Package org.apache.commons.collections4

Interface MultiSet<E>

Type Parameters:

E - the type held in the multiset

All Superinterfaces:

Collection<E>, Iterable<E>

All Known Implementing Classes:

AbstractMapMultiSet, AbstractMultiSet, AbstractMultiSetDecorator, HashMultiSet, PredicatedMultiSet, SynchronizedMultiSet, UnmodifiableMultiSet

public interface MultiSet<E>
extends Collection<E>

Defines a collection that counts the number of times an object appears in the collection.

Suppose you have a MultiSet that contains {a, a, b, c}. Calling getCount(Object) on a would return 2, while calling uniqueSet() would return {a, b, c}.

Since:

4.1

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	MultiSet.Entry<E>	An unmodifiable entry for an element and its occurrence as contained in a MultiSet.

Method Summary

Modifier and Type	Method	Description
boolean	add(E object)	Adds one copy of the specified object to the MultiSet.
int	add(E object, int occurrences)	Adds a number of occurrences of the specified object to the MultiSet.
boolean	containsAll(Collection<?> coll)	Returns true if the MultiSet contains at least one occurrence for each element contained in the given collection.
Set<MultiSet.Entry<E>>	entrySet()	Returns a Set of all entries contained in the MultiSet.
boolean	equals(Object obj)	Compares this MultiSet to another object.
int	getCount(Object object)	Returns the number of occurrences of the given object currently in the MultiSet.
int	hashCode()	Gets a hash code for the MultiSet compatible with the definition of equals.
Iterator<E>	iterator()	Returns an Iterator over the entire set of members, including copies due to cardinality.
boolean	remove(Object object)	Removes one occurrence of the given object from the MultiSet.
int	remove(Object object, int occurrences)	Removes a number of occurrences of the specified object from the MultiSet.
boolean	removeAll(Collection<?> coll)	Remove all occurrences of all elements from this MultiSet represented in the given collection.
boolean	retainAll(Collection<?> coll)	Remove any elements of this MultiSet that are not contained in the given collection.
int	setCount(E object, int count)	Sets the number of occurrences of the specified object in the MultiSet to the given count.
int	size()	Returns the total number of items in the MultiSet.
Set<E>	uniqueSet()	Returns a Set of unique elements in the MultiSet.

Methods inherited from interface java.util.Collection

addAll, clear, contains, isEmpty, parallelStream, removeIf, spliterator, stream, toArray, toArray, toArray

Methods inherited from interface java.lang.Iterable

forEach

Method Detail

getCount

int getCount(Object object)

Returns the number of occurrences of the given object currently in the MultiSet. If the object does not exist in the multiset, return 0.

Parameters:

object - the object to search for

Returns:

the number of occurrences of the object, zero if not found

setCount

int setCount(E object,
             int count)

Sets the number of occurrences of the specified object in the MultiSet to the given count.

If the provided count is zero, the object will be removed from the uniqueSet().

Parameters:

object - the object to update

count - the number of occurrences of the object

Returns:

the number of occurrences of the object before this operation, zero if the object was not contained in the multiset

Throws:

IllegalArgumentException - if count is negative

add

boolean add(E object)

Adds one copy of the specified object to the MultiSet.

If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise add it to the uniqueSet() and report its count as 1.

Specified by:

add in interface Collection<E>

Parameters:

object - the object to add

Returns:

true always, as the size of the MultiSet is increased in any case

add

int add(E object,
        int occurrences)

Adds a number of occurrences of the specified object to the MultiSet.

If the object is already in the uniqueSet() then increment its count as reported by getCount(Object). Otherwise add it to the uniqueSet() and report its count as occurrences.

Parameters:

object - the object to add

occurrences - the number of occurrences to add, may be zero, in which case no change is made to the multiset

Returns:

the number of occurrences of the object in the multiset before this operation; possibly zero

Throws:

IllegalArgumentException - if occurrences is negative

remove

boolean remove(Object object)

Removes one occurrence of the given object from the MultiSet.

If the number of occurrences after this operations is reduced to zero, the object will be removed from the uniqueSet().

Specified by:

remove in interface Collection<E>

Parameters:

object - the object to remove

Returns:

true if this call changed the collection

remove

int remove(Object object,
           int occurrences)

Removes a number of occurrences of the specified object from the MultiSet.

If the number of occurrences to remove is greater than the actual number of occurrences in the multiset, the object will be removed from the multiset.

Parameters:

object - the object to remove

occurrences - the number of occurrences to remove, may be zero, in which case no change is made to the multiset

Returns:

the number of occurrences of the object in the multiset before the operation; possibly zero

Throws:

IllegalArgumentException - if occurrences is negative

uniqueSet

Set<E> uniqueSet()

Returns a Set of unique elements in the MultiSet.

Uniqueness constraints are the same as those in Set.

The returned set is backed by this multiset, so any change to either is immediately reflected in the other. Only removal operations are supported, in which case all occurrences of the element are removed from the backing multiset.

Returns:

the Set of unique MultiSet elements

entrySet

Set<MultiSet.Entry<E>> entrySet()

Returns a Set of all entries contained in the MultiSet.

The returned set is backed by this multiset, so any change to either is immediately reflected in the other.

Returns:

the Set of MultiSet entries

iterator

Iterator<E> iterator()

Returns an Iterator over the entire set of members, including copies due to cardinality. This iterator is fail-fast and will not tolerate concurrent modifications.

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in interface Iterable<E>

Returns:

iterator over all elements in the MultiSet

size

int size()

Returns the total number of items in the MultiSet.

Specified by:

size in interface Collection<E>

Returns:

the total size of the multiset

containsAll

boolean containsAll(Collection<?> coll)

Returns true if the MultiSet contains at least one occurrence for each element contained in the given collection.

Specified by:

containsAll in interface Collection<E>

Parameters:

coll - the collection to check against

Returns:

true if the MultiSet contains all the collection

removeAll

boolean removeAll(Collection<?> coll)

Remove all occurrences of all elements from this MultiSet represented in the given collection.

Specified by:

removeAll in interface Collection<E>

Parameters:

coll - the collection of elements to remove

Returns:

true if this call changed the multiset

retainAll

boolean retainAll(Collection<?> coll)

Remove any elements of this MultiSet that are not contained in the given collection.

Specified by:

retainAll in interface Collection<E>

Parameters:

coll - the collection of elements to retain

Returns:

true if this call changed the multiset

equals

boolean equals(Object obj)

Compares this MultiSet to another object.

This MultiSet equals another object if it is also a MultiSet that contains the same number of occurrences of the same elements.

Specified by:

equals in interface Collection<E>

Overrides:

equals in class Object

Parameters:

obj - the object to compare to

Returns:

true if equal

hashCode

int hashCode()

Gets a hash code for the MultiSet compatible with the definition of equals. The hash code is defined as the sum total of a hash code for each element. The per element hash code is defined as (e==null ? 0 : e.hashCode()) ^ noOccurances).

Specified by:

hashCode in interface Collection<E>

Overrides:

hashCode in class Object

Returns:

the hash code of the MultiSet