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org.apache.commons.collections

Class BagUtils

java.lang.Object
|
+--org.apache.commons.collections.BagUtils


public class BagUtils
extends java.lang.Object

Provides utility methods and decorators for Bag and SortedBag instances.
Since:
Commons Collections 2.1
Authors:
Paul Jack
Stephen Colebourne
Andrew Freeman
Matthew Hawthorne

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 bag backed by the given bag.

static SortedBag

predicatedSortedBag(SortedBag bag, Predicate predicate)

Returns a predicated 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 bag backed by the given bag. Only objects that pass the test in the given predicate can be added to the bag. It is important not to use the original bag after invoking this method, as it is a backdoor for adding unvalidated 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:
- if the Bag or Predicate is null

predicatedSortedBag

public static SortedBag predicatedSortedBag(SortedBag bag, Predicate predicate)

Returns a predicated sorted bag backed by the given sorted bag. Only objects that pass the test in the given predicate can be added to the bag. It is important not to use the original bag after invoking this method, as it is a backdoor for adding unvalidated 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:
- 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:
- 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:
- 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:
- 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:
- 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:
- 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:
- if the SortedBag is null