Package org.apache.commons.collections4
Class QueueUtils
java.lang.Object
org.apache.commons.collections4.QueueUtils
Provides utility methods and decorators for
Queue
instances.- Since:
- 4.0
- Version:
- $Id: QueueUtils.java 1686855 2015-06-22 13:00:27Z tn $
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Field Summary
Fields -
Method Summary
Modifier and TypeMethodDescriptionstatic <E> Queue<E>
Get an emptyQueue
.static <E> Queue<E>
predicatedQueue
(Queue<E> queue, Predicate<? super E> predicate) Returns a predicated (validating) queue backed by the given queue.static <E> Queue<E>
transformingQueue
(Queue<E> queue, Transformer<? super E, ? extends E> transformer) Returns a transformed queue backed by the given queue.static <E> Queue<E>
unmodifiableQueue
(Queue<? extends E> queue) Returns an unmodifiable queue backed by the given queue.
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Field Details
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EMPTY_QUEUE
An empty unmodifiable queue.
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Method Details
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unmodifiableQueue
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
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predicatedQueue
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 nullpredicate
- the predicate used to evaluate new elements, must not be null- Returns:
- a predicated queue
- Throws:
NullPointerException
- if the queue or predicate is null
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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 nulltransformer
- 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
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emptyQueue
Get an emptyQueue
.- Type Parameters:
E
- the type of the elements in the queue- Returns:
- an empty
Queue
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