Added in API level 9

ArrayDeque

open class ArrayDeque<E : Any!> : AbstractCollection<E>, Deque<E>, Cloneable, Serializable
kotlin.Any
   ↳ java.util.AbstractCollection<E>
   ↳ java.util.ArrayDeque

Resizable-array implementation of the Deque interface. Array deques have no capacity restrictions; they grow as necessary to support usage. They are not thread-safe; in the absence of external synchronization, they do not support concurrent access by multiple threads. Null elements are prohibited. This class is likely to be faster than Stack when used as a stack, and faster than LinkedList when used as a queue.

Most ArrayDeque operations run in amortized constant time. Exceptions include #remove(java.lang.Object), removeFirstOccurrence, removeLastOccurrence, #contains, #iterator, and the bulk operations, all of which run in linear time.

The iterators returned by this class's #iterator() method are fail-fast: If the deque is modified at any time after the iterator is created, in any way except through the iterator's own remove method, the iterator will generally throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

This class and its iterator implement all of the optional methods of the Collection, SequencedCollection, and Iterator interfaces.

This class is a member of the Java Collections Framework.

Summary

Public constructors

Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

ArrayDeque(numElements: Int)

Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.

Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Public methods
open Boolean
add(element: E)

Inserts the specified element at the end of this deque.

open Boolean
addAll(elements: Collection<E>)

Adds all of the elements in the specified collection at the end of this deque, as if by calling #addLast on each one, in the order that they are returned by the 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

Removes all of the elements from this deque.

open ArrayDeque<E>

Returns a copy of this deque.

open Boolean
contains(element: E?)

Returns true if this deque contains the specified element.

open MutableIterator<E>

open E

Retrieves, but does not remove, the head of the queue represented by this deque.

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

open E

open E

open Boolean

Returns true if this deque contains no elements.

open MutableIterator<E>

Returns an iterator over the elements in this deque.

open Boolean
offer(e: E)

Inserts the specified element at the end 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?

Retrieves, but does not remove, the head of the queue represented by this deque, or returns null if this deque is empty.

open E?

open E?

open 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.

open E?

open E?

open E
pop()

Pops an element from the stack represented by this deque.

open Unit
push(e: E)

Pushes an element onto the stack represented by this deque.

open E

Retrieves and removes the head of the queue represented by this deque.

open Boolean
remove(element: E?)

Removes a single instance of the specified element from this deque.

open Boolean
removeAll(elements: Collection<E>)

open E

open Boolean

Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail).

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

open E

open Boolean

Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail).

open Boolean
retainAll(elements: Collection<E>)

open Spliterator<E>

Creates a late-binding and fail-fast Spliterator over the elements in this deque.

open Array<Any!>

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.

Inherited functions
Properties
open Int

Returns the number of elements in this deque.

Public constructors

ArrayDeque

Added in API level 9
ArrayDeque()

Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

ArrayDeque

Added in API level 9
ArrayDeque(numElements: Int)

Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.

Parameters
numElements Int: lower bound on initial capacity of the deque

ArrayDeque

Added in API level 9
ArrayDeque(c: MutableCollection<out E>)

Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator. (The first element returned by the collection's iterator becomes the first element, or front of the deque.)

Parameters
c MutableCollection<out E>: the collection whose elements are to be placed into the deque
Exceptions
java.lang.NullPointerException if the specified collection is null

Public methods

add

Added in API level 9
open fun add(element: E): Boolean

Inserts the specified element at the end of this deque.

This method is equivalent to #addLast.

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 9
open fun addAll(elements: Collection<E>): Boolean

Adds all of the elements in the specified collection at the end of this deque, as if by calling #addLast on each one, in the order that they are returned by the collection's iterator.

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 some property of an element of the specified collection prevents it from being added to 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 9
open fun addFirst(e: E): Unit

Inserts the specified element at the front of this deque.

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
open fun addLast(e: E): Unit

Inserts the specified element at the end of this deque.

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 9
open fun clear(): Unit

Removes all of the elements from this deque. The deque will be empty after this call returns.

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

clone

Added in API level 9
open fun clone(): ArrayDeque<E>

Returns a copy of this deque.

Return
ArrayDeque<E> a copy of this deque
Exceptions
java.lang.CloneNotSupportedException if the object's class does not support the Cloneable interface. Subclasses that override the clone method can also throw this exception to indicate that an instance cannot be cloned.

contains

Added in API level 9
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 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 (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 9
open fun descendingIterator(): MutableIterator<E>
Return
MutableIterator<E> an iterator over the elements in this deque in reverse sequence

element

Added in API level 9
open fun element(): E

Retrieves, but does not remove, the head of the queue represented by 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 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 9
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 9
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 9
open fun isEmpty(): Boolean

Returns true if this deque contains no elements.

Return
Boolean true if this deque contains no elements

iterator

Added in API level 9
open fun iterator(): MutableIterator<E>

Returns an iterator over the elements in this deque. The elements will be ordered from first (head) to last (tail). This is the same order that elements would be dequeued (via successive calls to #remove or popped (via successive calls to pop).

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

offer

Added in API level 9
open fun offer(e: E): Boolean

Inserts the specified element at the end of this deque.

This method is equivalent to offerLast.

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 9
open fun offerFirst(e: E): Boolean

Inserts the specified element at the front of this deque.

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 9
open fun offerLast(e: E): Boolean

Inserts the specified element at the end of this deque.

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 9
open fun peek(): E?

Retrieves, but does not remove, the head of the queue represented by this deque, or returns null if this deque is empty.

This method is equivalent to peekFirst.

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

peekFirst

Added in API level 9
open fun peekFirst(): E?
Return
E? the head of this deque, or null if this deque is empty

peekLast

Added in API level 9
open fun peekLast(): E?
Return
E? the tail of this deque, or null if this deque is empty

poll

Added in API level 9
open 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 the queue represented by this deque, or null if this deque is empty

pollFirst

Added in API level 9
open fun pollFirst(): E?
Return
E? the head of this deque, or null if this deque is empty

pollLast

Added in API level 9
open fun pollLast(): E?
Return
E? the tail of this deque, or null if this deque is empty

pop

Added in API level 9
open fun pop(): E

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().

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 9
open fun push(e: E): Unit

Pushes an element onto the stack represented by this deque. In other words, inserts the element at the front of this deque.

This method is equivalent to #addFirst.

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

remove

Added in API level 9
open fun remove(): E

Retrieves and removes the head of the queue represented by 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
open fun remove(element: E?): Boolean

Removes a single instance 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 this 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 and this deque does not permit null elements (java.util.Collection#)
java.lang.UnsupportedOperationException if the remove operation is not supported by this collection

removeAll

Added in API level 9
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 9
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 9
open fun removeFirstOccurrence(o: Any?): Boolean

Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail). 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 and this deque does not permit null elements (java.util.Collection#)

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 9
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 9
open fun removeLastOccurrence(o: Any?): Boolean

Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail). 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 and this deque does not permit null elements (java.util.Collection#)

retainAll

Added in API level 9
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>

Creates a late-binding and fail-fast Spliterator over the elements in this deque.

The Spliterator reports Spliterator#SIZED, Spliterator#SUBSIZED, Spliterator#ORDERED, and Spliterator#NONNULL. Overriding implementations should document the reporting of additional characteristic values.

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

toArray

Added in API level 9
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 9
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

Properties

size

Added in API level 9
open val size: Int

Returns the number of elements in this deque.

Return
Int the number of elements in this deque