com.google.common.collect

Class HashMultimap<K,V>

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,V>
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. To allow concurrent update operations, wrap your multimap with a call to Multimaps.synchronizedSetMultimap(com.google.common.collect.SetMultimap<K, V>).

Since:

2.0

Author:

Jared Levy

See Also:

Serialized Form

Method Summary

Modifier and Type	Method and 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(Object key, Object value) Returns true if this multimap contains at least one key-value pair with the key key and the value value.
boolean	containsKey(Object key) Returns true if this multimap contains at least one key-value pair with the key key.
boolean	containsValue(Object value) Returns true if this multimap contains at least one key-value pair with the value value.
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.
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(Object object) Compares the specified object to this multimap for equality.
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(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	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	remove(Object key, 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(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, hashCode, isEmpty, keys, keySet, putAll, putAll, remove, size, values

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:

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 Set<V> get(@Nullable
                  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,V>

Specified by:

get in interface SetMultimap<K,V>

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,V>

Specified by:

entries in interface SetMultimap<K,V>

removeAll

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,V>

Specified by:

removeAll in interface SetMultimap<K,V>

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

public Set<V> replaceValues(@Nullable
                            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,V>

Specified by:

replaceValues in interface SetMultimap<K,V>

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,V>

Specified by:

asMap in interface SetMultimap<K,V>

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
                      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 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,V>

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,V>

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,V>

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,V>

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,V>

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,V>

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,V>

remove

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,V>

Returns:

true if the multimap changed

putAll

public boolean putAll(@Nullable
                      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,V>

Returns:

true if the multimap changed

putAll

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,V>

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,V>

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,V>

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 Object

See Also:

Map.hashCode()

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