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Java.util.LinkedList.poll(), pollFirst(), pollLast() with examples in Java

Last Updated : 10 Dec, 2018
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Java's Linked list class offers a function that allows a "Queue Based" working called poll(). This function not only returns deletes the first element, but also displays them while being deleted and hence can have a lot of usage in daily life problems and competitive programming as well. There are 3 variants of poll(), all three are discussed in this article. 1. poll() : This method retrieves and removes the head (first element) of this list. 
Declaration : 
   public E poll()
Return Value : 
      This method returns the first element of this list, or null if this list is empty.
Java 
// Java code to demonstrate the working
// of poll() in linked list
import java.util.*;
public class LinkedListPoll {

public static void main(String[] args)
    {

        // Declaring a LinkedList
        LinkedList list = new LinkedList();

        // adding  elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);

        // printing the list
        System.out.println("The initial Linked List is : " + list);

        // using poll() to retrieve and remove the head
        // removes and displays "Geeks"
        System.out.println("Head element of the list is : " + list.poll());

        // printing the resultant list
        System.out.println("Linked List after removal using poll() : " + list);
    }
}
Output : 
The initial Linked List is : [Geeks, 4, Geeks, 8]
Head element of the list is : Geeks
Linked List after removal using poll() : [4, Geeks, 8]

2. pollFirst() : This method retrieves and removes the first element of this list, or returns null if this list is empty. 
Declaration : 
  public E pollFirst()
Return Value : 
   This method returns the first element of this list, or null if this list is empty
Java 
// Java code to demonstrate the working
// of pollFirst() in linked list
import java.util.*;
public class LinkedListPollFirst {

public static void main(String[] args)
    {

        // Declaring a LinkedList
        LinkedList list = new LinkedList();

        // adding  elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);

        // printing the list
        System.out.println("The initial Linked List is : " + list);

        // using pollFirst() to retrieve and remove the head
        // removes and displays "Geeks"
        System.out.println("Head element of the list is : " + list.pollFirst());

        // printing the resultant list
        System.out.println("Linked List after removal using pollFirst() : " + list);
    }
}
Output : 
The initial Linked List is : [Geeks, 4, Geeks, 8]
Head element of the list is : Geeks
Linked List after removal using pollFirst() : [4, Geeks, 8]

3. pollLast() : This method retrieves and removes the last element of this list, or returns null if this list is empty. 
Declaration : 
  public E pollLast()
Return Value : 
   This method returns the last element of this list, or null if this list is empty.
Java 
// Java code to demonstrate the working
// of pollLast() in linked list
import java.util.*;
public class LinkedListPollLast {

public static void main(String[] args)
    {

        // Declaring a LinkedList
        LinkedList list = new LinkedList();

        // adding  elements
        list.add("Geeks");
        list.add(4);
        list.add("Geeks");
        list.add(8);

        // printing the list
        System.out.println("The initial Linked List is : " + list);

        // using pollLast() to retrieve and remove the tail
        // removes and displays 8
        System.out.println("Tail element of the list is : " + list.pollLast());

        // printing the resultant list
        System.out.println("Linked List after removal using pollLast() : " + list);
    }
}
Output : 
The initial Linked List is : [Geeks, 4, Geeks, 8]
Tail element of the list is : 8
Linked List after removal using pollLast() : [Geeks, 4, Geeks]

Practical Application : This function has potential usage in the "queue management" systems and also in "1st elimination" games that can be thought of. The former example is discussed below. Java 
// Java code to demonstrate the practical
// application of poll() in linked list
import java.util.*;
public class LinkedListPollApp {

public static void main(String[] args)
    {

        // Declaring a LinkedList
        LinkedList list = new LinkedList();

        // adding queue entry of people
        // in order
        list.add("Astha");
        list.add("Shambhavi");
        list.add("Nikhil");
        list.add("Manjeet");

        // printing the list
        System.out.println("The initial queue is : " + list);

        System.out.print("The order of exit is : ");

        while (!list.isEmpty()) {
            // using poll() to display the order of exit from queue
            System.out.print(list.poll() + " <-- ");
        }
    }
}
Output : 
The initial queue is : [Astha, Shambhavi, Nikhil, Manjeet]
The order of exit is : Astha <-- Shambhavi <-- Nikhil <-- Manjeet <--

A

Astha Tyagi
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