edu.emory.mathcs.backport.java.util
public class ArrayDeque extends AbstractCollection implements Deque, Cloneable, Serializable
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.
Since: 1.6
Constructor Summary | |
---|---|
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 c)
Constructs a deque containing the elements of the specified
collection, in the order they are returned by the collection's
iterator. |
Method Summary | |
---|---|
boolean | add(Object e)
Inserts the specified element at the end of this deque.
|
void | addFirst(Object e)
Inserts the specified element at the front of this deque.
|
void | addLast(Object e)
Inserts the specified element at the end of this deque.
|
void | clear()
Removes all of the elements from this deque.
|
Object | clone()
Returns a copy of this deque.
|
boolean | contains(Object o)
Returns true if this deque contains the specified element.
|
Iterator | descendingIterator() |
Object | element()
Retrieves, but does not remove, the head of the queue represented by
this deque. |
Object | getFirst() |
Object | getLast() |
boolean | isEmpty()
Returns true if this deque contains no elements.
|
Iterator | iterator()
Returns an iterator over the elements in this deque. |
boolean | offer(Object e)
Inserts the specified element at the end of this deque.
|
boolean | offerFirst(Object e)
Inserts the specified element at the front of this deque.
|
boolean | offerLast(Object e)
Inserts the specified element at the end of this deque.
|
Object | peek()
Retrieves, but does not remove, the head of the queue represented by
this deque, or returns null if this deque is empty.
|
Object | peekFirst() |
Object | peekLast() |
Object | 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.
|
Object | pollFirst() |
Object | pollLast() |
Object | pop()
Pops an element from the stack represented by this deque. |
void | push(Object e)
Pushes an element onto the stack represented by this deque. |
Object | 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.
|
Object | removeFirst() |
boolean | removeFirstOccurrence(Object o)
Removes the first occurrence of the specified element in this
deque (when traversing the deque from head to tail).
|
Object | removeLast() |
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).
|
Object[] | toArray(Object[] 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. |
Parameters: numElements lower bound on initial capacity of the deque
Parameters: c the collection whose elements are to be placed into the deque
Throws: NullPointerException if the specified collection is null
This method is equivalent to ArrayDeque.
Parameters: e the element to add
Returns: true (as specified by Collection#add)
Throws: NullPointerException if the specified element is null
Parameters: e the element to add
Throws: NullPointerException if the specified element is null
This method is equivalent to ArrayDeque.
Parameters: e the element to add
Throws: NullPointerException if the specified element is null
Returns: a copy of this deque
Parameters: o object to be checked for containment in this deque
Returns: true if this deque contains the specified element
peek
only in
that it throws an exception if this deque is empty.
This method is equivalent to ArrayDeque.
Returns: the head of the queue represented by this deque
Throws: NoSuchElementException {@inheritDoc }
Throws: NoSuchElementException {@inheritDoc }
Throws: NoSuchElementException {@inheritDoc }
Returns: true if this deque contains no elements
Returns: an iterator over the elements in this deque
This method is equivalent to ArrayDeque.
Parameters: e the element to add
Returns: true (as specified by Queue)
Throws: NullPointerException if the specified element is null
Parameters: e the element to add
Returns: true (as specified by Deque)
Throws: NullPointerException if the specified element is null
Parameters: e the element to add
Returns: true (as specified by Deque)
Throws: NullPointerException if the specified element is null
This method is equivalent to ArrayDeque.
Returns: the head of the queue represented by this deque, or null if this deque is empty
This method is equivalent to ArrayDeque.
Returns: the head of the queue represented by this deque, or null if this deque is empty
This method is equivalent to removeFirst.
Returns: the element at the front of this deque (which is the top of the stack represented by this deque)
Throws: NoSuchElementException {@inheritDoc }
This method is equivalent to ArrayDeque.
Parameters: e the element to push
Throws: NullPointerException if the specified element is null
poll
only in that it throws an
exception if this deque is empty.
This method is equivalent to ArrayDeque.
Returns: the head of the queue represented by this deque
Throws: NoSuchElementException {@inheritDoc }
This method is equivalent to ArrayDeque.
Parameters: o element to be removed from this deque, if present
Returns: true if this deque contained the specified element
Throws: NoSuchElementException {@inheritDoc }
Parameters: o element to be removed from this deque, if present
Returns: true if the deque contained the specified element
Throws: NoSuchElementException {@inheritDoc }
Parameters: o element to be removed from this deque, if present
Returns: true if the deque contained the specified element
Returns: the number of elements in this deque
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: an array containing all of the elements in 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 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: 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