DelayQueue (Java Platform SE 6) (original) (raw)

java.util.concurrent

Class DelayQueue<E extends Delayed>

java.lang.Object extended by java.util.AbstractCollection java.util.AbstractQueue java.util.concurrent.DelayQueue

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Iterable, Collection, BlockingQueue, Queue

public class DelayQueue<E extends Delayed>

extends AbstractQueue

implements BlockingQueue

An unbounded blocking queue ofDelayed elements, in which an element can only be taken when its delay has expired. The head of the queue is thatDelayed element whose delay expired furthest in the past. If no delay has expired there is no head and poll will return null. Expiration occurs when an element'sgetDelay(TimeUnit.NANOSECONDS) method returns a value less than or equal to zero. Even though unexpired elements cannot be removed using take or poll, they are otherwise treated as normal elements. For example, the size method returns the count of both expired and unexpired elements. This queue does not permit null elements.

This class and its iterator implement all of the_optional_ methods of the Collection and Iterator interfaces.

This class is a member of the Java Collections Framework.

Since:

1.5

Constructor Summary
DelayQueue() Creates a new DelayQueue that is initially empty.
DelayQueue(Collection<? extends E> c) Creates a DelayQueue initially containing the elements of the given collection of Delayed instances.

Method Summary
boolean	add(E e) Inserts the specified element into this delay queue.
void	clear() Atomically removes all of the elements from this delay queue.
int	drainTo(Collection<? super E> c) Removes all available elements from this queue and adds them to the given collection.
int	[drainTo](../../../java/util/concurrent/DelayQueue.html#drainTo%28java.util.Collection, int%29)(Collection<? super E> c, int maxElements) Removes at most the given number of available elements from this queue and adds them to the given collection.
Iterator<E>	iterator() Returns an iterator over all the elements (both expired and unexpired) in this queue.
boolean	offer(E e) Inserts the specified element into this delay queue.
boolean	[offer](../../../java/util/concurrent/DelayQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29)(E e, long timeout,TimeUnit unit) Inserts the specified element into this delay queue.
E	peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll() Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired delay.
E	[poll](../../../java/util/concurrent/DelayQueue.html#poll%28long, java.util.concurrent.TimeUnit%29)(long timeout,TimeUnit unit) Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue, or the specified wait time expires.
void	put(E e) Inserts the specified element into this delay queue.
int	remainingCapacity() Always returns Integer.MAX_VALUE because a DelayQueue is not capacity constrained.
boolean	remove(Object o) Removes a single instance of the specified element from this queue, if it is present, whether or not it has expired.
int	size() Returns the number of elements in this collection.
E	take() Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue.
Object[]	toArray() Returns an array containing all of the elements in this queue.
T[]	toArray(T[] a) Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.

Methods inherited from class java.util.AbstractQueue
addAll, element, remove

Methods inherited from class java.util.AbstractCollection
contains, containsAll, isEmpty, removeAll, retainAll, toString

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, [wait](../../../java/lang/Object.html#wait%28long, int%29)

Methods inherited from interface java.util.concurrent.BlockingQueue
contains

Methods inherited from interface java.util.Queue
element, remove

Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll

Constructor Detail

DelayQueue

public DelayQueue()

Creates a new DelayQueue that is initially empty.

DelayQueue

public DelayQueue(Collection<? extends E> c)

Creates a DelayQueue initially containing the elements of the given collection of Delayed instances.

Parameters:

c - the collection of elements to initially contain

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection or any of its elements are null

Method Detail

add

public boolean add(E e)

Inserts the specified element into this delay queue.

Specified by:

[add](../../../java/util/Collection.html#add%28E%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[add](../../../java/util/concurrent/BlockingQueue.html#add%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[add](../../../java/util/Queue.html#add%28E%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Overrides:

[add](../../../java/util/AbstractQueue.html#add%28E%29) in class [AbstractQueue](../../../java/util/AbstractQueue.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(E))

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

offer

public boolean offer(E e)

Inserts the specified element into this delay queue.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[offer](../../../java/util/Queue.html#offer%28E%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

e - the element to add

Returns:

true

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

put

public void put(E e)

Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.

Specified by:

[put](../../../java/util/concurrent/BlockingQueue.html#put%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

e - the element to add

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

offer

public boolean offer(E e, long timeout, TimeUnit unit)

Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

e - the element to add

timeout - This parameter is ignored as the method never blocks

unit - This parameter is ignored as the method never blocks

Returns:

true

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null

poll

public E poll()

Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired delay.

Specified by:

[poll](../../../java/util/Queue.html#poll%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

the head of this queue, or null if this queue has no elements with an expired delay

take

public E take() throws InterruptedException

Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue.

Specified by:

[take](../../../java/util/concurrent/BlockingQueue.html#take%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

the head of this queue

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

poll

public E poll(long timeout, TimeUnit unit) throws InterruptedException

Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue, or the specified wait time expires.

Specified by:

[poll](../../../java/util/concurrent/BlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

timeout - how long to wait before giving up, in units ofunit

unit - a TimeUnit determining how to interpret thetimeout parameter

Returns:

the head of this queue, or null if the specified waiting time elapses before an element with an expired delay becomes available

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting

peek

public E peek()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. Unlikepoll, if no expired elements are available in the queue, this method returns the element that will expire next, if one exists.

Specified by:

[peek](../../../java/util/Queue.html#peek%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

the head of this queue, or null if this queue is empty.

size

public int size()

Description copied from interface: [Collection](../../../java/util/Collection.html#size%28%29)

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returnsInteger.MAX_VALUE.

Specified by:

[size](../../../java/util/Collection.html#size%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[size](../../../java/util/AbstractCollection.html#size%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

the number of elements in this collection

drainTo

public int drainTo(Collection<? super E> c)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29)

Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

[UnsupportedOperationException](../../../java/lang/UnsupportedOperationException.html "class in java.lang") - if addition of elements is not supported by the specified collection

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the class of an element of this queue prevents it from being added to the specified collection

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection is null

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

drainTo

public int drainTo(Collection<? super E> c, int maxElements)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29)

Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

[UnsupportedOperationException](../../../java/lang/UnsupportedOperationException.html "class in java.lang") - if addition of elements is not supported by the specified collection

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the class of an element of this queue prevents it from being added to the specified collection

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified collection is null

clear

public void clear()

Atomically removes all of the elements from this delay queue. The queue will be empty after this call returns. Elements with an unexpired delay are not waited for; they are simply discarded from the queue.

Specified by:

[clear](../../../java/util/Collection.html#clear%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Overrides:

[clear](../../../java/util/AbstractQueue.html#clear%28%29) in class [AbstractQueue](../../../java/util/AbstractQueue.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

remainingCapacity

public int remainingCapacity()

Always returns Integer.MAX_VALUE because a DelayQueue is not capacity constrained.

Specified by:

[remainingCapacity](../../../java/util/concurrent/BlockingQueue.html#remainingCapacity%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

Integer.MAX_VALUE

toArray

public Object[] toArray()

Returns an array containing all of the elements in this queue. The returned array elements are in no particular order.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

an array containing all of the elements in this queue

toArray

public T[] toArray(T[] a)

Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array. The returned array elements are in no particular order. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this queue.

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set tonull.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

The following code can be used to dump a delay queue into a newly allocated array of Delayed:

 Delayed[] a = q.toArray(new Delayed[0]);

Note that toArray(new Object[0]) is identical in function totoArray().

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28T[]%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28T[]%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

a - the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose

Returns:

an array containing all of the elements in this queue

Throws:

[ArrayStoreException](../../../java/lang/ArrayStoreException.html "class in java.lang") - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified array is null

remove

public boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present, whether or not it has expired.

Specified by:

[remove](../../../java/util/Collection.html#remove%28java.lang.Object%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[remove](../../../java/util/concurrent/BlockingQueue.html#remove%28java.lang.Object%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Overrides:

[remove](../../../java/util/AbstractCollection.html#remove%28java.lang.Object%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Parameters:

o - element to be removed from this collection, if present

Returns:

true if an element was removed as a result of this call

iterator

public Iterator<E> iterator()

Returns an iterator over all the elements (both expired and unexpired) in this queue. The iterator does not return the elements in any particular order. The returnedIterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Specified by:

[iterator](../../../java/lang/Iterable.html#iterator%28%29) in interface [Iterable](../../../java/lang/Iterable.html "interface in java.lang")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[iterator](../../../java/util/Collection.html#iterator%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Specified by:

[iterator](../../../java/util/AbstractCollection.html#iterator%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/DelayQueue.html "type parameter in DelayQueue") extends [Delayed](../../../java/util/concurrent/Delayed.html "interface in java.util.concurrent")>

Returns:

an iterator over the elements in this queue

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