Java Collection Framework – The ArrayDeque Class

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The ArrayDeque class in Java is introduced from JDK 1.6. It is an implementation of Deque Interface which allows insertion of elements at both the ends. It does not have any restrictions on capacity. It expands automatically as we add more elements. The ArrayDeque class extends AbstractCollection class and implements Deque interface. It also implements Cloneable and Serializable marker interfaces.

Below is the hierarchy diagram of ArrayDeque class.

Properties Of ArrayDeque Class :

• ArrayDeque is a resizable-array implementation of Deque interface like ArrayList class which is a resizable-array implementation of List interface. But, ArrayDeque is not a List.

• ArrayDeque does not have any capacity limit. It will grow automatically as we add elements.

• Default initial capacity of ArrayDeque is 16. It will increase at a power of 2 (24, 25, 26 and so on) when size exceeds capacity.

• ArrayDeque can be used as a stack (LIFO) as well as a queue (FIFO). ArrayDeque is faster than the Stack class when used as a stack and faster than the LinkedList class when used as a queue.

• Performance of ArrayDeque is sometimes considered as the best among the collection framework. It gives performance of O(1) for insertion, removal and retrieval operations. ArrayDeque class is recommended instead of Stack class (when you want stack data structure) and instead of LinkedList class (when you want queue data structure).

• You can’t perform indexed operations on ArrayDeque. ArrayDeque doesn’t have the methods to support those operations.

• ArrayDeque is not a thread safe.

Examples Of ArrayDeque class :

1) ArrayDeque As Queue

public class ArrayDequeExample
{
	public static void main(String[] args)
	{
		//Creating an array deque

		ArrayDeque<String> arrayDeque = new ArrayDeque<String>();

		//Adding elements at the tail of arrayDeque

		arrayDeque.offer("One");

		arrayDeque.offer("Two");

		arrayDeque.offer("Three");

		arrayDeque.offer("Four");

		arrayDeque.offer("Five");

		//Printing the elements of arrayDeque

		System.out.println(arrayDeque);     //Output : [One, Two, Three, Four, Five]

		//Removing the elements from the head of arrayDeque

		System.out.println(arrayDeque.poll());    //Output : One

		System.out.println(arrayDeque.poll());    //Output : Two
	}
}

2) ArrayDeque As Stack

public class ArrayDequeExample
{
	public static void main(String[] args)
	{
		//Creating an array deque

		ArrayDeque<String> arrayDeque = new ArrayDeque<String>();

		//pushing elements into arrayDeque

		arrayDeque.push("One");

		arrayDeque.push("Two");

		arrayDeque.push("Three");

		arrayDeque.push("Four");

		arrayDeque.push("Five");

		//Printing the elements of arrayDeque

		System.out.println(arrayDeque);     //Output : [Five, Four, Three, Two, One]

		//popping up the elements from arrayDeque

		System.out.println(arrayDeque.pop());    //Output : Five

		System.out.println(arrayDeque.pop());    //Output : Four
	}
}

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