org.apache.commons.collections

Interface Bag

All Superinterfaces:
Collection
Known Subinterfaces:
SortedBag
Known Implementing Classes:
AbstractBagDecorator, AbstractMapBag, AbstractSortedBagDecorator, DefaultMapBag, HashBag, HashBag, PredicatedBag, PredicatedSortedBag, SynchronizedBag, SynchronizedSortedBag, TransformedBag, TransformedSortedBag, TreeBag, TreeBag, UnmodifiableBag, UnmodifiableSortedBag

public interface Bag
extends Collection

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.

Version:
$Revision: 1.18 $ $Date: 2004/05/03 15:12:20 $
Authors:
Chuck Burdick
Stephen Colebourne
Since:
Commons Collections 2.0

Method Summary

boolean
add(Object object)
(Violation) Adds one copy the specified object to the Bag.
boolean
add(Object 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
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
uniqueSet()
Returns a Set of unique elements in the Bag.

Method Details

add

public boolean add(Object object)
(Violation) Adds one copy 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.

Parameters:
object - the object to add
Returns:
true if the object was not already in the uniqueSet

add

public boolean add(Object 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

containsAll

public 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.

Parameters:
coll - the collection to check against
Returns:
true if the Bag contains all the collection

getCount

public 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

iterator

public Iterator 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.
Returns:
iterator over all elements in the Bag

remove

public 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.

Returns:
true if this call changed the collection

remove

public 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

removeAll

public 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.

Parameters:
coll - the collection to remove
Returns:
true if this call changed the collection

retainAll

public 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.

Parameters:
coll - the collection to retain
Returns:
true if this call changed the collection

size

public int size()
Returns the total number of items in the bag across all types.
Returns:
the total size of the Bag

uniqueSet

public Set uniqueSet()
Returns a Set of unique elements in the Bag.

Uniqueness constraints are the same as those in java.util.Set.

Returns:
the Set of unique Bag elements

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