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) 2017 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 java.util.Set;


A non-public interface for the methods shared between Graph and ValueGraph. 
Author:James Sexton
Type parameters:
  • <N> – Node parameter type
/**
 * A non-public interface for the methods shared between {@link Graph} and {@link ValueGraph}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 */
interface BaseGraph<N> extends SuccessorsFunction<N>, PredecessorsFunction<N> {
  //
  // Graph-level accessors
  //

  
Returns all nodes in this graph, in the order specified by nodeOrder(). 
/** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */
  Set<N> nodes();

  
Returns all edges in this graph. 
/** Returns all edges in this graph. */
  Set<EndpointPair<N>> edges();

  //
  // Graph properties
  //

  
Returns true if the edges in this graph are directed. Directed edges connect a source node to a target node, while undirected edges connect a pair of nodes to each other. 
/**
   * Returns true if the edges in this graph are directed. Directed edges connect a {@link
   * EndpointPair#source() source node} to a {@link EndpointPair#target() target node}, while
   * undirected edges connect a pair of nodes to each other.
   */
  boolean isDirected();

  
Returns true if this graph allows 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 IllegalArgumentException. 
/**
   * Returns true if this graph allows 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
   * IllegalArgumentException}.
   */
  boolean allowsSelfLoops();

  
Returns the order of iteration for the elements of nodes(). 
/** Returns the order of iteration for the elements of {@link #nodes()}. */
  ElementOrder<N> nodeOrder();

  
Returns an ElementOrder that specifies the order of iteration for the elements of edges(), adjacentNodes(Object), predecessors(Object), successors(Object) and incidentEdges(Object). 
Since:29.0
/**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors
  //

  
Returns the nodes which have an incident edge in common with node in this graph. 
This is equal to the union of predecessors(Object) and successors(Object). 
Throws:
/**
   * Returns the nodes which have an incident edge in common with {@code node} in this graph.
   *
   * <p>This is equal to the union of {@link #predecessors(Object)} and {@link #successors(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  Set<N> adjacentNodes(N node);

  
Returns all nodes in this graph adjacent to node which can be reached by traversing node's incoming edges against the direction (if any) of the edge.

In an undirected graph, this is equivalent to adjacentNodes(Object). 
Throws:
/**
   * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing
   * {@code node}'s incoming edges <i>against</i> the direction (if any) of the edge.
   *
   * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  @Override
  Set<N> predecessors(N node);

  
Returns all nodes in this graph adjacent to node which can be reached by traversing node's outgoing edges in the direction (if any) of the edge. 
In an undirected graph, this is equivalent to adjacentNodes(Object). 
This is not the same as "all nodes reachable from node by following outgoing edges". For that functionality, see Graphs.reachableNodes(Graph<Object>, Object). 
Throws:
/**
   * Returns all nodes in this graph adjacent to {@code node} which can be reached by traversing
   * {@code node}'s outgoing edges in the direction (if any) of the edge.
   *
   * <p>In an undirected graph, this is equivalent to {@link #adjacentNodes(Object)}.
   *
   * <p>This is <i>not</i> the same as "all nodes reachable from {@code node} by following outgoing
   * edges". For that functionality, see {@link Graphs#reachableNodes(Graph, Object)}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  @Override
  Set<N> successors(N node);

  
Returns the edges in this graph whose endpoints include node. 
This is equal to the union of incoming and outgoing edges.

Throws:
Since:24.0
/**
   * Returns the edges in this graph whose endpoints include {@code node}.
   *
   * <p>This is equal to the union of incoming and outgoing edges.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   * @since 24.0
   */
  Set<EndpointPair<N>> incidentEdges(N node);

  
Returns the count of node's incident edges, counting self-loops twice (equivalently, the number of times an edge touches node). 
For directed graphs, this is equal to inDegree(node) + outDegree(node). 
For undirected graphs, this is equal to incidentEdges(node).size() + (number of self-loops incident to node). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s incident edges, counting self-loops twice (equivalently,
   * the number of times an edge touches {@code node}).
   *
   * <p>For directed graphs, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected graphs, this is equal to {@code incidentEdges(node).size()} + (number of
   * self-loops incident to {@code node}).
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  int degree(N node);

  
Returns the count of node's incoming edges (equal to predecessors(node).size()) in a directed graph. In an undirected graph, returns the degree(Object). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s incoming edges (equal to {@code predecessors(node).size()})
   * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}.
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  int inDegree(N node);

  
Returns the count of node's outgoing edges (equal to successors(node).size()) in a directed graph. In an undirected graph, returns the degree(Object). 
If the count is greater than Integer.MAX_VALUE, returns Integer.MAX_VALUE. 
Throws:
/**
   * Returns the count of {@code node}'s outgoing edges (equal to {@code successors(node).size()})
   * in a directed graph. In an undirected graph, returns the {@link #degree(Object)}.
   *
   * <p>If the count is greater than {@code Integer.MAX_VALUE}, returns {@code Integer.MAX_VALUE}.
   *
   * @throws IllegalArgumentException if {@code node} is not an element of this graph
   */
  int outDegree(N node);

  
Returns true if there is an edge that directly connects nodeU to nodeV. This is equivalent to nodes().contains(nodeU) && successors(nodeU).contains(nodeV). 
In an undirected graph, this is equal to hasEdgeConnecting(nodeV, nodeU). 
Since:23.0
/**
   * Returns true if there is an edge that directly connects {@code nodeU} to {@code nodeV}. This is
   * equivalent to {@code nodes().contains(nodeU) && successors(nodeU).contains(nodeV)}.
   *
   * <p>In an undirected graph, this is equal to {@code hasEdgeConnecting(nodeV, nodeU)}.
   *
   * @since 23.0
   */
  boolean hasEdgeConnecting(N nodeU, N nodeV);

  
Returns true if there is an edge that directly connects endpoints (in the order, if any, specified by endpoints). This is equivalent to 
edges().contains(endpoints). 
Unlike the other EndpointPair-accepting methods, this method does not throw if the endpoints are unordered; it simply returns false. This is for consistency with the behavior of contains.contains(Object) (which does not generally throw if the object cannot be present in the collection), and the desire to have this method's behavior be compatible with edges().contains(endpoints). 
Since:27.1
/**
   * Returns true if there is an edge that directly connects {@code endpoints} (in the order, if
   * any, specified by {@code endpoints}). This is equivalent to {@code
   * edges().contains(endpoints)}.
   *
   * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the
   * endpoints are unordered; it simply returns false. This is for consistency with the behavior of
   * {@link Collection#contains(Object)} (which does not generally throw if the object cannot be
   * present in the collection), and the desire to have this method's behavior be compatible with
   * {@code edges().contains(endpoints)}.
   *
   * @since 27.1
   */
  boolean hasEdgeConnecting(EndpointPair<N> endpoints);
}