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java.util.concurrent
Class DelayQueue<E extends
Delayed
>
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 collection
-
All Implemented Interfaces:
-
Iterable
<E>,
Collection
<E>,
BlockingQueue
<E>,
Queue
<E>
-
public class DelayQueue<E extends Delayed>
- extends AbstractQueue<E>
- implements BlockingQueue<E>
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
. 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.
This class is a member of the
Java Collections Framework
Java Collections Framework
.
-
Since:
-
1.5
Constructor Summary
|
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. |
Method Summary
|
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. |
|
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. |
DelayQueue
public DelayQueue()
-
Creates a new
DelayQueue
that is initially empty.
DelayQueue
public DelayQueue(Collection<? extends E> c)
-
Creates a
DelayQueue
initially containing the elements of the given collection of
Delayed
instances.
-
Parameters:
-
c - the collection of elements to initially contain
-
Throws:
-
NullPointerException
- if the specified collection or any of its elements are null
add
public boolean add(E e)
-
Inserts the specified element into this delay queue.
-
-
Specified by:
-
add
in interface
Collection
<
E
extends
Delayed
>
-
Specified by:
-
add
in interface
BlockingQueue
<
E
extends
Delayed
>
-
Specified by:
-
add
in interface
Queue
<
E
extends
Delayed
>
-
Overrides:
-
add
in class
AbstractQueue
<
E
extends
Delayed
>
-
-
Parameters:
-
e - the element to add
-
Returns:
-
true
(as specified by
Collection.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
extends
Delayed
>
-
Specified by:
-
offer
in interface
Queue
<
E
extends
Delayed
>
-
-
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
extends
Delayed
>
-
-
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
extends
Delayed
>
-
-
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 the head of this queue, or returns
null
if this queue has no elements with an expired delay.
-
-
Specified by:
-
poll
in interface
Queue
<
E
extends
Delayed
>
-
-
Returns:
-
the head of this queue, or
null
if this queue has no elements with an expired delay
take
public E take()
throws InterruptedException
-
Retrieves and removes the head of this queue, waiting if necessary until an element with an expired delay is available on this queue.
-
-
Specified by:
-
take
in interface
BlockingQueue
<
E
extends
Delayed
>
-
-
Returns:
-
the head of this queue
-
Throws:
-
InterruptedException
- if interrupted while waiting
poll
public E poll(long timeout,
TimeUnit unit)
throws InterruptedException
-
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.
-
-
Specified by:
-
poll
in interface
BlockingQueue
<
E
extends
Delayed
>
-
-
Parameters:
-
timeout - 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 with an expired delay becomes available
-
Throws:
-
InterruptedException
- if interrupted while waiting
peek
public E peek()
-
Retrieves, but does not remove, the head of this queue, or returns
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.
-
-
Specified by:
-
peek
in interface
Queue
<
E
extends
Delayed
>
-
-
Returns:
-
the head of this queue, or
null
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 than
Integer.MAX_VALUE
elements, returns
Integer.MAX_VALUE
.
-
-
Specified by:
-
size
in interface
Collection
<
E
extends
Delayed
>
-
Specified by:
-
size
in class
AbstractCollection
<
E
extends
Delayed
>
-
-
Returns:
-
the number of elements in this collection
drainTo
public int drainTo(Collection<? super E> 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 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.
-
-
Specified by:
-
drainTo
in interface
BlockingQueue
<
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 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<? super E> 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 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.
-
-
Specified by:
-
drainTo
in interface
BlockingQueue
<
E
extends
Delayed
>
-
-
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
extends
Delayed
>
-
Overrides:
-
clear
in class
AbstractQueue
<
E
extends
Delayed
>
-
remainingCapacity
public int remainingCapacity()
-
Always returns
Integer.MAX_VALUE
because a
DelayQueue
is not capacity constrained.
-
-
Specified by:
-
remainingCapacity
in interface
BlockingQueue
<
E
extends
Delayed
>
-
-
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
extends
Delayed
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
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]);
Note that
toArray(new Object[0])
is identical in function to
toArray()
.
-
-
Specified by:
-
toArray
in interface
Collection
<
E
extends
Delayed
>
-
Overrides:
-
toArray
in class
AbstractCollection
<
E
extends
Delayed
>
-
-
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
Collection
<
E
extends
Delayed
>
-
Specified by:
-
remove
in interface
BlockingQueue
<
E
extends
Delayed
>
-
Overrides:
-
remove
in class
AbstractCollection
<
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
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
iterator
is a
"weakly consistent"
thread-safe "fast-fail"
iterator that will
never
throw
ConcurrentModificationException
, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
upon detected interference.
-
-
Specified by:
-
iterator
in interface
Iterable
<
E
extends
Delayed
>
-
Specified by:
-
iterator
in interface
Collection
<
E
extends
Delayed
>
-
Specified by:
-
iterator
in class
AbstractCollection
<
E
extends
Delayed
>
-
-
Returns:
-
an iterator over the elements in this queue