- Type Parameters:
E
- the type of elements held in this deque
- All Superinterfaces:
BlockingQueue<E>
,Collection<E>
,Deque<E>
,Iterable<E>
,Queue<E>
,SequencedCollection<E>
- All Known Implementing Classes:
LinkedBlockingDeque
Deque
that additionally supports blocking operations that wait
for the deque to become non-empty when retrieving an element, and wait for
space to become available in the deque when storing an element.
BlockingDeque
methods come in four forms, with different ways
of handling operations that cannot be satisfied immediately, but may be
satisfied at some point in the future:
one throws an exception, the second returns a special value (either
null
or false
, depending on the operation), the third
blocks the current thread indefinitely until the operation can succeed,
and the fourth blocks for only a given maximum time limit before giving
up. These methods are summarized in the following table:
First Element (Head) | ||||
---|---|---|---|---|
Throws exception | Special value | Blocks | Times out | |
Insert | addFirst(e) |
offerFirst(e) |
putFirst(e) |
offerFirst(e, time, unit) |
Remove | removeFirst() |
pollFirst() |
takeFirst() |
pollFirst(time, unit) |
Examine | getFirst() |
peekFirst() |
not applicable | not applicable |
Last Element (Tail) | ||||
Throws exception | Special value | Blocks | Times out | |
Insert | addLast(e) |
offerLast(e) |
putLast(e) |
offerLast(e, time, unit) |
Remove | removeLast() |
pollLast() |
takeLast() |
pollLast(time, unit) |
Examine | getLast() |
peekLast() |
not applicable | not applicable |
Like any BlockingQueue
, a BlockingDeque
is thread safe,
does not permit null elements, and may (or may not) be
capacity-constrained.
A BlockingDeque
implementation may be used directly as a FIFO
BlockingQueue
. The methods inherited from the
BlockingQueue
interface are precisely equivalent to
BlockingDeque
methods as indicated in the following table:
BlockingQueue Method |
Equivalent BlockingDeque Method |
|
---|---|---|
Insert | add(e) |
addLast(e) |
offer(e) |
offerLast(e) |
|
put(e) |
putLast(e) |
|
offer(e, time, unit) |
offerLast(e, time, unit) |
|
Remove | remove() |
removeFirst() |
poll() |
pollFirst() |
|
take() |
takeFirst() |
|
poll(time, unit) |
pollFirst(time, unit) |
|
Examine | element() |
getFirst() |
peek() |
peekFirst() |
Memory consistency effects: As with other concurrent
collections, actions in a thread prior to placing an object into a
BlockingDeque
happen-before
actions subsequent to the access or removal of that element from
the BlockingDeque
in another thread.
This interface is a member of the Java Collections Framework.
- Since:
- 1.6
-
Method Summary
Modifier and TypeMethodDescriptionboolean
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success and throwing anIllegalStateException
if no space is currently available.void
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available.void
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available.boolean
Returnstrue
if this deque contains the specified element.element()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).iterator()
Returns an iterator over the elements in this deque in proper sequence.boolean
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available.boolean
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.boolean
offerFirst
(E e) Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available.boolean
offerFirst
(E e, long timeout, TimeUnit unit) Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary for space to become available.boolean
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available.boolean
Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for space to become available.peek()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnull
if this deque is empty.poll()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnull
if this deque is empty.Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.void
Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available.void
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting if necessary for space to become available.void
Inserts the specified element at the front of this deque, waiting if necessary for space to become available.void
Inserts the specified element at the end of this deque, waiting if necessary for space to become available.remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).boolean
Removes the first occurrence of the specified element from this deque.boolean
Removes the first occurrence of the specified element from this deque.boolean
Removes the last occurrence of the specified element from this deque.int
size()
Returns the number of elements in this deque.take()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting if necessary until an element becomes available.Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.takeLast()
Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.Methods declared in interface java.util.concurrent.BlockingQueue
drainTo, drainTo, remainingCapacity
Methods declared in interface java.util.Collection
clear, containsAll, equals, hashCode, isEmpty, parallelStream, removeAll, removeIf, retainAll, spliterator, stream, toArray, toArray, toArray
Methods declared in interface java.util.Deque
addAll, descendingIterator, getFirst, getLast, peekFirst, peekLast, pollFirst, pollLast, pop, removeFirst, removeLast, reversed
-
Method Details
-
addFirst
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available. When using a capacity-restricted deque, it is generally preferable to useofferFirst
.- Specified by:
addFirst
in interfaceDeque<E>
- Specified by:
addFirst
in interfaceSequencedCollection<E>
- Parameters:
e
- the element to add- Throws:
IllegalStateException
- if the element cannot be added at this time due to capacity restrictionsClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
addLast
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available. When using a capacity-restricted deque, it is generally preferable to useofferLast
.- Specified by:
addLast
in interfaceDeque<E>
- Specified by:
addLast
in interfaceSequencedCollection<E>
- Parameters:
e
- the element to add- Throws:
IllegalStateException
- if the element cannot be added at this time due to capacity restrictionsClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offerFirst
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theaddFirst
method, which can fail to insert an element only by throwing an exception.- Specified by:
offerFirst
in interfaceDeque<E>
- Parameters:
e
- the element to add- Returns:
true
if the element was added to this deque, elsefalse
- Throws:
ClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offerLast
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theaddLast
method, which can fail to insert an element only by throwing an exception.- Specified by:
offerLast
in interfaceDeque<E>
- Parameters:
e
- the element to add- Returns:
true
if the element was added to this deque, elsefalse
- Throws:
ClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
putFirst
Inserts the specified element at the front of this deque, waiting if necessary for space to become available.- Parameters:
e
- the element to add- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
putLast
Inserts the specified element at the end of this deque, waiting if necessary for space to become available.- Parameters:
e
- the element to add- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offerFirst
Inserts the specified element at the front of this deque, waiting up to the specified wait time if necessary for space to become available.- Parameters:
e
- the element to addtimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if successful, orfalse
if the specified waiting time elapses before space is available- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offerLast
Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for space to become available.- Parameters:
e
- the element to addtimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if successful, orfalse
if the specified waiting time elapses before space is available- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
takeFirst
Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.- Returns:
- the head of this deque
- Throws:
InterruptedException
- if interrupted while waiting
-
takeLast
Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.- Returns:
- the tail of this deque
- Throws:
InterruptedException
- if interrupted while waiting
-
pollFirst
Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.- 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 deque, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
pollLast
Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.- Parameters:
timeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- the tail of this deque, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
removeFirstOccurrence
Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first elemente
such thato.equals(e)
(if such an element exists). Returnstrue
if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
removeFirstOccurrence
in interfaceDeque<E>
- Parameters:
o
- element to be removed from this deque, if present- Returns:
true
if an element was removed as a result of this call- Throws:
ClassCastException
- if the class of the specified element is incompatible with this deque (optional)NullPointerException
- if the specified element is null (optional)
-
removeLastOccurrence
Removes the last occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the last elemente
such thato.equals(e)
(if such an element exists). Returnstrue
if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).- Specified by:
removeLastOccurrence
in interfaceDeque<E>
- Parameters:
o
- element to be removed from this deque, if present- Returns:
true
if an element was removed as a result of this call- Throws:
ClassCastException
- if the class of the specified element is incompatible with this deque (optional)NullPointerException
- if the specified element is null (optional)
-
add
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success and throwing anIllegalStateException
if no space is currently available. When using a capacity-restricted deque, it is generally preferable to useoffer
.This method is equivalent to
addLast
.- Specified by:
add
in interfaceBlockingQueue<E>
- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceDeque<E>
- Specified by:
add
in interfaceQueue<E>
- Parameters:
e
- the element to add- Returns:
true
(as specified byCollection.add(E)
)- Throws:
IllegalStateException
- if the element cannot be added at this time due to capacity restrictionsClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offer
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque) if it is possible to do so immediately without violating capacity restrictions, returningtrue
upon success andfalse
if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to theadd(E)
method, which can fail to insert an element only by throwing an exception.This method is equivalent to
offerLast
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Specified by:
offer
in interfaceDeque<E>
- Specified by:
offer
in interfaceQueue<E>
- Parameters:
e
- the element to add- Returns:
true
if the element was added to this queue, elsefalse
- Throws:
ClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
put
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting if necessary for space to become available.This method is equivalent to
putLast
.- Specified by:
put
in interfaceBlockingQueue<E>
- Parameters:
e
- the element to add- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
offer
Inserts the specified element into the queue represented by this deque (in other words, at the tail of this deque), waiting up to the specified wait time if necessary for space to become available.This method is equivalent to
offerLast
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Parameters:
e
- the element to addtimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if the element was added to this deque, elsefalse
- Throws:
InterruptedException
- if interrupted while waitingClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-
remove
E remove()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs frompoll()
only in that it throws an exception if this deque is empty.This method is equivalent to
removeFirst
. -
poll
E poll()Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returnsnull
if this deque is empty.This method is equivalent to
Deque.pollFirst()
. -
take
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting if necessary until an element becomes available.This method is equivalent to
takeFirst
.- Specified by:
take
in interfaceBlockingQueue<E>
- Returns:
- the head of this deque
- Throws:
InterruptedException
- if interrupted while waiting
-
poll
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), waiting up to the specified wait time if necessary for an element to become available.This method is equivalent to
pollFirst
.- Specified by:
poll
in interfaceBlockingQueue<E>
- 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 deque, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
element
-
peek
-
remove
Removes the first occurrence of the specified element from this deque. If the deque does not contain the element, it is unchanged. More formally, removes the first elemente
such thato.equals(e)
(if such an element exists). Returnstrue
if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).This method is equivalent to
removeFirstOccurrence
.- Specified by:
remove
in interfaceBlockingQueue<E>
- Specified by:
remove
in interfaceCollection<E>
- Specified by:
remove
in interfaceDeque<E>
- Parameters:
o
- element to be removed from this deque, if present- Returns:
true
if this deque changed as a result of the call- Throws:
ClassCastException
- if the class of the specified element is incompatible with this deque (optional)NullPointerException
- if the specified element is null (optional)
-
contains
Returnstrue
if this deque contains the specified element. More formally, returnstrue
if and only if this deque contains at least one elemente
such thato.equals(e)
.- Specified by:
contains
in interfaceBlockingQueue<E>
- Specified by:
contains
in interfaceCollection<E>
- Specified by:
contains
in interfaceDeque<E>
- Parameters:
o
- object to be checked for containment in this deque- Returns:
true
if this deque contains the specified element- Throws:
ClassCastException
- if the class of the specified element is incompatible with this deque (optional)NullPointerException
- if the specified element is null (optional)
-
size
-
iterator
Returns an iterator over the elements in this deque in proper sequence. The elements will be returned in order from first (head) to last (tail). -
push
Pushes an element onto the stack represented by this deque (in other words, at the head of this deque) if it is possible to do so immediately without violating capacity restrictions, throwing anIllegalStateException
if no space is currently available.This method is equivalent to
addFirst
.- Specified by:
push
in interfaceDeque<E>
- Parameters:
e
- the element to push- Throws:
IllegalStateException
- if the element cannot be added at this time due to capacity restrictionsClassCastException
- if the class of the specified element prevents it from being added to this dequeNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this deque
-