E
- the type of elements held in this collectionpublic class ArrayDeque<E> extends AbstractCollection<E> implements Deque<E>, Cloneable
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.
Constructor and Description |
---|
ArrayDeque()
Constructs an empty array deque with an initial capacity
sufficient to hold 16 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.
|
ArrayDeque(int numElements)
Constructs an empty array deque with an initial capacity
sufficient to hold the specified number of elements.
|
Modifier and Type | Method and Description |
---|---|
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.
|
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.
|
addAll, containsAll, removeAll, retainAll, toString
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait
addAll, containsAll, equals, hashCode, removeAll, retainAll
public ArrayDeque()
public ArrayDeque(Collection<? extends E> c)
c
- the collection whose elements are to be placed into the dequeNullPointerException
- if the specified collection is nullpublic ArrayDeque(int numElements)
numElements
- lower bound on initial capacity of the dequepublic 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 void addFirst(E e)
addFirst
in interface Deque<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>
e
- the element to addNullPointerException
- if the specified element is nullpublic void clear()
clear
in interface Collection<E>
clear
in class AbstractCollection<E>
public ArrayDeque<E> clone()
public 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 Iterator<E> descendingIterator()
Deque
descendingIterator
in interface Deque<E>
public E element()
peek
only in
that it throws an exception if this deque is empty.
This method is equivalent to getFirst()
.
public E getFirst()
Deque
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()
Deque
peekLast
only in that it
throws an exception if this deque is empty.getLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic 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 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 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 peek()
null
if this deque is empty.
This method is equivalent to peekFirst()
.
public E peekFirst()
Deque
null
if this deque is empty.public E peekLast()
Deque
null
if this deque is empty.public E poll()
null
if this deque is empty.
This method is equivalent to pollFirst()
.
public E pollFirst()
Deque
null
if this deque is empty.public E pollLast()
Deque
null
if this deque is empty.public E pop()
This method is equivalent to removeFirst()
.
pop
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic 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 remove()
poll
only in that it throws an
exception if this deque is empty.
This method is equivalent to removeFirst()
.
public 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 E removeFirst()
Deque
pollFirst
only in that it throws an
exception if this deque is empty.removeFirst
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic 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 E removeLast()
Deque
pollLast
only in that it throws an
exception if this deque is empty.removeLast
in interface Deque<E>
NoSuchElementException
- if this deque is emptypublic 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 int size()
size
in interface Collection<E>
size
in interface Deque<E>
size
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 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 nullCopyright (c) 2014, Oracle and/or its affiliates. All rights reserved. Use of this specification is subject to license terms.