java.util.concurrent
Class DelayQueue<E extends Delayed >

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

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Iterable <E>, Collection <E>, BlockingQueue <E>, Queue <E>

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

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 This queue does not permit take null 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. 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           Inserts           Adds the specified element into to this delay queue.
void	clear ()           Atomically removes all of the elements from this delay queue.
int	drainTo ( Collection <? super E           Removes all available elements from this queue and adds them to into the given collection.
int	drainTo ( Collection <? super E           Removes at most the given number of available elements from this queue and adds them to into the given collection.
Iterator < E	iterator ()           Returns an iterator over all the elements (both expired and unexpired) in this queue.
boolean	offer ( E           Inserts the specified element into this delay queue.
boolean	offer ( E  e,  o, long timeout, TimeUnit           Inserts the specified element into this delay queue.
E	peek ()           Retrieves, but does not remove, the head of this queue, or returns returning null if this queue is empty. has no elements with an unexpired delay.
E	poll ()           Retrieves and removes the head of this queue, or returns null if this queue has no elements with an expired unexpired delay.
E	poll (long timeout, TimeUnit           Retrieves and removes the head of this queue, waiting if necessary until an element up to the specified wait time if no elements with an expired unexpired delay is available are present on this queue, or the specified wait time expires. queue.
void	put ( E           Inserts           Adds the specified element into to this delay queue.
int	remainingCapacity ()           Always returns Integer.MAX_VALUE because a DelayQueue is not capacity constrained.
boolean	remove ( Object           Removes a single instance of the specified element from this queue, if it is present, whether or not it has expired. present.
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 no elements with an expired unexpired delay is available are present on this queue.
Object	toArray ()           Returns an array containing all of the elements in this queue. collection.
<T> T[]	toArray (T[] a) (T[] array)           Returns an array containing all of the elements in this queue; collection; 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

 

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 , contains , 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 - if the specified collection or any of its elements are null - if c or any element within it is null

add offer

public boolean add offer (E e)  o) 

Inserts the specified element into this delay queue.

Specified by:

add offer in interface Collection < E extends Delayed >

Specified by:

add in interface BlockingQueue < E extends Delayed >

Specified by:

add offer in interface Queue < E extends Delayed >

Overrides:

add in class AbstractQueue < E extends Delayed >

Parameters:

e o - the element to add

Returns:

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

Throws:

NullPointerException - if the specified element is null .

offer put

public boolean void offer put (E e)  o) 

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

Specified by:

offer put in interface BlockingQueue < E extends Delayed >

Specified by:

offer in interface Queue < E extends Delayed >

Parameters:

e o - the element to add

Returns:

true

Throws:

NullPointerException - if the specified element is null .

put offer

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

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

Specified by:

put offer in interface BlockingQueue < E extends Delayed >

Parameters:

e - the element to add o - 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 - if the specified element is null .

offer add

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

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

Specified by:

offer add in interface Collection < E extends Delayed >

Specified by:

add in interface BlockingQueue < E extends Delayed >

Overrides:

add in class AbstractQueue < E extends Delayed >

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 o - the element to add

Returns:

true (as per the general contract of Collection.add ).

Throws:

NullPointerException - if the specified element is null .

poll take

public Epoll take () ()
 throws InterruptedException

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

Specified by:

poll take in interface Queue BlockingQueue < E extends Delayed >

Returns:

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

Throws:

InterruptedException - if interrupted while waiting.

take poll

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

Retrieves and removes the head of this queue, waiting if necessary until an element up to the specified wait time if no elements with an expired unexpired delay is available are present on this queue.

Specified by:

take poll in interface BlockingQueue < E extends Delayed >

Parameters:

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

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

the head of this queue the head of this queue, or null if the specified waiting time elapses before an element with an unexpired delay is present.

Throws:

InterruptedException - if interrupted while waiting waiting.

poll

public Epoll(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. Retrieves and removes the head of this queue, or null if this queue has no elements with an unexpired delay.

Specified by:

poll poll in interface BlockingQueue Queue < E extends Delayed >

Parameters:

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

unit - a TimeUnit determining how to interpret the timeout 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 - if interrupted while waiting if this queue has no elements with an unexpired delay.

peek

public E peek()

Retrieves, but does not remove, the head of this queue, or returns returning 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. if this queue has no elements with an unexpired delay.

Specified by:

peek in interface Queue < E extends Delayed >

Returns:

the head of this queue, or null if this queue is empty. if this queue has no elements with an unexpired delay.

size

public int size()

Description copied from interface: Collection class: AbstractCollection

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

Specified by:

size in interface Collection < E extends Delayed >

Specified by:

size in class AbstractCollection < E extends Delayed >

Returns:

the number of elements in this collection collection.

drainTo

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

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them to into the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection 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.

Specified by:

drainTo in interface BlockingQueue < E extends Delayed >

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

IllegalArgumentException - 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 the number of elements transferred.

drainTo

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

Description copied from interface: BlockingQueue

Removes at most the given number of available elements from this queue and adds them to into the given collection. A failure encountered while attempting to add elements to collection 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.

Specified by:

drainTo in interface BlockingQueue < E extends Delayed >

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

IllegalArgumentException - 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 the number of elements transferred.

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 in interface Collection < E extends Delayed >

Overrides:

clear in class AbstractQueue < E extends Delayed >

remainingCapacity

public int remainingCapacity()

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

Specified by:

remainingCapacity in interface BlockingQueue < E extends Delayed >

Returns:

Integer.MAX_VALUE

toArray

public Object[] toArray()

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this queue. The collection. If the collection makes any guarantees as to what order its elements are returned array by its iterator, this method must return the elements are in no particular the same order.

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

This method acts as bridge between array-based and collection-based APIs. This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

Specified by:

toArray in interface Collection < E extends Delayed >

Overrides:

toArray in class AbstractCollection < E extends Delayed >

Returns:

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

toArray

public <T> T[] toArray(T[] a) (T[] array) 

Description copied from class: AbstractCollection

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

If this queue the collection fits in the specified array with room to spare (i.e., the array has more elements than this queue), the collection), the element in the array immediately following the end of the queue collection is set to null . This is useful in determining the length of the collection only if the caller knows that the collection does not contain any null elements.)

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. If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

The following code can be used to dump a delay queue into a newly allocated array of This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a Delayed null :

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

Note that toArray(new Object[0]) is identical in function to toArray() . is stored in the first location after the end of the collection.

Specified by:

toArray in interface Collection < E extends Delayed >

Overrides:

toArray in class AbstractCollection < E extends Delayed >

Parameters:

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

Returns:

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 an array containing the elements of the collection.

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. present.

Specified by:

remove in interface Collection < E extends Delayed >

Specified by:

remove in interface BlockingQueue < E extends Delayed >

Overrides:

remove in class AbstractCollection < E extends Delayed >

Parameters:

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

Returns:

true if an element was removed as a result of this call if the collection contained the specified element.

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 returned iterator is a thread-safe "fast-fail" iterator that will throw ConcurrentModificationException upon detected interference.

Specified by:

iterator in interface Iterable < E extends Delayed >

Specified by:

iterator in interface Collection < E extends Delayed >

Specified by:

iterator in class AbstractCollection < E extends Delayed >

Returns:

an iterator over the elements in this queue queue.