ConcurrentSkipListSet pollFirst() method in Java

Last Updated : 21 Sep, 2018
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 
// 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 
// 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
Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#pollFirst--
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