Package Summary Overview Summary

### class:ArrayDeque [NONE]
- 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:ArrayDeque() [NONE]
- #### ArrayDeque
      public ArrayDeque()
Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

### constructor:ArrayDeque(int) [NONE]
- #### 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

### constructor:ArrayDeque(java.util.Collection) [NONE]
- #### 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:addFirst(E) [NONE]
- #### 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

### method:addLast(E) [NONE]
- #### 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

### method:offerFirst(E) [NONE]
- #### 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

### method:offerLast(E) [NONE]
- #### 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

### method:removeFirst() [NONE]
- #### 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

### method:removeLast() [NONE]
- #### 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

### method:pollFirst() [NONE]
- #### 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

### method:pollLast() [NONE]
- #### 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

### method:getFirst() [NONE]
- #### 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

### method:getLast() [NONE]
- #### 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

### method:peekFirst() [NONE]
- #### 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

### method:peekLast() [NONE]
- #### 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

### method:removeFirstOccurrence(java.lang.Object) [NONE]
- #### 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

### method:removeLastOccurrence(java.lang.Object) [NONE]
- #### 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

### method:add(E) [NONE]
- #### 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

### method:offer(E) [NONE]
- #### 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

### method:remove() [NONE]
- #### 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

### method:poll() [NONE]
- #### 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

### method:element() [NONE]
- #### 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

### method:peek() [NONE]
- #### 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

### method:push(E) [NONE]
- #### 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

### method:pop() [NONE]
- #### 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

### method:size() [NONE]
- #### 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

### method:isEmpty() [NONE]
- #### 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

### method:iterator() [NONE]
- #### 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

### method:descendingIterator() [NONE]
- #### 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

### method:contains(java.lang.Object) [NONE]
- #### 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

### method:remove(java.lang.Object) [NONE]
- #### 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(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

### method:clear() [NONE]
- #### 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>`

### method:toArray() [NONE]
- #### 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

### method:toArray(T[]) [NONE]
- #### 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>` Type Parameters: `T` - the runtime type of the array to contain the collection 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

### method:clone() [NONE]
- #### 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`

### method:spliterator() [NONE]
- #### spliterator
      public Spliterator<E> spliterator()
Creates a late-binding and fail-fast `Spliterator` over the elements in this deque. The `Spliterator` reports `Spliterator.SIZED`, `Spliterator.SUBSIZED`, `Spliterator.ORDERED`, and `Spliterator.NONNULL`. Overriding implementations should document the reporting of additional characteristic values. Specified by: `spliterator` in interface `Iterable<E>` Specified by: `spliterator` in interface `Collection<E>` Returns: a `Spliterator` over the elements in this deque Since: 1.8