Java tutorial
/* * 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.CompatibleWith; import java.util.Set; import javax.annotation.Nullable; /** * An interface for <a * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data, * whose edges have associated non-unique values. * * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes. * * <p>There are three main 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 ValueGraph} 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 * <li>graphs whose edges have associated values * </ul> * * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges, * and forbids implementations or extensions with parallel edges. If you need parallel edges, use * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of * edge multiplicity, but the {@code *degree()} and mutation methods will not reflect your * interpretation of the edge value as its multiplicity.) * * <h3>Building a {@code ValueGraph}</h3> * * <p>The implementation classes that `common.graph` provides are not public, by design. To create * an instance of one of the built-in implementations of {@code ValueGraph}, use the {@link * ValueGraphBuilder} class: * * <pre>{@code * MutableValueGraph<Integer, Double> graph = ValueGraphBuilder.directed().build(); * }</pre> * * <p>{@link ValueGraphBuilder#build()} returns an instance of {@link MutableValueGraph}, which is a * subtype of {@code ValueGraph} 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 ValueGraph} interface, or an {@link * ImmutableValueGraph}. * * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link * ImmutableValueGraph#copyOf(ValueGraph)}: * * <pre>{@code * ImmutableValueGraph<Integer, Double> immutableGraph = ImmutableValueGraph.copyOf(graph); * }</pre> * * <p>Instances of {@link ImmutableValueGraph} do not implement {@link MutableValueGraph} * (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 * @param <V> Value parameter type * @since 20.0 */ @Beta public interface ValueGraph<N, V> extends BaseGraph<N> { // // ValueGraph-level accessors // /** {@inheritDoc} */ @Override Set<N> nodes(); /** {@inheritDoc} */ @Override Set<EndpointPair<N>> edges(); /** * Returns a live view of this graph as a {@link Graph}. The resulting {@link Graph} will have an * edge connecting node A to node B if this {@link ValueGraph} has an edge connecting A to B. */ Graph<N> asGraph(); // // ValueGraph properties // /** {@inheritDoc} */ @Override boolean isDirected(); /** {@inheritDoc} */ @Override boolean allowsSelfLoops(); /** {@inheritDoc} */ @Override ElementOrder<N> nodeOrder(); // // Element-level accessors // /** {@inheritDoc} */ @Override Set<N> adjacentNodes(Object node); /** {@inheritDoc} */ @Override Set<N> predecessors(Object node); /** {@inheritDoc} */ @Override Set<N> successors(Object node); /** {@inheritDoc} */ @Override int degree(Object node); /** {@inheritDoc} */ @Override int inDegree(Object node); /** {@inheritDoc} */ @Override int outDegree(Object node); /** {@inheritDoc} */ @Override boolean hasEdge(Object nodeU, Object nodeV); /** * If there is an edge connecting {@code nodeU} to {@code nodeV}, returns the non-null value * associated with that edge. * * <p>In an undirected graph, this is equal to {@code edgeValue(nodeV, nodeU)}. * * @throws IllegalArgumentException if there is no edge connecting {@code nodeU} to {@code nodeV}. */ V edgeValue(@CompatibleWith("N") Object nodeU, @CompatibleWith("N") Object nodeV); /** * If there is an edge connecting {@code nodeU} to {@code nodeV}, returns the non-null value * associated with that edge; otherwise, returns {@code defaultValue}. * * <p>In an undirected graph, this is equal to {@code edgeValueOrDefault(nodeV, nodeU, * defaultValue)}. */ V edgeValueOrDefault(@CompatibleWith("N") Object nodeU, @CompatibleWith("N") Object nodeV, @Nullable V defaultValue); // // ValueGraph identity // /** * Returns {@code true} iff {@code object} is a {@link ValueGraph} that has the same elements and * the same structural relationships as those in this graph. * * <p>Thus, two value 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}. * <li>Every edge in A and B are associated with equal {@link #edgeValue(Object, Object) values}. * </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 AbstractValueGraph#equals(Object)}. */ @Override boolean equals(@Nullable Object object); /** * Returns the hash code for this graph. The hash code of a graph is defined as the hash code of a * map from each of its {@link #edges() edges} to the associated {@link #edgeValue(Object, Object) * edge value}. * * <p>A reference implementation of this is provided by {@link AbstractValueGraph#hashCode()}. */ @Override int hashCode(); }