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;
020
021import java.util.Collection;
022import java.util.Map;
023import java.util.Set;
024
025import javax.annotation.Nullable;
026
027/**
028 * A collection similar to a {@code Map}, but which may associate multiple
029 * values with a single key. If you call {@link #put} twice, with the same key
030 * but different values, the multimap contains mappings from the key to both
031 * values.
032 *
033 * <p>The methods {@link #get}, {@link #keySet}, {@link #keys}, {@link #values},
034 * {@link #entries}, and {@link #asMap} return collections that are views of the
035 * multimap. If the multimap is modifiable, updating it can change the contents
036 * of those collections, and updating the collections will change the multimap.
037 * In contrast, {@link #replaceValues} and {@link #removeAll} return collections
038 * that are independent of subsequent multimap changes.
039 *
040 * <p>Depending on the implementation, a multimap may or may not allow duplicate
041 * key-value pairs. In other words, the multimap contents after adding the same
042 * key and value twice varies between implementations. In multimaps allowing
043 * duplicates, the multimap will contain two mappings, and {@code get} will
044 * return a collection that includes the value twice. In multimaps not
045 * supporting duplicates, the multimap will contain a single mapping from the
046 * key to the value, and {@code get} will return a collection that includes the
047 * value once.
048 *
049 * <p>All methods that alter the multimap are optional, and the views returned
050 * by the multimap may or may not be modifiable. When modification isn't
051 * supported, those methods will throw an {@link UnsupportedOperationException}.
052 *
053 * @author Jared Levy
054 * @param <K> the type of keys maintained by this multimap
055 * @param <V> the type of mapped values
056 * @since 2 (imported from Google Collections Library)
057 */
058@GwtCompatible
059public interface Multimap<K, V> {
060  // Query Operations
061
062  /** Returns the number of key-value pairs in the multimap. */
063  int size();
064
065  /** Returns {@code true} if the multimap contains no key-value pairs. */
066  boolean isEmpty();
067
068  /**
069   * Returns {@code true} if the multimap contains any values for the specified
070   * key.
071   *
072   * @param key key to search for in multimap
073   */
074  boolean containsKey(@Nullable Object key);
075
076  /**
077   * Returns {@code true} if the multimap contains the specified value for any
078   * key.
079   *
080   * @param value value to search for in multimap
081   */
082  boolean containsValue(@Nullable Object value);
083
084  /**
085   * Returns {@code true} if the multimap contains the specified key-value pair.
086   *
087   * @param key key to search for in multimap
088   * @param value value to search for in multimap
089   */
090  boolean containsEntry(@Nullable Object key, @Nullable Object value);
091
092  // Modification Operations
093
094  /**
095   * Stores a key-value pair in the multimap.
096   *
097   * <p>Some multimap implementations allow duplicate key-value pairs, in which
098   * case {@code put} always adds a new key-value pair and increases the
099   * multimap size by 1. Other implementations prohibit duplicates, and storing
100   * a key-value pair that's already in the multimap has no effect.
101   *
102   * @param key key to store in the multimap
103   * @param value value to store in the multimap
104   * @return {@code true} if the method increased the size of the multimap, or
105   *     {@code false} if the multimap already contained the key-value pair and
106   *     doesn't allow duplicates
107   */
108  boolean put(@Nullable K key, @Nullable V value);
109
110  /**
111   * Removes a key-value pair from the multimap.
112   *
113   * @param key key of entry to remove from the multimap
114   * @param value value of entry to remove the multimap
115   * @return {@code true} if the multimap changed
116   */
117  boolean remove(@Nullable Object key, @Nullable Object value);
118
119  // Bulk Operations
120
121  /**
122   * Stores a collection of values with the same key.
123   *
124   * @param key key to store in the multimap
125   * @param values values to store in the multimap
126   * @return {@code true} if the multimap changed
127   */
128  boolean putAll(@Nullable K key, Iterable<? extends V> values);
129
130  /**
131   * Copies all of another multimap's key-value pairs into this multimap. The
132   * order in which the mappings are added is determined by
133   * {@code multimap.entries()}.
134   *
135   * @param multimap mappings to store in this multimap
136   * @return {@code true} if the multimap changed
137   */
138  boolean putAll(Multimap<? extends K, ? extends V> multimap);
139
140  /**
141   * Stores a collection of values with the same key, replacing any existing
142   * values for that key.
143   *
144   * @param key key to store in the multimap
145   * @param values values to store in the multimap
146   * @return the collection of replaced values, or an empty collection if no
147   *     values were previously associated with the key. The collection
148   *     <i>may</i> be modifiable, but updating it will have no effect on the
149   *     multimap.
150   */
151  Collection<V> replaceValues(@Nullable K key, Iterable<? extends V> values);
152
153  /**
154   * Removes all values associated with a given key.
155   *
156   * @param key key of entries to remove from the multimap
157   * @return the collection of removed values, or an empty collection if no
158   *     values were associated with the provided key. The collection
159   *     <i>may</i> be modifiable, but updating it will have no effect on the
160   *     multimap.
161   */
162  Collection<V> removeAll(@Nullable Object key);
163
164  /**
165   * Removes all key-value pairs from the multimap.
166   */
167  void clear();
168
169  // Views
170
171  /**
172   * Returns a collection view of all values associated with a key. If no
173   * mappings in the multimap have the provided key, an empty collection is
174   * returned.
175   *
176   * <p>Changes to the returned collection will update the underlying multimap,
177   * and vice versa.
178   *
179   * @param key key to search for in multimap
180   * @return the collection of values that the key maps to
181   */
182  Collection<V> get(@Nullable K key);
183
184  /**
185   * Returns the set of all keys, each appearing once in the returned set.
186   * Changes to the returned set will update the underlying multimap, and vice
187   * versa.
188   *
189   * @return the collection of distinct keys
190   */
191  Set<K> keySet();
192
193  /**
194   * Returns a collection, which may contain duplicates, of all keys. The number
195   * of times of key appears in the returned multiset equals the number of
196   * mappings the key has in the multimap. Changes to the returned multiset will
197   * update the underlying multimap, and vice versa.
198   *
199   * @return a multiset with keys corresponding to the distinct keys of the
200   *     multimap and frequencies corresponding to the number of values that
201   *     each key maps to
202   */
203  Multiset<K> keys();
204
205  /**
206   * Returns a collection of all values in the multimap. Changes to the returned
207   * collection will update the underlying multimap, and vice versa.
208   *
209   * @return collection of values, which may include the same value multiple
210   *     times if it occurs in multiple mappings
211   */
212  Collection<V> values();
213
214  /**
215   * Returns a collection of all key-value pairs. Changes to the returned
216   * collection will update the underlying multimap, and vice versa. The entries
217   * collection does not support the {@code add} or {@code addAll} operations.
218   *
219   * @return collection of map entries consisting of key-value pairs
220   */
221  Collection<Map.Entry<K, V>> entries();
222
223  /**
224   * Returns a map view that associates each key with the corresponding values
225   * in the multimap. Changes to the returned map, such as element removal, will
226   * update the underlying multimap. The map does not support {@code setValue()}
227   * on its entries, {@code put}, or {@code putAll}.
228   *
229   * <p>When passed a key that is present in the map, {@code
230   * asMap().get(Object)} has the same behavior as {@link #get}, returning a
231   * live collection. When passed a key that is not present, however, {@code
232   * asMap().get(Object)} returns {@code null} instead of an empty collection.
233   *
234   * @return a map view from a key to its collection of values
235   */
236  Map<K, Collection<V>> asMap();
237
238  // Comparison and hashing
239
240  /**
241   * Compares the specified object with this multimap for equality. Two
242   * multimaps are equal when their map views, as returned by {@link #asMap},
243   * are also equal.
244   *
245   * <p>In general, two multimaps with identical key-value mappings may or may
246   * not be equal, depending on the implementation. For example, two
247   * {@link SetMultimap} instances with the same key-value mappings are equal,
248   * but equality of two {@link ListMultimap} instances depends on the ordering
249   * of the values for each key.
250   *
251   * <p>A non-empty {@link SetMultimap} cannot be equal to a non-empty
252   * {@link ListMultimap}, since their {@link #asMap} views contain unequal
253   * collections as values. However, any two empty multimaps are equal, because
254   * they both have empty {@link #asMap} views.
255   */
256  @Override
257  boolean equals(@Nullable Object obj);
258
259  /**
260   * Returns the hash code for this multimap.
261   *
262   * <p>The hash code of a multimap is defined as the hash code of the map view,
263   * as returned by {@link Multimap#asMap}.
264   */
265  @Override
266  int hashCode();
267}