ArrayDeque (Java Platform SE 7 )

java.lang.Object
- java.util.AbstractCollection<E>
- - java.util.ArrayDeque<E>

Type Parameters:
E - the type of elements held in this collection

All Implemented Interfaces:

Serializable, Cloneable, Iterable<E>, Collection<E>, Deque<E>, Queue<E>
```
public 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.

Since:

1.6

See Also:
Serialized Form

Constructor Summary

Constructors
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.

Method Summary

Methods
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.

Methods inherited from class java.util.AbstractCollection
addAll, containsAll, removeAll, retainAll, toString

Methods inherited from class java.lang.Object
equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, removeAll, retainAll

- Constructor Detail
  - ArrayDeque
```
public ArrayDeque()
```
    Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.
  - ArrayDeque
```
public ArrayDeque(int numElements)
```
    Constructs an empty array deque with an initial capacity sufficient to hold the specified number of elements.
    
    Parameters:
    numElements - lower bound on initial capacity of the deque
  - ArrayDeque
```
public 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.)
    
    Parameters:
    c - the collection whose elements are to be placed into the deque
    
    Throws:
    
    NullPointerException - if the specified collection is null
- Method Detail
  - addFirst
```
public void addFirst(E e)
```
    Inserts the specified element at the front of this deque.
    
    Specified by:
    
    addFirst in interface Deque<E>
    
    Parameters:
    e - the element to add
    
    Throws:
    
    NullPointerException - if the specified element is null
  - addLast
```
public void addLast(E e)
```
    Inserts the specified element at the end of this deque.
    This method is equivalent to add(E).
    
    Specified by:
    
    addLast in interface Deque<E>
    
    Parameters:
    e - the element to add
    
    Throws:
    
    NullPointerException - if the specified element is null
  - offerFirst
```
public boolean offerFirst(E e)
```
    Inserts the specified element at the front of this deque.
    
    Specified by:
    
    offerFirst in interface Deque<E>
    
    Parameters:
    e - the element to add
    
    Returns:
    true (as specified by Deque.offerFirst(E))
    
    Throws:
    
    NullPointerException - if the specified element is null
  - offerLast
```
public boolean offerLast(E e)
```
    Inserts the specified element at the end of this deque.
    
    Specified by:
    
    offerLast in interface Deque<E>
    
    Parameters:
    e - the element to add
    
    Returns:
    true (as specified by Deque.offerLast(E))
    
    Throws:
    
    NullPointerException - if the specified element is null
  - removeFirst
```
public 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.
    
    Specified by:
    
    removeFirst in interface Deque<E>
    
    Returns:
    the head of this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - removeLast
```
public 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.
    
    Specified by:
    
    removeLast in interface Deque<E>
    
    Returns:
    the tail of this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - pollFirst
```
public E pollFirst()
```
    Description copied from interface: Deque
    
    Retrieves and removes the first element of this deque, or returns null if this deque is empty.
    
    Specified by:
    
    pollFirst in interface Deque<E>
    
    Returns:
    the head of this deque, or null if this deque is empty
  - pollLast
```
public E pollLast()
```
    Description copied from interface: Deque
    
    Retrieves and removes the last element of this deque, or returns null if this deque is empty.
    
    Specified by:
    
    pollLast in interface Deque<E>
    
    Returns:
    the tail of this deque, or null if this deque is empty
  - getFirst
```
public 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.
    
    Specified by:
    
    getFirst in interface Deque<E>
    
    Returns:
    the head of this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - getLast
```
public 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.
    
    Specified by:
    
    getLast in interface Deque<E>
    
    Returns:
    the tail of this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - peekFirst
```
public 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.
    
    Specified by:
    
    peekFirst in interface Deque<E>
    
    Returns:
    the head of this deque, or null if this deque is empty
  - peekLast
```
public 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.
    
    Specified by:
    
    peekLast in interface Deque<E>
    
    Returns:
    the tail of this deque, or null if this deque is empty
  - removeFirstOccurrence
```
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).
    
    Specified by:
    
    removeFirstOccurrence in interface Deque<E>
    
    Parameters:
    o - element to be removed from this deque, if present
    
    Returns:
    true if the deque contained the specified element
  - removeLastOccurrence
```
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).
    
    Specified by:
    
    removeLastOccurrence in interface Deque<E>
    
    Parameters:
    o - element to be removed from this deque, if present
    
    Returns:
    true if the deque contained the specified element
  - add
```
public boolean add(E e)
```
    Inserts the specified element at the end of this deque.
    This method is equivalent to addLast(E).
    
    Specified by:
    
    add in interface Collection<E>
    
    Specified by:
    
    add in interface Deque<E>
    
    Specified by:
    
    add in interface Queue<E>
    
    Overrides:
    
    add in class AbstractCollection<E>
    
    Parameters:
    e - the element to add
    
    Returns:
    true (as specified by Collection.add(E))
    
    Throws:
    
    NullPointerException - if the specified element is null
  - offer
```
public boolean offer(E e)
```
    Inserts the specified element at the end of this deque.
    This method is equivalent to offerLast(E).
    
    Specified by:
    
    offer in interface Deque<E>
    
    Specified by:
    
    offer in interface Queue<E>
    
    Parameters:
    e - the element to add
    
    Returns:
    true (as specified by Queue.offer(E))
    
    Throws:
    
    NullPointerException - if the specified element is null
  - remove
```
public 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().
    
    Specified by:
    
    remove in interface Deque<E>
    
    Specified by:
    
    remove in interface Queue<E>
    
    Returns:
    the head of the queue represented by this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - poll
```
public 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().
    
    Specified by:
    
    poll in interface Deque<E>
    
    Specified by:
    
    poll in interface Queue<E>
    
    Returns:
    the head of the queue represented by this deque, or null if this deque is empty
  - element
```
public 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

Class ArrayDeque<E>

Constructor Summary

Method Summary

Methods inherited from class java.util.AbstractCollection

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Collection

Constructor Detail

ArrayDeque

ArrayDeque

ArrayDeque

Method Detail

addFirst

addLast

offerFirst

offerLast

removeFirst

removeLast

pollFirst

pollLast

getFirst

getLast

peekFirst

peekLast

removeFirstOccurrence

removeLastOccurrence

add

offer

remove

poll

element