ArrayDeque in Java

• ArrayDeque = Resizable array + Deque interface.
• ArrayDeque implements the Queue & Deque interface.
• There are no capacity restrictions for ArrayDeque, and it provides us the facility to add or remove any element from both sides of the queue.
• Also known as Array Double Ended Queue.
• It is faster than Linked list and stack.

Constructors of ArrayDeque class :

1. ArrayDeque(): Used to create an empty array deque that has the capacity to hold 16 elements.
2. ArrayDeque(int numElements): Used to create an empty array deque that has the capacity to hold the specified number of elements.
3. ArrayDeque(Collection<? extends E> c): Used to create an array deque containing all the elements of the specified collections.

Performing Various Operation On ArrayDeque() :

1. Inserting an element :

   • Insertion at front : add(), offerFirst() and addFirst() methods are used to insert an element at front of an array deque.

     Example :

     import java.util.*;
     public class CWH extends Thread{
         public static void main(String[] args) {
     
             ArrayDeque<Integer> ad1 = new ArrayDeque<>();
             ad1.add(6);
             ad1.add(56);
             ad1.add(9);
             ad1.addFirst(5);
             ad1.offerFirst(10);
             System.out.println(ad1);
     
         }
     }
     

Output :

[10, 5, 6, 56, 9]

Insertion At End: addLast() and offerLast() methods are used to insert an element at the end of the array deque.

Example :

import java.util.*;
public class CWH extends Thread{
    public static void main(String[] args) {

        ArrayDeque<Integer> ad1 = new ArrayDeque<>();
        ad1.add(6);
        ad1.add(56);
        ad1.add(9);
        ad1.addLast(5);
        ad1.offerLast(10);
        
        System.out.println(ad1);

    }
}

Output :

[6, 56, 9, 5, 10]

Accessing an element :

• Accessing an element from the head of the deque array: getFirst() & peekFirst() methods are used to get the first element of the deque array.

  Example :

  import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          ArrayDeque<Integer> ad1 = new ArrayDeque<>();
          ad1.add(6);
          ad1.add(56);
          ad1.add(9);
          ad1.add(10);
          ad1.add(91);
          ad1.add(19);
  
          System.out.println(ad1.getFirst());
          System.out.println(ad1.peekFirst());
  
      }
  }
  

Output :

6
6

Accessing the last element: getLast() or peekLast() methods are used to print the last element of the deque array.

Example :

import java.util.*;
public class CWH extends Thread{
    public static void main(String[] args) {

        ArrayDeque<Integer> ad1 = new ArrayDeque<>();
        ad1.add(6);
        ad1.add(56);
        ad1.add(9);
        ad1.add(10);
        ad1.add(91);
        ad1.add(19);

        System.out.println(ad1.getLast());
        System.out.println(ad1.peekLast());

    }
}

Output :

19
19

Removing an element :

• Removing the first element: removeFirst() & pollFirst() methods are used to delete an element from the head of the queue.
• removeFirst() throws an exception if the queue is empty.
• pollFirst() returns null if the queue is empty.

  Example :

  import java.util.*;
  public class CWH extends Thread{
      public static void main(String[] args) {
  
          ArrayDeque<Integer> ad1 = new ArrayDeque<>();
          ad1.add(6);
          ad1.add(56);
          ad1.add(9);
          ad1.add(10);
          ad1.add(91);
          ad1.add(19);
  
          ad1.pollFirst(); //deletes 6
          ad1.removeFirst(); //deletes 56
  
          System.out.println(ad1);
  
      }
  }
  

Output :

[9, 10, 91, 19]

Removing the last element: removeLast() & pollLast() methods are used to delete an element from the tail of the queue.

Example :

import java.util.*;
public class CWH extends Thread{
    public static void main(String[] args) {

        ArrayDeque<Integer> ad1 = new ArrayDeque<>();
        ad1.add(6);
        ad1.add(56);
        ad1.add(9);
        ad1.add(10);
        ad1.add(91);
        ad1.add(19);

        ad1.pollLast(); //deletes 19
        ad1.removeLast(); //deletes 91

        System.out.println(ad1);

    }
}

Output :

[6, 56, 9, 10]

Code as described/written in the video :

package com.company;

import java.util.ArrayDeque;

public class cwh_93_arraydeque {
    public static void main(String[] args) {
        ArrayDeque<Integer> ad1 = new ArrayDeque<>();
        ad1.add(6);
        ad1.add(56);
        ad1.add(9);
        ad1.addFirst(5);
        System.out.println(ad1.getFirst());
        System.out.println(ad1.getLast());
    }
}

Code as described/written in the video :

package com.company;

import java.util.ArrayDeque;

public class cwh_93_arraydeque {
    public static void main(String[] args) {
        ArrayDeque<Integer> ad1 = new ArrayDeque<>();
        ad1.add(6);
        ad1.add(56);
        ad1.add(9);
        ad1.addFirst(5);
        System.out.println(ad1.getFirst());
        System.out.println(ad1.getLast());
    }
}