Class QueueUtils

java.lang.Object
org.apache.commons.collections4.QueueUtils

public class QueueUtils extends Object
Provides utility methods and decorators for Queue instances.
Since:
4.0
Version:
$Id: QueueUtils.java 1686855 2015-06-22 13:00:27Z tn $
  • Field Details

    • EMPTY_QUEUE

      public static final Queue EMPTY_QUEUE
      An empty unmodifiable queue.
  • Method Details

    • unmodifiableQueue

      public static <E> Queue<E> unmodifiableQueue(Queue<? extends E> queue)
      Returns an unmodifiable queue backed by the given queue.
      Type Parameters:
      E - the type of the elements in the queue
      Parameters:
      queue - the queue to make unmodifiable, must not be null
      Returns:
      an unmodifiable queue backed by that queue
      Throws:
      NullPointerException - if the queue is null
    • predicatedQueue

      public static <E> Queue<E> predicatedQueue(Queue<E> queue, Predicate<? super E> predicate)
      Returns a predicated (validating) queue backed by the given queue.

      Only objects that pass the test in the given predicate can be added to the queue. Trying to add an invalid object results in an IllegalArgumentException. It is important not to use the original queue after invoking this method, as it is a backdoor for adding invalid objects.

      Type Parameters:
      E - the type of the elements in the queue
      Parameters:
      queue - the queue to predicate, must not be null
      predicate - the predicate used to evaluate new elements, must not be null
      Returns:
      a predicated queue
      Throws:
      NullPointerException - if the queue or predicate is null
    • transformingQueue

      public static <E> Queue<E> transformingQueue(Queue<E> queue, Transformer<? super E,? extends E> transformer)
      Returns a transformed queue backed by the given queue.

      Each object is passed through the transformer as it is added to the Queue. It is important not to use the original queue after invoking this method, as it is a backdoor for adding untransformed objects.

      Existing entries in the specified queue will not be transformed. If you want that behaviour, see TransformedQueue.transformedQueue(java.util.Queue<E>, org.apache.commons.collections4.Transformer<? super E, ? extends E>).

      Type Parameters:
      E - the type of the elements in the queue
      Parameters:
      queue - the queue to predicate, must not be null
      transformer - the transformer for the queue, must not be null
      Returns:
      a transformed queue backed by the given queue
      Throws:
      NullPointerException - if the queue or transformer is null
    • emptyQueue

      public static <E> Queue<E> emptyQueue()
      Get an empty Queue.
      Type Parameters:
      E - the type of the elements in the queue
      Returns:
      an empty Queue