Queue poll() method in Java

The poll() method of Queue Interface returns and removes the element at the front end of the container. It deletes the element in the container. 

The method does not throws an exception when the Queue is empty, it returns null instead.

Syntax: E poll();

Below program illustrate poll() method of Queue:

package com.practice;

import java.util.LinkedList;
import java.util.Queue;

public class QueuePollMethod {

    public static void main(String[] args)
            throws IllegalStateException
    {

        // create object of Queue
        Queue<Integer> queue = new LinkedList<Integer>();

        // Add numbers to end of Queue
        queue.add(123);
        queue.add(456);
        queue.add(789);

        // print queue
        System.out.println("Queue: " + queue);

        // print head and deletes the head
        System.out.println("Queue's head: " + queue.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + queue.poll());

        // print head and deleted the head
        System.out.println("Queue's head: " + queue.poll());

        // print head and deleted the head. Queue is enpty now hence it returns null
        System.out.println("Queue's head: " + queue.poll());
    }
}

Output:

Explanation:

Queue has "123", "456", "789"

First queue.poll() returns - 123

Now queue has "456", "789"

Second queue.poll() returns - 456

Now queue has  "789"

Third queue.poll() returns - 789

Queue is empty now

Fourth queue.poll() returns - null ( as queue is empty). It will not throw any exception.

Happy Coding!