Package com.google.common.collect

Class HashMultimap<K,​V>

  • All Implemented Interfaces:
    Multimap<K,​V>, SetMultimap<K,​V>, java.io.Serializable
    @GwtCompatible(serializable=true,
               emulated=true)
public final class HashMultimap<K,​V>
extends java.lang.Object
    Implementation of Multimap using hash tables.

    The multimap does not store duplicate key-value pairs. Adding a new key-value pair equal to an existing key-value pair has no effect.

    Keys and values may be null. All optional multimap methods are supported, and all returned views are modifiable.

    This class is not threadsafe when any concurrent operations update the multimap. Concurrent read operations will work correctly. To allow concurrent update operations, wrap your multimap with a call to Multimaps.synchronizedSetMultimap(com.google.common.collect.SetMultimap<K, V>).

    Since:
    2.0 (imported from Google Collections Library)
    See Also:
    Serialized Form

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      java.util.Map<K,​java.util.Collection<V>> asMap()
      Returns a map view that associates each key with the corresponding values in the multimap.
      void clear()
      Removes all key-value pairs from the multimap.
      boolean containsEntry​(java.lang.Object key, java.lang.Object value)
      Returns true if the multimap contains the specified key-value pair.
      boolean containsKey​(java.lang.Object key)
      Returns true if the multimap contains any values for the specified key.
      boolean containsValue​(java.lang.Object value)
      Returns true if the multimap contains the specified value for any key.
      static <K,​V>
      HashMultimap<K,​V>      		 create()
      Creates a new, empty HashMultimap with the default initial capacities.
      static <K,​V>
      HashMultimap<K,​V>      		 create​(int expectedKeys, int expectedValuesPerKey)
      Constructs an empty HashMultimap with enough capacity to hold the specified numbers of keys and values without rehashing.
      static <K,​V>
      HashMultimap<K,​V>      		 create​(Multimap<? extends K,​? extends V> multimap)
      Constructs a HashMultimap with the same mappings as the specified multimap.
      java.util.Set<java.util.Map.Entry<K,​V>> entries()
      Returns a collection of all key-value pairs.
      boolean equals​(java.lang.Object object)
      Compares the specified object to this multimap for equality.
      java.util.Set<V> get​(K key)
      Returns a collection view containing the values associated with key in this multimap, if any.
      int hashCode()
      Returns the hash code for this multimap.
      boolean isEmpty()
      Returns true if the multimap contains no key-value pairs.
      Multiset<K> keys()
      Returns a collection, which may contain duplicates, of all keys.
      java.util.Set<K> keySet()
      Returns the set of all keys, each appearing once in the returned set.
      boolean put​(K key, V value)
      Stores a key-value pair in the multimap.
      boolean putAll​(Multimap<? extends K,​? extends V> multimap)
      Copies all of another multimap's key-value pairs into this multimap.
      boolean putAll​(K key, java.lang.Iterable<? extends V> values)
      Stores key-value pairs in this multimap with one key and multiple values.
      boolean remove​(java.lang.Object key, java.lang.Object value)
      Removes a single key-value pair from the multimap.
      java.util.Set<V> removeAll​(java.lang.Object key)
      Removes all values associated with a given key.
      java.util.Set<V> replaceValues​(K key, java.lang.Iterable<? extends V> values)
      Stores a collection of values with the same key, replacing any existing values for that key.
      int size()
      Returns the number of key-value pairs in the multimap.
      java.lang.String toString()
      Returns a string representation of the multimap, generated by calling toString on the map returned by Multimap.asMap().
      java.util.Collection<V> values()
      Returns a collection of all values in the multimap.

      • Methods inherited from class java.lang.Object

        getClass, notify, notifyAll, wait, wait, wait

    • Method Detail

      • create

        public static <K,​V> HashMultimap<K,​V> create()
        Creates a new, empty HashMultimap with the default initial capacities.

      • create

        public static <K,​V> HashMultimap<K,​V> create​(int expectedKeys,
                                                         int expectedValuesPerKey)
        Constructs an empty HashMultimap with enough capacity to hold the specified numbers of keys and values without rehashing.
        Parameters:
        expectedKeys - the expected number of distinct keys
        expectedValuesPerKey - the expected average number of values per key
        Throws:
        java.lang.IllegalArgumentException - if expectedKeys or expectedValuesPerKey is negative

      • create

        public static <K,​V> HashMultimap<K,​V> create​(Multimap<? extends K,​? extends V> multimap)
        Constructs a HashMultimap with the same mappings as the specified multimap. If a key-value mapping appears multiple times in the input multimap, it only appears once in the constructed multimap.
        Parameters:
        multimap - the multimap whose contents are copied to this multimap

      • get

        public java.util.Set<V> get​(@Nullable
                            K key)
        Returns a collection view containing the values associated with key in this multimap, if any. Note that even when (containsKey(key) is false, get(key) still returns an empty collection, not null.

        Changes to the returned collection will update the underlying multimap, and vice versa.

        The returned collection is not serializable.

        Because a SetMultimap has unique values for a given key, this method returns a Set, instead of the Collection specified in the Multimap interface.

        Specified by:
        get in interface Multimap<K,​V>
        Specified by:
        get in interface SetMultimap<K,​V>
        Parameters:
        key - key to search for in multimap
        Returns:
        a view collection containing the zero or more values that the key maps to

      • entries

        public java.util.Set<java.util.Map.Entry<K,​V>> entries()
        Returns a collection of all key-value pairs. Changes to the returned collection will update the underlying multimap, and vice versa. The entries collection does not support the add or addAll operations.

        The iterator generated by the returned collection traverses the values for one key, followed by the values of a second key, and so on.

        Each entry is an immutable snapshot of a key-value mapping in the multimap, taken at the time the entry is returned by a method call to the collection or its iterator.

        Because a SetMultimap has unique values for a given key, this method returns a Set, instead of the Collection specified in the Multimap interface.

        Specified by:
        entries in interface Multimap<K,​V>
        Specified by:
        entries in interface SetMultimap<K,​V>
        Returns:
        collection of map entries consisting of key-value pairs

      • removeAll

        public java.util.Set<V> removeAll​(@Nullable
                                  java.lang.Object key)
        Removes all values associated with a given key.

        Once this method returns, key will not be mapped to any values, so it will not appear in Multimap.keySet(), Multimap.asMap(), or any other views.

        The returned collection is immutable.

        Because a SetMultimap has unique values for a given key, this method returns a Set, instead of the Collection specified in the Multimap interface.

        Specified by:
        removeAll in interface Multimap<K,​V>
        Specified by:
        removeAll in interface SetMultimap<K,​V>
        Parameters:
        key - key of entries to remove from the multimap
        Returns:
        the collection of removed values, or an empty collection if no values were associated with the provided key. The collection may be modifiable, but updating it will have no effect on the multimap.

      • replaceValues

        public java.util.Set<V> replaceValues​(@Nullable
                                      K key,
                                      java.lang.Iterable<? extends V> values)
        Stores a collection of values with the same key, replacing any existing values for that key.

        If values is empty, this is equivalent to removeAll(key).

        The returned collection is immutable.

        Because a SetMultimap has unique values for a given key, this method returns a Set, instead of the Collection specified in the Multimap interface.

        Any duplicates in values will be stored in the multimap once.

        Specified by:
        replaceValues in interface Multimap<K,​V>
        Specified by:
        replaceValues in interface SetMultimap<K,​V>
        Parameters:
        key - key to store in the multimap
        values - values to store in the multimap
        Returns:
        the collection of replaced values, or an empty collection if no values were previously associated with the key. The collection may be modifiable, but updating it will have no effect on the multimap.

      • asMap

        public java.util.Map<K,​java.util.Collection<V>> asMap()
        Returns a map view that associates each key with the corresponding values in the multimap. Changes to the returned map, such as element removal, will update the underlying multimap. The map does not support setValue() on its entries, put, or putAll.

        When passed a key that is present in the map, asMap().get(Object) has the same behavior as Multimap.get(K), returning a live collection. When passed a key that is not present, however, asMap().get(Object) returns null instead of an empty collection.

        Though the method signature doesn't say so explicitly, the returned map has Set values.

        Specified by:
        asMap in interface Multimap<K,​V>
        Specified by:
        asMap in interface SetMultimap<K,​V>
        Returns:
        a map view from a key to its collection of values

      • put

        public boolean put​(@Nullable
                   K key,
                   @Nullable
                   V value)
        Stores a key-value pair in the multimap.
        Specified by:
        put in interface Multimap<K,​V>
        Parameters:
        key - key to store in the multimap
        value - value to store in the multimap
        Returns:
        true if the method increased the size of the multimap, or false if the multimap already contained the key-value pair

      • equals

        public boolean equals​(@Nullable
                      java.lang.Object object)
        Compares the specified object to this multimap for equality.

        Two SetMultimap instances are equal if, for each key, they contain the same values. Equality does not depend on the ordering of keys or values.

        Specified by:
        equals in interface Multimap<K,​V>
        Specified by:
        equals in interface SetMultimap<K,​V>

      • size

        public int size()
        Description copied from interface: Multimap
        Returns the number of key-value pairs in the multimap.
        Specified by:
        size in interface Multimap<K,​V>

      • containsKey

        public boolean containsKey​(@Nullable
                           java.lang.Object key)
        Description copied from interface: Multimap
        Returns true if the multimap contains any values for the specified key.
        Specified by:
        containsKey in interface Multimap<K,​V>
        Parameters:
        key - key to search for in multimap

      • clear

        public void clear()
        Description copied from interface: Multimap
        Removes all key-value pairs from the multimap.
        Specified by:
        clear in interface Multimap<K,​V>

      • values

        public java.util.Collection<V> values()
        Returns a collection of all values in the multimap. Changes to the returned collection will update the underlying multimap, and vice versa.

        The iterator generated by the returned collection traverses the values for one key, followed by the values of a second key, and so on.

        Specified by:
        values in interface Multimap<K,​V>
        Returns:
        collection of values, which may include the same value multiple times if it occurs in multiple mappings

      • isEmpty

        public boolean isEmpty()
        Description copied from interface: Multimap
        Returns true if the multimap contains no key-value pairs.
        Specified by:
        isEmpty in interface Multimap<K,​V>

      • containsValue

        public boolean containsValue​(@Nullable
                             java.lang.Object value)
        Description copied from interface: Multimap
        Returns true if the multimap contains the specified value for any key.
        Specified by:
        containsValue in interface Multimap<K,​V>
        Parameters:
        value - value to search for in multimap

      • containsEntry

        public boolean containsEntry​(@Nullable
                             java.lang.Object key,
                             @Nullable
                             java.lang.Object value)
        Description copied from interface: Multimap
        Returns true if the multimap contains the specified key-value pair.
        Specified by:
        containsEntry in interface Multimap<K,​V>
        Parameters:
        key - key to search for in multimap
        value - value to search for in multimap

      • remove

        public boolean remove​(@Nullable
                      java.lang.Object key,
                      @Nullable
                      java.lang.Object value)
        Description copied from interface: Multimap
        Removes a single key-value pair from the multimap.
        Specified by:
        remove in interface Multimap<K,​V>
        Parameters:
        key - key of entry to remove from the multimap
        value - value of entry to remove the multimap
        Returns:
        true if the multimap changed

      • putAll

        public boolean putAll​(@Nullable
                      K key,
                      java.lang.Iterable<? extends V> values)
        Description copied from interface: Multimap
        Stores key-value pairs in this multimap with one key and multiple values.

        This is equivalent to 

           
 
   for (V value : values) {
     put(key, value);
   }

        In particular, this is a no-op if values is empty.

        Specified by:
        putAll in interface Multimap<K,​V>
        Parameters:
        key - key to store in the multimap
        values - values to store in the multimap
        Returns:
        true if the multimap changed

      • putAll

        public boolean putAll​(Multimap<? extends K,​? extends V> multimap)
        Description copied from interface: Multimap
        Copies all of another multimap's key-value pairs into this multimap. The order in which the mappings are added is determined by multimap.entries().
        Specified by:
        putAll in interface Multimap<K,​V>
        Parameters:
        multimap - mappings to store in this multimap
        Returns:
        true if the multimap changed

      • keySet

        public java.util.Set<K> keySet()
        Description copied from interface: Multimap
        Returns the set of all keys, each appearing once in the returned set. Changes to the returned set will update the underlying multimap, and vice versa.

        Note that the key set contains a key if and only if this multimap maps that key to at least one value.

        Specified by:
        keySet in interface Multimap<K,​V>
        Returns:
        the collection of distinct keys

      • keys

        public Multiset<K> keys()
        Description copied from interface: Multimap
        Returns a collection, which may contain duplicates, of all keys. The number of times of key appears in the returned multiset equals the number of mappings the key has in the multimap. Changes to the returned multiset will update the underlying multimap, and vice versa.
        Specified by:
        keys in interface Multimap<K,​V>
        Returns:
        a multiset with keys corresponding to the distinct keys of the multimap and frequencies corresponding to the number of values that each key maps to

      • hashCode

        public int hashCode()
        Returns the hash code for this multimap.

        The hash code of a multimap is defined as the hash code of the map view, as returned by Multimap.asMap().

        Specified by:
        hashCode in interface Multimap<K,​V>
        Overrides:
        hashCode in class java.lang.Object
        See Also:
        Map.hashCode()

      • toString

        public java.lang.String toString()
        Returns a string representation of the multimap, generated by calling toString on the map returned by Multimap.asMap().
        Overrides:
        toString in class java.lang.Object
        Returns:
        a string representation of the multimap