java.util
class ArrayDeque

java.lang.Object java.util.AbstractCollection java.util.ArrayDeque

All Implemented Interfaces:

Serializable, Cloneable, Collection, Deque

Most common way to construct:

ArrayDeque q = new ArrayDeque();

Based on 118 examples

public class ArrayDeque
extends AbstractCollection
implements Deque, Cloneable, Serializable

Resizable-array implementation of the {@link 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 {@link Stack} when used as a stack, and faster than {@link LinkedList} when used as a queue.

Most ArrayDeque operations run in amortized constant time. Exceptions include {@link #remove(Object) remove}, {@link #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence removeLastOccurrence}, {@link #contains contains}, {@link #iterator 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 {@link 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 {@link Collection} and {@link Iterator} interfaces.

This class is a member of the Java Collections Framework.

ArrayDeque

public ArrayDeque()

Constructs an empty array deque with an initial capacity sufficient to hold 16 elements.

ArrayDeque

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.)

Parameters:

c - the collection whose elements are to be placed into the deque

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

add

public boolean add(Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to {@link #addLast}.

Overrides:

add in class AbstractCollection

Parameters:

e - the element to add

Returns:

true (as specified by {@link Collection#add})

addFirst

public void addFirst(Object e)

Inserts the specified element at the front of this deque.

Parameters:

e - the element to add

addLast

public void addLast(Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to {@link #add}.

Parameters:

e - the element to add

clear

public void clear()

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

Overrides:

clear in class AbstractCollection

clone

public ArrayDeque clone()

Returns a copy of this deque.

Overrides:

clone in class Object

Returns:

a copy of this deque

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).

Overrides:

contains in class AbstractCollection

Parameters:

o - object to be checked for containment in this deque

Returns:

true if this deque contains the specified element

descendingIterator

public Iterator descendingIterator()

element

public Object element()

Retrieves, but does not remove, the head of the queue represented by this deque. This method differs from {@link #peek peek} only in that it throws an exception if this deque is empty.

This method is equivalent to {@link #getFirst}.

Returns:

the head of the queue represented by this deque

getFirst

public Object getFirst()

getLast

public Object getLast()

isEmpty

public boolean isEmpty()

Returns true if this deque contains no elements.

Overrides:

isEmpty in class AbstractCollection

Returns:

true if this deque contains no elements

iterator

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 {@link #remove} or popped (via successive calls to {@link #pop}).

Overrides:

iterator in class AbstractCollection

Returns:

an iterator over the elements in this deque

offer

public boolean offer(Object e)

Inserts the specified element at the end of this deque.

This method is equivalent to {@link #offerLast}.

Parameters:

e - the element to add

Returns:

true (as specified by {@link Queue#offer})

offerFirst

public boolean offerFirst(Object e)

Inserts the specified element at the front of this deque.

Parameters:

e - the element to add

Returns:

true (as specified by {@link Deque#offerFirst})

offerLast

public boolean offerLast(Object e)

Inserts the specified element at the end of this deque.

Parameters:

e - the element to add

Returns:

true (as specified by {@link Deque#offerLast})

peek

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 {@link #peekFirst}.

Returns:

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

peekFirst

public Object peekFirst()

peekLast

public Object peekLast()

poll

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 {@link #pollFirst}.

Returns:

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

pollFirst

public Object pollFirst()

pollLast

public Object pollLast()

pop

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 {@link #removeFirst()}.

Returns:

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

push

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 {@link #addFirst}.

Parameters:

e - the element to push

remove

public Object remove()

Retrieves and removes the head of the queue represented by this deque. This method differs from {@link #poll poll} only in that it throws an exception if this deque is empty.

This method is equivalent to {@link #removeFirst}.

Returns:

the head of the queue represented by this deque

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 {@link #removeFirstOccurrence}.

Overrides:

remove in class AbstractCollection

Parameters:

o - element to be removed from this deque, if present

Returns:

true if this deque contained the specified element

removeFirst

public Object removeFirst()

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).

Parameters:

o - element to be removed from this deque, if present

Returns:

true if the deque contained the specified element

removeLast

public Object removeLast()

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).

Parameters:

o - element to be removed from this deque, if present

Returns:

true if the deque contained the specified element

size

public int size()

Returns the number of elements in this deque.

Overrides:

size in class AbstractCollection

Returns:

the number of elements in this deque

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.

Overrides:

toArray in class AbstractCollection

Returns:

an array containing all of the elements in this deque

toArray

public 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. 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 {@link #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().

Overrides:

toArray in class AbstractCollection

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