ArrayDeque in Java

ArrayDeque is a resizable-array implementation of the Deque interface in Java. it allows elements to be added or removed from both ends efficiently and it not allow null element insertion .

• ArrayDeque grows dynamically.
• It generally provides faster operations than LinkedList as it is more cache friendly and does not require overhead of next previous reference management.
• Operations like addFirst(), addLast(), removeFirst(), removeLast() are done in O(1) amortized time.
• ArrayDeque is not Thread-Safe

Declaration of ArrayDeque

In Java, the declaration of ArrayDeque can be done as:

ArrayDeque<Type> deque = new ArrayDeque<>();

Here, "Type" is the type of the element the deque will hold (e.g. Integer, String).

First: 1, Last: 2

Hierarchy of ArrayDeque

It implements Queue and Deque interfaces and is a part of the Collection framework.

Constructors of ArrayDeque

1. ArrayDeque()

This constructor is used to create an empty ArrayDeque and by default holds an initial capacity to hold 16 elements.

ArrayDeque<Integer> deque = new ArrayDeque<>();

2. ArrayDeque(Collection<? extends E> c)

This constructor is used to create an ArrayDeque containing all the elements the same as that of the specified collection.

ArrayDeque<Integer> deque = new ArrayDeque<>(list);

3. ArrayDeque(int numofElements)

This constructor is used to create an empty ArrayDeque and holds the capacity to contain a specified number of elements.

ArrayDeque<String> deque = new ArrayDeque<>(25); // capacity = 25

Performing Various Operations on ArrayDeque

1. Adding Element

We can use methods like add(), addFirst(), addLast(), offer(), offerFirst(), offerLast() to insert element to the ArrayDeque.

ArrayDeque : [Welcome, To, The, Geeks, For, Geeks]

2. Accessing Elements

We can use methods like getFirst(), getLast(), peek(), peekFirst(), peekLast() to access elements of the ArrayDeque.

ArrayDeque: [Welcome, To, Geeks, for, Geeks]
The first element is: Welcome
The last element is: Geeks

3. Removing Elements

We can use various methods like remove(), removeFirst(), removeLast(), poll(), pollFirst(), pollLast(), pop() to remove elements from the ArrayDeque.

Initial Deque: [C++, Java, Python]
Removed element using pop(): C++
Removed element using poll(): Java
Removed element using pollFirst(): Python
Final Deque: []

4.Iterating Elements

We can use various methods like iterator(), descendingIterator() to iterate over the elements of ArrayDeque.

Iterating in ForwardOrder:
Geeks For Geeks is so good 
Iterating in ReverseOrder:
is so good Geeks For Geeks 

Methods in ArrayDeque class

Methods Declared in Interface java.util.Deque