org.apache.commons.collections
Interface Bag

All Superinterfaces:

java.util.Collection

All Known Subinterfaces:

SortedBag

All Known Implementing Classes:

DefaultMapBag, HashBag, TreeBag

public interface Bag

extends java.util.Collection

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 that 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)" in their summary line. A future version of this class will specify the same behavior as Collection, which unfortunately will break backwards compatibility with this version.

Since:

2.0

Author:

Chuck Burdick

Method Summary

boolean	add(java.lang.Object o) (Violation) Add the given object to the bag and keep a count.
boolean	add(java.lang.Object o, int i) Add i copies of the given object to the bag and keep a count.
boolean	containsAll(java.util.Collection c) (Violation) Returns true if the bag contains all elements in the given collection, respecting cardinality.
int	getCount(java.lang.Object o) Return the number of occurrences (cardinality) of the given object currently in the bag.
java.util.Iterator	iterator() Returns an Iterator over the entire set of members, including copies due to cardinality.
boolean	remove(java.lang.Object o) (Violation) Remove all occurrences of the given object from the bag, and do not represent the object in the uniqueSet().
boolean	remove(java.lang.Object o, int i) Remove the given number of occurrences from the bag.
boolean	removeAll(java.util.Collection c) (Violation) Remove all elements represented in the given collection, respecting cardinality.
boolean	retainAll(java.util.Collection c) (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.
java.util.Set	uniqueSet() The Set of unique members that represent all members in the bag.

Methods inherited from interface java.util.Collection

addAll, clear, contains, equals, hashCode, isEmpty, toArray, toArray

Method Detail

getCount

public int getCount(java.lang.Object o)

Return the number of occurrences (cardinality) of the given object currently in the bag. If the object does not exist in the bag, return 0.

add

public boolean add(java.lang.Object o)

(Violation) Add the given object to the bag and keep a count. 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. A future version of this method will comply by always returning true.

Specified by:

add in interface java.util.Collection

Returns:

true if the object was not already in the uniqueSet

See Also:

getCount(Object)

add

public boolean add(java.lang.Object o,
                   int i)

Add i copies of the given object to the bag and keep a count.

Returns:

true if the object was not already in the uniqueSet

See Also:

add(Object), getCount(Object)

remove

public boolean remove(java.lang.Object o)

(Violation) Remove all occurrences of the given object from the bag, and do not represent the object in the uniqueSet().

According to the Collection.remove(Object) method, this method should only remove the first occurrence of the given object, not all occurrences. A future version of this method will comply with the contract by only removing one occurrence of the given object.

Specified by:

remove in interface java.util.Collection

Returns:

true if this call changed the collection

See Also:

remove(Object, int)

remove

public boolean remove(java.lang.Object o,
                      int i)

Remove the given number of occurrences from the bag. If the bag contains i occurrences or less, the item will be removed from the uniqueSet().

Returns:

true if this call changed the collection

See Also:

getCount(Object), remove(Object)

uniqueSet

public java.util.Set uniqueSet()

The Set of unique members that represent all members in the bag. Uniqueness constraints are the same as those in Set.

size

public int size()

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

Specified by:

size in interface java.util.Collection

containsAll

public boolean containsAll(java.util.Collection c)

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

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. A future version of this method will comply with that contract.

Specified by:

containsAll in interface java.util.Collection

removeAll

public boolean removeAll(java.util.Collection c)

(Violation) Remove all elements represented in the given collection, respecting cardinality. That is, if the given collection C 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. A future version of this method will comply with that contract.

Specified by:

removeAll in interface java.util.Collection

Returns:

true if this call changed the collection

retainAll

public boolean retainAll(java.util.Collection c)

(Violation) Remove any members of the bag that are not in the given collection, respecting cardinality. That is, if the given collection C 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 !C.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. A future version of this method will comply with that contract.

Specified by:

retainAll in interface java.util.Collection

Returns:

true if this call changed the collection

iterator

public java.util.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.

Specified by:

iterator in interface java.util.Collection