ArrayDeque

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 getFirst().
    
    Specified by:
    
    element in interface Deque<E>
    
    Specified by:
    
    element in interface Queue<E>
    
    Returns:
    the head of the queue represented by this deque
    
    Throws:
    
    NoSuchElementException - if this deque is empty
  - peek
```
public E 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().
    
    Specified by:
    
    peek in interface Deque<E>
    
    Specified by:
    
    peek in interface Queue<E>
    
    Returns:
    the head of the queue represented by this deque, or null if this deque is empty
  - push
```
public void push(E 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).
    
    Specified by:
    
    push in interface Deque<E>
    
    Parameters:
    e - the element to push
    
    Throws:
    
    NullPointerException - if the specified element is null
  - pop
```
public E 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().
    
    Specified by:
    
    pop in interface Deque<E>
    
    Returns:
    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
  - size
```
public int size()
```
    Returns the number of elements in this deque.
    
    Specified by:
    
    size in interface Collection<E>
    
    Specified by:
    
    size in interface Deque<E>
    
    Specified by:
    
    size in class AbstractCollection<E>
    
    Returns:
    the number of elements in this deque
  - isEmpty
```
public boolean isEmpty()
```
    Returns true if this deque contains no elements.
    
    Specified by:
    
    isEmpty in interface Collection<E>
    
    Overrides:
    
    isEmpty in class AbstractCollection<E>
    
    Returns:
    true if this deque contains no elements
  - iterator
```
public Iterator<E> 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()).
    
    Specified by:
    
    iterator in interface Iterable<E>
    
    Specified by:
    
    iterator in interface Collection<E>
    
    Specified by:
    
    iterator in interface Deque<E>
    
    Specified by:
    
    iterator in class AbstractCollection<E>
    
    Returns:
    an iterator over the elements in this deque
  - descendingIterator
```
public Iterator<E> descendingIterator()
```
    Description copied from interface: 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).
    
    Specified by:
    
    descendingIterator in interface Deque<E>
    
    Returns:
    an iterator over the elements in this deque in reverse sequence
  - contains
```
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).
    
    Specified by:
    
    contains in interface Collection<E>
    
    Specified by:
    
    contains in interface Deque<E>
    
    Overrides:
    
    contains in class AbstractCollection<E>
    
    Parameters:
    o - object to be checked for containment in this deque
    
    Returns:
    true if this deque contains the specified element
  - remove
```
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(java.lang.Object).
    
    Specified by:
    
    remove in interface Collection<E>
    
    Specified by:
    
    remove in interface Deque<E>
    
    Overrides:
    
    remove in class AbstractCollection<E>
    
    Parameters:
    o - element to be removed from this deque, if present
    
    Returns:
    true if this deque contained the specified element
  - clear
```
public void clear()
```
    Removes all of the elements from this deque. The deque will be empty after this call returns.
    
    Specified by:
    
    clear in interface Collection<E>
    
    Overrides:
    
    clear in class AbstractCollection<E>
  - toArray
```
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.
    
    Specified by:
    
    toArray in interface Collection<E>
    
    Overrides:
    
    toArray in class AbstractCollection<E>
    
    Returns:
    an array containing all of the elements in this deque
  - toArray
```
public <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. 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().
    Specified by:
    
    toArray in interface Collection<E>
    
    Overrides:
    
    toArray in class AbstractCollection<E>
    
    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
  - clone
```
public ArrayDeque<E> clone()
```
    Returns a copy of this deque.
    
    Overrides:
    
    clone in class Object
    
    Returns:
    a copy of this deque
    See Also:
    Cloneable

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

peek

push

pop

size

isEmpty

iterator

descendingIterator

contains

remove

clear

toArray

toArray

clone