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.common.annotations.Beta;
024import com.google.common.base.Optional;
025import com.google.errorprone.annotations.CanIgnoreReturnValue;
026import com.google.errorprone.annotations.DoNotMock;
027
028/**
029 * A builder for constructing instances of {@link MutableGraph} or {@link ImmutableGraph} with
030 * user-defined properties.
031 *
032 * <p>A {@code Graph} built by this class has the following default properties:
033 *
034 * <ul>
035 *   <li>does not allow self-loops
036 *   <li>orders {@link Graph#nodes()} in the order in which the elements were added (insertion
037 *       order)
038 * </ul>
039 *
040 * <p>{@code Graph}s built by this class also guarantee that each collection-returning accessor
041 * returns a <b>(live) unmodifiable view</b>; see <a
042 * href="https://github.com/google/guava/wiki/GraphsExplained#accessor-behavior">the external
043 * documentation</a> for details.
044 *
045 * <p>Examples of use:
046 *
047 * <pre>{@code
048 * // Building a mutable graph
049 * MutableGraph<String> graph = GraphBuilder.undirected().allowsSelfLoops(true).build();
050 * graph.putEdge("bread", "bread");
051 * graph.putEdge("chocolate", "peanut butter");
052 * graph.putEdge("peanut butter", "jelly");
053 *
054 * // Building an immutable graph
055 * ImmutableGraph<String> immutableGraph =
056 *     GraphBuilder.undirected()
057 *         .allowsSelfLoops(true)
058 *         .<String>immutable()
059 *         .putEdge("bread", "bread")
060 *         .putEdge("chocolate", "peanut butter")
061 *         .putEdge("peanut butter", "jelly")
062 *         .build();
063 * }</pre>
064 *
065 * @author James Sexton
066 * @author Joshua O'Madadhain
067 * @param <N> The most general node type this builder will support. This is normally {@code Object}
068 *     unless it is constrained by using a method like {@link #nodeOrder}, or the builder is
069 *     constructed based on an existing {@code Graph} using {@link #from(Graph)}.
070 * @since 20.0
071 */
072@Beta
073@DoNotMock
074public final class GraphBuilder<N> extends AbstractGraphBuilder<N> {
075
076  /** Creates a new instance with the specified edge directionality. */
077  private GraphBuilder(boolean directed) {
078    super(directed);
079  }
080
081  /** Returns a {@link GraphBuilder} for building directed graphs. */
082  public static GraphBuilder<Object> directed() {
083    return new GraphBuilder<>(true);
084  }
085
086  /** Returns a {@link GraphBuilder} for building undirected graphs. */
087  public static GraphBuilder<Object> undirected() {
088    return new GraphBuilder<>(false);
089  }
090
091  /**
092   * Returns a {@link GraphBuilder} initialized with all properties queryable from {@code graph}.
093   *
094   * <p>The "queryable" properties are those that are exposed through the {@link Graph} interface,
095   * such as {@link Graph#isDirected()}. Other properties, such as {@link #expectedNodeCount(int)},
096   * are not set in the new builder.
097   */
098  public static <N> GraphBuilder<N> from(Graph<N> graph) {
099    return new GraphBuilder<N>(graph.isDirected())
100        .allowsSelfLoops(graph.allowsSelfLoops())
101        .nodeOrder(graph.nodeOrder())
102        .incidentEdgeOrder(graph.incidentEdgeOrder());
103  }
104
105  /**
106   * Returns an {@link ImmutableGraph.Builder} with the properties of this {@link GraphBuilder}.
107   *
108   * <p>The returned builder can be used for populating an {@link ImmutableGraph}.
109   *
110   * <p>Note that the returned builder will always have {@link #incidentEdgeOrder} set to {@link
111   * ElementOrder#stable()}, regardless of the value that was set in this builder.
112   *
113   * @since 28.0
114   */
115  public <N1 extends N> ImmutableGraph.Builder<N1> immutable() {
116    GraphBuilder<N1> castBuilder = cast();
117    return new ImmutableGraph.Builder<>(castBuilder);
118  }
119
120  /**
121   * Specifies whether the graph will allow self-loops (edges that connect a node to itself).
122   * Attempting to add a self-loop to a graph that does not allow them will throw an {@link
123   * UnsupportedOperationException}.
124   *
125   * <p>The default value is {@code false}.
126   */
127  @CanIgnoreReturnValue
128  public GraphBuilder<N> allowsSelfLoops(boolean allowsSelfLoops) {
129    this.allowsSelfLoops = allowsSelfLoops;
130    return this;
131  }
132
133  /**
134   * Specifies the expected number of nodes in the graph.
135   *
136   * @throws IllegalArgumentException if {@code expectedNodeCount} is negative
137   */
138  @CanIgnoreReturnValue
139  public GraphBuilder<N> expectedNodeCount(int expectedNodeCount) {
140    this.expectedNodeCount = Optional.of(checkNonNegative(expectedNodeCount));
141    return this;
142  }
143
144  /**
145   * Specifies the order of iteration for the elements of {@link Graph#nodes()}.
146   *
147   * <p>The default value is {@link ElementOrder#insertion() insertion order}.
148   */
149  public <N1 extends N> GraphBuilder<N1> nodeOrder(ElementOrder<N1> nodeOrder) {
150    GraphBuilder<N1> newBuilder = cast();
151    newBuilder.nodeOrder = checkNotNull(nodeOrder);
152    return newBuilder;
153  }
154
155  /**
156   * Specifies the order of iteration for the elements of {@link Graph#edges()}, {@link
157   * Graph#adjacentNodes(Object)}, {@link Graph#predecessors(Object)}, {@link
158   * Graph#successors(Object)} and {@link Graph#incidentEdges(Object)}.
159   *
160   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For
161   * immutable graphs, this value is ignored; they always have a {@link ElementOrder#stable()
162   * stable} order.
163   *
164   * @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
165   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
166   * @since 29.0
167   */
168  public <N1 extends N> GraphBuilder<N1> incidentEdgeOrder(ElementOrder<N1> incidentEdgeOrder) {
169    checkArgument(
170        incidentEdgeOrder.type() == ElementOrder.Type.UNORDERED
171            || incidentEdgeOrder.type() == ElementOrder.Type.STABLE,
172        "The given elementOrder (%s) is unsupported. incidentEdgeOrder() only supports"
173            + " ElementOrder.unordered() and ElementOrder.stable().",
174        incidentEdgeOrder);
175    GraphBuilder<N1> newBuilder = cast();
176    newBuilder.incidentEdgeOrder = checkNotNull(incidentEdgeOrder);
177    return newBuilder;
178  }
179
180  /** Returns an empty {@link MutableGraph} with the properties of this {@link GraphBuilder}. */
181  public <N1 extends N> MutableGraph<N1> build() {
182    return new StandardMutableGraph<>(this);
183  }
184
185  GraphBuilder<N> copy() {
186    GraphBuilder<N> newBuilder = new GraphBuilder<>(directed);
187    newBuilder.allowsSelfLoops = allowsSelfLoops;
188    newBuilder.nodeOrder = nodeOrder;
189    newBuilder.expectedNodeCount = expectedNodeCount;
190    newBuilder.incidentEdgeOrder = incidentEdgeOrder;
191    return newBuilder;
192  }
193
194  @SuppressWarnings("unchecked")
195  private <N1 extends N> GraphBuilder<N1> cast() {
196    return (GraphBuilder<N1>) this;
197  }
198}