@GwtCompatiblepublic interfaceMultiset<E>extendsCollection<E>
Set, but may have duplicate elements. A multiset is also sometimes called abag.Elements of a multiset that are equal to one another are referred to asoccurrences of the same single element. The total number of occurrences of an element in a multiset is called thecount of that element (the terms "frequency" and "multiplicity" are equivalent, but not used in this API). Since the count of an element is represented as anint, a multiset may never contain more thanInteger.MAX_VALUE occurrences of any one element.
Multiset refines the specifications of several methods fromCollection. It also defines an additional query operation,count(java.lang.Object), which returns the count of an element. There are five new bulk-modification operations, for exampleadd(Object, int), to add or remove multiple occurrences of an element at once, or to set the count of an element to a specific value. These modification operations are optional, but implementations which support the standard collection operationsadd(Object) orremove(Object) are encouraged to implement the related methods as well. Finally, two collection views are provided:elementSet() contains the distinct elements of the multiset "with duplicates collapsed", andentrySet() is similar but containsMultiset.Entry instances, each providing both a distinct element and the count of that element.
In addition to these required methods, implementations ofMultiset are expected to provide twostatic creation methods:create(), returning an empty multiset, andcreate(Iterable<? extends E>), returning a multiset containing the given initial elements. This is simply a refinement ofCollection's constructor recommendations, reflecting the new developments of Java 5.
As with other collection types, the modification operations are optional, and should throwUnsupportedOperationException when they are not implemented. Most implementations should support either all add operations or none of them, all removal operations or none of them, and if and only if all of these are supported, thesetCount methods as well.
A multiset usesObject.equals(java.lang.Object) to determine whether two instances should be considered "the same,"unless specified otherwise by the implementation.
Common implementations includeImmutableMultiset,HashMultiset, andConcurrentHashMultiset.
If your values may be zero, negative, or outside the range of an int, you may wish to useAtomicLongMap instead. Note, however, that unlikeMultiset,AtomicLongMap does not automatically remove zeros.
See the Guava User Guide article onMultiset.
| Modifier and Type | Interface and Description |
|---|---|
static interface | Multiset.Entry<E>An unmodifiable element-count pair for a multiset. |
| 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 an element to this multiset. |
boolean | contains(Object element)Determines whether this multiset contains the specified element. |
boolean | containsAll(Collection<?> elements)Returns true if this multiset contains at least one occurrence of each element in the specified collection. |
int | count(Object element)Returns the number of occurrences of an element in this multiset (thecount of the element). |
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. |
Iterator<E> | iterator() |
boolean | remove(Object element)Removes asingle 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<?> c) |
boolean | retainAll(Collection<?> c) |
int | setCount(E element, int count)Adds or removes the necessary occurrences of an element such that the element attains the desired count. |
boolean | setCount(E element, int oldCount, int newCount)Conditionally sets the count of an element to a new value, as described in setCount(Object, int), provided that the element has the expected current count. |
String | toString() |
addAll,clear,isEmpty,parallelStream,removeIf,size,spliterator,stream,toArray,toArrayint count(@NullableObject element)
Object.equals(java.lang.Object)-based multiset, this gives the same result asCollections.frequency(java.util.Collection<?>, java.lang.Object) (which would presumably perform more poorly).Note: the utility methodIterables.frequency(java.lang.Iterable<?>, java.lang.Object) generalizes this operation; it correctly delegates to this method when dealing with a multiset, but it can also accept any other iterable type.
element - the element to count occurrences ofint add(@NullableE element, int occurrences)
occurrences == 1, this method has the identical effect toadd(Object). This method is functionally equivalent (except in the case of overflow) to the calladdAll(Collections.nCopies(element, occurrences)), which would presumably perform much more poorly.element - the element to add occurrences of; may be null only if explicitly allowed by the implementationoccurrences - the number of occurrences of the element to add. May be zero, in which case no change will be made.IllegalArgumentException - ifoccurrences is negative, or if this operation would result in more thanInteger.MAX_VALUE occurrences of the elementNullPointerException - ifelement is null and this implementation does not permit null elements. Note that ifoccurrences is zero, the implementation may opt to return normally.int remove(@NullableObject element, int occurrences)
occurrences == 1, this is functionally equivalent to the callremove(element).element - the element to conditionally remove occurrences ofoccurrences - the number of occurrences of the element to remove. May be zero, in which case no change will be made.IllegalArgumentException - ifoccurrences is negativeint setCount(E element, int count)
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 multisetIllegalArgumentException - ifcount is negativeNullPointerException - ifelement is null and this implementation does not permit null elements. Note that ifcount is zero, the implementor may optionally return zero instead.boolean setCount(E element, int oldCount, int newCount)
setCount(Object, int), provided that the element has the expected current count. If the current count is notoldCount, no change is made.element - the element to conditionally set the count of; may be null only if explicitly allowed by the implementationoldCount - the expected present count of the element in this multisetnewCount - the desired count of the element in this multisettrue if the condition for modification was met. This implies that the multiset was indeed modified, unlessoldCount == newCount.IllegalArgumentException - ifoldCount ornewCount is negativeNullPointerException - ifelement is null and the implementation does not permit null elements. Note that ifoldCount andnewCount are both zero, the implementor may optionally returntrue instead.Set<E> elementSet()
If the element set supports any removal operations, these necessarily causeall 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().
Set<Multiset.Entry<E>> entrySet()
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 theelementSet()). 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 anyEntry 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 theEntry instances themselves don't even have methods for modification. See the specific implementation class for more details on how its entry set handles modifications.
boolean equals(@NullableObject object)
true if the given object is also a multiset and contains equal elements with equal counts, regardless of order.equals in interface Collection<E>equals in class Objectint hashCode()
((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.
hashCode in interface Collection<E>hashCode in class ObjectString toString()
It is recommended, though not mandatory, that this method return the result of invokingtoString() on theentrySet(), yielding a result such as[a x 3, c, d x 2, e].
Iterator<E> iterator()
Elements that occur multiple times in the multiset will appear multiple times in this iterator, though not necessarily sequentially.
boolean contains(@NullableObject element)
This method refinesCollection.contains(java.lang.Object) to further specify that itmay not throw an exception in response toelement being null or of the wrong type.
contains in interface Collection<E>element - the element to check fortrue if this multiset contains at least one occurrence of the elementboolean containsAll(Collection<?> elements)
true if this multiset contains at least one occurrence of each element in the specified collection.This method refinesCollection.containsAll(java.util.Collection<?>) to further specify that itmay not throw an exception in response to any ofelements being null or of the wrong type.
Note: this method does not take into account the occurrence count of an element in the two collections; it may still returntrue even ifelements contains several occurrences of an element and this multiset contains only one. This is no different than any other collection type likeList, but it may be unexpected to the user of a multiset.
containsAll in interface Collection<E>elements - the collection of elements to be checked for containment in this multisettrue if this multiset contains at least one occurrence of each element contained inelementsNullPointerException - ifelements is nullboolean add(E element)
This method refinesCollection.add(E), which onlyensures 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, useadd(element, 1) instead.
add in interface Collection<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 otherCollection typesNullPointerException - ifelement is null and this implementation does not permit null elementsIllegalArgumentException - ifInteger.MAX_VALUE occurrences ofelement are already contained in this multisetboolean remove(@NullableObject element)
This method refinesCollection.remove(java.lang.Object) to further specify that itmay not throw an exception in response toelement being null or of the wrong type.
To both remove the element and obtain the previous count of that element, useremove(element, 1) instead.
remove in interface Collection<E>element - the element to remove one occurrence oftrue if an occurrence was found and removedboolean removeAll(Collection<?> c)
Note: This method ignores how often any element might appear inc, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence inc, seeMultisets.removeOccurrences(Multiset, Multiset).
This method refinesCollection.removeAll(java.util.Collection<?>) to further specify that itmay not throw an exception in response to any ofelements being null or of the wrong type.
removeAll in interface Collection<E>boolean retainAll(Collection<?> c)
Note: This method ignores how often any element might appear inc, and only cares whether or not an element appears at all. If you wish to remove one occurrence in this multiset for every occurrence inc, seeMultisets.retainOccurrences(Multiset, Multiset).
This method refinesCollection.retainAll(java.util.Collection<?>) to further specify that itmay not throw an exception in response to any ofelements being null or of the wrong type.
retainAll in interface Collection<E>Multisets.retainOccurrences(Multiset, Multiset)Copyright © 2010-2016. All Rights Reserved.