ConcurrentLinkedDeque pollFirst() method in Java

The java.util.concurrent.ConcurrentLinkedDeque.pollFirst() is an in-built method in Java which retrieves the first element of this deque and removes it. If the deque is empty, the method returns NULL.

Syntax:

Conn_Linked_Deque.pollFirst()

Parameters: This function does not accepts any parameter.

Return Values: The function returns the first element of this deque. If this deque is empty, the function returns NULL.

Below program illustrates the use of pollFirst() method:

Program 1: This program involves deque with Integer elements.

// Java Program Demonstrate pollFirst()
// method of ConcurrentLinkedDeque

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<Integer> cld =
                    new ConcurrentLinkedDeque<Integer>();

        cld.addFirst(12);
        cld.addFirst(70);
        cld.addFirst(1009);
        cld.addFirst(475);

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

        // Display and remove the first element
        System.out.println("Element removed : "
                           + cld.pollFirst());

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

Output:

Elements inthe LinkedDeque: [475, 1009, 70, 12]
Element removed : 475
Elements inthe LinkedDeque: [1009, 70, 12]

Program 2: This program involves deque with String elements.

// Java Program Demonstrate pollFirst()
// method of ConcurrentLinkedDeque

import java.util.concurrent.*;

class ConcurrentLinkedDequeDemo {
    public static void main(String[] args)
    {
        ConcurrentLinkedDeque<String> cld =
                        new ConcurrentLinkedDeque<String>();

        cld.addFirst("GFG");
        cld.addFirst("Geeks");
        cld.addFirst("Gfg");
        cld.addFirst("Geeks");

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

        // Display and remove the First element
        System.out.println("Element removed : "
                           + cld.pollFirst());

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

Output:

Elements inthe LinkedDeque: [Geeks, Gfg, Geeks, GFG]
Element removed : Geeks
Elements inthe LinkedDeque: [Gfg, Geeks, GFG]

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