Class DelayQueue<E extendsDelayed>

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 queue
All Implemented Interfaces:
Iterable<E>,Collection<E>,BlockingQueue<E>,Queue<E>
public classDelayQueue<E extendsDelayed>extendsAbstractQueue<E>implementsBlockingQueue<E>
An unboundedblocking queue ofDelayed elements, in which an element generally becomes eligible for removal when its delay has expired.

An element is consideredexpired when itsgetDelay(TimeUnit.NANOSECONDS) method would return a value less than or equal to zero.

An element is considered thehead of the queue if it is the element with the earliest expiration time, whether in the past or the future, if there is such an element.

An element is considered theexpired head of the queue if it is theexpired element with the earliest expiration time in the past, if there is such an element. Theexpired head, when present, is also thehead.

While this class implements theBlockingQueue interface, it intentionally violates the general contract ofBlockingQueue, in that the following methods disregard the presence of unexpired elements and only ever remove theexpired head:

All other methods operate on both expired and unexpired elements. For example, thesize() method returns the count of all elements. Methodpeek() may return the (non-null)head even whentake() would block waiting for that element to expire.

This queue does not permit null elements.

This class and its iterator implement all of theoptional methods of theCollection andIterator interfaces. The Iterator provided in methoditerator() isnot guaranteed to traverse the elements of the DelayQueue in any particular order.

This class is a member of the Java Collections Framework.

Since:
1.5

  • Constructor Details

    • DelayQueue

      public DelayQueue()
      Creates a newDelayQueue that is initially empty.

    • DelayQueue

      public DelayQueue(Collection<? extendsE> c)
      Creates aDelayQueue initially containing the elements of the given collection ofDelayed instances.
      Parameters:
      c - the collection of elements to initially contain
      Throws:
      NullPointerException - if the specified collection or any of its elements are null

  • Method Details

    • add

      public boolean add(E e)
      Inserts the specified element into this delay queue.
      Specified by:
      add in interface BlockingQueue<E extendsDelayed>
      Specified by:
      add in interface Collection<E extendsDelayed>
      Specified by:
      add in interface Queue<E extendsDelayed>
      Overrides:
      add in class AbstractQueue<E extendsDelayed>
      Parameters:
      e - the element to add
      Returns:
      true (as specified byCollection.add(E))
      Throws:
      NullPointerException - if the specified element is null

    • offer

      public boolean offer(E e)
      Inserts the specified element into this delay queue.
      Specified by:
      offer in interface BlockingQueue<E extendsDelayed>
      Specified by:
      offer in interface Queue<E extendsDelayed>
      Parameters:
      e - the element to add
      Returns:
      true
      Throws:
      NullPointerException - if the specified element is null

    • put

      public void put(E e)
      Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.
      Specified by:
      put in interface BlockingQueue<E extendsDelayed>
      Parameters:
      e - the element to add
      Throws:
      NullPointerException - if the specified element is null

    • offer

      public boolean offer(E e, 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 extendsDelayed>
      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
      Throws:
      NullPointerException - if the specified element is null

    • poll

      public E poll()
      Retrieves and removes theexpired head of this queue, or returnsnull if this queue has noexpired elements.
      Specified by:
      poll in interface Queue<E extendsDelayed>
      Returns:
      theexpired head of this queue, ornull if this queue has no elements with an expired delay

    • take

      public E take() throwsInterruptedException
      Retrieves and removes theexpired head of this queue, waiting if necessary until anexpired element is available on this queue.
      Specified by:
      take in interface BlockingQueue<E extendsDelayed>
      Returns:
      theexpired head of this queue
      Throws:
      InterruptedException - if interrupted while waiting

    • poll

      public E poll(long timeout,TimeUnit unit) throwsInterruptedException
      Retrieves and removes theexpired head of this queue, waiting if necessary until anexpired element is available on this queue, or the specified wait time expires.
      Specified by:
      poll in interface BlockingQueue<E extendsDelayed>
      Parameters:
      timeout - how long to wait before giving up, in units ofunit
      unit - aTimeUnit determining how to interpret thetimeout parameter
      Returns:
      theexpired head of this queue, ornull if the specified waiting time elapses before an element with an expired delay becomes available
      Throws:
      InterruptedException - if interrupted while waiting

    • remove

      public E remove()
      Retrieves and removes theexpired head of this queue, or throws an exception if this queue has noexpired elements.
      Specified by:
      remove in interface Queue<E extendsDelayed>
      Overrides:
      remove in class AbstractQueue<E extendsDelayed>
      Returns:
      theexpired head of this queue
      Throws:
      NoSuchElementException - if this queue has no elements with an expired delay
      Since:
      21

    • peek

      public E peek()
      Retrieves, but does not remove, thehead of this queue, or returnsnull if this queue is empty. Unlikepoll, if no expired elements are available in the queue, this method returns the element that will expire next, if one exists.
      Specified by:
      peek in interface Queue<E extendsDelayed>
      Returns:
      thehead of this queue, ornull if this queue is empty

    • size

      public int size()
      Description copied from interface: Collection
      Returns the number of elements in this collection. If this collection contains more thanInteger.MAX_VALUE elements, returnsInteger.MAX_VALUE.
      Specified by:
      size in interface Collection<E extendsDelayed>
      Returns:
      the number of elements in this collection

    • drainTo

      public int drainTo(Collection<? superE> c)
      Description copied from interface: BlockingQueue
      Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collectionc 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 inIllegalArgumentException. 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 extendsDelayed>
      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

    • drainTo

      public int drainTo(Collection<? superE> c, int maxElements)
      Description copied from interface: BlockingQueue
      Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collectionc 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 inIllegalArgumentException. 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 extendsDelayed>
      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

    • 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 extendsDelayed>
      Overrides:
      clear in class AbstractQueue<E extendsDelayed>

    • remainingCapacity

      public int remainingCapacity()
      Always returnsInteger.MAX_VALUE because aDelayQueue is not capacity constrained.
      Specified by:
      remainingCapacity in interface BlockingQueue<E extendsDelayed>
      Returns:
      Integer.MAX_VALUE

    • 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.

      Specified by:
      toArray in interface Collection<E extendsDelayed>
      Overrides:
      toArray in class AbstractCollection<E extendsDelayed>
      Returns:
      an array containing all of the elements in this queue

    • toArray

      public <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. 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 tonull.

      Like thetoArray() 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 ofDelayed:

      Delayed[] a = q.toArray(new Delayed[0]);
      Note thattoArray(new Object[0]) is identical in function totoArray().

      Specified by:
      toArray in interface Collection<E extendsDelayed>
      Overrides:
      toArray in class AbstractCollection<E extendsDelayed>
      Type Parameters:
      T - the component type of the array to contain the collection
      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
      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

    • 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.
      Specified by:
      remove in interface BlockingQueue<E extendsDelayed>
      Specified by:
      remove in interface Collection<E extendsDelayed>
      Overrides:
      remove in class AbstractCollection<E extendsDelayed>
      Parameters:
      o - element to be removed from this collection, if present
      Returns:
      true if an element was removed as a result of this call

    • 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 isweakly consistent.

      Specified by:
      iterator in interface Collection<E extendsDelayed>
      Specified by:
      iterator in interface Iterable<E extendsDelayed>
      Specified by:
      iterator in class AbstractCollection<E extendsDelayed>
      Returns:
      an iterator over the elements in this queue