ArrayDeque addFirst() Method in Java

The java.util.ArrayDeque.addFirst(Object element) method in Java is used to insert a specific element at the front of this deque.

Syntax:

Array_Deque.addFirst(Object element)

Parameters: The parameter element is of the type ArrayDeque and refers to the element to be added.

Return Value: The function does not return any value.

Exceptions: The method throws NullPointerException if the passed parameter is NULL.

Below programs illustrate the Java.util.ArrayDeque.addFirst() method:
Program 1:

// Java code to illustrate addFirst()
import java.util.*;

public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        Deque<Integer> de_que = new ArrayDeque<Integer>();

        // Use add() method to add elements into the Deque
        de_que.add(10);
        de_que.add(15);
        de_que.add(30);
        de_que.add(20);
        de_que.add(5);

        // Displaying the ArrayDeque
        System.out.println("ArrayDeque: " + de_que);

        // Adding elements at front
        de_que.addFirst(40);
        de_que.addFirst(50);
        de_que.addFirst(60);
        de_que.addFirst(70);

        // Displaying the ArrayDeque
        System.out.println("ArrayDeque_front_addition: " + de_que);

        // Adding elements using add()
        de_que.add(1);
        de_que.add(2);
        de_que.add(3);

        // Displaying the final ArrayDeque
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

Output:

ArrayDeque: [10, 15, 30, 20, 5]
ArrayDeque_front_addition: [70, 60, 50, 40, 10, 15, 30, 20, 5]
Final ArrayDeque: [70, 60, 50, 40, 10, 15, 30, 20, 5, 1, 2, 3]

Program 2:

// Java code to illustrate addFirst()
import java.util.*;

public class ArrayDequeDemo {
    public static void main(String args[])
    {
        // Creating an empty ArrayDeque
        Deque<String> de_que = new ArrayDeque<String>();

        // Use add() method to add elements into the Deque
        de_que.add("Welcome");
        de_que.add("To");
        de_que.add("Geeks");
        de_que.add("4");
        de_que.add("Geeks");

        // Displaying the ArrayDeque
        System.out.println("ArrayDeque: " + de_que);

        // Adding elements at front
        de_que.addFirst("GFG");
        de_que.addFirst("World");
        de_que.addFirst("Hello");

        // Displaying the ArrayDeque
        System.out.println("ArrayDeque_front_addition: " + de_que);

        // Adding elements using add()
        de_que.add("Coding");
        de_que.add("At");
        de_que.add("BEST");

        // Displaying the final ArrayDeque
        System.out.println("Final ArrayDeque: " + de_que);
    }
}

Output:

ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
ArrayDeque_front_addition: [Hello, World, GFG, Welcome, To, Geeks, 4, Geeks]
Final ArrayDeque: [Hello, World, GFG, Welcome, To, Geeks, 4, Geeks, Coding, At, BEST]