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>, java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>

public final class ConcurrentHashMultiset<E>
extends java.util.AbstractCollection<E>
implements java.io.Serializable

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

Author:

Cliff L. Biffle

See Also:

Serialized Form

Nested Class Summary

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

Multiset.Entry<E>

Method Summary

boolean	add(E element) Ensures that this collection contains the specified element.
int	add(E element, int occurrences) Adds a number of occurrences of the specified element to this multiset.
boolean	addAll(java.util.Collection<? extends E> elementsToAdd) Adds all of the elements in the specified collection to this multiset.
void	clear() Removes all of the elements from this multiset.
boolean	contains(java.lang.Object element) Returns true if this collection contains the specified element.
boolean	containsAll(java.util.Collection<?> elements) Returns true if this multiset contains all of the elements in the specified collection.
int	count(java.lang.Object element) Returns the number of occurrences of element in this multiset.
static <E> ConcurrentHashMultiset<E>	create() Creates a new empty ConcurrentMultiset using the default initial capacity, load factor, and concurrency settings.
static <E> ConcurrentHashMultiset<E>	create(java.lang.Iterable<? extends E> elements) Creates a new ConcurrentMultiset containing the specified elements, using the default initial capacity, load factor, and concurrency settings.
protected java.util.Set<E>	createElementSet() Creates a new instance of this multiset's element set, which will be returned by elementSet().
java.util.Set<E>	elementSet() Returns the set of distinct elements contained in this multiset.
java.util.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(java.lang.Object object) Compares the specified object with this multiset for equality.
int	hashCode() Returns the hash code for this multiset.
boolean	isEmpty()
java.util.Iterator<E>	iterator()
boolean	remove(java.lang.Object element) Removes a single instance of the specified element from this collection, if it is present.
int	remove(java.lang.Object element, int occurrences) Removes a number of occurrences of the specified element from this multiset.
boolean	removeAll(java.util.Collection<?> elementsToRemove) Removes all of this multiset's elements that are also contained in the specified collection.
boolean	removeExactly(java.lang.Object element, int occurrences) Removes exactly the specified number of occurrences of element, or makes no change if this is not possible.
boolean	retainAll(java.util.Collection<?> elementsToRetain) Retains only the elements in this multiset that are contained in the specified collection.
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 oldCount, int newCount) Sets the number of occurrences of element to newCount, but only if the count is currently oldCount.
int	size()
java.lang.Object[]	toArray()
<T> T[]	toArray(T[] array)
java.lang.String	toString()

Methods inherited from class java.lang.Object

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

Method Detail

create

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

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

create

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

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

Parameters:

elements - the elements that the multiset should contain

count

public int count(@Nullable
                 java.lang.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()

This implementation iterates across Multiset.entrySet() and sums the counts of the entries.

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 java.util.Collection<E>

toArray

public java.lang.Object[] toArray()

Specified by:

toArray in interface java.util.Collection<E>

Overrides:

toArray in class java.util.AbstractCollection<E>

toArray

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

Specified by:

toArray in interface java.util.Collection<E>

Overrides:

toArray in class java.util.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:

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

remove

public int remove(@Nullable
                  java.lang.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:

java.lang.IllegalArgumentException - if occurrences is negative

removeExactly

public boolean removeExactly(@Nullable
                             java.lang.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:

java.lang.IllegalArgumentException - if count is negative

setCount

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

Sets the number of occurrences of element to newCount, but only if the count is currently oldCount. If element does not appear in the multiset exactly oldCount 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

oldCount - 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 oldCount == newCount, the method will return true if the condition was met.

Throws:

java.lang.IllegalArgumentException - if oldCount or newCount is negative

createElementSet

protected java.util.Set<E> createElementSet()

Creates a new instance of this multiset's element set, which will be returned by elementSet().

entrySet

public java.util.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 java.util.Collection<E>

Overrides:

isEmpty in class java.util.AbstractCollection<E>

contains

public boolean contains(@Nullable
                        java.lang.Object element)

Returns true if this collection contains the specified element.

This implementation checks whether elementSet contains the element.

Specified by:

contains in interface Multiset<E>

Specified by:

contains in interface java.util.Collection<E>

Overrides:

contains in class java.util.AbstractCollection<E>

Parameters:

element - the element to check for

Returns:

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

iterator

public java.util.Iterator<E> iterator()

This implementation usually invokes methods of the Multiset.entrySet() iterator. However, the iterator's remove method sometimes calls the multiset's remove.

Specified by:

iterator in interface java.lang.Iterable<E>

Specified by:

iterator in interface java.util.Collection<E>

Specified by:

iterator in class java.util.AbstractCollection<E>

add

public boolean add(@Nullable
                   E element)

Ensures that this collection contains the specified element.

This implementation calls add(Object, int) with one occurrence.

Specified by:

add in interface Multiset<E>

Specified by:

add in interface java.util.Collection<E>

Overrides:

add in class java.util.AbstractCollection<E>

Parameters:

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

Returns:

true always

remove

public boolean remove(java.lang.Object element)

Removes a single instance of the specified element from this collection, if it is present.

This implementation calls remove(Object, int) with 1 occurrence.

Specified by:

remove in interface Multiset<E>

Specified by:

remove in interface java.util.Collection<E>

Overrides:

remove in class java.util.AbstractCollection<E>

Parameters:

element - the element to remove one occurrence of

Returns:

true if an occurrence was found and removed

containsAll

public boolean containsAll(java.util.Collection<?> elements)

Returns true if this multiset contains all of the elements in the specified collection.

Note: this method does not take into account the occurrence count of an element in the two collections; it may still return true even if elements contains several occurrences of an element and this multiset contains only one. This is no different than any other collection type like List, but it may be unexpected to the user of a multiset.

This implementation checks whether elementSet contains the elements.

Specified by:

containsAll in interface Multiset<E>

Specified by:

containsAll in interface java.util.Collection<E>

Overrides:

containsAll in class java.util.AbstractCollection<E>

Parameters:

elements - the collection of elements to be checked for containment in this multiset

Returns:

true if this multiset contains at least one occurrence of each element contained in elements

addAll

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

Adds all of the elements in the specified collection to this multiset.

If the collection being added is a multiset, this implementation iterates over that multiset's entry set to add the appropriate number of occurrences of each of its elements to this multiset. Otherwise, it calls AbstractCollection.addAll(java.util.Collection).

Specified by:

addAll in interface java.util.Collection<E>

Overrides:

addAll in class java.util.AbstractCollection<E>

removeAll

public boolean removeAll(java.util.Collection<?> elementsToRemove)

Removes all of this multiset's elements that are also contained in the specified collection.

This implementation calls removeAll() on its elementSet() with the given collection or, if elementsToRemove is a multiset, the elements in its element set. In some cases, this approach has better performance than AbstractCollection.removeAll(java.util.Collection).

Specified by:

removeAll in interface Multiset<E>

Specified by:

removeAll in interface java.util.Collection<E>

Overrides:

removeAll in class java.util.AbstractCollection<E>

retainAll

public boolean retainAll(java.util.Collection<?> elementsToRetain)

Retains only the elements in this multiset that are contained in the specified collection.

This implementation iterates over entrySet(), checking each entry's element to see if it's contained in the provided collection. If it's not found, the remove method of the entry set's iterator is invoked. In some cases, this approach has better performance than AbstractCollection.removeAll(java.util.Collection).

Specified by:

retainAll in interface Multiset<E>

Specified by:

retainAll in interface java.util.Collection<E>

Overrides:

retainAll in class java.util.AbstractCollection<E>

clear

public void clear()

Removes all of the elements from this multiset.

This implementation calls clear on Multiset.entrySet().

Specified by:

clear in interface java.util.Collection<E>

Overrides:

clear in class java.util.AbstractCollection<E>

elementSet

public java.util.Set<E> elementSet()

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().

The returned set's methods are implemented by calling Multiset.entrySet() methods.

Specified by:

elementSet in interface Multiset<E>

Returns:

a view of the set of distinct elements in this multiset

equals

public boolean equals(@Nullable
                      java.lang.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. TODO: caveats about equivalence-relation.

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

Specified by:

equals in interface Multiset<E>

Specified by:

equals in interface java.util.Collection<E>

Overrides:

equals in class java.lang.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 Multiset<E>

Specified by:

hashCode in interface java.util.Collection<E>

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.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 java.util.AbstractCollection<E>