E
- the type of elements held in this collectionpublic class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>, Cloneable, Serializable
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.
This class is a member of the Java Collections Framework.
public ArrayDeque()
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.
public ArrayDeque(int numElements)
Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.
numElements
- lower bound on initial capacity of the dequepublic 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.)
c
- the collection whose elements are to be placed into the dequeNullPointerException
- if the specified collection is nullpublic void addFirst(E e)
Inserts the specified element at the front of this deque.
addFirst
in interface Deque<E>
e
- the element to addNullPointerException
- if the specified element is nullpublic void addLast(E e)
Inserts the specified element at the end of this deque.
This method is equivalent to add(E)
.
addLast
in interface Deque<E>
e
- the element to addNullPointerException
- if the specified element is nullpublic boolean offerFirst(E e)
Inserts the specified element at the front of this deque.
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)
Inserts the specified element at the end of this deque.
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()
Description copied from interface: Deque
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.
removeFirst
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E removeLast()
Description copied from interface: Deque
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.
removeLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E pollFirst()
Description copied from interface: Deque
Retrieves and removes the first element of this deque, or returns null
if this deque is empty.
pollFirst
in interface Deque<E>
null
if this deque is emptypublic E pollLast()
Description copied from interface: Deque
Retrieves and removes the last element of this deque, or returns null
if this deque is empty.
pollLast
in interface Deque<E>
null
if this deque is emptypublic E getFirst()
Description copied from interface: Deque
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.
getFirst
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E getLast()
Description copied from interface: Deque
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.
getLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic E peekFirst()
Description copied from interface: Deque
Retrieves, but does not remove, the first element of this deque, or returns null
if this deque is empty.
peekFirst
in interface Deque<E>
null
if this deque is emptypublic E peekLast()
Description copied from interface: Deque
Retrieves, but does not remove, the last element of this deque, or returns null
if this deque is empty.
peekLast
in interface Deque<E>
null
if this deque is emptypublic 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).
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)
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).
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)
Inserts the specified element at the end of this deque.
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)
Inserts the specified element at the end of this deque.
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()
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()
.
remove
in interface Deque<E>
remove
in interface Queue<E>
NoSuchElementException
- if this deque is emptypublic 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()
.
poll
in interface Deque<E>
poll
in interface Queue<E>
null
if this deque is emptypublic 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()
.
element
in interface Deque<E>
element
in interface Queue<E>
NoSuchElementException
- if this deque is emptypublic 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()
.
peek
in interface Deque<E>
peek
in interface Queue<E>
null
if this deque is emptypublic 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)
.
push
in interface Deque<E>
e
- the element to pushNullPointerException
- if the specified element is nullpublic 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()
.
pop
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic int size()
Returns the number of elements in this deque.
size
in interface Collection<E>
size
in interface Deque<E>
size
in class AbstractCollection<E>
public boolean isEmpty()
Returns 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()
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()
).
iterator
in interface Iterable<E>
iterator
in interface Collection<E>
iterator
in interface Deque<E>
iterator
in class AbstractCollection<E>
public Iterator<E> descendingIterator()
Description copied from interface: Deque
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).
descendingIterator
in interface Deque<E>
public 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)
.
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)
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)
.
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()
Removes all of the elements from this deque. The deque will be empty after this call returns.
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public 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.
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
public <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. 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()
.toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
T
- the runtime 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()
Returns a copy of this deque.
public Spliterator<E> spliterator()
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.
spliterator
in interface Iterable<E>
spliterator
in interface Collection<E>
Spliterator
over the elements in this deque
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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.
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