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ArrayDeque

public class ArrayDeque
extends AbstractCollection<E> implements Deque<E>, Cloneable, Serializable

java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.ArrayDeque<E>


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, removeFirstOccurrence, removeLastOccurrence, contains, iterator.remove(), 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 and Iterator interfaces.

Summary

Public constructors

ArrayDeque()

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

ArrayDeque(int numElements)

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

ArrayDeque(Collection<? extends E> c)

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

Public methods

boolean add(E e)

Inserts the specified element at the end of this deque.

void addFirst(E e)

Inserts the specified element at the front of this deque.

void addLast(E e)

Inserts the specified element at the end of this deque.

void clear()

Removes all of the elements from this deque.

ArrayDeque<E> clone()

Returns a copy of this deque.

boolean contains(Object o)

Returns true if this deque contains the specified element.

Iterator<E> descendingIterator()

Returns an iterator over the elements in this deque in reverse sequential order.

E element()

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

E getFirst()

Retrieves, but does not remove, the first element of this deque.

E getLast()

Retrieves, but does not remove, the last element of this deque.

boolean isEmpty()

Returns true if this deque contains no elements.

Iterator<E> iterator()

Returns an iterator over the elements in this deque.

boolean offer(E e)

Inserts the specified element at the end of this deque.

boolean offerFirst(E e)

Inserts the specified element at the front of this deque.

boolean offerLast(E e)

Inserts the specified element at the end of this deque.

E peek()

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

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.

void push(E e)

Pushes an element onto the stack represented by this deque.

E remove()

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

boolean remove(Object o)

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

E removeFirst()

Retrieves and removes the first element of this deque.

boolean removeFirstOccurrence(Object o)

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

E removeLast()

Retrieves and removes the last element of this deque.

boolean removeLastOccurrence(Object o)

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

int size()

Returns the number of elements in this deque.

Spliterator<E> spliterator()

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

Object[] toArray()

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

<T> T[] toArray(T[] a)

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 methods

From class java.util.AbstractCollection
From class java.lang.Object
From interface java.util.Collection
From interface java.util.Deque
From interface java.lang.Iterable
From interface java.util.Queue

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 (int numElements)

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 (Collection<? extends E> c)

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 Collection: the collection whose elements are to be placed into the deque
Throws
NullPointerException if the specified collection is null

Public methods

add

Added in API level 9
boolean add (E e)

Inserts the specified element at the end of this deque.

This method is equivalent to addLast(E).

Parameters
e E: the element to add
Returns
boolean true (as specified by add(E))
Throws
NullPointerException if the specified element is null

addFirst

Added in API level 9
void addFirst (E e)

Inserts the specified element at the front of this deque.

Parameters
e E: the element to add
Throws
NullPointerException if the specified element is null

addLast

Added in API level 9
void addLast (E e)

Inserts the specified element at the end of this deque.

This method is equivalent to add(E).

Parameters
e E: the element to add
Throws
NullPointerException if the specified element is null

clear

Added in API level 9
void clear ()

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

clone

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

Returns a copy of this deque.

Returns
ArrayDeque<E> a copy of this deque

contains

Added in API level 9
boolean contains (Object o)

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: object to be checked for containment in this deque
Returns
boolean true if this deque contains the specified element

descendingIterator

Added in API level 9
Iterator<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).

Returns
Iterator<E> an iterator over the elements in this deque in reverse sequence

element

Added in API level 9
E element ()

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().

Returns
E the head of the queue represented by this deque
Throws
NoSuchElementException

getFirst

Added in API level 9
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.

Returns
E the head of this deque
Throws
NoSuchElementException

getLast

Added in API level 9
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.

Returns
E the tail of this deque
Throws
NoSuchElementException

isEmpty

Added in API level 9
boolean isEmpty ()

Returns true if this deque contains no elements.

Returns
boolean true if this deque contains no elements

iterator

Added in API level 9
Iterator<E> iterator ()

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()).

Returns
Iterator<E> an iterator over the elements in this deque

offer

Added in API level 9
boolean offer (E e)

Inserts the specified element at the end of this deque.

This method is equivalent to offerLast(E).

Parameters
e E: the element to add
Returns
boolean true (as specified by offer(E))
Throws
NullPointerException if the specified element is null

offerFirst

Added in API level 9
boolean offerFirst (E e)

Inserts the specified element at the front of this deque.

Parameters
e E: the element to add
Returns
boolean true (as specified by offerFirst(E))
Throws
NullPointerException if the specified element is null

offerLast

Added in API level 9
boolean offerLast (E e)

Inserts the specified element at the end of this deque.

Parameters
e E: the element to add
Returns
boolean true (as specified by offerLast(E))
Throws
NullPointerException if the specified element is null

peek

Added in API level 9
E peek ()

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().

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

peekFirst

Added in API level 9
E peekFirst ()

Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.

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

peekLast

Added in API level 9
E peekLast ()

Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.

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

poll

Added in API level 9
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.

This method is equivalent to pollFirst().

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

pollFirst

Added in API level 9
E pollFirst ()

Retrieves and removes the first element of this deque, or returns null if this deque is empty.

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

pollLast

Added in API level 9
E pollLast ()

Retrieves and removes the last element of this deque, or returns null if this deque is empty.

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

pop

Added in API level 9
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().

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

push

Added in API level 9
void push (E e)

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(E).

Parameters
e E: the element to push
Throws
NullPointerException if the specified element is null

remove

Added in API level 9
E remove ()

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().

Returns
E the head of the queue represented by this deque
Throws
NoSuchElementException

remove

Added in API level 9
boolean remove (Object o)

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(Object).

Parameters
o Object: element to be removed from this deque, if present
Returns
boolean true if this deque contained the specified element

removeFirst

Added in API level 9
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.

Returns
E the head of this deque
Throws
NoSuchElementException

removeFirstOccurrence

Added in API level 9
boolean removeFirstOccurrence (Object o)

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 Object: element to be removed from this deque, if present
Returns
boolean true if the deque contained the specified element

removeLast

Added in API level 9
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.

Returns
E the tail of this deque
Throws
NoSuchElementException

removeLastOccurrence

Added in API level 9
boolean removeLastOccurrence (Object o)

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 Object: element to be removed from this deque, if present
Returns
boolean true if the deque contained the specified element

size

Added in API level 9
int size ()

Returns the number of elements in this deque.

Returns
int the number of elements in this deque

spliterator

Added in API level 24
Spliterator<E> spliterator ()

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

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

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

toArray

Added in API level 9
Object[] toArray ()

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.

Returns
Object[] an array containing all of the elements in this deque

toArray

Added in API level 9
T[] toArray (T[] a)

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:

 String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to toArray().

Parameters
a 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
Returns
T[] an array containing all of the elements in this deque
Throws
ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this deque
NullPointerException if the specified array is null
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