Package com.google.common.collect

Class ConcurrentHashMultiset<E>

java.lang.Object

java.util.AbstractCollection<E>

com.google.common.collect.ConcurrentHashMultiset<E>

All Implemented Interfaces:

Multiset<E>, Serializable, Iterable<E>, Collection<E>

public final class ConcurrentHashMultiset<E>
extends AbstractCollection<E>
implements Serializable

A multiset that supports concurrent modifications and that provides atomic versions of most Multiset operations (exceptions where noted). Null elements are not supported.

See the Guava User Guide article on Multiset.

Since:

2.0 (imported from Google Collections Library)

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface com.google.common.collect.Multiset

Multiset.Entry<E>

Method Summary

Modifier and Type	Method	Description
boolean	add(E element)	Adds a single occurrence of the specified element to this multiset.
int	add(E element, int occurrences)	Adds a number of occurrences of the specified element to this multiset.
boolean	addAll(Collection<? extends E> elementsToAdd)
void	clear()
boolean	contains(Object element)	Determines whether this multiset contains the specified element.
int	count(Object element)	Returns the number of occurrences of element in this multiset.
static <E> ConcurrentHashMultiset<E>	create()	Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.
static <E> ConcurrentHashMultiset<E>	create(MapMaker mapMaker)	Creates a new, empty ConcurrentHashMultiset using mapMaker to construct the internal backing map.
static <E> ConcurrentHashMultiset<E>	create(Iterable<? extends E> elements)	Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.
Set<E>	elementSet()	Returns the set of distinct elements contained in this multiset.
Set<Multiset.Entry<E>>	entrySet()	Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element.
boolean	equals(Object object)	Compares the specified object with this multiset for equality.
int	hashCode()	Returns the hash code for this multiset.
boolean	isEmpty()
Iterator<E>	iterator()
boolean	remove(Object element)	Removes a single occurrence of the specified element from this multiset, if present.
int	remove(Object element, int occurrences)	Removes a number of occurrences of the specified element from this multiset.
boolean	removeAll(Collection<?> elementsToRemove)
boolean	removeExactly(Object element, int occurrences)	Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.
boolean	retainAll(Collection<?> elementsToRetain)
int	setCount(E element, int count)	Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.
boolean	setCount(E element, int expectedOldCount, int newCount)	Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount.
int	size()
Object[]	toArray()
<T> T[]	toArray(T[] array)
String	toString()

Methods inherited from class java.util.AbstractCollection

containsAll

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

parallelStream, removeIf, spliterator, stream, toArray

Methods inherited from interface java.lang.Iterable

forEach

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

containsAll

Method Detail

create

public static <E> ConcurrentHashMultiset<E> create()

Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.

create

public static <E> ConcurrentHashMultiset<E> create(Iterable<? extends E> elements)

Creates a new ConcurrentHashMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.

This implementation is highly efficient when elements is itself a Multiset.

Parameters:

elements - the elements that the multiset should contain

create

@Beta
public static <E> ConcurrentHashMultiset<E> create(MapMaker mapMaker)

Creates a new, empty ConcurrentHashMultiset using mapMaker to construct the internal backing map.

If this MapMaker is configured to use entry eviction of any kind, this eviction applies to all occurrences of a given element as a single unit. However, most updates to the multiset do not count as map updates at all, since we're usually just mutating the value stored in the map, so MapMaker.expireAfterAccess(long, java.util.concurrent.TimeUnit) makes sense (evict the entry that was queried or updated longest ago), but MapMaker.expireAfterWrite(long, java.util.concurrent.TimeUnit) doesn't, because the eviction time is measured from when we saw the first occurrence of the object.

The returned multiset is serializable but any serialization caveats given in MapMaker apply.

Finally, soft/weak values can be used but are not very useful: the values are created internally and not exposed externally, so no one else will have a strong reference to the values. Weak keys on the other hand can be useful in some scenarios.

Since:

15.0 (source compatible (accepting the since removed GenericMapMaker class) since 7.0)

count

public int count(@Nullable
                 Object element)

Returns the number of occurrences of element in this multiset.

Specified by:

count in interface Multiset<E>

Parameters:

element - the element to look for

Returns:

the nonnegative number of occurrences of the element

size

public int size()

If the data in the multiset is modified by any other threads during this method, it is undefined which (if any) of these modifications will be reflected in the result.

Specified by:

size in interface Collection<E>

toArray

public Object[] toArray()

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

toArray

public <T> T[] toArray(T[] array)

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

add

public int add(E element,
               int occurrences)

Adds a number of occurrences of the specified element to this multiset.

Specified by:

add in interface Multiset<E>

Parameters:

element - the element to add

occurrences - the number of occurrences to add

Returns:

the previous count of the element before the operation; possibly zero

Throws:

IllegalArgumentException - if occurrences is negative, or if the resulting amount would exceed Integer.MAX_VALUE

remove

public int remove(@Nullable
                  Object element,
                  int occurrences)

Removes a number of occurrences of the specified element from this multiset. If the multiset contains fewer than this number of occurrences to begin with, all occurrences will be removed.

Specified by:

remove in interface Multiset<E>

Parameters:

element - the element whose occurrences should be removed

occurrences - the number of occurrences of the element to remove

Returns:

the count of the element before the operation; possibly zero

Throws:

IllegalArgumentException - if occurrences is negative

removeExactly

public boolean removeExactly(@Nullable
                             Object element,
                             int occurrences)

Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.

This method, in contrast to remove(Object, int), has no effect when the element count is smaller than occurrences.

Parameters:

element - the element to remove

occurrences - the number of occurrences of element to remove

Returns:

true if the removal was possible (including if occurrences is zero)

setCount

public int setCount(E element,
                    int count)

Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.

Specified by:

setCount in interface Multiset<E>

Parameters:

element - the element to add or remove occurrences of; may be null only if explicitly allowed by the implementation

count - the desired count of the element in this multiset

Returns:

the count of element in the multiset before this call

Throws:

IllegalArgumentException - if count is negative

setCount

public boolean setCount(E element,
                        int expectedOldCount,
                        int newCount)

Sets the number of occurrences of element to newCount, but only if the count is currently expectedOldCount. If element does not appear in the multiset exactly expectedOldCount times, no changes will be made.

Specified by:

setCount in interface Multiset<E>

Parameters:

element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementation

expectedOldCount - the expected present count of the element in this multiset

newCount - the desired count of the element in this multiset

Returns:

true if the change was successful. This usually indicates that the multiset has been modified, but not always: in the case that expectedOldCount == newCount, the method will return true if the condition was met.

Throws:

IllegalArgumentException - if expectedOldCount or newCount is negative

entrySet

public Set<Multiset.Entry<E>> entrySet()

Description copied from interface: Multiset

Returns a view of the contents of this multiset, grouped into Multiset.Entry instances, each providing an element of the multiset and the count of that element. This set contains exactly one entry for each distinct element in the multiset (thus it always has the same size as the Multiset.elementSet()). The order of the elements in the element set is unspecified.

The entry set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. However, multiset changes may or may not be reflected in any Entry instances already retrieved from the entry set (this is implementation-dependent). Furthermore, implementations are not required to support modifications to the entry set at all, and the Entry instances themselves don't even have methods for modification. See the specific implementation class for more details on how its entry set handles modifications.

Specified by:

entrySet in interface Multiset<E>

Returns:

a set of entries representing the data of this multiset

isEmpty

public boolean isEmpty()

Specified by:

isEmpty in interface Collection<E>

clear

public void clear()

Specified by:

clear in interface Collection<E>

contains

public boolean contains(@Nullable
                        Object element)

Description copied from interface: Multiset

Determines whether this multiset contains the specified element.

This method refines Collection.contains(java.lang.Object) to further specify that it may not throw an exception in response to element being null or of the wrong type.

Specified by:

contains in interface Collection<E>

Specified by:

contains in interface Multiset<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

element - the element to check for

Returns:

true if this multiset contains at least one occurrence of the element

iterator

public Iterator<E> iterator()

Description copied from interface: Multiset

Elements that occur multiple times in the multiset will appear multiple times in this iterator, though not necessarily sequentially.

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Specified by:

iterator in interface Multiset<E>

Specified by:

iterator in class AbstractCollection<E>

add

public boolean add(@Nullable
                   E element)

Description copied from interface: Multiset

Adds a single occurrence of the specified element to this multiset.

This method refines Collection.add(E), which only ensures the presence of the element, to further specify that a successful call must always increment the count of the element, and the overall size of the collection, by one.

Specified by:

add in interface Collection<E>

Specified by:

add in interface Multiset<E>

Overrides:

add in class AbstractCollection<E>

Parameters:

element - the element to add one occurrence of; may be null only if explicitly allowed by the implementation

Returns:

true always, since this call is required to modify the multiset, unlike other Collection types

remove

public boolean remove(@Nullable
                      Object element)

Description copied from interface: Multiset

Removes a single occurrence of the specified element from this multiset, if present.

This method refines Collection.remove(java.lang.Object) to further specify that it may not throw an exception in response to element being null or of the wrong type.

Specified by:

remove in interface Collection<E>

Specified by:

remove in interface Multiset<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

element - the element to remove one occurrence of

Returns:

true if an occurrence was found and removed

addAll

public boolean addAll(Collection<? extends E> elementsToAdd)

This implementation is highly efficient when elementsToAdd is itself a Multiset.

Specified by:

addAll in interface Collection<E>

Overrides:

addAll in class AbstractCollection<E>

removeAll

public boolean removeAll(Collection<?> elementsToRemove)

Description copied from interface: Multiset

Note: This method ignores how often any element might appear in c, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence in c, see Multisets.removeOccurrences(Multiset, Multiset).

This method refines Collection.removeAll(java.util.Collection<?>) to further specify that it may not throw an exception in response to any of elements being null or of the wrong type.

Specified by:

removeAll in interface Collection<E>

Specified by:

removeAll in interface Multiset<E>

Overrides:

removeAll in class AbstractCollection<E>

retainAll

public boolean retainAll(Collection<?> elementsToRetain)

Description copied from interface: Multiset

Note: This method ignores how often any element might appear in c, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence in c, see Multisets.retainOccurrences(Multiset, Multiset).

This method refines Collection.retainAll(java.util.Collection<?>) to further specify that it may not throw an exception in response to any of elements being null or of the wrong type.

Specified by:

retainAll in interface Collection<E>

Specified by:

retainAll in interface Multiset<E>

Overrides:

retainAll in class AbstractCollection<E>

See Also:

Multisets.retainOccurrences(Multiset, Multiset)

elementSet

public Set<E> elementSet()

Description copied from interface: Multiset

Returns the set of distinct elements contained in this multiset. The element set is backed by the same data as the multiset, so any change to either is immediately reflected in the other. The order of the elements in the element set is unspecified.

If the element set supports any removal operations, these necessarily cause all occurrences of the removed element(s) to be removed from the multiset. Implementations are not expected to support the add operations, although this is possible.

A common use for the element set is to find the number of distinct elements in the multiset: elementSet().size().

Specified by:

elementSet in interface Multiset<E>

Returns:

a view of the set of distinct elements in this multiset

equals

public boolean equals(@Nullable
                      Object object)

Compares the specified object with this multiset for equality. Returns true if the given object is also a multiset and contains equal elements with equal counts, regardless of order.

This implementation returns true if object is a multiset of the same size and if, for each element, the two multisets have the same count.

Specified by:

equals in interface Collection<E>

Specified by:

equals in interface Multiset<E>

Overrides:

equals in class Object

hashCode

public int hashCode()

Returns the hash code for this multiset. This is defined as the sum of

   

   ((element == null) ? 0 : element.hashCode()) ^ count(element)

over all distinct elements in the multiset. It follows that a multiset and its entry set always have the same hash code.

This implementation returns the hash code of Multiset.entrySet().

Specified by:

hashCode in interface Collection<E>

Specified by:

hashCode in interface Multiset<E>

Overrides:

hashCode in class Object

toString

public String toString()

It is recommended, though not mandatory, that this method return the result of invoking Multiset.toString() on the Multiset.entrySet(), yielding a result such as [a x 3, c, d x 2, e].

This implementation returns the result of invoking toString on Multiset.entrySet().

Specified by:

toString in interface Multiset<E>

Overrides:

toString in class AbstractCollection<E>