java.util.concurrent
class DelayQueue

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

All Implemented Interfaces:

Collection, Queue, BlockingQueue

Most common way to construct:

DelayQueue q = new DelayQueue();

Based on 21 examples

public class DelayQueue
extends AbstractQueue
implements BlockingQueue

An unbounded {@linkplain BlockingQueue 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 {@link Collection} and {@link Iterator} interfaces.

This class is a member of the Java Collections Framework.

DelayQueue

public DelayQueue()

Creates a new DelayQueue that is initially empty.

DelayQueue

public DelayQueue(Collection c)

Creates a DelayQueue initially containing the elements of the given collection of {@link Delayed} instances.

Parameters:

c - the collection of elements to initially contain

add

public boolean add(Delayed e)

Inserts the specified element into this delay queue.

Overrides:

add in class AbstractQueue

Parameters:

e - the element to add

Returns:

true (as specified by {@link Collection#add})

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.

Overrides:

clear in class AbstractQueue

drainTo

public int drainTo(Collection c)

Parameters:

c

drainTo

public int drainTo(Collection c,
                   int maxElements)

Parameters:

c

maxElements

iterator

public Iterator 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 "weakly consistent" iterator that will never throw {@link 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.

Overrides:

iterator in class AbstractCollection

Returns:

an iterator over the elements in this queue

offer

public boolean offer(Delayed e)

Inserts the specified element into this delay queue.

Parameters:

e - the element to add

Returns:

true

offer

public boolean offer(Delayed 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 - 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

peek

public Delayed 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:

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

poll

public Delayed poll()

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

Returns:

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

poll

public Delayed 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.

Parameters:

timeout

unit

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 - {@inheritDoc}

put

public void put(Delayed e)

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

Parameters:

e - the element to add

remainingCapacity

public int remainingCapacity()

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

Returns:

Integer.MAX_VALUE

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.

Overrides:

remove in class AbstractCollection

Parameters:

o

size

public int size()

Overrides:

size in class AbstractCollection

take

public Delayed 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.

Returns:

the head of this queue

Throws:

InterruptedException - {@inheritDoc}

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.

Overrides:

toArray in class AbstractCollection

Returns:

an array containing all of the elements in this queue

toArray

public Object[] toArray(Object[] 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 {@link #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().

Overrides:

toArray in class AbstractCollection

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