org.apache.commons.collections

Class BagUtils


public class BagUtils
extends java.lang.Object

Provides utility methods and decorators for Bag and SortedBag instances.
Version:
$Revision: 1.20 $ $Date: 2004/04/01 20:12:00 $
Authors:
Paul Jack
Stephen Colebourne
Andrew Freeman
Matthew Hawthorne
Since:
Commons Collections 2.1

Field Summary

static Bag
EMPTY_BAG
An empty unmodifiable bag.
static Bag
EMPTY_SORTED_BAG
An empty unmodifiable sorted bag.

Constructor Summary

BagUtils()
Instantiation of BagUtils is not intended or required.

Method Summary

static Bag
predicatedBag(Bag bag, Predicate predicate)
Returns a predicated (validating) bag backed by the given bag.
static SortedBag
predicatedSortedBag(SortedBag bag, Predicate predicate)
Returns a predicated (validating) sorted bag backed by the given sorted bag.
static Bag
synchronizedBag(Bag bag)
Returns a synchronized (thread-safe) bag backed by the given bag.
static SortedBag
synchronizedSortedBag(SortedBag bag)
Returns a synchronized (thread-safe) sorted bag backed by the given sorted bag.
static Bag
transformedBag(Bag bag, Transformer transformer)
Returns a transformed bag backed by the given bag.
static SortedBag
transformedSortedBag(SortedBag bag, Transformer transformer)
Returns a transformed sorted bag backed by the given bag.
static Bag
typedBag(Bag bag, Class type)
Returns a typed bag backed by the given bag.
static SortedBag
typedSortedBag(SortedBag bag, Class type)
Returns a typed sorted bag backed by the given bag.
static Bag
unmodifiableBag(Bag bag)
Returns an unmodifiable view of the given bag.
static SortedBag
unmodifiableSortedBag(SortedBag bag)
Returns an unmodifiable view of the given sorted bag.

Field Details

EMPTY_BAG

public static final Bag EMPTY_BAG
An empty unmodifiable bag.

EMPTY_SORTED_BAG

public static final Bag EMPTY_SORTED_BAG
An empty unmodifiable sorted bag.

Constructor Details

BagUtils

public BagUtils()
Instantiation of BagUtils is not intended or required. However, some tools require an instance to operate.

Method Details

predicatedBag

public static Bag predicatedBag(Bag bag,
                                Predicate predicate)
Returns a predicated (validating) bag backed by the given bag.

Only objects that pass the test in the given predicate can be added to the bag. Trying to add an invalid object results in an IllegalArgumentException. It is important not to use the original bag after invoking this method, as it is a backdoor for adding invalid objects.

Parameters:
bag - the bag to predicate, must not be null
predicate - the predicate for the bag, must not be null
Returns:
a predicated bag backed by the given bag

predicatedSortedBag

public static SortedBag predicatedSortedBag(SortedBag bag,
                                            Predicate predicate)
Returns a predicated (validating) sorted bag backed by the given sorted bag.

Only objects that pass the test in the given predicate can be added to the bag. Trying to add an invalid object results in an IllegalArgumentException. It is important not to use the original bag after invoking this method, as it is a backdoor for adding invalid objects.

Parameters:
bag - the sorted bag to predicate, must not be null
predicate - the predicate for the bag, must not be null
Returns:
a predicated bag backed by the given bag

synchronizedBag

public static Bag synchronizedBag(Bag bag)
Returns a synchronized (thread-safe) bag backed by the given bag. In order to guarantee serial access, it is critical that all access to the backing bag is accomplished through the returned bag.

It is imperative that the user manually synchronize on the returned bag when iterating over it:

 Bag bag = BagUtils.synchronizedBag(new HashBag());
 ...
 synchronized(bag) {
     Iterator i = bag.iterator(); // Must be in synchronized block
     while (i.hasNext())
         foo(i.next());
     }
 }
 
Failure to follow this advice may result in non-deterministic behavior.
Parameters:
bag - the bag to synchronize, must not be null
Returns:
a synchronized bag backed by that bag

synchronizedSortedBag

public static SortedBag synchronizedSortedBag(SortedBag bag)
Returns a synchronized (thread-safe) sorted bag backed by the given sorted bag. In order to guarantee serial access, it is critical that all access to the backing bag is accomplished through the returned bag.

It is imperative that the user manually synchronize on the returned bag when iterating over it:

 SortedBag bag = BagUtils.synchronizedSortedBag(new TreeBag());
 ...
 synchronized(bag) {
     Iterator i = bag.iterator(); // Must be in synchronized block
     while (i.hasNext())
         foo(i.next());
     }
 }
 
Failure to follow this advice may result in non-deterministic behavior.
Parameters:
bag - the bag to synchronize, must not be null
Returns:
a synchronized bag backed by that bag

transformedBag

public static Bag transformedBag(Bag bag,
                                 Transformer transformer)
Returns a transformed bag backed by the given bag.

Each object is passed through the transformer as it is added to the Bag. It is important not to use the original bag after invoking this method, as it is a backdoor for adding untransformed objects.

Parameters:
bag - the bag to predicate, must not be null
transformer - the transformer for the bag, must not be null
Returns:
a transformed bag backed by the given bag

transformedSortedBag

public static SortedBag transformedSortedBag(SortedBag bag,
                                             Transformer transformer)
Returns a transformed sorted bag backed by the given bag.

Each object is passed through the transformer as it is added to the Bag. It is important not to use the original bag after invoking this method, as it is a backdoor for adding untransformed objects.

Parameters:
bag - the bag to predicate, must not be null
transformer - the transformer for the bag, must not be null
Returns:
a transformed bag backed by the given bag

typedBag

public static Bag typedBag(Bag bag,
                           Class type)
Returns a typed bag backed by the given bag.

Only objects of the specified type can be added to the bag.

Parameters:
bag - the bag to limit to a specific type, must not be null
type - the type of objects which may be added to the bag
Returns:
a typed bag backed by the specified bag

typedSortedBag

public static SortedBag typedSortedBag(SortedBag bag,
                                       Class type)
Returns a typed sorted bag backed by the given bag.

Only objects of the specified type can be added to the bag.

Parameters:
bag - the bag to limit to a specific type, must not be null
type - the type of objects which may be added to the bag
Returns:
a typed bag backed by the specified bag

unmodifiableBag

public static Bag unmodifiableBag(Bag bag)
Returns an unmodifiable view of the given bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException.
Parameters:
bag - the bag whose unmodifiable view is to be returned, must not be null
Returns:
an unmodifiable view of that bag

unmodifiableSortedBag

public static SortedBag unmodifiableSortedBag(SortedBag bag)
Returns an unmodifiable view of the given sorted bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException.
Parameters:
bag - the bag whose unmodifiable view is to be returned, must not be null
Returns:
an unmodifiable view of that bag

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