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
DelayQueue that is initially empty. |
DelayQueue(Collection<? extends E> c)
Creates a
DelayQueue initially containing the elements of the
given collection of Delayed instances. |
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
null if this queue is empty. |
E |
poll()
Retrieves and removes the head of this queue, or returns
null
if 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_VALUE because
a DelayQueue is 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, remove
contains, containsAll, isEmpty, removeAll, retainAll, toString
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
contains
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, stream
public 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 addtrue
NullPointerException
- 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 blockstrue
NullPointerException
- 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
unit
unit
- 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()
Collection
size
in interface Collection<E extends Delayed>
size
in class AbstractCollection<E extends Delayed>
public int drainTo(Collection<? super E> c)
BlockingQueue
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.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)
BlockingQueue
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.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_VALUE
public 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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For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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