Class DelayQueue<E extends Delayed>
- Type Parameters:
E
- the type of elements held in this queue
- All Implemented Interfaces:
Iterable<E>
,Collection<E>
,BlockingQueue<E>
,Queue<E>
Delayed
elements, in which an element generally becomes eligible for removal when its
delay has expired.
While this class implements the BlockingQueue
interface, it
intentionally violates the general contract of BlockingQueue
, in that
the following methods disregard the presence of unexpired elements and only
ever remove the expired head:
All other methods operate on both expired and unexpired elements.
For example, the size()
method returns the count of all elements.
Method peek()
may return the (non-null) head even when
take()
would block waiting for that element to expire.
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.
- Since:
- 1.5
-
Constructor Summary
ConstructorDescriptionCreates a newDelayQueue
that is initially empty.DelayQueue
(Collection<? extends E> c) Creates aDelayQueue
initially containing the elements of the given collection ofDelayed
instances. -
Method Summary
Modifier and TypeMethodDescriptionboolean
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()
Returns an iterator over all the elements (both expired and unexpired) in this queue.boolean
Inserts the specified element into this delay queue.boolean
Inserts the specified element into this delay queue.peek()
Retrieves, but does not remove, the head of this queue, or returnsnull
if this queue is empty.poll()
Retrieves and removes the expired head of this queue, or returnsnull
if this queue has no expired elements.Retrieves and removes the expired head of this queue, waiting if necessary until an expired element is available on this queue, or the specified wait time expires.void
Inserts the specified element into this delay queue.int
Always returnsInteger.MAX_VALUE
because aDelayQueue
is not capacity constrained.remove()
Retrieves and removes the expired head of this queue, or throws an exception if this queue has no expired elements.boolean
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.take()
Retrieves and removes the expired head of this queue, waiting if necessary until an expired element 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.Methods declared in class java.util.AbstractQueue
addAll, element
Methods declared in class java.util.AbstractCollection
contains, containsAll, isEmpty, removeAll, retainAll, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.concurrent.BlockingQueue
contains
Methods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, stream, toArray
-
Constructor Details
-
DelayQueue
public DelayQueue()Creates a newDelayQueue
that is initially empty. -
DelayQueue
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
Inserts the specified element into this delay queue.- Specified by:
add
in interfaceBlockingQueue<E extends Delayed>
- Specified by:
add
in interfaceCollection<E extends Delayed>
- Specified by:
add
in interfaceQueue<E extends Delayed>
- Overrides:
add
in classAbstractQueue<E extends Delayed>
- Parameters:
e
- the element to add- Returns:
true
(as specified byCollection.add(E)
)- Throws:
NullPointerException
- if the specified element is null
-
offer
Inserts the specified element into this delay queue.- Specified by:
offer
in interfaceBlockingQueue<E extends Delayed>
- Specified by:
offer
in interfaceQueue<E extends Delayed>
- Parameters:
e
- the element to add- Returns:
true
- Throws:
NullPointerException
- if the specified element is null
-
put
Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.- Specified by:
put
in interfaceBlockingQueue<E extends Delayed>
- Parameters:
e
- the element to add- Throws:
NullPointerException
- if the specified element is null
-
offer
Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.- Specified by:
offer
in interfaceBlockingQueue<E extends Delayed>
- Parameters:
e
- the element to addtimeout
- This parameter is ignored as the method never blocksunit
- This parameter is ignored as the method never blocks- Returns:
true
- Throws:
NullPointerException
- if the specified element is null
-
poll
Retrieves and removes the expired head of this queue, or returnsnull
if this queue has no expired elements. -
take
Retrieves and removes the expired head of this queue, waiting if necessary until an expired element is available on this queue.- Specified by:
take
in interfaceBlockingQueue<E extends Delayed>
- Returns:
- the expired head of this queue
- Throws:
InterruptedException
- if interrupted while waiting
-
poll
Retrieves and removes the expired head of this queue, waiting if necessary until an expired element is available on this queue, or the specified wait time expires.- Specified by:
poll
in interfaceBlockingQueue<E extends Delayed>
- Parameters:
timeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- the expired head of this queue, or
null
if the specified waiting time elapses before an element with an expired delay becomes available - Throws:
InterruptedException
- if interrupted while waiting
-
remove
Retrieves and removes the expired head of this queue, or throws an exception if this queue has no expired elements.- Specified by:
remove
in interfaceQueue<E extends Delayed>
- Overrides:
remove
in classAbstractQueue<E extends Delayed>
- Returns:
- the expired head of this queue
- Throws:
NoSuchElementException
- if this queue has no elements with an expired delay
-
peek
Retrieves, but does not remove, the head 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. -
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 interfaceCollection<E extends Delayed>
- Returns:
- the number of elements in this collection
-
drainTo
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 interfaceBlockingQueue<E extends Delayed>
- 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 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 collection
-
drainTo
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 interfaceBlockingQueue<E extends Delayed>
- Parameters:
c
- the collection to transfer elements intomaxElements
- 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 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 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 interfaceCollection<E extends Delayed>
- Overrides:
clear
in classAbstractQueue<E extends Delayed>
-
remainingCapacity
public int remainingCapacity()Always returnsInteger.MAX_VALUE
because aDelayQueue
is not capacity constrained.- Specified by:
remainingCapacity
in interfaceBlockingQueue<E extends Delayed>
- Returns:
Integer.MAX_VALUE
-
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 interfaceCollection<E extends Delayed>
- Overrides:
toArray
in classAbstractCollection<E extends Delayed>
- 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 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]);
toArray(new Object[0])
is identical in function totoArray()
.- Specified by:
toArray
in interfaceCollection<E extends Delayed>
- Overrides:
toArray
in classAbstractCollection<E extends Delayed>
- 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 queueNullPointerException
- if the specified array is null
-
remove
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 interfaceBlockingQueue<E extends Delayed>
- Specified by:
remove
in interfaceCollection<E extends Delayed>
- Overrides:
remove
in classAbstractCollection<E extends Delayed>
- 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
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 weakly consistent.
-