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 (imported from Google Collections Library)

Author:

Jared Levy

See Also:

Serialized Form

Method Summary

Methods

Modifier and Type	Method and Description
Map<K,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(Object key, Object value) Returns true if the multimap contains the specified key-value pair.
boolean	containsKey(Object key) Returns true if the multimap contains any values for the specified key.
boolean	containsValue(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.
Set<Map.Entry<K,V>>	entries() Returns a collection of all key-value pairs.
boolean	equals(Object object) Compares the specified object to this multimap for equality.
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.
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(K key, Iterable<? extends V> values) Stores key-value pairs in this multimap with one key and multiple values.
boolean	putAll(Multimap<? extends K,? extends V> multimap) Copies all of another multimap's key-value pairs into this multimap.
boolean	remove(Object key, Object value) Removes a single key-value pair from the multimap.
Set<V>	removeAll(Object key) Removes all values associated with a given 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 the 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 collection of all values in the multimap.

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 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 Set<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 Set<V> removeAll(@Nullable
               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 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>

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 Map<K,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
             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>

Parameters:

object - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), HashMap

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
                  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 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
                    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
                    Object key,
                    @Nullable
                    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
             Object key,
             @Nullable
             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,
             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 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 Object

Returns:

a hash code value for this 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