Java.util.LinkedList.poll(), pollFirst(), pollLast() with examples in Java
Last Updated :
10 Dec, 2018
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.
import java.util.*;
public class LinkedListPollLast {
public static void main(String[] args)
{
LinkedList list = new LinkedList();
list.add("Geeks");
list.add(4);
list.add("Geeks");
list.add(8);
System.out.println("The initial Linked List is : " + list);
System.out.println("Tail element of the list is : " + list.pollLast());
System.out.println("Linked List after removal using pollLast() : " + 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
import java.util.*;
public class LinkedListPollApp {
public static void main(String[] args)
{
LinkedList list = new LinkedList();
list.add("Astha");
list.add("Shambhavi");
list.add("Nikhil");
list.add("Manjeet");
System.out.println("The initial queue is : " + list);
System.out.print("The order of exit is : ");
while (!list.isEmpty()) {
System.out.print(list.poll() + " <-- ");
}
}
}
|
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.
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.
import java.util.*;
public class LinkedListPollApp {
public static void main(String[] args)
{
LinkedList list = new LinkedList();
list.add("Astha");
list.add("Shambhavi");
list.add("Nikhil");
list.add("Manjeet");
System.out.println("The initial queue is : " + list);
System.out.print("The order of exit is : ");
while (!list.isEmpty()) {
System.out.print(list.poll() + " <-- ");
}
}
}
|
Output :
The initial queue is : [Astha, Shambhavi, Nikhil, Manjeet]
The order of exit is : Astha <-- Shambhavi <-- Nikhil <-- Manjeet <--
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