A 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.
extends
<E> | the type of elements held in this collection |