org.apache.commons.collections4

Class QueueUtils

java.lang.Object

org.apache.commons.collections4.QueueUtils

public class QueueUtils
extends java.lang.Object

Provides utility methods and decorators for Queue instances.

Since:

4.0

Field Summary

Fields

Modifier and Type	Field and Description
static java.util.Queue	EMPTY_QUEUE An empty unmodifiable queue.

Method Summary

Modifier and Type	Method and Description
static <E> java.util.Queue<E>	emptyQueue() Get an empty Queue.
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.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

EMPTY_QUEUE

public static final java.util.Queue EMPTY_QUEUE

An empty unmodifiable queue.

Method Detail

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

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 null

predicate - 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

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 null

transformer - 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

emptyQueue

public static <E> java.util.Queue<E> emptyQueue()

Get an empty Queue.

Type Parameters:

E - the type of the elements in the queue

Returns:

an empty Queue