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    
017    package com.google.common.collect;
018    
019    import com.google.common.annotations.GwtCompatible;
020    
021    import java.util.Collection;
022    import java.util.Map;
023    import java.util.Set;
024    
025    import 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 2.0 (imported from Google Collections Library)
057     */
058    @GwtCompatible
059    public 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    }