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 code to demonstrate the working// of poll() in linked listimport 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 code to demonstrate the working// of pollFirst() in linked listimport 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 code to demonstrate the working// of pollLast() in linked listimport 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 code to demonstrate the practical// application of poll() in linked listimport 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 <--
This article is contributed by Astha Tyagi. If you like Lazyroar and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the Lazyroar main page and help other Geeks.
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