BlockingDeque pollFirst() method in Java with examples

The pollFirst() method of BlockingDeque returns the front element in the Deque container, and deletes it. It returns null if the container is empty.

Syntax:

public E pollFirst()

Parameters: This method does not accept any parameters.

Returns: This method returns front element in the Deque container if the container is not empty and deletes the element. It returns null if the container is empty.

Note: The pollFirst() method of BlockingDeque has been inherited from the LinkedBlockingDeque class in Java.

Below programs illustrate pollFirst() method of BlockingDeque:

Program 1:

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

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // create object of BlockingDeque
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of BlockingDeque
        BD.addFirst(7855642);
        BD.addFirst(35658786);
        BD.addFirst(5278367);
        BD.addFirst(74381793);

        // Print the queue
        System.out.println("Blocking Deque: " + BD);

        // prints and deletes
        System.out.println("Front element in Deque: " + BD.pollFirst());

        // Deque after deletion of front element
        System.out.println("Blocking Deque: " + BD);
    }
}

Output:

Blocking Deque: [74381793, 5278367, 35658786, 7855642]
Front element in Deque: 74381793
Blocking Deque: [5278367, 35658786, 7855642]

Program 2:

// Java Program Demonstrate pollFirst()
// method of BlockingDeque
// when Deque is empty

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)

    {

        // create object of LinkedBlockingDeque
        LinkedBlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of BlockingDeque
        BD.add(7855642);
        BD.add(35658786);
        BD.add(5278367);
        BD.add(74381793);

        // Print the queue
        System.out.println("Blocking Deque: " + BD);

        // empty deque
        BD.clear();

        System.out.println("Front element in Deque: " + BD.pollFirst());
    }
}

Output:

Blocking Deque: [7855642, 35658786, 5278367, 74381793]
Front element in Deque: null

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingDeque.html#pollFirst(long, %20java.util.concurrent.TimeUnit)