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. This queue does not permit null elements.

This class implements all of the optional methods of the Collection and Iterator interfaces.

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() Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.
E	poll() Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.
E	poll(long time, TimeUnit unit) Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements 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 the first occurrence of the specified object from this Collection.
int	size() Returns the number of elements in this Collection.
E	take() Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
Object[]	toArray() Returns a new array containing all elements contained in this Collection.
<T> T[]	toArray(T[] array) Returns an array containing all elements contained in this Collection.

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

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if no elements 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 time,
              TimeUnit unit)
                       throws InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.

Specified by:

poll in interface BlockingQueue<E extends Delayed>

Parameters:

time - 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 is present.

Throws:

InterruptedException - if interrupted while waiting.

poll

public E poll()

Description copied from interface: Queue

Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.

Specified by:

poll in interface Queue<E extends Delayed>

Returns:

the element in the head of the queue or null if there is no element in the queue.

peek

public E peek()

Description copied from interface: Queue

Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.

Specified by:

peek in interface Queue<E extends Delayed>

Returns:

the element in the head of the queue or null if there is no element in the queue.

size

public int size()

Description copied from class: AbstractCollection

Returns the number of elements in this Collection.

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>

See Also:

Collection.isEmpty(), Collection.size()

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 a new array containing all elements contained in this Collection. All the elements in the array will not be referenced by the collection. The elements in the returned array will be sorted to the same order as those returned by the iterator of this collection itself if the collection guarantees the order.

Specified by:

toArray in interface Collection<E extends Delayed>

Overrides:

toArray in class AbstractCollection<E extends Delayed>

Returns:

an array of the elements from this Collection

toArray

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

Description copied from class: AbstractCollection

Returns an array containing all elements contained in this Collection. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this Collection, the array element following the collection elements is set to null.

Specified by:

toArray in interface Collection<E extends Delayed>

Overrides:

toArray in class AbstractCollection<E extends Delayed>

Parameters:

array - the array

Returns:

an array of the elements from this Collection

remove

public boolean remove(Object o)

Description copied from class: AbstractCollection

Removes the first occurrence of the specified object from this Collection. This operation traverses over the collection, looking for the specified object. Once the object is found, the object will be removed from the collection using the iterator's remove method. This collection will throw an UnsupportedOperationException if the iterator returned does not implement remove method, and the specified object is in this collection.

Specified by:

remove in interface Collection<E extends Delayed>

Overrides:

remove in class AbstractCollection<E extends Delayed>

Parameters:

o - the object to remove

Returns:

true if this Collection is modified, false otherwise

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.

See Also:

Iterator