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
