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| 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.
| Public Constructors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Constructs an empty array deque with an initial capacity
sufficient to hold 16 elements.
|
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|
|
Constructs an empty array deque with an initial capacity
sufficient to hold the specified number of elements.
|
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|
|
Constructs a deque containing the elements of the specified
collection, in the order they are returned by the collection's
iterator.
|
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| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Inserts the specified element at the end of this deque.
|
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|
|
Inserts the specified element at the front of this deque.
|
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|
|
Inserts the specified element at the end of this deque.
|
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|
|
Removes all of the elements from this deque.
|
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|
|
Returns a copy of this deque.
|
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|
|
Returns
true
if this deque contains the specified element.
|
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|
|
Returns an iterator over the elements in this deque in reverse
sequential order.
|
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|
|
Retrieves, but does not remove, the head of the queue represented by
this deque.
|
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|
|
Retrieves, but does not remove, the first element of this deque.
|
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|
|
Retrieves, but does not remove, the last element of this deque.
|
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|
|
Returns
true
if this deque contains no elements.
|
||||||||||
|
|
Returns an iterator over the elements in this deque.
|
||||||||||
|
|
Inserts the specified element at the end of this deque.
|
||||||||||
|
|
Inserts the specified element at the front of this deque.
|
||||||||||
|
|
Inserts the specified element at the end of this deque.
|
||||||||||
|
|
Retrieves, but does not remove, the head of the queue represented by
this deque, or returns
null
if this deque is empty.
|
||||||||||
|
|
Retrieves, but does not remove, the first element of this deque,
or returns
null
if this deque is empty.
|
||||||||||
|
|
Retrieves, but does not remove, the last element of this deque,
or returns
null
if this deque is empty.
|
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|
|
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.
|
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|
|
Retrieves and removes the first element of this deque,
or returns
null
if this deque is empty.
|
||||||||||
|
|
Retrieves and removes the last element of this deque,
or returns
null
if this deque is empty.
|
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|
|
Pops an element from the stack represented by this deque.
|
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|
|
Pushes an element onto the stack represented by this deque.
|
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|
|
Retrieves and removes the head of the queue represented by this deque.
|
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|
|
Removes a single instance of the specified element from this deque.
|
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|
|
Retrieves and removes the first element of this deque.
|
||||||||||
|
|
Removes the first occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
||||||||||
|
|
Retrieves and removes the last element of this deque.
|
||||||||||
|
|
Removes the last occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
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|
|
Returns the number of elements in this deque.
|
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|
|
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.
|
||||||||||
|
|
Returns an array containing all of the elements in this deque
in proper sequence (from first to last element).
|
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|
[Expand]
Inherited Methods
|
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|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.util.AbstractCollection
|
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|
From class
java.lang.Object
|
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|
From interface
java.lang.Iterable
|
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|
From interface
java.util.Collection
|
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|
From interface
java.util.Deque
|
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|
From interface
java.util.Queue
|
|||||||||||
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.
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 deque |
|---|
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 deque |
|---|
| NullPointerException | if the specified collection is null |
|---|
Inserts the specified element at the end of this deque.
This method is equivalent to
addLast(E)
.
| e | the element to add |
|---|
add(E)
)
| NullPointerException | if the specified element is null |
|---|
Inserts the specified element at the front of this deque.
| e | the element to add |
|---|
| NullPointerException | if the specified element is null |
|---|
Inserts the specified element at the end of this deque.
This method is equivalent to
add(E)
.
| e | the element to add |
|---|
| NullPointerException | if the specified element is null |
|---|
Removes all of the elements from this deque. The deque will be empty after this call returns.
Returns a copy of this deque.
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) .
| o | object to be checked for containment in this 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).
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()
.
| NoSuchElementException |
|---|
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.
| NoSuchElementException |
|---|
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.
| NoSuchElementException |
|---|
Returns true if this deque contains no elements.
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()
).
Inserts the specified element at the end of this deque.
This method is equivalent to
offerLast(E)
.
| e | the element to add |
|---|
offer(E)
)
| NullPointerException | if the specified element is null |
|---|
Inserts the specified element at the front of this deque.
| e | the element to add |
|---|
offerFirst(E)
)
| NullPointerException | if the specified element is null |
|---|
Inserts the specified element at the end of this deque.
| e | the element to add |
|---|
offerLast(E)
)
| NullPointerException | if the specified element is null |
|---|
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()
.
Retrieves, but does not remove, the first element of this deque, or returns null if this deque is empty.
Retrieves, but does not remove, the last element of this deque, or returns null if this deque is empty.
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()
.
Retrieves and removes the first element of this deque, or returns null if this deque is empty.
Retrieves and removes the last element of this deque, or returns null if this deque is empty.
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()
.
| NoSuchElementException |
|---|
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)
.
| e | the element to push |
|---|
| NullPointerException | if the specified element is null |
|---|
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()
.
| NoSuchElementException |
|---|
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)
.
| o | element to be removed from this deque, if present |
|---|
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.
| NoSuchElementException |
|---|
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).
| o | element to be removed from this deque, if present |
|---|
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.
| NoSuchElementException |
|---|
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).
| o | element to be removed from this deque, if present |
|---|
Returns the number of elements in this deque.
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()
.
| a | 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 |
|---|
| 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 |
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.