Bag

Type Parameters:

E - the type held in the 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

All Methods

Instance Methods

Abstract Methods
Modifier and Type	Method and 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

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

Interface Bag<E>

Method Summary

Methods inherited from interface java.util.Collection

Methods inherited from interface java.lang.Iterable

Method Detail

getCount

add

add

remove

remove

uniqueSet

size

containsAll

removeAll

retainAll

iterator