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Added in API level 1

DelayQueue

public class DelayQueue
extends AbstractQueue<E extends Delayed> implements BlockingQueue<E extends Delayed>

java.lang.Object
   ↳ java.util.AbstractCollection<E extends java.util.concurrent.Delayed>
     ↳ java.util.AbstractQueue<E extends java.util.concurrent.Delayed>
       ↳ java.util.concurrent.DelayQueue<E extends java.util.concurrent.Delayed>


An unbounded blocking queue of Delayed elements, in which an element can only be taken when its delay has expired. The head of the queue is that Delayed 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's getDelay(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. The Iterator provided in method iterator() is not guaranteed to traverse the elements of the DelayQueue in any particular order.

Summary

Public constructors

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.

Public methods

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, int maxElements)

Removes at most the given number of available elements from this queue and adds them to the given collection.

int drainTo(Collection<? super E> c)

Removes all 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(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(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.

E poll()

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

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.

<T> 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.

Object[] toArray()

Returns an array containing all of the elements in this queue.

Inherited methods

From class java.util.AbstractQueue
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.Queue
From interface java.util.Collection
From interface java.util.concurrent.BlockingQueue
From interface java.lang.Iterable

Public constructors

DelayQueue

Added in API level 1
DelayQueue ()

Creates a new DelayQueue that is initially empty.

DelayQueue

Added in API level 1
DelayQueue (Collection<? extends E> c)

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

Parameters
c Collection: the collection of elements to initially contain
Throws
NullPointerException if the specified collection or any of its elements are null

Public methods

add

Added in API level 1
boolean add (E e)

Inserts the specified element into this delay queue.

Parameters
e E: the element to add
Returns
boolean true (as specified by add(E))
Throws
NullPointerException if the specified element is null

clear

Added in API level 1
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.

drainTo

Added in API level 1
int drainTo (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. 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 in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters
c Collection: the collection to transfer elements into
maxElements int: the maximum number of elements to transfer
Returns
int the number of elements transferred
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

drainTo

Added in API level 1
int drainTo (Collection<? super E> c)

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 in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Parameters
c Collection: the collection to transfer elements into
Returns
int the number of elements transferred
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

iterator

Added in API level 1
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 returned iterator is weakly consistent.

Returns
Iterator<E> an iterator over the elements in this queue

offer

Added in API level 1
boolean offer (E e)

Inserts the specified element into this delay queue.

Parameters
e E: the element to add
Returns
boolean true
Throws
NullPointerException if the specified element is null

offer

Added in API level 1
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.

Parameters
e E: the element to add
timeout long: This parameter is ignored as the method never blocks
unit TimeUnit: This parameter is ignored as the method never blocks
Returns
boolean true
Throws
NullPointerException

peek

Added in API level 1
E peek ()

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

Returns
E the head of this queue, or null if this queue is empty

poll

Added in API level 1
E poll (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.

Parameters
timeout long: how long to wait before giving up, in units of unit
unit TimeUnit: a TimeUnit determining how to interpret the timeout parameter
Returns
E the head of this queue, or null if the specified waiting time elapses before an element with an expired delay becomes available
Throws
InterruptedException

poll

Added in API level 1
E poll ()

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

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

put

Added in API level 1
void put (E e)

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

Parameters
e E: the element to add
Throws
NullPointerException

remainingCapacity

Added in API level 1
int remainingCapacity ()

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

Returns
int Integer.MAX_VALUE

remove

Added in API level 1
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.

Parameters
o Object: element to be removed from this collection, if present
Returns
boolean true if an element was removed as a result of this call

size

Added in API level 1
int size ()

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

Returns
int the number of elements in this collection

take

Added in API level 1
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.

Returns
E the head of this queue
Throws
InterruptedException

toArray

Added in API level 1
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 to null.

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 to toArray().

Parameters
a T: 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
T[] an array containing all of the elements in this queue
Throws
ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue
NullPointerException if the specified array is null

toArray

Added in API level 1
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.

Returns
Object[] an array containing all of the elements in this queue
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