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Java – LinkedList poll(), pollFirst() and pollLast() methods

By Chaitanya Singh | Filed Under: Java.util package

Description

Example Programs for poll(), pollFirst() and pollLast() methods of LinkedList class.

LinkedList.poll()

Retrieves and removes the head (first element) of this list.

import java.util.LinkedList;
class LinkedListPollMethod{

  public static void main(String[] args) {

     // Create a LinkedList of Strings
     LinkedList<String> list = new LinkedList<String>();

     // Add few Elements
     list.add("Element1");
     list.add("Element2");
     list.add("Element3");
     list.add("Element4");

     // Display LinkList elements
     System.out.println("LinkedList before: "+list);

     /* poll(): Retrieves and removes the head (first element)
      * of this list.
      */
     System.out.println("Element removed: "+list.poll());

     // Displaying list elements after poll() operation
     System.out.println("LinkedList after: "+list);
  }
}

Output:

LinkedList before: [Element1, Element2, Element3, Element4]
Element removed: Element1
LinkedList after: [Element2, Element3, Element4]

LinkedList.pollFirst()

public E pollFirst(): Retrieves and removes the first element of this list, or returns null if this list is empty.

import java.util.LinkedList;
class LinkedListPollFirstDemo{

  public static void main(String[] args) {

     // Create a LinkedList of Strings
     LinkedList<String> list = new LinkedList<String>();

     // Add few Elements
     list.add("Element1");
     list.add("Element2");
     list.add("Element3");
     list.add("Element4");

     // Display LinkList elements
     System.out.println("LinkedList before: "+list);

     /* pollFirst(): Retrieves and removes the first element 
      * of this list, or returns null if this list is empty.
      */
     System.out.println("Element removed: "+list.pollFirst());

     // Display list after calling pollFirst() method
     System.out.println("LinkedList after: "+list);
  }
}

Output:

LinkedList before: [Element1, Element2, Element3, Element4]
Element removed: Element1
LinkedList after: [Element2, Element3, Element4]

LinkedList.pollLast()

public E pollLast(): Retrieves and removes the last element of this list, or returns null if this list is empty.

import java.util.LinkedList;
class LinkedListPollLastDemo{

  public static void main(String[] args) {

     // Create a LinkedList of Strings
     LinkedList<String> list = new LinkedList<String>();

     // Add few Elements
     list.add("Element1");
     list.add("Element2");
     list.add("Element3");
     list.add("Element4");

     // Display LinkList elements
     System.out.println("LinkedList before: "+list);

     /* pollFirst(): Retrieves and removes the first element 
      * of this list, or returns null if this list is empty.
      */
     System.out.println("Element removed: "+list.pollLast());

     // Display after calling pollLast() method
     System.out.println("LinkedList after: "+list);
  }
}

Output:

LinkedList before: [Element1, Element2, Element3, Element4]
Element removed: Element4
LinkedList after: [Element1, Element2, Element3]

Comments

  1. Giulio Di Santo says

    February 25, 2016 at 11:21 AM

    What’s the difference between poll() and pollFirst()? Both retrieves and remove the first list’s element and both return null if list is empty.

    Thanks
    Giulio

    Reply
  2. mohamed althaf says

    April 5, 2018 at 5:45 AM

    what is the difference between removeFirst() and pollFirst() method?

    Reply
    • Chaitanya Singh says

      April 6, 2018 at 4:30 AM

      poll() : This method returns the head element of the list, or null if the list is empty

      pollFirst(): This method works same as poll() method.

      remove(): It returns the head element of the LinkedList, it throws NoSuchElementException if the list is empty

      pollLast(): This method returns the last element of the list, it returns null if the list is empty

      removeFirst(): This method works same as remove() method

      I hope this answers your question.

      Reply

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