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. 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 o) Adds the specified element to this 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 into the given collection.
int	drainTo (Collection <? super E> c, int maxElements) Removes at most the given number of available elements from this queue and adds them into the given collection.
Iterator <E>	iterator () Returns an iterator over the elements in this queue.
boolean	offer (E o) Inserts the specified element into this delay queue.
boolean	offer (E o, long timeout, TimeUnit unit) Inserts the specified element into this delay queue.
E	peek () Retrieves, but does not remove, the head of this queue, returning null if this queue has no elements with an unexpired delay.
E	poll () Retrieves and removes the head of this queue, or null if this queue has no elements with an unexpired delay.
E	poll (long timeout, TimeUnit unit) Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements with an unexpired delay are present on this queue.
void	put (E o) Adds the specified element to 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.
int	size () Returns the number of elements in this collection.
E	take () Retrieves and removes the head of this queue, waiting if no elements with an unexpired delay are present on this queue.
Object []	toArray () Returns an array containing all of the elements in this collection.
<T> T[]	toArray (T[] array) Returns an array containing all of the elements in this 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.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

Throws:

NullPointerException - if c or any element within it is null

Method Detail

offer

public boolean offer(E o)

Inserts the specified element into this delay queue.

Specified by:

offer in interface BlockingQueue <E extends Delayed >

Specified by:

offer in interface Queue <E extends Delayed >

Parameters:

o - the element to add

Returns:

true

Throws:

NullPointerException - if the specified element is null.

put

public void put(E o)

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

Specified by:

put in interface BlockingQueue <E extends Delayed >

Parameters:

o - the element to add

Throws:

NullPointerException - if the specified element is null.

offer

public boolean offer(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:

offer in interface BlockingQueue <E extends Delayed >

Parameters:

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.

add

public boolean add(E o)

Adds the specified element to this queue.

Specified by:

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:

o - the element to add

Returns:

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

Throws:

NullPointerException - if the specified element is null.

take

public E take()
                       throws InterruptedException   

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

Specified by:

take in interface BlockingQueue <E extends Delayed >

Returns:

the head of this queue

Throws:

InterruptedException - 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 up to the specified wait time if no elements with an unexpired delay are present on this queue.

Specified by:

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

Throws:

InterruptedException - if interrupted while waiting.

poll

public E poll()

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

Specified by:

poll in interface Queue <E extends Delayed >

Returns:

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

peek

public E peek()

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

size

public int size()

Description copied from class: AbstractCollection

Returns the number of elements in this collection. If 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.

drainTo

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

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them 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 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.

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 into 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.

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.

clear

public void clear()

Atomically removes all of the elements from this delay queue. The queue will be empty after this call returns.

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

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 collection.

toArray

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

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the 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 collection.

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

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.

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 null 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:

array - the array into which the elements of the collection 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 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.

Specified by:

remove in interface Collection <E extends Delayed >

Overrides:

remove in class AbstractCollection <E extends Delayed >

Parameters:

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

Returns:

true if the collection contained the specified element.

iterator

public Iterator   <E> iterator()

Returns an iterator over the elements 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.