The pollFirst() method of LinkedBlockingDeque 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.
Below programs illustrate pollFirst() method of LinkedBlockingDeque:
Program 1:
// Java Program Demonstrate pollFirst()// method of LinkedBlockingDeque  import java.util.concurrent.LinkedBlockingDeque;import java.util.*;  public class GFG {    public static void main(String[] args)      {          // create object of LinkedBlockingDeque        LinkedBlockingDeque<Integer> LBD            = new LinkedBlockingDeque<Integer>();          // Add numbers to end of LinkedBlockingDeque        LBD.addFirst(7855642);        LBD.addFirst(35658786);        LBD.addFirst(5278367);        LBD.addFirst(74381793);          // Print the queue        System.out.println("Linked Blocking Deque: " + LBD);          // prints and deletes        System.out.println("Front element in Deque: " + LBD.pollFirst());          // Deque after deletion of front element        System.out.println("Linked Blocking Deque: " + LBD);    }} |
Output:
Linked Blocking Deque: [74381793, 5278367, 35658786, 7855642] Front element in Deque: 74381793 Linked Blocking Deque: [5278367, 35658786, 7855642]
Program 2:
// Java Program Demonstrate pollFirst()// method of LinkedBlockingDeque// when Deque is empty  import java.util.concurrent.LinkedBlockingDeque;import java.util.*;  public class GFG {    public static void main(String[] args)      {          // create object of LinkedBlockingDeque        LinkedBlockingDeque<Integer> LBD            = new LinkedBlockingDeque<Integer>();          // Add numbers to end of LinkedBlockingDeque        LBD.add(7855642);        LBD.add(35658786);        LBD.add(5278367);        LBD.add(74381793);          // Print the queue        System.out.println("Linked Blocking Deque: " + LBD);          // empty deque        LBD.clear();          System.out.println("Front element in Deque: " + LBD.pollFirst());    }} |
Output:
Linked Blocking Deque: [7855642, 35658786, 5278367, 74381793] Front element in Deque: null
Reference: https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingDeque.html#pollFirst()
