org.apache.commons.collections

Class BagUtils

public class BagUtils extends Object

Provides utility methods and decorators for Bag and SortedBag instances.

Since: Commons Collections 2.1

Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $

Author: Paul Jack Stephen Colebourne Andrew Freeman Matthew Hawthorne

Field Summary
static BagEMPTY_BAG
An empty unmodifiable bag.
static BagEMPTY_SORTED_BAG
An empty unmodifiable sorted bag.
Constructor Summary
BagUtils()
Instantiation of BagUtils is not intended or required.
Method Summary
static BagpredicatedBag(Bag bag, Predicate predicate)
Returns a predicated (validating) bag backed by the given bag.
static SortedBagpredicatedSortedBag(SortedBag bag, Predicate predicate)
Returns a predicated (validating) sorted bag backed by the given sorted bag.
static BagsynchronizedBag(Bag bag)
Returns a synchronized (thread-safe) bag backed by the given bag.
static SortedBagsynchronizedSortedBag(SortedBag bag)
Returns a synchronized (thread-safe) sorted bag backed by the given sorted bag.
static BagtransformedBag(Bag bag, Transformer transformer)
Returns a transformed bag backed by the given bag.
static SortedBagtransformedSortedBag(SortedBag bag, Transformer transformer)
Returns a transformed sorted bag backed by the given bag.
static BagtypedBag(Bag bag, Class type)
Returns a typed bag backed by the given bag.
static SortedBagtypedSortedBag(SortedBag bag, Class type)
Returns a typed sorted bag backed by the given bag.
static BagunmodifiableBag(Bag bag)
Returns an unmodifiable view of the given bag.
static SortedBagunmodifiableSortedBag(SortedBag bag)
Returns an unmodifiable view of the given sorted bag.

Field Detail

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 Detail

BagUtils

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

Method Detail

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

Throws: IllegalArgumentException if the Bag or Predicate is null

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

Throws: IllegalArgumentException if the SortedBag or Predicate is null

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

Throws: IllegalArgumentException if the Bag is null

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

Throws: IllegalArgumentException if the SortedBag is null

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

Throws: IllegalArgumentException if the Bag or Transformer is null

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

Throws: IllegalArgumentException if the Bag or Transformer is null

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

Throws: IllegalArgumentException if the Bag is null

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

Throws: IllegalArgumentException if the SortedBag is null

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