Package com.google.common.collect

Class HashMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

  • All Implemented Interfaces:
    Multimap<K,​V>, SetMultimap<K,​V>, java.io.Serializable
    @GwtCompatible(serializable=true,
               emulated=true)
public final class HashMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
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 if the last write happens-before any reads. To allow concurrent update operations, wrap your multimap with a call to Multimaps.synchronizedSetMultimap(com.google.common.collect.SetMultimap<K, V>).

    Warning: Do not modify either a key or a value of a HashMultimap in a way that affects its Object.equals(java.lang.Object) behavior. Undefined behavior and bugs will result.

    Since:
    2.0
    Author:
    Jared Levy
    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 view of this multimap as a Map from each distinct key to the nonempty collection of that key's associated values.
      void clear()
      Removes all key-value pairs from the multimap, leaving it empty.
      boolean containsEntry​(java.lang.Object key, java.lang.Object value)
      Returns true if this multimap contains at least one key-value pair with the key key and the value value.
      boolean containsKey​(java.lang.Object key)
      Returns true if this multimap contains at least one key-value pair with the key key.
      boolean containsValue​(java.lang.Object value)
      Returns true if this multimap contains at least one key-value pair with the value value.
      static <K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
      HashMultimap<K,​V>      		 create()
      Creates a new, empty HashMultimap with the default initial capacities.
      static <K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
      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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
      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 view collection of all key-value pairs contained in this multimap, as Map.Entry instances.
      boolean equals​(java.lang.Object object)
      Compares the specified object to this multimap for equality.
      void forEach​(java.util.function.BiConsumer<? super K,​? super V> action)
      Performs the given action for all key-value pairs contained in this multimap.
      java.util.Set<V> get​(K key)
      Returns a view collection of the values associated with key in this multimap, if any.
      int hashCode()
      Returns the hash code for this multimap.
      boolean isEmpty()
      Returns true if this multimap contains no key-value pairs.
      Multiset<K> keys()
      Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates.
      java.util.Set<K> keySet()
      Returns a view collection of all distinct keys contained in this multimap.
      boolean put​(K key, V value)
      Stores a key-value pair in the multimap.
      boolean putAll​(Multimap<? extends K,​? extends V> multimap)
      Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries().
      boolean putAll​(K key, java.lang.Iterable<? extends V> values)
      Stores a key-value pair in this multimap for each of values, all using the same key, key.
      boolean remove​(java.lang.Object key, java.lang.Object value)
      Removes a single key-value pair with the key key and the value value from this multimap, if such exists.
      java.util.Set<V> removeAll​(java.lang.Object key)
      Removes all values associated with the key 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 this 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 view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()).

      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, wait, wait, wait

    • Method Detail

      • create

        public static <K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object> HashMultimap<K,​V> create()
        Creates a new, empty HashMultimap with the default initial capacities.

        You may also consider the equivalent MultimapBuilder.hashKeys().hashSetValues().build(), which provides more control over the underlying data structure.

      • create

        public static <K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object> 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.

        You may also consider the equivalent MultimapBuilder.hashKeys(expectedKeys).hashSetValues(expectedValuesPerKey).build(), which provides more control over the underlying data structure.

        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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object> 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.

        You may also consider the equivalent MultimapBuilder.hashKeys().hashSetValues().build(multimap), which provides more control over the underlying data structure.

        Parameters:
        multimap - the multimap whose contents are copied to this multimap

      • get

        public java.util.Set<V> get​(K key)
        Returns a view collection of the values associated with key in this multimap, if any. Note that when containsKey(key) is false, this 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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        get in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • entries

        public java.util.Set<java.util.Map.Entry<K,​V>> entries()
        Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances.

        Changes to the returned collection or the entries it contains will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

        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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        entries in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • removeAll

        @CanIgnoreReturnValue
public java.util.Set<V> removeAll​(@CheckForNull
                                  java.lang.Object key)
        Removes all values associated with the key 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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        removeAll in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Returns:
        the values that were removed (possibly empty). The returned collection may be modifiable, but updating it will have no effect on the multimap.

      • replaceValues

        @CanIgnoreReturnValue
public 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.

        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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        replaceValues in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        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 view of this multimap as a Map from each distinct key to the nonempty collection of that key's associated values. Note that this.asMap().get(k) is equivalent to this.get(k) only when k is a key contained in the multimap; otherwise it returns null as opposed to an empty collection.

        Changes to the returned map or the collections that serve as its values will update the underlying multimap, and vice versa. The map does not support put or putAll, nor do its entries support setValue.

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

        Specified by:
        asMap in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        asMap in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • put

        @CanIgnoreReturnValue
public boolean put​(K key,
                   V value)
        Stores a key-value pair in the multimap.
        Specified by:
        put in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        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​(@CheckForNull
                      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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Specified by:
        equals in interface SetMultimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • size

        public int size()
        Description copied from interface: Multimap
        Returns the number of key-value pairs in this multimap.

        Note: this method does not return the number of distinct keys in the multimap, which is given by keySet().size() or asMap().size(). See the opening section of the Multimap class documentation for clarification.

        Specified by:
        size in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • containsKey

        public boolean containsKey​(@CheckForNull
                           java.lang.Object key)
        Description copied from interface: Multimap
        Returns true if this multimap contains at least one key-value pair with the key key.
        Specified by:
        containsKey in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • clear

        public void clear()
        Description copied from interface: Multimap
        Removes all key-value pairs from the multimap, leaving it empty.
        Specified by:
        clear in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • values

        public java.util.Collection<V> values()
        Returns a view collection containing the value from each key-value pair contained in this multimap, without collapsing duplicates (so values().size() == size()).

        Changes to the returned collection will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

        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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • forEach

        public void forEach​(java.util.function.BiConsumer<? super K,​? super V> action)
        Description copied from interface: Multimap
        Performs the given action for all key-value pairs contained in this multimap. If an ordering is specified by the Multimap implementation, actions will be performed in the order of iteration of Multimap.entries(). Exceptions thrown by the action are relayed to the caller.

        To loop over all keys and their associated value collections, write Multimaps.asMap(multimap).forEach((key, valueCollection) -> action()).

        Specified by:
        forEach in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • isEmpty

        public boolean isEmpty()
        Description copied from interface: Multimap
        Returns true if this multimap contains no key-value pairs. Equivalent to size() == 0, but can in some cases be more efficient.
        Specified by:
        isEmpty in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • containsValue

        public boolean containsValue​(@CheckForNull
                             java.lang.Object value)
        Description copied from interface: Multimap
        Returns true if this multimap contains at least one key-value pair with the value value.
        Specified by:
        containsValue in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • containsEntry

        public boolean containsEntry​(@CheckForNull
                             java.lang.Object key,
                             @CheckForNull
                             java.lang.Object value)
        Description copied from interface: Multimap
        Returns true if this multimap contains at least one key-value pair with the key key and the value value.
        Specified by:
        containsEntry in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • remove

        @CanIgnoreReturnValue
public boolean remove​(@CheckForNull
                      java.lang.Object key,
                      @CheckForNull
                      java.lang.Object value)
        Description copied from interface: Multimap
        Removes a single key-value pair with the key key and the value value from this multimap, if such exists. If multiple key-value pairs in the multimap fit this description, which one is removed is unspecified.
        Specified by:
        remove in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Returns:
        true if the multimap changed

      • putAll

        @CanIgnoreReturnValue
public boolean putAll​(K key,
                      java.lang.Iterable<? extends V> values)
        Description copied from interface: Multimap
        Stores a key-value pair in this multimap for each of values, all using the same key, key. Equivalent to (but expected to be more efficient than): 
        
 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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Returns:
        true if the multimap changed

      • putAll

        @CanIgnoreReturnValue
public boolean putAll​(Multimap<? extends K,​? extends V> multimap)
        Description copied from interface: Multimap
        Stores all key-value pairs of multimap in this multimap, in the order returned by multimap.entries().
        Specified by:
        putAll in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        Returns:
        true if the multimap changed

      • keySet

        public java.util.Set<K> keySet()
        Description copied from interface: Multimap
        Returns a view collection of all distinct keys contained in this multimap. Note that the key set contains a key if and only if this multimap maps that key to at least one value.

        Changes to the returned set will update the underlying multimap, and vice versa. However, adding to the returned set is not possible.

        Specified by:
        keySet in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • keys

        public Multiset<K> keys()
        Description copied from interface: Multimap
        Returns a view collection containing the key from each key-value pair in this multimap, without collapsing duplicates. This collection has the same size as this multimap, and keys().count(k) == get(k).size() for all k.

        Changes to the returned multiset will update the underlying multimap, and vice versa. However, adding to the returned collection is not possible.

        Specified by:
        keys in interface Multimap<K extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>

      • 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 extends @Nullable java.lang.Object,​V extends @Nullable java.lang.Object>
        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