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


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

  
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; associate that edge with value. In an undirected graph, the edge will also connect nodeV to nodeU. 
Values do not have to be unique. However, values must be non-null.

If nodeU and nodeV are not already present in this graph, this method will silently add nodeU and nodeV to the graph. 
Throws:
Returns:the value previously associated with the edge connecting nodeU to 
    nodeV, or null if there was no such edge.
/**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present; associate
   * that edge with {@code value}. In an undirected graph, the edge will also connect {@code nodeV}
   * to {@code nodeU}.
   *
   * <p>Values do not have to be unique. However, values must be non-null.
   *
   * <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 the value previously associated with the edge connecting {@code nodeU} to {@code
   *     nodeV}, or null if there was no such edge.
   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  V putEdgeValue(N nodeU, N nodeV, V value);

  
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:the value previously associated with the edge connecting nodeU to 
    nodeV, or null if there was no such edge.
/**
   * Removes the edge connecting {@code nodeU} to {@code nodeV}, if it is present.
   *
   * @return the value previously associated with the edge connecting {@code nodeU} to {@code
   *     nodeV}, or null if there was no such edge.
   */
  @CanIgnoreReturnValue
  V removeEdge(N nodeU, N nodeV);
}