E
- the type of elements held in this dequeSerializable
, Cloneable
, Iterable<E>
, Collection<E>
, Deque<E>
, Queue<E>
, SequencedCollection<E>
public class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>, Cloneable, Serializable
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
, SequencedCollection
, and Iterator
interfaces.
This class is a member of the Java Collections Framework.
Constructor | Description |
---|---|
ArrayDeque() |
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements. |
ArrayDeque |
Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements. |
ArrayDeque |
Constructs a deque containing the elements of the specified collection, in the order they are returned by the collection's iterator. |
Modifier and Type | Method | Description |
---|---|---|
boolean |
add |
Inserts the specified element at the end of this deque. |
boolean |
addAll |
Adds all of the elements in the specified collection at the end of this deque, as if by calling addLast(E) on each one, in the order that they are returned by the collection's iterator. |
void |
addFirst |
Inserts the specified element at the front of this deque. |
void |
addLast |
Inserts the specified element at the end of this deque. |
void |
clear() |
Removes all of the elements from this deque. |
ArrayDeque |
clone() |
Returns a copy of this deque. |
boolean |
contains |
Returns true if this deque contains the specified element. |
Iterator |
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. |
void |
forEach |
Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. |
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 |
iterator() |
Returns an iterator over the elements in this deque. |
boolean |
offer |
Inserts the specified element at the end of this deque. |
boolean |
offerFirst |
Inserts the specified element at the front of this deque. |
boolean |
offerLast |
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 |
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 |
Removes a single instance of the specified element from this deque. |
boolean |
removeAll |
Removes all of this collection's elements that are also contained in the specified collection (optional operation). |
E |
removeFirst() |
Retrieves and removes the first element of this deque. |
boolean |
removeFirstOccurrence |
Removes the first occurrence of the specified element in this deque (when traversing the deque from head to tail). |
boolean |
removeIf |
Removes all of the elements of this collection that satisfy the given predicate. |
E |
removeLast() |
Retrieves and removes the last element of this deque. |
boolean |
removeLastOccurrence |
Removes the last occurrence of the specified element in this deque (when traversing the deque from head to tail). |
boolean |
retainAll |
Retains only the elements in this collection that are contained in the specified collection (optional operation). |
int |
size() |
Returns the number of elements in this deque. |
Spliterator |
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 |
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. |
containsAll, toString
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
containsAll, equals, hashCode, parallelStream, stream, toArray
public ArrayDeque()
public ArrayDeque(int numElements)
numElements
- lower bound on initial capacity of the dequepublic ArrayDeque(Collection<? extends E> c)
c
- the collection whose elements are to be placed into the dequeNullPointerException
- if the specified collection is nullpublic void addFirst(E e)
addFirst
in interface Deque<E>
addFirst
in interface SequencedCollection<E>
e
- the element to addNullPointerException
- if the specified element is nullpublic void addLast(E e)
This method is equivalent to add(E)
.
addLast
in interface Deque<E>
addLast
in interface SequencedCollection<E>
e
- the element to addNullPointerException
- if the specified element is nullpublic boolean addAll(Collection<? extends E> c)
addLast(E)
on each one, in the order that they are returned by the collection's iterator.addAll
in interface Collection<E>
addAll
in interface Deque<E>
addAll
in class AbstractCollection<E>
c
- the elements to be inserted into this dequetrue
if this deque changed as a result of the callNullPointerException
- if the specified collection or any of its elements are nullpublic boolean offerFirst(E e)
offerFirst
in interface Deque<E>
e
- the element to addtrue
(as specified by Deque.offerFirst(E)
)NullPointerException
- if the specified element is nullpublic boolean offerLast(E e)
offerLast
in interface Deque<E>
e
- the element to addtrue
(as specified by Deque.offerLast(E)
)NullPointerException
- if the specified element is nullpublic E removeFirst()
Deque
pollFirst
only in that it throws an exception if this deque is empty.removeFirst
in interface Deque<E>
removeFirst
in interface SequencedCollection<E>
NoSuchElementException
- if this deque is emptypublic E removeLast()
Deque
pollLast
only in that it throws an exception if this deque is empty.removeLast
in interface Deque<E>
removeLast
in interface SequencedCollection<E>
NoSuchElementException
- if this deque is emptypublic E pollFirst()
Deque
null
if this deque is empty.public E pollLast()
Deque
null
if this deque is empty.public E getFirst()
Deque
peekFirst
only in that it throws an exception if this deque is empty.getFirst
in interface Deque<E>
getFirst
in interface SequencedCollection<E>
NoSuchElementException
- if this deque is emptypublic E getLast()
Deque
peekLast
only in that it throws an exception if this deque is empty.getLast
in interface Deque<E>
getLast
in interface SequencedCollection<E>
NoSuchElementException
- if this deque is emptypublic E peekFirst()
Deque
null
if this deque is empty.public E peekLast()
Deque
null
if this deque is empty.public boolean removeFirstOccurrence(Object o)
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).removeFirstOccurrence
in interface Deque<E>
o
- element to be removed from this deque, if presenttrue
if the deque contained the specified elementpublic boolean removeLastOccurrence(Object o)
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).removeLastOccurrence
in interface Deque<E>
o
- element to be removed from this deque, if presenttrue
if the deque contained the specified elementpublic boolean add(E e)
This method is equivalent to addLast(E)
.
add
in interface Collection<E>
add
in interface Deque<E>
add
in interface Queue<E>
add
in class AbstractCollection<E>
e
- the element to addtrue
(as specified by Collection.add(E)
)NullPointerException
- if the specified element is nullpublic boolean offer(E e)
This method is equivalent to offerLast(E)
.
offer
in interface Deque<E>
offer
in interface Queue<E>
e
- the element to addtrue
(as specified by Queue.offer(E)
)NullPointerException
- if the specified element is nullpublic E remove()
poll()
only in that it throws an exception if this deque is empty. This method is equivalent to removeFirst()
.
public E poll()
null
if this deque is empty. This method is equivalent to pollFirst()
.
public E element()
peek
only in that it throws an exception if this deque is empty. This method is equivalent to getFirst()
.
public E peek()
null
if this deque is empty. This method is equivalent to peekFirst()
.
public void push(E e)
This method is equivalent to addFirst(E)
.
push
in interface Deque<E>
e
- the element to pushNullPointerException
- if the specified element is nullpublic E pop()
This method is equivalent to removeFirst()
.
pop
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic int size()
public boolean isEmpty()
true
if this deque contains no elements.isEmpty
in interface Collection<E>
isEmpty
in class AbstractCollection<E>
true
if this deque contains no elementspublic Iterator<E> iterator()
public Iterator<E> descendingIterator()
Deque
descendingIterator
in interface Deque<E>
public Spliterator<E> spliterator()
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.
spliterator
in interface Collection<E>
spliterator
in interface Iterable<E>
Spliterator
over the elements in this dequepublic void forEach(Consumer<? super E> action)
Iterable
Iterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller. The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
forEach
in interface Iterable<E>
action
- The action to be performed for each elementNullPointerException
- if the specified action is nullpublic boolean removeIf(Predicate<? super E> filter)
Collection
removeIf
in interface Collection<E>
filter
- a predicate which returns true
for elements to be removedtrue
if any elements were removedNullPointerException
- if the specified filter is nullpublic boolean removeAll(Collection<?> c)
AbstractCollection
removeAll
in interface Collection<E>
removeAll
in class AbstractCollection<E>
c
- collection containing elements to be removed from this collectiontrue
if this collection changed as a result of the callNullPointerException
- 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 nullpublic boolean retainAll(Collection<?> c)
AbstractCollection
retainAll
in interface Collection<E>
retainAll
in class AbstractCollection<E>
c
- collection containing elements to be retained in this collectiontrue
if this collection changed as a result of the callNullPointerException
- 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 nullpublic boolean contains(Object o)
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)
.contains
in interface Collection<E>
contains
in interface Deque<E>
contains
in class AbstractCollection<E>
o
- object to be checked for containment in this dequetrue
if this deque contains the specified elementpublic boolean remove(Object o)
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)
.
remove
in interface Collection<E>
remove
in interface Deque<E>
remove
in class AbstractCollection<E>
o
- element to be removed from this deque, if presenttrue
if this deque contained the specified elementpublic void clear()
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public Object[] toArray()
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.
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
public <T> T[] toArray(T[] a)
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()
.toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
T
- the component type of the array to contain the collectiona
- 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 purposeArrayStoreException
- if the runtime type of the specified array is not a supertype of the runtime type of every element in this dequeNullPointerException
- if the specified array is nullpublic ArrayDeque<E> clone()
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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/ArrayDeque.html