| /* |
| * 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 java.util.Set; |
| import org.checkerframework.checker.nullness.compatqual.NullableDecl; |
| |
| /** |
| * An interface for <a |
| * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, |
| * whose edges are anonymous entities with no identity or information of their own. |
| * |
| * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes. |
| * |
| * <p>There are three primary interfaces provided to represent graphs. In order of increasing |
| * complexity they are: {@link Graph}, {@link ValueGraph}, and {@link Network}. You should generally |
| * prefer the simplest interface that satisfies your use case. See the <a |
| * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type"> |
| * "Choosing the right graph type"</a> section of the Guava User Guide for more details. |
| * |
| * <h3>Capabilities</h3> |
| * |
| * <p>{@code Graph} supports the following use cases (<a |
| * href="https://github.com/google/guava/wiki/GraphsExplained#definitions">definitions of |
| * terms</a>): |
| * |
| * <ul> |
| * <li>directed graphs |
| * <li>undirected graphs |
| * <li>graphs that do/don't allow self-loops |
| * <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered |
| * </ul> |
| * |
| * <p>{@code Graph} explicitly does not support parallel edges, and forbids implementations or |
| * extensions with parallel edges. If you need parallel edges, use {@link Network}. |
| * |
| * <h3>Building a {@code Graph}</h3> |
| * |
| * <p>The implementation classes that {@code common.graph} provides are not public, by design. To |
| * create an instance of one of the built-in implementations of {@code Graph}, use the {@link |
| * GraphBuilder} class: |
| * |
| * <pre>{@code |
| * MutableGraph<Integer> graph = GraphBuilder.undirected().build(); |
| * }</pre> |
| * |
| * <p>{@link GraphBuilder#build()} returns an instance of {@link MutableGraph}, which is a subtype |
| * of {@code Graph} that provides methods for adding and removing nodes and edges. If you do not |
| * need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on the graph), |
| * you should use the non-mutating {@link Graph} interface, or an {@link ImmutableGraph}. |
| * |
| * <p>You can create an immutable copy of an existing {@code Graph} using {@link |
| * ImmutableGraph#copyOf(Graph)}: |
| * |
| * <pre>{@code |
| * ImmutableGraph<Integer> immutableGraph = ImmutableGraph.copyOf(graph); |
| * }</pre> |
| * |
| * <p>Instances of {@link ImmutableGraph} do not implement {@link MutableGraph} (obviously!) and are |
| * contractually guaranteed to be unmodifiable and thread-safe. |
| * |
| * <p>The Guava User Guide has <a |
| * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more |
| * information on (and examples of) building graphs</a>. |
| * |
| * <h3>Additional documentation</h3> |
| * |
| * <p>See the Guava User Guide for the {@code common.graph} package (<a |
| * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for |
| * additional documentation, including: |
| * |
| * <ul> |
| * <li><a |
| * href="https://github.com/google/guava/wiki/GraphsExplained#equals-hashcode-and-graph-equivalence"> |
| * {@code equals()}, {@code hashCode()}, and graph equivalence</a> |
| * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#synchronization"> |
| * Synchronization policy</a> |
| * <li><a href="https://github.com/google/guava/wiki/GraphsExplained#notes-for-implementors">Notes |
| * for implementors</a> |
| * </ul> |
| * |
| * @author James Sexton |
| * @author Joshua O'Madadhain |
| * @param <N> Node parameter type |
| * @since 20.0 |
| */ |
| @Beta |
| public interface Graph<N> extends BaseGraph<N> { |
| // |
| // Graph-level accessors |
| // |
| |
| /** Returns all nodes in this graph, in the order specified by {@link #nodeOrder()}. */ |
| @Override |
| Set<N> nodes(); |
| |
| /** Returns all edges in this graph. */ |
| @Override |
| Set<EndpointPair<N>> edges(); |
| |
| // |
| // Graph properties |
| // |
| |
| /** |
| * 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. |
| */ |
| @Override |
| 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 {@link |
| * IllegalArgumentException}. |
| */ |
| @Override |
| boolean allowsSelfLoops(); |
| |
| /** Returns the order of iteration for the elements of {@link #nodes()}. */ |
| @Override |
| ElementOrder<N> nodeOrder(); |
| |
| // |
| // Element-level accessors |
| // |
| |
| /** |
| * Returns the nodes which have an incident edge in common with {@code node} in this graph. |
| * |
| * @throws IllegalArgumentException if {@code node} is not an element of this graph |
| */ |
| @Override |
| Set<N> adjacentNodes(N node); |
| |
| /** |
| * 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 {@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 {@code node}. |
| * |
| * @throws IllegalArgumentException if {@code node} is not an element of this graph |
| * @since 24.0 |
| */ |
| @Override |
| Set<EndpointPair<N>> incidentEdges(N node); |
| |
| /** |
| * 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 |
| */ |
| @Override |
| int degree(N node); |
| |
| /** |
| * 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 |
| */ |
| @Override |
| int inDegree(N node); |
| |
| /** |
| * 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 |
| */ |
| @Override |
| int outDegree(N node); |
| |
| /** |
| * 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 |
| */ |
| @Override |
| boolean hasEdgeConnecting(N nodeU, N nodeV); |
| |
| /** |
| * 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 and the graph is directed; it simply returns {@code 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 |
| */ |
| @Override |
| boolean hasEdgeConnecting(EndpointPair<N> endpoints); |
| |
| // |
| // Graph identity |
| // |
| |
| /** |
| * Returns {@code true} iff {@code object} is a {@link Graph} that has the same elements and the |
| * same structural relationships as those in this graph. |
| * |
| * <p>Thus, two graphs A and B are equal if <b>all</b> of the following are true: |
| * |
| * <ul> |
| * <li>A and B have equal {@link #isDirected() directedness}. |
| * <li>A and B have equal {@link #nodes() node sets}. |
| * <li>A and B have equal {@link #edges() edge sets}. |
| * </ul> |
| * |
| * <p>Graph properties besides {@link #isDirected() directedness} do <b>not</b> affect equality. |
| * For example, two graphs may be considered equal even if one allows self-loops and the other |
| * doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order |
| * in which they are iterated over, are irrelevant. |
| * |
| * <p>A reference implementation of this is provided by {@link AbstractGraph#equals(Object)}. |
| */ |
| @Override |
| boolean equals(@NullableDecl Object object); |
| |
| /** |
| * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of |
| * the set returned by {@link #edges()}. |
| * |
| * <p>A reference implementation of this is provided by {@link AbstractGraph#hashCode()}. |
| */ |
| @Override |
| int hashCode(); |
| } |