Package org.apache.commons.collections4

Class BagUtils

java.lang.Object
org.apache.commons.collections4.BagUtils
public class BagUtils extends Object
Provides utility methods and decorators for Bag and SortedBag instances.
Since:
2.1

  • 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.

  • Method Details

    • collectionBag

      public static <E> Bag<E> collectionBag(Bag<E> bag)
      Returns a bag that complies to the Collection contract, backed by the given bag.
      Type Parameters:
      E - the element type
      Parameters:
      bag - the bag to decorate, must not be null
      Returns:
      a Bag that complies to the Collection contract
      Throws:
      NullPointerException - if bag is null
      Since:
      4.0

    • emptyBag

      public static <E> Bag<E> emptyBag()
      Gets an empty Bag.
      Type Parameters:
      E - the element type
      Returns:
      an empty Bag

    • emptySortedBag

      public static <E> SortedBag<E> emptySortedBag()
      Gets an empty SortedBag.
      Type Parameters:
      E - the element type
      Returns:
      an empty sorted Bag

    • predicatedBag

      public static <E> Bag<E> predicatedBag(Bag<E> bag, Predicate<? super E> 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.

      Type Parameters:
      E - the element type
      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:
      NullPointerException - if the Bag or Predicate is null

    • predicatedSortedBag

      public static <E> SortedBag<E> predicatedSortedBag(SortedBag<E> bag, Predicate<? super E> 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.

      Type Parameters:
      E - the element type
      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:
      NullPointerException - if the SortedBag or Predicate is null

    • synchronizedBag

      public static <E> Bag<E> synchronizedBag(Bag<E> 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.
      Type Parameters:
      E - the element type
      Parameters:
      bag - the bag to synchronize, must not be null
      Returns:
      a synchronized bag backed by that bag
      Throws:
      NullPointerException - if the Bag is null

    • synchronizedSortedBag

      public static <E> SortedBag<E> synchronizedSortedBag(SortedBag<E> 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.
      Type Parameters:
      E - the element type
      Parameters:
      bag - the bag to synchronize, must not be null
      Returns:
      a synchronized bag backed by that bag
      Throws:
      NullPointerException - if the SortedBag is null

    • transformingBag

      public static <E> Bag<E> transformingBag(Bag<E> bag, Transformer<? super E,? extends E> 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.

      Existing entries in the specified bag will not be transformed. If you want that behavior, see TransformedBag.transformedBag(Bag, Transformer).

      Type Parameters:
      E - the element type
      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:
      NullPointerException - if the Bag or Transformer is null

    • transformingSortedBag

      public static <E> SortedBag<E> transformingSortedBag(SortedBag<E> bag, Transformer<? super E,? extends E> 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.

      Existing entries in the specified bag will not be transformed. If you want that behavior, see TransformedSortedBag.transformedSortedBag(SortedBag, Transformer).

      Type Parameters:
      E - the element type
      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:
      NullPointerException - if the Bag or Transformer is null

    • unmodifiableBag

      public static <E> Bag<E> unmodifiableBag(Bag<? extends E> bag)
      Returns an unmodifiable view of the given bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException.
      Type Parameters:
      E - the element type
      Parameters:
      bag - the bag whose unmodifiable view is to be returned, must not be null
      Returns:
      an unmodifiable view of that bag
      Throws:
      NullPointerException - if the Bag is null

    • unmodifiableSortedBag

      public static <E> SortedBag<E> unmodifiableSortedBag(SortedBag<E> bag)
      Returns an unmodifiable view of the given sorted bag. Any modification attempts to the returned bag will raise an UnsupportedOperationException.
      Type Parameters:
      E - the element type
      Parameters:
      bag - the bag whose unmodifiable view is to be returned, must not be null
      Returns:
      an unmodifiable view of that bag
      Throws:
      NullPointerException - if the SortedBag is null