implements BlockingQueue<E extends Delayed>
An unbounded {@linkplain BlockingQueue 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. The Iterator provided in method iterator()
is not guaranteed to traverse the elements of
the DelayQueue in any particular order.
Public 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. |
Public 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, int maxElements)
Removes at most the given number of available elements from
this queue and adds them to the given collection.
|
int |
drainTo(Collection<? super E> c)
Removes all 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 | |
E |
peek()
Retrieves, but does not remove, the head of this queue, or
returns
null if this queue is empty. |
E | |
E |
poll()
Retrieves and removes the head of this queue, or returns
null
if this queue has no elements with an expired delay. |
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 | |
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.
|
<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.
|
Object[] |
toArray()
Returns an array containing all of the elements in this queue.
|
Inherited Method Summary
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 of elements to initially contain |
---|
Throws
NullPointerException | if the specified collection or any of its elements are null |
---|
Public Methods
public boolean add (E e)
Inserts the specified element into this delay queue.
Parameters
e | the element to add |
---|
Returns
true
(as specified byCollection.add(E)
)
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. Elements with an unexpired delay are not waited for; they are simply discarded from the queue.
public 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. 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
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.
Parameters
c | the collection to transfer elements into |
---|
Returns
- the number of elements transferred
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 is weakly consistent.
Returns
- an iterator over the elements in this queue
public boolean offer (E e)
Inserts the specified element into this delay queue.
Parameters
e | the element to add |
---|
Returns
true
Throws
NullPointerException | if the specified element is null |
---|
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.
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 |
---|
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.
Returns
- the head of this queue, or
null
if this queue is empty
public 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.
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 |
---|
public E poll ()
Retrieves and removes the head of this queue, or returns null
if this queue has no elements with an expired delay.
Returns
- the head of this queue, or
null
if this queue has no elements with an expired delay
public void put (E e)
Inserts the specified element into this delay queue. As the queue is unbounded this method will never block.
Parameters
e | the element to add |
---|
Throws
NullPointerException |
---|
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 a single instance of the specified element from this queue, if it is present, whether or not it has expired.
Parameters
o | element to be removed from this collection, if present |
---|
Returns
- true if an element was removed as a result of this call
public int size ()
Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
Returns
- the number of elements in this collection
public 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.
Returns
- the head of this queue
Throws
InterruptedException |
---|
public 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()
.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 |
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.
Returns
- an array containing all of the elements in this queue