001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.errorprone.annotations.CanIgnoreReturnValue;
021import java.util.Collection;
022import java.util.Map;
023import java.util.Map.Entry;
024import java.util.Set;
025import javax.annotation.CheckForNull;
026import org.checkerframework.checker.nullness.qual.Nullable;
027
028/**
029 * A {@code Multimap} that cannot hold duplicate key-value pairs. Adding a key-value pair that's
030 * already in the multimap has no effect. See the {@link Multimap} documentation for information
031 * common to all multimaps.
032 *
033 * <p>The {@link #get}, {@link #removeAll}, and {@link #replaceValues} methods each return a {@link
034 * Set} of values, while {@link #entries} returns a {@code Set} of map entries. Though the method
035 * signature doesn't say so explicitly, the map returned by {@link #asMap} has {@code Set} values.
036 *
037 * <p>If the values corresponding to a single key should be ordered according to a {@link
038 * java.util.Comparator} (or the natural order), see the {@link SortedSetMultimap} subinterface.
039 *
040 * <p>Since the value collections are sets, the behavior of a {@code SetMultimap} is not specified
041 * if key <em>or value</em> objects already present in the multimap change in a manner that affects
042 * {@code equals} comparisons. Use caution if mutable objects are used as keys or values in a {@code
043 * SetMultimap}.
044 *
045 * <p><b>Warning:</b> Do not modify either a key <i>or a value</i> of a {@code SetMultimap} in a way
046 * that affects its {@link Object#equals} behavior. Undefined behavior and bugs will result.
047 *
048 * <p>See the Guava User Guide article on <a href=
049 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#multimap"> {@code
050 * Multimap}</a>.
051 *
052 * @author Jared Levy
053 * @since 2.0
054 */
055@GwtCompatible
056@ElementTypesAreNonnullByDefault
057public interface SetMultimap<K extends @Nullable Object, V extends @Nullable Object>
058    extends Multimap<K, V> {
059  /**
060   * {@inheritDoc}
061   *
062   * <p>Because a {@code SetMultimap} has unique values for a given key, this method returns a
063   * {@link Set}, instead of the {@link java.util.Collection} specified in the {@link Multimap}
064   * interface.
065   */
066  @Override
067  Set<V> get(@ParametricNullness K key);
068
069  /**
070   * {@inheritDoc}
071   *
072   * <p>Because a {@code SetMultimap} has unique values for a given key, this method returns a
073   * {@link Set}, instead of the {@link java.util.Collection} specified in the {@link Multimap}
074   * interface.
075   */
076  @CanIgnoreReturnValue
077  @Override
078  Set<V> removeAll(@CheckForNull Object key);
079
080  /**
081   * {@inheritDoc}
082   *
083   * <p>Because a {@code SetMultimap} has unique values for a given key, this method returns a
084   * {@link Set}, instead of the {@link java.util.Collection} specified in the {@link Multimap}
085   * interface.
086   *
087   * <p>Any duplicates in {@code values} will be stored in the multimap once.
088   */
089  @CanIgnoreReturnValue
090  @Override
091  Set<V> replaceValues(@ParametricNullness K key, Iterable<? extends V> values);
092
093  /**
094   * {@inheritDoc}
095   *
096   * <p>Because a {@code SetMultimap} has unique values for a given key, this method returns a
097   * {@link Set}, instead of the {@link java.util.Collection} specified in the {@link Multimap}
098   * interface.
099   */
100  @Override
101  Set<Entry<K, V>> entries();
102
103  /**
104   * {@inheritDoc}
105   *
106   * <p><b>Note:</b> The returned map's values are guaranteed to be of type {@link Set}. To obtain
107   * this map with the more specific generic type {@code Map<K, Set<V>>}, call {@link
108   * Multimaps#asMap(SetMultimap)} instead.
109   */
110  @Override
111  Map<K, Collection<V>> asMap();
112
113  /**
114   * Compares the specified object to this multimap for equality.
115   *
116   * <p>Two {@code SetMultimap} instances are equal if, for each key, they contain the same values.
117   * Equality does not depend on the ordering of keys or values.
118   *
119   * <p>An empty {@code SetMultimap} is equal to any other empty {@code Multimap}, including an
120   * empty {@code ListMultimap}.
121   */
122  @Override
123  boolean equals(@CheckForNull Object obj);
124}