https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * 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 static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.graph.Graphs.checkNonNegative;

import com.google.common.annotations.Beta;
import com.google.common.base.Optional;
import com.google.errorprone.annotations.DoNotMock;


A builder for constructing instances of MutableGraph or ImmutableGraph with user-defined properties. 
A graph built by this class will have the following properties by default:

    
  
  • does not allow self-loops
  
  • orders Graph.nodes() in the order in which the elements were added 


Examples of use:


// Building a mutable graph
MutableGraph<String> graph = GraphBuilder.undirected().allowsSelfLoops(true).build();
graph.putEdge("bread", "bread");
graph.putEdge("chocolate", "peanut butter");
graph.putEdge("peanut butter", "jelly");
// Building an immutable graph
ImmutableGraph<String> immutableGraph =
    GraphBuilder.undirected()
        .allowsSelfLoops(true)
        .<String>immutable()
        .putEdge("bread", "bread")
        .putEdge("chocolate", "peanut butter")
        .putEdge("peanut butter", "jelly")
        .build();



Author:James Sexton, Joshua O'Madadhain
Type parameters:
Since:20.0
/**
 * A builder for constructing instances of {@link MutableGraph} or {@link ImmutableGraph} with
 * user-defined properties.
 *
 * <p>A graph built by this class will have the following properties by default:
 *
 * <ul>
 *   <li>does not allow self-loops
 *   <li>orders {@link Graph#nodes()} in the order in which the elements were added
 * </ul>
 *
 * <p>Examples of use:
 *
 * <pre>{@code
 * // Building a mutable graph
 * MutableGraph<String> graph = GraphBuilder.undirected().allowsSelfLoops(true).build();
 * graph.putEdge("bread", "bread");
 * graph.putEdge("chocolate", "peanut butter");
 * graph.putEdge("peanut butter", "jelly");
 *
 * // Building an immutable graph
 * ImmutableGraph<String> immutableGraph =
 *     GraphBuilder.undirected()
 *         .allowsSelfLoops(true)
 *         .<String>immutable()
 *         .putEdge("bread", "bread")
 *         .putEdge("chocolate", "peanut butter")
 *         .putEdge("peanut butter", "jelly")
 *         .build();
 * }</pre>
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @param <N> The most general node type this builder will support. This is normally {@code Object}
 *     unless it is constrained by using a method like {@link #nodeOrder}, or the builder is
 *     constructed based on an existing {@code Graph} using {@link #from(Graph)}.
 * @since 20.0
 */
@Beta
@DoNotMock
public final class GraphBuilder<N> extends AbstractGraphBuilder<N> {

  
Creates a new instance with the specified edge directionality. 
/** Creates a new instance with the specified edge directionality. */
  private GraphBuilder(boolean directed) {
    super(directed);
  }

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

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

  
Returns a GraphBuilder initialized with all properties queryable from graph. 
The "queryable" properties are those that are exposed through the Graph interface, such as Graph.isDirected(). Other properties, such as expectedNodeCount(int), are not set in the new builder. 
/**
   * 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) {
    return new GraphBuilder<N>(graph.isDirected())
        .allowsSelfLoops(graph.allowsSelfLoops())
        .nodeOrder(graph.nodeOrder())
        .incidentEdgeOrder(graph.incidentEdgeOrder());
  }

  
Returns an Builder with the properties of this GraphBuilder. 
The returned builder can be used for populating an ImmutableGraph. 
Note that the returned builder will always have AbstractGraphBuilder<N>.incidentEdgeOrder set to ElementOrder.stable(), regardless of the value that was set in this builder. 
Since:28.0
/**
   * Returns an {@link ImmutableGraph.Builder} with the properties of this {@link GraphBuilder}.
   *
   * <p>The returned builder can be used for populating an {@link ImmutableGraph}.
   *
   * <p>Note that the returned builder will always have {@link #incidentEdgeOrder} set to {@link
   * ElementOrder#stable()}, regardless of the value that was set in this builder.
   *
   * @since 28.0
   */
  public <N1 extends N> ImmutableGraph.Builder<N1> immutable() {
    GraphBuilder<N1> castBuilder = cast();
    return new ImmutableGraph.Builder<>(castBuilder);
  }

  
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 UnsupportedOperationException. 
The default value is false. 
/**
   * 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}.
   *
   * <p>The default value is {@code false}.
   */
  public GraphBuilder<N> allowsSelfLoops(boolean allowsSelfLoops) {
    this.allowsSelfLoops = allowsSelfLoops;
    return this;
  }

  
Specifies the expected number of nodes in the graph.

Throws:
  • IllegalArgumentException – if expectedNodeCount is negative
/**
   * Specifies the expected number of nodes in the graph.
   *
   * @throws IllegalArgumentException if {@code expectedNodeCount} is negative
   */
  public GraphBuilder<N> expectedNodeCount(int expectedNodeCount) {
    this.expectedNodeCount = Optional.of(checkNonNegative(expectedNodeCount));
    return this;
  }

  
Specifies the order of iteration for the elements of Graph.nodes(). 
The default value is insertion order. 
/**
   * Specifies the order of iteration for the elements of {@link Graph#nodes()}.
   *
   * <p>The default value is {@link ElementOrder#insertion() insertion order}.
   */
  public <N1 extends N> GraphBuilder<N1> nodeOrder(ElementOrder<N1> nodeOrder) {
    GraphBuilder<N1> newBuilder = cast();
    newBuilder.nodeOrder = checkNotNull(nodeOrder);
    return newBuilder;
  }

  
Specifies the order of iteration for the elements of Graph.edges(), Graph.adjacentNodes(Object), Graph.predecessors(Object), Graph.successors(Object) and Graph.incidentEdges(Object). 
The default value is unordered for mutable graphs. For immutable graphs, this value is ignored; they always have a 
stable order. 
Throws:
Since:29.0
/**
   * Specifies the order of iteration for the elements of {@link Graph#edges()}, {@link
   * Graph#adjacentNodes(Object)}, {@link Graph#predecessors(Object)}, {@link
   * Graph#successors(Object)} and {@link Graph#incidentEdges(Object)}.
   *
   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For
   * immutable graphs, this value is ignored; they always have a {@link ElementOrder#stable()
   * stable} order.
   *
   * @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
   * @since 29.0
   */
  public <N1 extends N> GraphBuilder<N1> incidentEdgeOrder(ElementOrder<N1> incidentEdgeOrder) {
    checkArgument(
        incidentEdgeOrder.type() == ElementOrder.Type.UNORDERED
            || incidentEdgeOrder.type() == ElementOrder.Type.STABLE,
        "The given elementOrder (%s) is unsupported. incidentEdgeOrder() only supports"
            + " ElementOrder.unordered() and ElementOrder.stable().",
        incidentEdgeOrder);
    GraphBuilder<N1> newBuilder = cast();
    newBuilder.incidentEdgeOrder = checkNotNull(incidentEdgeOrder);
    return newBuilder;
  }

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

  GraphBuilder<N> copy() {
    GraphBuilder<N> newBuilder = new GraphBuilder<>(directed);
    newBuilder.allowsSelfLoops = allowsSelfLoops;
    newBuilder.nodeOrder = nodeOrder;
    newBuilder.expectedNodeCount = expectedNodeCount;
    newBuilder.incidentEdgeOrder = incidentEdgeOrder;
    return newBuilder;
  }

  @SuppressWarnings("unchecked")
  private <N1 extends N> GraphBuilder<N1> cast() {
    return (GraphBuilder<N1>) this;
  }
}