Class QueueUtils
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Field SummaryFields
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Method SummaryModifier and TypeMethodDescriptionstatic <E> Queue<E> Gets 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> synchronizedQueue(Queue<E> queue) Returns a synchronized (thread-safe) 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- 
EMPTY_QUEUEAn empty unmodifiable queue.
 
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Method Details- 
emptyQueueGets an emptyQueue.- Type Parameters:
- E- the type of the elements in the queue
- Returns:
- an empty Queue
 
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predicatedQueueReturns 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
 
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synchronizedQueueReturns a synchronized (thread-safe) queue backed by the given queue. In order to guarantee serial access, it is critical that all access to the backing queue is accomplished through the returned queue.It is imperative that the user manually synchronize on the returned queue when iterating over it: Queue queue = QueueUtils.synchronizedQueue(new CircularFifoQueue()); ... synchronized(queue) { Iterator i = queue.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:
- queue- the queue to synchronize, must not be null
- Returns:
- a synchronized queue backed by that queue
- Throws:
- NullPointerException- if the queue is null
- Since:
- 4.2
 
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transformingQueuepublic 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 behavior, 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
 
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unmodifiableQueueReturns 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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