public class

DelayQueue

extends AbstractQueue<E>
implements BlockingQueue<E>
java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractQueue<E>
       ↳ java.util.concurrent.DelayQueue<E extends java.util.concurrent.Delayed>

Class Overview

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.

Summary

Public Constructors
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.
Public Methods
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, int maxElements)
Removes at most the given number of available elements from this queue and adds them into the given collection.
int drainTo(Collection<? super E> c)
Removes all 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, long timeout, TimeUnit unit)
Inserts the specified element into this delay queue.
boolean offer(E o)
Inserts the specified element into this delay queue.
E peek()
Gets but does not remove the element at the head of 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.
E poll()
Gets and removes the element at the head of the queue, or returns null if there is no element in the 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 one instance of the specified object from this Collection if one is contained (optional).
int size()
Returns a count of how many objects this Collection contains.
E take()
Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
<T> T[] toArray(T[] array)
Returns an array containing all elements contained in this Collection.
Object[] toArray()
Returns a new array containing all elements contained in this Collection.
[Expand]
Inherited Methods
From class java.util.AbstractQueue
From class java.util.AbstractCollection
From class java.lang.Object
From interface java.lang.Iterable
From interface java.util.Collection
From interface java.util.Queue
From interface java.util.concurrent.BlockingQueue

Public Constructors

public DelayQueue ()

Creates a new DelayQueue that is initially empty.

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

Public Methods

public boolean add (E o)

Adds the specified element to this queue.

Parameters
o the element to add
Returns
  • true (as per the general contract of Collection.add).
Throws
NullPointerException if the specified element is null.

public void clear ()

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

public 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. 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.

Parameters
c the collection to transfer elements into
maxElements the maximum number of elements to transfer
Returns
  • the number of elements transferred.

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

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.

Parameters
c the collection to transfer elements into
Returns
  • the number of elements transferred.

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.

Returns
  • an iterator over the elements in this queue.

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.

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.

public boolean offer (E o)

Inserts the specified element into this delay queue.

Parameters
o the element to add
Returns
  • true
Throws
NullPointerException if the specified element is null.

public E peek ()

Gets but does not remove the element at the head of the queue.

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

public 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.

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

public E poll ()

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

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

public void put (E o)

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

Parameters
o the element to add
Throws
NullPointerException if the specified element is null.

public int remainingCapacity ()

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

Returns
  • Integer.MAX_VALUE

public boolean remove (Object o)

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters
o the object to remove.
Returns
  • true if this Collection is modified, false otherwise.

public int size ()

Returns a count of how many objects this Collection contains.

In this class this method is declared abstract and has to be implemented by concrete Collection implementations.

Returns
  • how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

public E take ()

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

Returns
  • the head of this queue
Throws
InterruptedException

public T[] toArray (T[] array)

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. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. toArray(new Object[0]) behaves exactly the same way as toArray() does.

Parameters
array the array.
Returns
  • an array of the elements from this Collection.

public Object[] toArray ()

Returns a new array containing all elements contained in this Collection. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. The array returned does not reflect any changes of the Collection. A new array is created even if the underlying data structure is already an array.

Returns
  • an array of the elements from this Collection.