E - the type of elements held in this collectionpublic class DelayQueue<E extends Delayed> extends AbstractQueue<E> implements BlockingQueue<E>
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.
 
This class is a member of the Java Collections Framework.
| Constructor and Description | 
|---|
| DelayQueue()Creates a new  DelayQueuethat is initially empty. | 
| DelayQueue(Collection<? extends E> c)Creates a  DelayQueueinitially containing the elements of the
 given collection ofDelayedinstances. | 
| Modifier and Type | Method and Description | 
|---|---|
| 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)Removes all available elements from this queue and adds them
 to 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 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  nullif this queue is empty. | 
| E | poll()Retrieves and removes the head of this queue, or returns  nullif this queue has no elements with an expired delay. | 
| 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. | 
| void | put(E e)Inserts the specified element into this delay queue. | 
| int | remainingCapacity()Always returns  Integer.MAX_VALUEbecause
 aDelayQueueis 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. | 
| Object[] | toArray()Returns an array containing all of the elements in 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. | 
addAll, element, removecontains, containsAll, isEmpty, removeAll, retainAll, toStringclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitcontainsaddAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, streampublic DelayQueue()
DelayQueue that is initially empty.public DelayQueue(Collection<? extends E> c)
DelayQueue initially containing the elements of the
 given collection of Delayed instances.c - the collection of elements to initially containNullPointerException - if the specified collection or any
         of its elements are nullpublic boolean add(E e)
add in interface Collection<E extends Delayed>add in interface BlockingQueue<E extends Delayed>add in interface Queue<E extends Delayed>add in class AbstractQueue<E extends Delayed>e - the element to addtrue (as specified by Collection.add(E))NullPointerException - if the specified element is nullpublic boolean offer(E e)
offer in interface BlockingQueue<E extends Delayed>offer in interface Queue<E extends Delayed>e - the element to addtrueNullPointerException - if the specified element is nullpublic void put(E e)
put in interface BlockingQueue<E extends Delayed>e - the element to addNullPointerException - if the specified element is nullpublic boolean offer(E e, long timeout, TimeUnit unit)
offer in interface BlockingQueue<E extends Delayed>e - the element to addtimeout - This parameter is ignored as the method never blocksunit - This parameter is ignored as the method never blockstrueNullPointerException - if the specified element is nullpublic E poll()
null
 if this queue has no elements with an expired delay.public E take() throws InterruptedException
take in interface BlockingQueue<E extends Delayed>InterruptedException - if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
poll in interface BlockingQueue<E extends Delayed>timeout - how long to wait before giving up, in units of
        unitunit - a TimeUnit determining how to interpret the
        timeout parameternull if the
         specified waiting time elapses before an element with
         an expired delay becomes availableInterruptedException - if interrupted while waitingpublic E peek()
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.public int size()
Collectionsize in interface Collection<E extends Delayed>size in class AbstractCollection<E extends Delayed>public int drainTo(Collection<? super E> c)
BlockingQueuec 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.drainTo in interface BlockingQueue<E extends Delayed>c - the collection to transfer elements intoUnsupportedOperationException - if addition of elements
         is not supported by the specified collectionClassCastException - if the class of an element of this queue
         prevents it from being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this
         queue, or some property of an element of this queue prevents
         it from being added to the specified collectionpublic int drainTo(Collection<? super E> c, int maxElements)
BlockingQueuec 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.drainTo in interface BlockingQueue<E extends Delayed>c - the collection to transfer elements intomaxElements - the maximum number of elements to transferUnsupportedOperationException - if addition of elements
         is not supported by the specified collectionClassCastException - if the class of an element of this queue
         prevents it from being added to the specified collectionNullPointerException - if the specified collection is nullIllegalArgumentException - if the specified collection is this
         queue, or some property of an element of this queue prevents
         it from being added to the specified collectionpublic void clear()
clear in interface Collection<E extends Delayed>clear in class AbstractQueue<E extends Delayed>public int remainingCapacity()
Integer.MAX_VALUE because
 a DelayQueue is not capacity constrained.remainingCapacity in interface BlockingQueue<E extends Delayed>Integer.MAX_VALUEpublic Object[] toArray()
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.
toArray in interface Collection<E extends Delayed>toArray in class AbstractCollection<E extends Delayed>public <T> T[] toArray(T[] a)
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().toArray in interface Collection<E extends Delayed>toArray in class AbstractCollection<E extends Delayed>T - the runtime type of the array to contain the collectiona - 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 purposeArrayStoreException - if the runtime type of the specified array
         is not a supertype of the runtime type of every element in
         this queueNullPointerException - if the specified array is nullpublic boolean remove(Object o)
remove in interface Collection<E extends Delayed>remove in interface BlockingQueue<E extends Delayed>remove in class AbstractCollection<E extends Delayed>o - element to be removed from this collection, if presentpublic Iterator<E> iterator()
The returned iterator is weakly consistent.
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