfLoops(true).build();
048 * graph.putEdge("bread", "bread");
049 * graph.putEdge("chocolate", "peanut butter");
050 * graph.putEdge("peanut butter", "jelly");
051 *
052 * // Building an immutable graph
053 * ImmutableGraph<String> immutableGraph =
054 *     GraphBuilder.undirected()
055 *         .allowsSelfLoops(true)
056 *         .<String>immutable()
057 *         .putEdge("bread", "bread")
058 *         .putEdge("chocolate", "peanut butter")
059 *         .putEdge("peanut butter", "jelly")
060 *         .build();
061 * }
062 *
063 * @author James Sexton
064 * @author Joshua O'Madadhain
065 * @param <N> The most general node type this builder will support. This is normally {@code Object}
066 *     unless it is constrained by using a method like {@link #nodeOrder}, or the builder is
067 *     constructed based on an existing {@code Graph} using {@link #from(Graph)}.
068 * @since 20.0
069 */
070@DoNotMock
071public final class GraphBuilder<N> extends AbstractGraphBuilder<N> {
072
073  /** Creates a new instance with the specified edge directionality. */
074  private GraphBuilder(boolean directed) {
075    super(directed);
076  }
077
078  /** Returns a {@link GraphBuilder} for building directed graphs. */
079  public static GraphBuilder<Object> directed() {
080    return new GraphBuilder<>(true);
081  }
082
083  /** Returns a {@link GraphBuilder} for building undirected graphs. */
084  public static GraphBuilder<Object> undirected() {
085    return new GraphBuilder<>(false);
086  }
087
088  /**
089   * Returns a {@link GraphBuilder} initialized with all properties queryable from {@code graph}.
090   *
091   * <p>The "queryable" properties are those that are exposed through the {@link Graph} interface,
092   * such as {@link Graph#isDirected()}. Other properties, such as {@link #expectedNodeCount(int)},
093   * are not set in the new builder.
094   */
095  public static <N> GraphBuilder<N> from(Graph<N> graph) {
096    return new GraphBuilder<N>(graph.isDirected())
097        .allowsSelfLoops(graph.allowsSelfLoops())
098        .nodeOrder(graph.nodeOrder())
099        .incidentEdgeOrder(graph.incidentEdgeOrder());
100  }
101
102  /**
103   * Returns an {@link ImmutableGraph.Builder} with the properties of this {@link GraphBuilder}.
104   *
105   * <p>The returned builder can be used for populating an {@link ImmutableGraph}.
106   *
107   * <p>Note that the returned builder will always have {@link #incidentEdgeOrder} set to {@link
108   * ElementOrder#stable()}, regardless of the value that was set in this builder.
109   *
110   * @since 28.0
111   */
112  public <N1 extends N> ImmutableGraph.Builder<N1> immutable() {
113    GraphBuilder<N1> castBuilder = cast();
114    return new ImmutableGraph.Builder<>(castBuilder);
115  }
116
117  /**
118   * Specifies whether the graph will allow self-loops (edges that connect a node to itself).
119   * Attempting to add a self-loop to a graph that does not allow them will throw an {@link
120   * UnsupportedOperationException}.
121   *
122   * <p>The default value is {@code false}.
123   */
124  @CanIgnoreReturnValue
125  public GraphBuilder<N> allowsSelfLoops(boolean allowsSelfLoops) {
126    this.allowsSelfLoops = allowsSelfLoops;
127    return this;
128  }
129
130  /**
131   * Specifies the expected number of nodes in the graph.
132   *
133   * @throws IllegalArgumentException if {@code expectedNodeCount} is negative
134   */
135  @CanIgnoreReturnValue
136  public GraphBuilder<N> expectedNodeCount(int expectedNodeCount) {
137    this.expectedNodeCount = checkNonNegative(expectedNodeCount);
138    return this;
139  }
140
141  /**
142   * Specifies the order of iteration for the elements of {@link Graph#nodes()}.
143   *
144   * <p>The default value is {@link ElementOrder#insertion() insertion order}.
145   */
146  public <N1 extends N> GraphBuilder<N1> nodeOrder(ElementOrder<N1> nodeOrder) {
147    GraphBuilder<N1> newBuilder = cast();
148    newBuilder.nodeOrder = checkNotNull(nodeOrder);
149    return newBuilder;
150  }
151
152  /**
153   * Specifies the order of iteration for the elements of {@link Graph#edges()}, {@link
154   * Graph#adjacentNodes(Object)}, {@link Graph#predecessors(Object)}, {@link
155   * Graph#successors(Object)} and {@link Graph#incidentEdges(Object)}.
156   *
157   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For
158   * immutable graphs, this value is ignored; they always have a {@link ElementOrder#stable()
159   * stable} order.
160   *
161   * @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
162   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
163   * @since 29.0
164   */
165  public <N1 extends N> GraphBuilder<N1> incidentEdgeOrder(ElementOrder<N1> incidentEdgeOrder) {
166    checkArgument(
167        incidentEdgeOrder.type() == ElementOrder.Type.UNORDERED
168            || incidentEdgeOrder.type() == ElementOrder.Type.STABLE,
169        "The given elementOrder (%s) is unsupported. incidentEdgeOrder() only supports"
170            + " ElementOrder.unordered() and ElementOrder.stable().",
171        incidentEdgeOrder);
172    GraphBuilder<N1> newBuilder = cast();
173    newBuilder.incidentEdgeOrder = checkNotNull(incidentEdgeOrder);
174    return newBuilder;
175  }
176
177  /** Returns an empty {@link MutableGraph} with the properties of this {@link GraphBuilder}. */
178  public <N1 extends N> MutableGraph<N1> build() {
179    return new StandardMutableGraph<>(this);
180  }
181
182  GraphBuilder<N> copy() {
183    GraphBuilder<N> newBuilder = new GraphBuilder<>(directed);
184    newBuilder.allowsSelfLoops = allowsSelfLoops;
185    newBuilder.nodeOrder = nodeOrder;
186    newBuilder.expectedNodeCount = expectedNodeCount;
187    newBuilder.incidentEdgeOrder = incidentEdgeOrder;
188    return newBuilder;
189  }
190
191  @SuppressWarnings("unchecked")
192  private <N1 extends N> GraphBuilder<N1> cast() {
193    return (GraphBuilder<N1>) this;
194  }
195}