public class

BagUtils

extends Object
java.lang.Object
   ↳ org.apache.commons.collections.BagUtils

Class Overview

Provides utility methods and decorators for Bag and SortedBag instances.

Summary

Fields
public static final Bag EMPTY_BAG An empty unmodifiable bag.
public static final Bag EMPTY_SORTED_BAG An empty unmodifiable sorted bag.
Public Constructors
BagUtils()
Instantiation of BagUtils is not intended or required.
Public Methods
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.
[Expand]
Inherited Methods
From class java.lang.Object

Fields

public static final Bag EMPTY_BAG

An empty unmodifiable bag.

public static final Bag EMPTY_SORTED_BAG

An empty unmodifiable sorted bag.

Public Constructors

public BagUtils ()

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

Public Methods

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

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

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

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

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

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

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

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

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

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