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