BlockingDeque

public interface BlockingDeque implements BlockingQueue<E> Deque<E>
Known Indirect Subclasses

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:

Summary of BlockingDeque methods
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:

Comparison of BlockingQueue and BlockingDeque methods
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.

Public Method Summary

abstract boolean
add(E e)
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, returning true upon success and throwing an IllegalStateException if no space is currently available.
abstract void
addFirst(E e)
Inserts the specified element at the front of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.
abstract void
addLast(E e)
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, throwing an IllegalStateException if no space is currently available.
abstract boolean
contains(Object o)
Returns true if this deque contains the specified element.
abstract E
element()
Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque).
abstract Iterator<E>
iterator()
Returns an iterator over the elements in this deque in proper sequence.
abstract boolean
offer(E e, long timeout, TimeUnit unit)
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.
abstract boolean
offer(E e)
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, returning true upon success and false if no space is currently available.
abstract 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, returning true upon success and false if no space is currently available.
abstract 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.
abstract boolean
offerLast(E e)
Inserts the specified element at the end of this deque if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
abstract boolean
offerLast(E e, long timeout, TimeUnit unit)
Inserts the specified element at the end of this deque, waiting up to the specified wait time if necessary for space to become available.
abstract E
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 returns null if this deque is empty.
abstract E
poll(long timeout, TimeUnit unit)
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.
abstract E
poll()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque), or returns null if this deque is empty.
abstract E
pollFirst(long timeout, TimeUnit unit)
Retrieves and removes the first element of this deque, waiting up to the specified wait time if necessary for an element to become available.
abstract E
pollLast(long timeout, TimeUnit unit)
Retrieves and removes the last element of this deque, waiting up to the specified wait time if necessary for an element to become available.
abstract void
push(E e)
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 an IllegalStateException if no space is currently available.
abstract void
put(E e)
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.
abstract void
putFirst(E e)
Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
abstract void
putLast(E e)
Inserts the specified element at the end of this deque, waiting if necessary for space to become available.
abstract E
remove()
Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque).
abstract boolean
remove(Object o)
Removes the first occurrence of the specified element from this deque.