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.
Multiset.Entry<E>| Modifier and Type | Method and 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(Iterable<? extends E> elements)
Creates a new
ConcurrentHashMultiset containing the specified elements, 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. |
Set<Multiset.Entry<E>> |
createEntrySet() |
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() |
containsAllclone, finalize, getClass, notify, notifyAll, wait, wait, waitcontainsAllparallelStream, removeIf, spliterator, streampublic static <E> ConcurrentHashMultiset<E> create()
Creates a new, empty ConcurrentHashMultiset using the default initial capacity, load factor, and concurrency settings.
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.
elements - the elements that the multiset should contain@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.
GenericMapMaker class) since 7.0)public int count(@Nullable Object element)
Returns the number of occurrences of element in this multiset.
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.
size in interface Collection<E>public Object[] toArray()
toArray in interface Collection<E>toArray in class AbstractCollection<E>public <T> T[] toArray(T[] array)
toArray in interface Collection<E>toArray in class AbstractCollection<E>public int add(E element, int occurrences)
Adds a number of occurrences of the specified element to this multiset.
add in interface Multiset<E>element - the element to addoccurrences - the number of occurrences to addIllegalArgumentException - if occurrences is negative, or if the resulting amount would exceed Integer.MAX_VALUEpublic 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.
remove in interface Multiset<E>element - the element whose occurrences should be removedoccurrences - the number of occurrences of the element to removeIllegalArgumentException - if occurrences is negativepublic 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.
element - the element to removeoccurrences - the number of occurrences of element to removetrue if the removal was possible (including if occurrences is zero)IllegalArgumentException - if occurrences is negativepublic int setCount(E element, int count)
Adds or removes occurrences of element such that the count(java.lang.Object) of the element becomes count.
setCount in interface Multiset<E>element - the element to add or remove occurrences of; may be null only if explicitly allowed by the implementationcount - the desired count of the element in this multisetelement in the multiset before this callIllegalArgumentException - if count is negativepublic 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.
setCount in interface Multiset<E>element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementationexpectedOldCount - the expected present count of the element in this multisetnewCount - the desired count of the element in this multisettrue 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.IllegalArgumentException - if expectedOldCount or newCount is negativepublic Set<Multiset.Entry<E>> createEntrySet()
public boolean isEmpty()
isEmpty in interface Collection<E>public void clear()
clear in interface Collection<E>public boolean contains(@Nullable Object element)
MultisetDetermines 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.
contains in interface Multiset<E>contains in interface Collection<E>contains in class AbstractCollection<E>element - the element to check fortrue if this multiset contains at least one occurrence of the elementpublic Iterator<E> iterator()
MultisetElements that occur multiple times in the multiset will appear multiple times in this iterator, though not necessarily sequentially.
public boolean add(@Nullable E element)
MultisetAdds 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.
To both add the element and obtain the previous count of that element, use add(element, 1) instead.
add in interface Multiset<E>add in interface Collection<E>add in class AbstractCollection<E>element - the element to add one occurrence of; may be null only if explicitly allowed by the implementationtrue always, since this call is required to modify the multiset, unlike other Collection typespublic boolean remove(@Nullable Object element)
MultisetRemoves 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.
To both remove the element and obtain the previous count of that element, use remove(element, 1) instead.
remove in interface Multiset<E>remove in interface Collection<E>remove in class AbstractCollection<E>element - the element to remove one occurrence oftrue if an occurrence was found and removedpublic boolean addAll(Collection<? extends E> elementsToAdd)
This implementation is highly efficient when elementsToAdd
is itself a Multiset.
addAll in interface Collection<E>addAll in class AbstractCollection<E>public boolean removeAll(Collection<?> elementsToRemove)
MultisetNote: 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.
removeAll in interface Multiset<E>removeAll in interface Collection<E>removeAll in class AbstractCollection<E>public boolean retainAll(Collection<?> elementsToRetain)
MultisetNote: 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.
retainAll in interface Multiset<E>retainAll in interface Collection<E>retainAll in class AbstractCollection<E>Multisets.retainOccurrences(Multiset, Multiset)public Set<E> elementSet()
MultisetReturns 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().
elementSet in interface Multiset<E>public Set<Multiset.Entry<E>> entrySet()
MultisetReturns 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.
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.
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().
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().