edu.emory.mathcs.backport.java.util.concurrent
Class DelayQueue
java.util.AbstractCollection
- BlockingQueue, Collection, Queue
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
../../../../../../../../guide/collections/index.html">
Java Collections Framework.
DelayQueue() - Creates a new DelayQueue that is initially empty.
|
DelayQueue(Collection c) - Creates a DelayQueue initially containing the elements of the
given collection of
Delayed instances.
|
boolean | add(Object e) - Inserts the specified element into this delay queue.
|
void | clear() - Atomically removes all of the elements from this delay queue.
|
int | drainTo(Collection c)
|
int | drainTo(Collection c, int maxElements)
|
Iterator | iterator() - Returns an iterator over all the elements (both expired and
unexpired) in this queue.
|
boolean | offer(Object e) - Inserts the specified element into this delay queue.
|
boolean | offer(Object e, long timeout, TimeUnit unit) - Inserts the specified element into this delay queue.
|
Object | peek() - Retrieves, but does not remove, the head of this queue, or
returns null if this queue is empty.
|
Object | poll() - Retrieves and removes the head of this queue, or returns null
if this queue has no elements with an expired delay.
|
Object | 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(Object 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()
|
Object | 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.
|
Object[] | toArray(Object[] 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 c)
Creates a
DelayQueue initially containing the elements of the
given collection of
Delayed
instances.
c
- the collection of elements to initially contain
add
public boolean add(Object e)
Inserts the specified element into this delay queue.
- add in interface BlockingQueue
- add in interface Queue
- add in interface AbstractQueue
- true (as specified by
Collection.add
)
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.
- clear in interface AbstractQueue
iterator
public Iterator 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 a "weakly consistent" iterator that will
never throw java.util.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.
- an iterator over the elements in this queue
offer
public boolean offer(Object e)
Inserts the specified element into this delay queue.
- offer in interface BlockingQueue
- offer in interface Queue
offer
public boolean offer(Object e,
long timeout,
TimeUnit unit)
Inserts the specified element into this delay queue. As the queue is
unbounded this method will never block.
- offer in interface BlockingQueue
e
- the element to addtimeout
- This parameter is ignored as the method never blocksunit
- This parameter is ignored as the method never blocks
peek
public Object 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.
- peek in interface Queue
- the head of this queue, or null if this
queue is empty.
poll
public Object poll()
Retrieves and removes the head of this queue, or returns null
if this queue has no elements with an expired delay.
- poll in interface Queue
- the head of this queue, or null if this
queue has no elements with an expired delay
poll
public Object 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.
- poll in interface BlockingQueue
- the head of this queue, or null if the
specified waiting time elapses before an element with
an expired delay becomes available
put
public void put(Object e)
Inserts the specified element into this delay queue. As the queue is
unbounded this method will never block.
- put in interface BlockingQueue
remainingCapacity
public int remainingCapacity()
Always returns Integer.MAX_VALUE because
a DelayQueue is not capacity constrained.
- remainingCapacity in interface BlockingQueue
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.
- remove in interface BlockingQueue
take
public Object 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.
- take in interface BlockingQueue
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.
- toArray in interface AbstractCollection
- an array containing all of the elements in this queue
toArray
public Object[] toArray(Object[] 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().
- toArray in interface AbstractCollection
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
- an array containing all of the elements in this queue