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Multiset (Guava: Google Core Libraries for Java 11.0.1 API)























  
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com.google.common.collect


Interface Multiset<E>

All Superinterfaces: 
Collection<E>, Iterable<E>


All Known Subinterfaces: 
SortedMultiset<E>


All Known Implementing Classes: 
ConcurrentHashMultiset, EnumMultiset, ForwardingMultiset, HashMultiset, ImmutableMultiset, LinkedHashMultiset, TreeMultiset



@GwtCompatible
public interface Multiset<E>extends Collection<E>




A collection that supports order-independent equality, like Set, but
 may have duplicate elements. A multiset is also sometimes called a
 bag.

 
Elements of a multiset that are equal to one another (see "Note on
 element equivalence", below) are referred to as occurrences of the
 same single element. The total number of occurrences of an element in a
 multiset is called the count 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 an int, a multiset may never contain
 more than Integer.MAX_VALUE occurrences of any one element.

 
Multiset refines the specifications of several methods from
 Collection. 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 example add(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 operations add(Object) or remove(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", and entrySet() is similar but contains Multiset.Entry instances, each providing both a distinct element and the
 count of that element.

 
In addition to these required methods, implementations of Multiset are expected to provide two static creation methods:
 create(), returning an empty multiset, and create(Iterable<? extends E>), returning a multiset containing the
 given initial elements. This is simply a refinement of Collection's
 constructor recommendations, reflecting the new developments of Java 5.

 
As with other collection types, the modification operations are optional,
 and should throw UnsupportedOperationException 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, the setCount methods as well.

 
A multiset uses Object.equals(java.lang.Object) to determine whether two instances
 should be considered "the same," unless specified otherwise by the
 implementation.

 
Common implementations include ImmutableMultiset, HashMultiset, and ConcurrentHashMultiset.

 
If your values may be zero, negative, or outside the range of an int, you
 may wish to use AtomicLongMap
 instead. Note, however, that unlike Multiset, AtomicLongMap
 does not automatically remove zeros.




Since:
  2.0 (imported from Google Collections Library)
Author:
  Kevin Bourrillion










Nested Class Summary



static interface
Multiset.Entry<E>



          An unmodifiable element-count pair for a multiset.


 






Method Summary



 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 (the
 count 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 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<?> 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()



          


 


Methods inherited from interface java.util.Collection


addAll, clear, isEmpty, size, toArray, toArray


 








Method Detail




count
int count(@Nullable
          Object element)

Returns the number of occurrences of an element in this multiset (the
 count of the element). Note that for an Object.equals(java.lang.Object)-based
 multiset, this gives the same result as Collections.frequency(java.util.Collection, java.lang.Object)
 (which would presumably perform more poorly).

 Note: the utility method Iterables.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.





Parameters:
element - the element to count occurrences of
Returns:
the number of occurrences of the element in this multiset; possibly
     zero but never negative





add
int add(@Nullable
        E element,
        int occurrences)

Adds a number of occurrences of an element to this multiset. Note that if
 occurrences == 1, this method has the identical effect to add(Object). This method is functionally equivalent (except in the case
 of overflow) to the call addAll(Collections.nCopies(element,
 occurrences)), which would presumably perform much more poorly.





Parameters:
element - the element to add occurrences of; may be null only if
     explicitly allowed by the implementation
occurrences - the number of occurrences of the element to add. May be
     zero, in which case no change will be made.
Returns:
the count of the element before the operation; possibly zero
Throws:
IllegalArgumentException - if occurrences is negative, or if
     this operation would result in more than Integer.MAX_VALUE
     occurrences of the element
NullPointerException - if element is null and this
     implementation does not permit null elements. Note that if occurrences is zero, the implementation may opt to return normally.





remove
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.  Note that if
 occurrences == 1, this is functionally equivalent to the call
 remove(element).





Parameters:
element - the element to conditionally remove occurrences of
occurrences - the number of occurrences of the element to remove. May
     be zero, in which case no change will be made.
Returns:
the count of the element before the operation; possibly zero
Throws:
IllegalArgumentException - if occurrences is negative





setCount
int setCount(E element,
             int count)

Adds or removes the necessary occurrences of an element such that the
 element attains the desired count.





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 the element before the operation; possibly zero
Throws:
IllegalArgumentException - if count is negative
NullPointerException - if element is null and this
     implementation does not permit null elements. Note that if count is zero, the implementor may optionally return zero instead.





setCount
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. If the current count is not oldCount, no change is
 made.





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 condition for modification was met. This
     implies that the multiset was indeed modified, unless
     oldCount == newCount.
Throws:
IllegalArgumentException - if oldCount or newCount is
     negative
NullPointerException - if element is null and the
     implementation does not permit null elements. Note that if oldCount and newCount are both zero, the implementor may
     optionally return true instead.





elementSet
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().






Returns:
a view of the set of distinct elements in this multiset





entrySet
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. This set contains exactly one entry for each
 distinct element in the multiset (thus it always has the same size as the
 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.






Returns:
a set of entries representing the data of this multiset





equals
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.


Specified by:
equals in interface Collection<E>
Overrides:
equals in class Object








hashCode
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.


Specified by:
hashCode in interface Collection<E>
Overrides:
hashCode in class Object








toString
String toString()



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


Overrides:
toString in class Object








iterator
Iterator<E> iterator()



 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>








contains
boolean contains(@Nullable
                 Object element)

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>


Parameters:
element - the element to check for
Returns:
true if this multiset contains at least one occurrence of
     the element





containsAll
boolean containsAll(Collection<?> elements)

Returns true if this multiset contains at least one occurrence of
 each element in the specified collection.

 This method refines Collection.containsAll(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.

 
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.


Specified by:
containsAll in interface Collection<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
Throws:
NullPointerException - if elements is null





add
boolean add(E element)

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>


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
Throws:
NullPointerException - if element is null and this
     implementation does not permit null elements
IllegalArgumentException - if Integer.MAX_VALUE occurrences
     of element are already contained in this multiset





remove
boolean remove(@Nullable
               Object element)

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>


Parameters:
element - the element to remove one occurrence of
Returns:
true if an occurrence was found and removed





removeAll
boolean removeAll(Collection<?> c)



 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>








retainAll
boolean retainAll(Collection<?> c)



 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>


See Also:
Multisets.retainOccurrences(Multiset, Multiset)














  
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Copyright © 2010-2012. All Rights Reserved.

Method Summary
`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 (the count 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 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<?> 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()`

javadoc.com.google.common.collect.Multiset.html Maven / Gradle / Ivy

com.google.common.collect Interface Multiset<E>

count

add

remove

setCount

setCount

elementSet

entrySet

equals

hashCode

toString

iterator

contains

containsAll

add

remove

removeAll

retainAll

com.google.common.collect
Interface Multiset<E>