TreeSet first() in Java

first(): This method is available in java.util.TreeSet class of Java.

Syntax:

String java.util.TreeSet.first()

This method returns the first (lowest) element currently in this set.

Parameters: NA

Returns: the first (lowest) element currently in this set.

Throws:

NoSuchElementException - if this set is empty

Approach 1: When no exception

Java

import java.util.TreeSet;

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

        TreeSet<String> treeSet = new TreeSet<String>();

        treeSet.add("Hello");
        treeSet.add("Java");
        treeSet.add("Program");
        treeSet.add("C++");

        System.out.println(treeSet.first());

    }
}

Output:

C++

Approach 2: NoSuchElementException 

Java

import java.util.TreeSet;

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

        TreeSet<String> treeSet = new TreeSet<String>();

        System.out.println(treeSet.first());

    }
}

Output:

Exception in thread "main" java.util.NoSuchElementException
	at java.base/java.util.TreeMap.key(TreeMap.java:1596)
	at java.base/java.util.TreeMap.firstKey(TreeMap.java:291)
	at java.base/java.util.TreeSet.first(TreeSet.java:392)