Added in API level 9

BlockingDeque

interface BlockingDeque<E : Any!> : BlockingQueue<E>, Deque<E>

java.util.concurrent.BlockingDeque

Known Direct Subclasses LinkedBlockingDeque LinkedBlockingDeque An optionally-bounded blocking deque based on linked nodes.

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(java.lang.Object)	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(java.lang.Object)	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(java.lang.Object)	addLast(java.lang.Object)
	offer(java.lang.Object)	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.

Summary

Public methods
abstract Boolean	add(element: 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 Unit	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 Unit	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(element: E?) 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 MutableIterator<E>	iterator() Returns an iterator over the elements in this deque in proper sequence.
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	offer(e: E, timeout: Long, unit: TimeUnit!) 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	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, timeout: Long, unit: TimeUnit!) 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, timeout: Long, unit: TimeUnit!) 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() 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	poll(timeout: Long, unit: TimeUnit!) 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	pollFirst(timeout: Long, unit: TimeUnit!) 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(timeout: Long, unit: TimeUnit!) 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 Unit	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 Unit	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 Unit	putFirst(e: E) Inserts the specified element at the front of this deque, waiting if necessary for space to become available.
abstract Unit	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(element: E?) Removes the first occurrence of the specified element from this deque.
abstract Boolean	removeFirstOccurrence(o: Any?) Removes the first occurrence of the specified element from this deque.
abstract Boolean	removeLastOccurrence(o: Any?) Removes the last occurrence of the specified element from this deque.
abstract E	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.
abstract E	takeFirst() Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.
abstract E	takeLast() Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.

Inherited functions
From class Deque MutableIterator<E> descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order. The elements will be returned in order from last (tail) to first (head). E getFirst() Retrieves, but does not remove, the first element of this deque. This method differs from peekFirst only in that it throws an exception if this deque is empty. E getLast() Retrieves, but does not remove, the last element of this deque. This method differs from peekLast only in that it throws an exception if this deque is empty. E? peekFirst() Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty. E? peekLast() Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty. E? pollFirst() Retrieves and removes the first element of this deque, or returns null if this deque is empty. E? pollLast() Retrieves and removes the last element of this deque, or returns null if this deque is empty. E pop() Pops an element from the stack represented by this deque. In other words, removes and returns the first element of this deque. This method is equivalent to removeFirst(). E removeFirst() Retrieves and removes the first element of this deque. This method differs from pollFirst only in that it throws an exception if this deque is empty. E removeLast() Retrieves and removes the last element of this deque. This method differs from pollLast only in that it throws an exception if this deque is empty. Deque<E> reversed() Returns a reverse-ordered view of this collection. The encounter order of elements in the returned view is the inverse of the encounter order of elements in this collection. The reverse ordering affects all order-sensitive operations, including those on the view collections of the returned view. If the collection implementation permits modifications to this view, the modifications "write through" to the underlying collection. Changes to the underlying collection might or might not be visible in this reversed view, depending upon the implementation.
From class BlockingQueue Int drainTo(c: MutableCollection<in E>!) 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. Int drainTo(c: MutableCollection<in E>!, maxElements: Int) 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. Int remainingCapacity() Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or Integer.MAX_VALUE if there is no intrinsic limit. Note that you cannot always tell if an attempt to insert an element will succeed by inspecting remainingCapacity because it may be the case that another thread is about to insert or remove an element.
From class Queue E element() Retrieves, but does not remove, the head of this queue. This method differs from peek only in that it throws an exception if this queue is empty. E? peek() Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. E? poll() Retrieves and removes the head of this queue, or returns null if this queue is empty. E remove() Retrieves and removes the head of this queue. This method differs from poll() only in that it throws an exception if this queue is empty.

Properties
abstract Int	size Returns the number of elements in this deque.

Public methods

add

Added in API level 9

abstract fun add(element: E): 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, returning true upon success and throwing an IllegalStateException if no space is currently available. When using a capacity-restricted deque, it is generally preferable to use #offer(java.lang.Object).

This method is equivalent to #addLast(java.lang.Object).

Parameters
e	the element to add

Return
Boolean	true (as specified by Collection.add)

Exceptions
java.lang.UnsupportedOperationException	if the add operation is not supported by this collection
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque
java.lang.IllegalStateException	if the element cannot be added at this time due to capacity restrictions

addFirst

Added in API level 9

abstract fun addFirst(e: E): Unit

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. When using a capacity-restricted deque, it is generally preferable to use offerFirst.

Parameters
e	E: the element to add

Exceptions
java.lang.NullPointerException	if the specified element is null
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation
java.lang.IllegalStateException	if the element cannot be added at this time due to capacity restrictions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

addLast

Added in API level 9

abstract fun addLast(e: E): Unit

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. When using a capacity-restricted deque, it is generally preferable to use offerLast.

Parameters
e	E: the element to add

Exceptions
java.lang.NullPointerException	if the specified element is null
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation
java.lang.IllegalStateException	if the element cannot be added at this time due to capacity restrictions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

contains

Added in API level 9

abstract fun contains(element: E?): Boolean

Returns true if this deque contains the specified element. More formally, returns true if and only if this deque contains at least one element e such that o.equals(e).

Parameters
o	object to be checked for containment in this deque

Return
Boolean	true if this deque contains the specified element

Exceptions
java.lang.ClassCastException	if the class of the specified element is incompatible with this deque (optional)
java.lang.NullPointerException	if the specified element is null (optional)

element

Added in API level 9

abstract fun element(): E

Retrieves, but does not remove, the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from peek only in that it throws an exception if this deque is empty.

This method is equivalent to getFirst.

Return
E	the head of this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty

iterator

Added in API level 9

abstract fun iterator(): MutableIterator<E>

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).

Return
MutableIterator<E>	an iterator over the elements in this deque in proper sequence

offer

Added in API level 9

abstract fun offer(e: E): 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, returning true upon success and false if no space is currently available. When using a capacity-restricted deque, this method is generally preferable to the #add method, which can fail to insert an element only by throwing an exception.

This method is equivalent to offerLast.

Parameters
e	E: the element to add

Return
Boolean	true if the element was added to this deque, else false

Exceptions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

offer

Added in API level 9

abstract fun offer(
    e: E, 
    timeout: Long, 
    unit: TimeUnit!
): 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.

This method is equivalent to offerLast.

Parameters
e	E: the element to add
timeout	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
Boolean	true if the element was added to this deque, else false

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

offerFirst

Added in API level 9

abstract fun offerFirst(e: E): Boolean

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. When using a capacity-restricted deque, this method is generally preferable to the #addFirst(java.lang.Object) method, which can fail to insert an element only by throwing an exception.

Parameters
e	E: the element to add

Return
Boolean	true if the element was added to this deque, else false

Exceptions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

offerFirst

Added in API level 9

abstract fun offerFirst(
    e: E, 
    timeout: Long, 
    unit: TimeUnit!
): Boolean

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	E: the element to add
timeout	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
Boolean	true if successful, or false if the specified waiting time elapses before space is available

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

offerLast

Added in API level 9

abstract fun offerLast(e: E): Boolean

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. When using a capacity-restricted deque, this method is generally preferable to the #addLast(java.lang.Object) method, which can fail to insert an element only by throwing an exception.

Parameters
e	E: the element to add

Return
Boolean	true if the element was added to this deque, else false

Exceptions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

offerLast

Added in API level 9

abstract fun offerLast(
    e: E, 
    timeout: Long, 
    unit: TimeUnit!
): 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.

Parameters
e	E: the element to add
timeout	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
Boolean	true if successful, or false if the specified waiting time elapses before space is available

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

peek

Added in API level 9

abstract fun peek(): E?

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.

This method is equivalent to peekFirst.

Return
E?	the head of this deque, or null if this deque is empty

poll

Added in API level 9

abstract fun poll(): E?

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.

This method is equivalent to pollFirst().

Return
E?	the head of this deque, or null if this deque is empty

poll

Added in API level 9

abstract fun poll(
    timeout: Long, 
    unit: TimeUnit!
): E

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.

Parameters
timeout	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
E	the head of this deque, or null if the specified waiting time elapses before an element is available

Exceptions
java.lang.InterruptedException	if interrupted while waiting

pollFirst

Added in API level 9

abstract fun pollFirst(
    timeout: Long, 
    unit: TimeUnit!
): E

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	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
E	the head of this deque, or null if the specified waiting time elapses before an element is available

Exceptions
java.lang.InterruptedException	if interrupted while waiting

pollLast

Added in API level 9

abstract fun pollLast(
    timeout: Long, 
    unit: TimeUnit!
): E

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	Long: how long to wait before giving up, in units of unit
unit	TimeUnit!: a TimeUnit determining how to interpret the timeout parameter

Return
E	the tail of this deque, or null if the specified waiting time elapses before an element is available

Exceptions
java.lang.InterruptedException	if interrupted while waiting

push

Added in API level 9

abstract fun push(e: E): Unit

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.

This method is equivalent to #addFirst(java.lang.Object).

Parameters
e	E: the element to push

Exceptions
java.lang.IllegalStateException	if the element cannot be added at this time due to capacity restrictions
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

put

Added in API level 9

abstract fun put(e: E): Unit

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.

Parameters
e	E: the element to add

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

putFirst

Added in API level 9

abstract fun putFirst(e: E): Unit

Inserts the specified element at the front of this deque, waiting if necessary for space to become available.

Parameters
e	E: the element to add

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

putLast

Added in API level 9

abstract fun putLast(e: E): Unit

Inserts the specified element at the end of this deque, waiting if necessary for space to become available.

Parameters
e	E: the element to add

Exceptions
java.lang.InterruptedException	if interrupted while waiting
java.lang.ClassCastException	if the class of the specified element prevents it from being added to this deque
java.lang.NullPointerException	if the specified element is null
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

remove

Added in API level 9

abstract fun remove(): E

Retrieves and removes the head of the queue represented by this deque (in other words, the first element of this deque). This method differs from poll() only in that it throws an exception if this deque is empty.

This method is equivalent to removeFirst.

Return
E	the head of the queue represented by this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty

remove

Added in API level 9

abstract fun remove(element: E?): Boolean

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 element e such that o.equals(e) (if such an element exists). Returns true 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.

Parameters
o	element to be removed from this deque, if present

Return
Boolean	true if this deque changed as a result of the call

Exceptions
java.lang.ClassCastException	if the class of the specified element is incompatible with this deque (optional)
java.lang.NullPointerException	if the specified element is null (optional)
java.lang.UnsupportedOperationException	if the remove operation is not supported by this collection

removeFirstOccurrence

Added in API level 9

abstract fun removeFirstOccurrence(o: Any?): Boolean

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 element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Parameters
o	Any?: element to be removed from this deque, if present

Return
Boolean	true if an element was removed as a result of this call

Exceptions
java.lang.ClassCastException	if the class of the specified element is incompatible with this deque (optional)
java.lang.NullPointerException	if the specified element is null (optional)

removeLastOccurrence

Added in API level 9

abstract fun removeLastOccurrence(o: Any?): Boolean

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 element e such that o.equals(e) (if such an element exists). Returns true if this deque contained the specified element (or equivalently, if this deque changed as a result of the call).

Parameters
o	Any?: element to be removed from this deque, if present

Return
Boolean	true if an element was removed as a result of this call

Exceptions
java.lang.ClassCastException	if the class of the specified element is incompatible with this deque (optional)
java.lang.NullPointerException	if the specified element is null (optional)

take

Added in API level 9

abstract fun take(): E

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.

Return
E	the head of this deque

Exceptions
java.lang.InterruptedException	if interrupted while waiting

takeFirst

Added in API level 9

abstract fun takeFirst(): E

Retrieves and removes the first element of this deque, waiting if necessary until an element becomes available.

Return
E	the head of this deque

Exceptions
java.lang.InterruptedException	if interrupted while waiting

takeLast

Added in API level 9

abstract fun takeLast(): E

Retrieves and removes the last element of this deque, waiting if necessary until an element becomes available.

Return
E	the tail of this deque

Exceptions
java.lang.InterruptedException	if interrupted while waiting

Properties

size

Added in API level 9

abstract val size: Int

Returns the number of elements in this deque.

Return
Int	the number of elements in this deque