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

Field Summary

Fields

Modifier and Type	Field and Description
static Bag	EMPTY_BAG An empty unmodifiable bag.
static Bag	EMPTY_SORTED_BAG An empty unmodifiable sorted bag.

Constructor Summary

Constructors

Constructor and Description
BagUtils() Instantiation of BagUtils is not intended or required.

Method Summary

Modifier and Type	Method and Description
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, java.lang.Class type) Returns a typed bag backed by the given bag.
static SortedBag	typedSortedBag(SortedBag bag, java.lang.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.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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

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:

java.lang.IllegalArgumentException - if the Bag is null

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:

java.lang.IllegalArgumentException - if the Bag is null

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:

java.lang.IllegalArgumentException - if the Bag or Predicate is null

typedBag

public static Bag typedBag(Bag bag,
                           java.lang.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

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:

java.lang.IllegalArgumentException - if the Bag or Transformer 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:

java.lang.IllegalArgumentException - if the SortedBag 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:

java.lang.IllegalArgumentException - if the SortedBag 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:

java.lang.IllegalArgumentException - if the SortedBag or Predicate is null

typedSortedBag

public static SortedBag typedSortedBag(SortedBag bag,
                                       java.lang.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

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:

java.lang.IllegalArgumentException - if the Bag or Transformer is null