The pollFirst() method of java.util.concurrent.ConcurrentSkipListSet is an in-built function in Java which returns retrieves and removes the first (lowest) element, or returns null if this set is empty.
Syntax:
public E pollFirst()
Return Value: The function returns retrieves and removes the first (lowest) element, or returns null if this set is empty.
Below programs illustrate the ConcurrentSkipListSet.pollFirst() method:
Program 1:
// Java program to demonstrate pollFirst()// method of ConcurrentSkipListSet  import java.util.concurrent.*;  class ConcurrentSkipListSetpollFirstExample1 {    public static void main(String[] args)    {        // Creating a set object        ConcurrentSkipListSet<Integer> Lset = new ConcurrentSkipListSet<Integer>();          // Adding elements to this set        for (int i = 10; i <= 50; i += 10)            Lset.add(i);          // Printing the content of the set        System.out.println("Contents of the set: " + Lset);          // Retrieving and removing first element of the set        System.out.println("The first element of the set: " + Lset.pollFirst());          // Printing the content of the set after pollFirst()        System.out.println("Contents of the set after pollFirst: " + Lset);    }} |
Output:
Contents of the set: [10, 20, 30, 40, 50] The first element of the set: 10 Contents of the set after pollFirst: [20, 30, 40, 50]
Program 2:
// Java program to demonstrate pollFirst()// method of ConcurrentSkipListSet  import java.util.concurrent.*;  class ConcurrentSkipListSetpollFirstExample2 {    public static void main(String[] args)    {        // Creating a set object        ConcurrentSkipListSet<Integer> Lset = new ConcurrentSkipListSet<Integer>();          // Printing the content of the set        System.out.println("Contents of the set: " + Lset);          // Retrieving and removing first element of the set        System.out.println("The first element of the set: " + Lset.pollFirst());    }} |
Output:
Contents of the set: [] The first element of the set: null
