Class HashMultimap<K extends @Nullable Object,V extends @Nullable Object>

java.lang.Object
com.google.common.collect.HashMultimap<K,V>
All Implemented Interfaces:
Multimap<K,V>, SetMultimap<K,V>, Serializable
@GwtCompatible(serializable=true, emulated=true) public final class HashMultimap<K extends @Nullable Object,V extends @Nullable Object> extends 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:

  • Method Summary

    Modifier and Type
    Method
    Description
    Map<K,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(@Nullable Object key, @Nullable Object value)
    Returns true if this multimap contains at least one key-value pair with the key key and the value value.
    boolean
    containsKey(@Nullable Object key)
    Returns true if this multimap contains at least one key-value pair with the key key.
    boolean
    containsValue(@Nullable Object value)
    Returns true if this multimap contains at least one key-value pair with the value value.
    static <K extends @Nullable Object, V extends @Nullable Object>
    HashMultimap<K,V>
    create()
    Creates a new, empty HashMultimap with the default initial capacities.
    static <K extends @Nullable Object, V extends @Nullable 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 Object, V extends @Nullable Object>
    HashMultimap<K,V>
    create(Multimap<? extends K,? extends V> multimap)
    Constructs a HashMultimap with the same mappings as the specified multimap.
    Set<Map.Entry<K,V>>
    entries()
    Returns a view collection of all key-value pairs contained in this multimap, as Map.Entry instances.
    boolean
    equals(@Nullable Object object)
    Compares the specified object to this multimap for equality.
    void
    forEach(BiConsumer<? super K,? super V> action)
    Performs the given action for all key-value pairs contained in this multimap.
    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.
    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, Iterable<? extends V> values)
    Stores a key-value pair in this multimap for each of values, all using the same key, key.
    boolean
    remove(@Nullable Object key, @Nullable Object value)
    Removes a single key-value pair with the key key and the value value from this multimap, if such exists.
    Set<V>
    removeAll(@Nullable Object key)
    Removes all values associated with the key key.
    Set<V>
    replaceValues(K key, 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.
    String
    toString()
    Returns a string representation of the multimap, generated by calling toString on the map returned by Multimap.asMap().
    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

    Methods inherited from interface com.google.common.collect.Multimap

    clear, containsEntry, containsKey, containsValue, forEach, hashCode, isEmpty, keys, keySet, putAll, putAll, remove, size, values

  • Method Details

    • create

      public static <K extends @Nullable Object, V extends @Nullable 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 Object, V extends @Nullable 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:
      IllegalArgumentException - if expectedKeys or expectedValuesPerKey is negative

    • create

      public static <K extends @Nullable Object, V extends @Nullable 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 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 Object,V extends @Nullable Object>
      Specified by:
      get in interface SetMultimap<K extends @Nullable Object,V extends @Nullable Object>

    • entries

      public Set<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 Object,V extends @Nullable Object>
      Specified by:
      entries in interface SetMultimap<K extends @Nullable Object,V extends @Nullable Object>

    • removeAll

      @CanIgnoreReturnValue public Set<V> removeAll(@Nullable 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 Object,V extends @Nullable Object>
      Specified by:
      removeAll in interface SetMultimap<K extends @Nullable Object,V extends @Nullable 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 Set<V> replaceValues(K key, 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 Object,V extends @Nullable Object>
      Specified by:
      replaceValues in interface SetMultimap<K extends @Nullable Object,V extends @Nullable 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 Map<K,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 Object,V extends @Nullable Object>
      Specified by:
      asMap in interface SetMultimap<K extends @Nullable Object,V extends @Nullable 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 Object,V extends @Nullable 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(@Nullable 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 Object,V extends @Nullable Object>
      Specified by:
      equals in interface SetMultimap<K extends @Nullable Object,V extends @Nullable 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 Object,V extends @Nullable Object>

    • containsKey

      public boolean containsKey(@Nullable 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 Object,V extends @Nullable 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 Object,V extends @Nullable Object>

    • values

      public 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 Object,V extends @Nullable Object>

    • forEach

      public void forEach(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 Object,V extends @Nullable 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 Object,V extends @Nullable Object>

    • containsValue

      public boolean containsValue(@Nullable 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 Object,V extends @Nullable Object>

    • containsEntry

      public boolean containsEntry(@Nullable Object key, @Nullable 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 Object,V extends @Nullable Object>

    • remove

      @CanIgnoreReturnValue public boolean remove(@Nullable Object key, @Nullable 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 Object,V extends @Nullable Object>
      Returns:
      true if the multimap changed

    • putAll

      @CanIgnoreReturnValue public boolean putAll(K key, 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 Object,V extends @Nullable 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 Object,V extends @Nullable Object>
      Returns:
      true if the multimap changed

    • keySet

      public 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 Object,V extends @Nullable 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 Object,V extends @Nullable 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 Object,V extends @Nullable Object>
      Overrides:
      hashCode in class Object
      See Also:

    • toString

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