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) 2014 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 com.google.common.annotations.Beta;
import com.google.errorprone.annotations.CanIgnoreReturnValue;


A subinterface of Graph which adds mutation methods. When mutation is not required, users should prefer the Graph interface. 
Author:James Sexton, Joshua O'Madadhain
Type parameters:
  • <N> – Node parameter type
Since:20.0
/**
 * A subinterface of {@link Graph} which adds mutation methods. When mutation is not required, users
 * should prefer the {@link Graph} interface.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 * @param <N> Node parameter type
 * @since 20.0
 */
@Beta
public interface MutableGraph<N> extends Graph<N> {

  
Adds node if it is not already present. 
Nodes must be unique, just as Map keys must be. They must also be non-null. 
Returns:true if the graph was modified as a result of this call
/**
   * Adds {@code node} if it is not already present.
   *
   * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  
Adds an edge connecting nodeU to nodeV if one is not already present. In an undirected graph, the edge will also connect nodeV to nodeU. 
If nodeU and nodeV are not already present in this graph, this method will silently add nodeU and nodeV to the graph. 
Throws:
Returns:true if the graph was modified as a result of this call
/**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present. In an
   * undirected graph, the edge will also connect {@code nodeV} to {@code nodeU}.
   *
   * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will
   * silently {@link #addNode(Object) add} {@code nodeU} and {@code nodeV} to the graph.
   *
   * @return {@code true} if the graph was modified as a result of this call
   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  boolean putEdge(N nodeU, N nodeV);

  
Removes node if it is present; all edges incident to node will also be removed. 
Returns:true if the graph was modified as a result of this call
/**
   * Removes {@code node} if it is present; all edges incident to {@code node} will also be removed.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean removeNode(N node);

  
Removes the edge connecting nodeU to nodeV, if it is present. 
Returns:true if the graph was modified as a result of this call
/**
   * Removes the edge connecting {@code nodeU} to {@code nodeV}, if it is present.
   *
   * @return {@code true} if the graph was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean removeEdge(N nodeU, N nodeV);
}