java.util.ArrayDeque<E>

public class java.util

ArrayDeque<E>

Java SE 6

Extends: AbstractCollection

Implements: Deque, 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.

since 1.6

E the type of elements held in this collection

Constructors

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 deque

public

ArrayDeque(Collection 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 deque
Throws	NullPointerException: if the specified collection is null

Methods

public boolean

add(Object e)
Inserts the specified element at the end of this deque.

This method is equivalent to #addLast.

e the element to add

return true (as specified by Collection#add)

Throws NullPointerException: als het gespecifieerde element null is

public void

addFirst(Object e)
Inserts the specified element at the front of this deque.

e	the element to add
Throws	NullPointerException: als het gespecifieerde element null is

public void

addLast(Object e)
Inserts the specified element at the end of this deque.

This method is equivalent to #add.

e the element to add

Throws NullPointerException: als het gespecifieerde element null is

public void

clear()
Removes all of the elements from this deque. The deque will be empty after this call returns.

public ArrayDeque

clone()
Returns a copy of this deque.

return

a copy of this deque

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).

o	object to be checked for containment in this deque
return	`true` if this deque contains the specified element

public Iterator

descendingIterator()

public Object

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.

return the head of the queue represented by this deque

Throws NoSuchElementException: if this deque is empty

public Iterator

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).

return

an iterator over the elements in this deque

public boolean

offer(Object e)
Inserts the specified element at the end of this deque.

This method is equivalent to #offerLast.

e the element to add

return true (as specified by Queue#offer)

Throws NullPointerException: als het gespecifieerde element null is

public boolean

offerFirst(Object e)
Inserts the specified element at the front of this deque.

e	the element to add
return	`true` (as specified by `Deque#offerFirst`)
Throws	NullPointerException: als het gespecifieerde element null is

public boolean

offerLast(Object e)
Inserts the specified element at the end of this deque.

e	the element to add
return	`true` (as specified by `Deque#offerLast`)
Throws	NullPointerException: als het gespecifieerde element null is

public Object

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.

return the head of the queue represented by this deque, or null if this deque is empty

public Object

peekFirst()

public Object

peekLast()

public 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.

This method is equivalent to #pollFirst.

return the head of the queue represented by this deque, or null if this deque is empty

public Object

pollFirst()

public Object

pollLast()

public Object

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().

return the element at the front of this deque (which is the top of the stack represented by this deque)

Throws NoSuchElementException: if this deque is empty

public void

push(Object 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 the element to push

Throws NullPointerException: als het gespecifieerde element null is

public Object

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.

return the head of the queue represented by this deque

Throws NoSuchElementException: if this deque is empty

public 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.

o element to be removed from this deque, if present

return true if this deque contained the specified element

public Object

removeFirst()

Throws

NoSuchElementException: if this deque is empty

public 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).

o	element to be removed from this deque, if present
return	`true` if the deque contained the specified element

public Object

removeLast()

Throws

NoSuchElementException: if this deque is empty

public 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).

o	element to be removed from this deque, if present
return	`true` if the deque contained the specified element

public int

size()
Returns the number of elements in this deque.

return

the number of elements in this deque

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.

return an array containing all of the elements in this deque

public Object[]<T>

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. 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
return	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
Throws	NullPointerException: if the specified array is null

Properties

public boolean

isEmpty()
Returns true if this deque contains no elements.

return true if this deque contains no elements

public Object

getFirst()

Throws

NoSuchElementException: if this deque is empty

public Object

getLast()

Throws

NoSuchElementException: if this deque is empty

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Java SE 6

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