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The first() method of java.util.concurrent.ConcurrentSkipListSet is an in-built function in Java which returns the first (lowest) element currently in this set. Syntax:

ConcurrentSkipListSet.first()

Return Value: The function returns the first (lowest) element currently in this set. Exception: The function throws NoSuchElementException if this set is empty. Below programs illustrate the ConcurrentSkipListSet.first() method: Program 1:

Java

// Java Program Demonstrate first()
// method of ConcurrentSkipListSet

import java.util.concurrent.ConcurrentSkipListSet;

class ConcurrentSkipListSetFirstExample1 {
    public static void main(String[] args)
    {

        // Initializing the set
        ConcurrentSkipListSet<Integer>
            set = new ConcurrentSkipListSet<Integer>();

        // Adding elements to first set
        set.add(10);
        set.add(35);
        set.add(20);
        set.add(25);

        System.out.println("The lowest element in the set: "
                                              + set.first());
    }
}

Output:

The lowest element in the set: 10

Program 2: Program to show NoSuchElementException in first().

Java

// Java Program Demonstrate first()
// method of ConcurrentSkipListSet

import java.util.concurrent.ConcurrentSkipListSet;

class ConcurrentSkipListSetFirstExample2 {
    public static void main(String[] args) throws InterruptedException
    {

        // Initializing the set
        ConcurrentSkipListSet<Integer>
            set = new ConcurrentSkipListSet<Integer>();
        try {
            System.out.println("The lowest element in the set: " +
                                                       set.first());
        }
        catch (Exception e) {
            System.out.println("Exception :" + e);
        }
    }
}

Output:

Exception :java.util.NoSuchElementException

Reference: https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ConcurrentSkipListSet.html#first--

ConcurrentSkipListSet first() method in Java

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