LinkedTransferQueue poll() method in Java

The java.util.concurrent.LinkedTransferQueue.poll() method is an in-built function in Java which retrieves and remove the head of the queue if the queue is non-empty.

Syntax:

LinkedTransferQueue.poll()  

Parameters: The function does not accept any parameter.

Return Value: The function returns the head of the queue if the queue is non-empty, otherwise it returns null.

Below programs illustrate the LinkedTransferQueue.poll() method:

Program 1:

/* Java Program Demonstrate poll()
   method of LinkedTransferQueue */

import java.util.concurrent.LinkedTransferQueue;

class LinkedTransferQueuePollExample1 {
    public static void main(String[] args)
    {
        // Initializing the queue
        LinkedTransferQueue<Character> queue =
                       new LinkedTransferQueue<Character>();

        // Adding elements to this queue
        for (char ch = 'A'; ch <= 'Z'; ch++) {
            queue.add(ch);
        }

        // Printing the head of the queue
        System.out.println("The head of the queue is "
                                           + queue.poll());

        // Printing remaining elements of the queue
        System.out.println("The elements in the queue :");
        for (Character i : queue)
            System.out.print(i + " ");
    }
}

Output:

The head of the queue is A
The elements in the queue :
B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Program 2:

/* Java Program Demonstrate poll()
   method of LinkedTransferQueue */

import java.util.concurrent.LinkedTransferQueue;

class LinkedTransferQueuePollExample2 {
    public static void main(String[] args)
    {
        // Initializing the queue
        LinkedTransferQueue<Integer> queue =
                     new LinkedTransferQueue<Integer>();

        // Adding elements to this queue
        for (int i = 10; i <= 50; i += 10)
            queue.add(i);

        // Printing the head of the queue
        System.out.println("The head of the queue is "
                                           + queue.poll());

        // Printing remaining elements of the queue
        System.out.println("The elements in the queue :");
        for (Integer i : queue)
            System.out.print(i + " ");
    }
}

Output:

The head of the queue is 10
The elements in the queue :
20 30 40 50

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedTransferQueue.html#poll()