Added in API level 21

ConcurrentLinkedDeque

open class ConcurrentLinkedDeque<E : Any!> : AbstractCollection<E>, Deque<E>, Serializable

kotlin.Any
↳	java.util.AbstractCollection<E>
	↳	java.util.concurrent.ConcurrentLinkedDeque

An unbounded concurrent deque based on linked nodes. Concurrent insertion, removal, and access operations execute safely across multiple threads. A ConcurrentLinkedDeque is an appropriate choice when many threads will share access to a common collection. Like most other concurrent collection implementations, this class does not permit the use of null elements.

Iterators and spliterators are weakly consistent.

Beware that, unlike in most collections, the size method is NOT a constant-time operation. Because of the asynchronous nature of these deques, determining the current number of elements requires a traversal of the elements, and so may report inaccurate results if this collection is modified during traversal.

Bulk operations that add, remove, or examine multiple elements, such as #addAll, removeIf or forEach, are not guaranteed to be performed atomically. For example, a forEach traversal concurrent with an addAll operation might observe only some of the added elements.

This class and its iterator implement all of the optional methods of the Deque and Iterator interfaces.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentLinkedDeque happen-before actions subsequent to the access or removal of that element from the ConcurrentLinkedDeque in another thread.

This class is a member of the Java Collections Framework.

Summary

Public constructors
ConcurrentLinkedDeque() Constructs an empty deque.
ConcurrentLinkedDeque(c: MutableCollection<out E>!) Constructs a deque initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Public methods
open Boolean	add(element: E) Inserts the specified element at the tail of this deque.
open Boolean	addAll(elements: Collection<E>) Appends all of the elements in the specified collection to the end of this deque, in the order that they are returned by the specified collection's iterator.
open Unit	addFirst(e: E) Inserts the specified element at the front of this deque.
open Unit	addLast(e: E) Inserts the specified element at the end of this deque.
open Unit	clear() Removes all of the elements from this deque.
open Boolean	contains(element: E?) Returns true if this deque contains the specified element.
open MutableIterator<E>	descendingIterator() Returns an iterator over the elements in this deque in reverse sequential order.
open E	element()
open Unit	forEach(action: Consumer<in E>)
open E	getFirst()
open E	getLast()
open Boolean	isEmpty() Returns true if this collection contains no elements.
open MutableIterator<E>	iterator() Returns an iterator over the elements in this deque in proper sequence.
open Boolean	offer(e: E) Inserts the specified element at the tail of this deque.
open Boolean	offerFirst(e: E) Inserts the specified element at the front of this deque.
open Boolean	offerLast(e: E) Inserts the specified element at the end of this deque.
open E?	peek()
open E?	peekFirst()
open E?	peekLast()
open E?	poll()
open E?	pollFirst()
open E?	pollLast()
open E	pop()
open Unit	push(e: E)
open E	remove()
open Boolean	remove(element: E?) Removes the first occurrence of the specified element from this deque.
open Boolean	removeAll(elements: Collection<E>)
open E	removeFirst()
open Boolean	removeFirstOccurrence(o: Any?) Removes the first occurrence of the specified element from this deque.
open Boolean	removeIf(filter: Predicate<in E>)
open E	removeLast()
open Boolean	removeLastOccurrence(o: Any?) Removes the last occurrence of the specified element from this deque.
open Boolean	retainAll(elements: Collection<E>)
open Spliterator<E>	spliterator() Returns a Spliterator over the elements in this deque.
open Array<Any!>	toArray() Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).
open Array<T>	toArray(a: Array<T>) Returns an array containing all of the elements in this deque, in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array.
open String	toString()

Inherited functions
From class AbstractCollection Boolean containsAll(elements: Collection<E>) Returns true if this collection contains all of the elements in the specified collection.
From class Deque 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.

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

Public constructors

ConcurrentLinkedDeque

Added in API level 21

ConcurrentLinkedDeque()

Constructs an empty deque.

ConcurrentLinkedDeque

Added in API level 21

ConcurrentLinkedDeque(c: MutableCollection<out E>!)

Constructs a deque initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Parameters
c	MutableCollection<out E>!: the collection of elements to initially contain

Exceptions
java.lang.NullPointerException	if the specified collection or any of its elements are null

Public methods

add

Added in API level 21

open fun add(element: E): Boolean

Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never throw IllegalStateException or return false.

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

addAll

Added in API level 21

open fun addAll(elements: Collection<E>): Boolean

Appends all of the elements in the specified collection to the end of this deque, in the order that they are returned by the specified collection's iterator. Attempts to addAll of a deque to itself result in IllegalArgumentException.

Parameters
c	the elements to be inserted into this deque

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

Exceptions
java.lang.UnsupportedOperationException	if the addAll operation is not supported by this collection
java.lang.ClassCastException	if the class of an element of the specified collection prevents it from being added to this deque
java.lang.NullPointerException	if the specified collection or any of its elements are null
java.lang.IllegalArgumentException	if the collection is this deque
java.lang.IllegalStateException	if not all the elements can be added at this time due to insertion restrictions

addFirst

Added in API level 21

open fun addFirst(e: E): Unit

Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never throw IllegalStateException.

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 21

open fun addLast(e: E): Unit

Inserts the specified element at the end of this deque. As the deque is unbounded, this method will never throw IllegalStateException.

This method is equivalent to #add.

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

clear

Added in API level 21

open fun clear(): Unit

Removes all of the elements from this deque.

Exceptions
java.lang.UnsupportedOperationException	if the clear operation is not supported by this collection

contains

Added in API level 21

open 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	element whose presence in this deque is to be tested

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 (java.util.Collection#)
java.lang.NullPointerException	if the specified element is null and this deque does not permit null elements (java.util.Collection#)

descendingIterator

Added in API level 21

open fun descendingIterator(): MutableIterator<E>

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).

The returned iterator is weakly consistent.

Return
MutableIterator<E>	an iterator over the elements in this deque in reverse order

element

Added in API level 21

open fun element(): E

Return
E	the head of the queue represented by this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty

forEach

Added in API level 24

open fun forEach(action: Consumer<in E>): Unit

Parameters
action	Consumer<in E>: The action to be performed for each element

Exceptions
java.lang.NullPointerException	if the specified action is null

getFirst

Added in API level 21

open fun getFirst(): E

Return
E	the head of this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty

getLast

Added in API level 21

open fun getLast(): E

Return
E	the tail of this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty

isEmpty

Added in API level 21

open fun isEmpty(): Boolean

Returns true if this collection contains no elements.

Return
Boolean	true if this collection contains no elements

iterator

Added in API level 21

open 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).

The returned iterator is weakly consistent.

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

offer

Added in API level 21

open fun offer(e: E): Boolean

Inserts the specified element at the tail of this deque. As the deque is unbounded, this method will never return false.

Parameters
e	E: the element to add

Return
Boolean	true (as specified by Queue#offer)

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 21

open fun offerFirst(e: E): Boolean

Inserts the specified element at the front of this deque. As the deque is unbounded, this method will never return false.

Parameters
e	E: the element to add

Return
Boolean	true (as specified by Deque#offerFirst)

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 21

open fun offerLast(e: E): Boolean

Inserts the specified element at the end of this deque. As the deque is unbounded, this method will never return false.

This method is equivalent to #add.

Parameters
e	E: the element to add

Return
Boolean	true (as specified by Deque#offerLast)

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

peek

Added in API level 21

open fun peek(): E?

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

peekFirst

Added in API level 21

open fun peekFirst(): E?

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

peekLast

Added in API level 21

open fun peekLast(): E?

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

poll

Added in API level 21

open fun poll(): E?

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

pollFirst

Added in API level 21

open fun pollFirst(): E?

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

pollLast

Added in API level 21

open fun pollLast(): E?

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

pop

Added in API level 21

open fun pop(): E

Return
E	the element at the front of this deque (which is the top of the stack represented by this deque)

Exceptions
java.util.NoSuchElementException	if this deque is empty

push

Added in API level 21

open fun push(e: E): Unit

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 and this deque does not permit null elements
java.lang.IllegalArgumentException	if some property of the specified element prevents it from being added to this deque

remove

Added in API level 21

open fun remove(): E

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 21

open 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(java.lang.Object).

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

Return
Boolean	true if the deque contained the specified element

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

removeAll

Added in API level 21

open fun removeAll(elements: Collection<E>): Boolean

Parameters
c	collection containing elements to be removed from this collection

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

Exceptions
java.lang.UnsupportedOperationException	if the removeAll method is not supported by this collection
java.lang.ClassCastException	if the types of one or more elements in this collection are incompatible with the specified collection (optional)
java.lang.NullPointerException	if this collection contains one or more null elements and the specified collection does not support null elements (optional), or if the specified collection is null

removeFirst

Added in API level 21

open fun removeFirst(): E

Return
E	the head of this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

removeFirstOccurrence

Added in API level 21

open 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 the deque contained the specified element

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

removeIf

Added in API level 24

open fun removeIf(filter: Predicate<in E>): Boolean

Parameters
filter	Predicate<in E>: a predicate which returns true for elements to be removed

Return
Boolean	true if any elements were removed

Exceptions
java.lang.NullPointerException	if the specified filter is null
java.lang.UnsupportedOperationException	if elements cannot be removed from this collection. Implementations may throw this exception if a matching element cannot be removed or if, in general, removal is not supported.

removeLast

Added in API level 21

open fun removeLast(): E

Return
E	the tail of this deque

Exceptions
java.util.NoSuchElementException	if this deque is empty
java.lang.UnsupportedOperationException	if this collection implementation does not support this operation

removeLastOccurrence

Added in API level 21

open 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 the deque contained the specified element

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

retainAll

Added in API level 21

open fun retainAll(elements: Collection<E>): Boolean

Parameters
c	collection containing elements to be retained in this collection

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

Exceptions
java.lang.UnsupportedOperationException	if the retainAll operation is not supported by this collection
java.lang.ClassCastException	if the types of one or more elements in this collection are incompatible with the specified collection (optional)
java.lang.NullPointerException	if this collection contains one or more null elements and the specified collection does not permit null elements (optional), or if the specified collection is null

spliterator

Added in API level 24

open fun spliterator(): Spliterator<E>

Returns a Spliterator over the elements in this deque.

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator#CONCURRENT, Spliterator#ORDERED, and Spliterator#NONNULL.

Return
Spliterator<E>	a Spliterator over the elements in this deque

toArray

Added in API level 21

open fun toArray(): Array<Any!>

Returns an array containing all of the elements in this deque, in proper sequence (from first to last element).

The returned array will be "safe" in that no references to it are maintained by this deque. (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.

Return
Array<Any!>	an array containing all of the elements in this deque

toArray

Added in API level 21

open fun <T : Any!> toArray(a: Array<T>): Array<T>

Returns an array containing all of the elements in this deque, in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the deque 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 deque.

If this deque fits in the specified array with room to spare (i.e., the array has more elements than this deque), the element in the array immediately following the end of the deque 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.

Suppose x is a deque known to contain only strings. The following code can be used to dump the deque into a newly allocated array of String:

<code>String[] y = x.toArray(new String[0]);</code>

Note that toArray(new Object[0]) is identical in function to toArray().

Parameters
<T>	the component type of the array to contain the collection
a	Array<T>: the array into which the elements of the deque are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose

Return
Array<T>	an array containing all of the elements in this deque

Exceptions
java.lang.ArrayStoreException	if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque
java.lang.NullPointerException	if the specified array is null

toString

Added in API level 21

open fun toString(): String

Return
String	a string representation of the object.

Properties

size

Added in API level 21

open val size: Int

Returns the number of elements in this deque. If this deque contains more than Integer.MAX_VALUE elements, it returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these deques, determining the current number of elements requires traversing them all to count them. Additionally, it is possible for the size to change during execution of this method, in which case the returned result will be inaccurate. Thus, this method is typically not very useful in concurrent applications.

Return
Int	the number of elements in this deque