Package org.apache.commons.collections4

Interface Bag<E>

Type Parameters:

E - the type of elements in this bag

All Superinterfaces:

Collection<E>, Iterable<E>

All Known Subinterfaces:

SortedBag<E>

All Known Implementing Classes:

AbstractBagDecorator, AbstractMapBag, AbstractSortedBagDecorator, CollectionBag, CollectionSortedBag, HashBag, PredicatedBag, PredicatedSortedBag, SynchronizedBag, SynchronizedSortedBag, TransformedBag, TransformedSortedBag, TreeBag, UnmodifiableBag, UnmodifiableSortedBag

public interface Bag<E>
extends Collection<E>

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

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

NOTE: This interface violates the Collection contract. The behavior specified in many of these methods is not the same as the behavior specified by Collection. The noncompliant methods are clearly marked with "(Violation)". Exercise caution when using a bag as a Collection.

This violation resulted from the original specification of this interface. In an ideal world, the interface would be changed to fix the problems, however it has been decided to maintain backwards compatibility instead.

Since:

2.0

Method Summary

Modifier and Type	Method	Description
boolean	add(E object)	(Violation) Adds one copy of the specified object to the Bag.
boolean	add(E object, int nCopies)	Adds nCopies copies of the specified object to the Bag.
boolean	containsAll(Collection<?> coll)	(Violation) Returns true if the bag contains all elements in the given collection, respecting cardinality.
int	getCount(Object object)	Returns the number of occurrences (cardinality) of the given object currently in the bag.
Iterator<E>	iterator()	Returns an Iterator over the entire set of members, including copies due to cardinality.
boolean	remove(Object object)	(Violation) Removes all occurrences of the given object from the bag.
boolean	remove(Object object, int nCopies)	Removes nCopies copies of the specified object from the Bag.
boolean	removeAll(Collection<?> coll)	(Violation) Remove all elements represented in the given collection, respecting cardinality.
boolean	retainAll(Collection<?> coll)	(Violation) Remove any members of the bag that are not in the given collection, respecting cardinality.
int	size()	Returns the total number of items in the bag across all types.
Set<E>	uniqueSet()	Returns a Set of unique elements in the Bag.

Methods inherited from interface java.util.Collection

addAll, clear, contains, equals, hashCode, 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 (cardinality) of the given object currently in the bag. If the object does not exist in the bag, return 0.

Parameters:

object - the object to search for

Returns:

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

add

boolean add(E object)

(Violation) Adds one copy of the specified object to the Bag.

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.

Since this method always increases the size of the bag, according to the Collection.add(Object) contract, it should always return true. Since it sometimes returns false, this method violates the contract.

Specified by:

add in interface Collection<E>

Parameters:

object - the object to add

Returns:

true if the object was not already in the uniqueSet

add

boolean add(E object,
            int nCopies)

Adds nCopies copies of the specified object to the Bag.

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 nCopies.

Parameters:

object - the object to add

nCopies - the number of copies to add

Returns:

true if the object was not already in the uniqueSet

remove

boolean remove(Object object)

(Violation) Removes all occurrences of the given object from the bag.

This will also remove the object from the uniqueSet().

According to the Collection.remove(Object) method, this method should only remove the first occurrence of the given object, not all occurrences.

Specified by:

remove in interface Collection<E>

Parameters:

object - the object to remove

Returns:

true if this call changed the collection

remove

boolean remove(Object object,
               int nCopies)

Removes nCopies copies of the specified object from the Bag.

If the number of copies to remove is greater than the actual number of copies in the Bag, no error is thrown.

Parameters:

object - the object to remove

nCopies - the number of copies to remove

Returns:

true if this call changed the collection

uniqueSet

Set<E> uniqueSet()

Returns a Set of unique elements in the Bag.

Uniqueness constraints are the same as those in Set.

Returns:

the Set of unique Bag elements

size

int size()

Returns the total number of items in the bag across all types.

Specified by:

size in interface Collection<E>

Returns:

the total size of the Bag

containsAll

boolean containsAll(Collection<?> coll)

(Violation) Returns true if the bag contains all elements in the given collection, respecting cardinality. That is, if the given collection coll contains n copies of a given object, calling getCount(Object) on that object must be >= n for all n in coll.

The Collection.containsAll(Collection) method specifies that cardinality should not be respected; this method should return true if the bag contains at least one of every object contained in the given collection.

Specified by:

containsAll in interface Collection<E>

Parameters:

coll - the collection to check against

Returns:

true if the Bag contains all the collection

removeAll

boolean removeAll(Collection<?> coll)

(Violation) Remove all elements represented in the given collection, respecting cardinality. That is, if the given collection coll contains n copies of a given object, the bag will have n fewer copies, assuming the bag had at least n copies to begin with.

The Collection.removeAll(Collection) method specifies that cardinality should not be respected; this method should remove all occurrences of every object contained in the given collection.

Specified by:

removeAll in interface Collection<E>

Parameters:

coll - the collection to remove

Returns:

true if this call changed the collection

retainAll

boolean retainAll(Collection<?> coll)

(Violation) Remove any members of the bag that are not in the given collection, respecting cardinality. That is, if the given collection coll contains n copies of a given object and the bag has m > n copies, then delete m - n copies from the bag. In addition, if e is an object in the bag but !coll.contains(e), then remove e and any of its copies.

The Collection.retainAll(Collection) method specifies that cardinality should not be respected; this method should keep all occurrences of every object contained in the given collection.

Specified by:

retainAll in interface Collection<E>

Parameters:

coll - the collection to retain

Returns:

true if this call changed the collection

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 Bag