ConcurrentLinkedDeque offerFirst() method in Java

The java.util.concurrent.ConcurrentLinkedDeque.offerFirst() method is an inbuilt method in Java which inserts the specified element, passed as a parameter, in the front of the deque.

Syntax:

Conn_Linked_Deque.offerFirst(Object elem)

Parameters: The method accepts a parameter elem which species the element to be inserted to the front of the deque.

Return Value: The function returns True if the element is successfully added into the deque and returns False otherwise.

Exception: The function throws a NullPointerException if the passed parameter is NULL.

Below programs illustrate the ConcurrentLinkedDeque.offerFirst() method:

Program 1:

/* Java Program to Demonstrate offerFirst()
   method of ConcurrentLinkedDeque */

import java.util.concurrent.*;
class GFG {
    public static void main(String[] args)
    {

        // Creating an empty Deque
        ConcurrentLinkedDeque<String> cld =
                     new ConcurrentLinkedDeque<String>();

        // Add elements into the Deque
        cld.add("Welcome");
        cld.add("To");
        cld.add("Geeks");
        cld.add("4");
        cld.add("Geeks");

        // Displaying the Deque
        System.out.println("Elements in Deque: "
                           + cld);

        // Displaying the First element
        System.out.println("The First element is: " +
                                       cld.getFirst());

        /* Insert an element at the front
            of the deque */
        if (cld.offerFirst("GFG")) {
            // Displaying the First element
            System.out.println("The Inserted element is: " +
                                             cld.getFirst());
        }

        // Displaying the Deque
        System.out.println("Elements in Deque: "
                           + cld);

        // Displaying the First element
        System.out.println("The First element is: " +
                                      cld.getFirst());
    }
}

Output:

Elements in Deque: [Welcome, To, Geeks, 4, Geeks]
The First element is: Welcome
The Inserted element is: GFG
Elements in Deque: [GFG, Welcome, To, Geeks, 4, Geeks]
The First element is: GFG

Program 2:

/* Java Program to Demonstrate offerFirst()
   method of ConcurrentLinkedDeque */

import java.util.concurrent.*;
class GFG {
    public static void main(String[] args)
    {

        // Creating an empty Deque
        ConcurrentLinkedDeque<Integer> cld =
                   new ConcurrentLinkedDeque<Integer>();

        // Add elements into the Deque
        cld.add(12);
        cld.add(43);
        cld.add(29);
        cld.add(16);
        cld.add(70);

        // Displaying the Deque
        System.out.println("Elements in Deque: "
                           + cld);

        // Displaying the First element
        System.out.println("The First element is: " +
                                     cld.getFirst());

        try {
            cld.offerFirst(null);
        }
        catch (Exception e) {
            System.out.println(e);
        }

        /* Insert an element at the front
            of the deque */
        if (cld.offerFirst(74)) {
            // Displaying the First element
            System.out.println("The Inserted element is: " +
                                            cld.getFirst());
        }

        // Displaying the Deque
        System.out.println("Elements in Deque: "
                           + cld);

        // Displaying the First element
        System.out.println("The First element is: " +
                                      cld.getFirst());
    }
}

Output:

Elements in Deque: [12, 43, 29, 16, 70]
The First element is: 12
java.lang.NullPointerException
The Inserted element is: 74
Elements in Deque: [74, 12, 43, 29, 16, 70]
The First element is: 74

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentLinkedDeque.html#offerFirst()