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 queue
- 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. 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
Constructor | Description |
---|---|
DelayQueue() | Creates a new |
DelayQueue(Collection<? extends E> c) | Creates a |
Method Summary
Modifier and Type | Method | 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 |
E | poll() | Retrieves and removes the head of this queue, or returns |
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 |
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. |
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. |
Methods declared in class java.util.AbstractQueue
addAll, element, remove
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, size, spliterator, stream, toArray
Methods declared in interface java.lang.Iterable
forEach
Methods declared in interface java.util.Queue
element, remove
Constructor Detail
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
Method Detail
add
public boolean add(E e)
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
public boolean offer(E e)
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
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 interfaceBlockingQueue<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 interfaceBlockingQueue<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 interfaceQueue<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 interfaceBlockingQueue<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 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 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 interfaceQueue<E extends Delayed>
- Returns:
- the head of this queue, or
null
if this queue is empty
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 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 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 interfaceBlockingQueue<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 interfaceCollection<E extends Delayed>
- Overrides:
-
clear
in classAbstractQueue<E extends Delayed>
remainingCapacity
public int remainingCapacity()
Always returns Integer.MAX_VALUE
because a DelayQueue
is not capacity constrained.
- Specified by:
-
remainingCapacity
in interfaceBlockingQueue<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 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]);Note that
toArray(new Object[0])
is identical in function to toArray()
.- 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 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 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
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.