What is the bug in this Java program?

The compiler is not executing the catch part when no value is entered:

import java.util.Scanner;
import java.lang.*;

public class Ruff {

    public static void main(String[] args) 
    {
        String a;

        Scanner scanf=new Scanner(System.in);

        System.out.println("Enter your name!!");
        a=scanf.nextLine();

        try
        {
            if(a.toLowerCase().equals("Harsh"))
            {
                System.out.print("Good Name");
            }
            else
            {
                System.out.print("Ok!");
            }  
        }
        catch(Exception e)
        {
            System.out.print("Name Required");
        }
    }
}

The only possible exception for a in the code is a NullpointerException, but a is the empty string not a null pointer If the user enters no value. You should check for that value instead of using exceptions:

if(a.equals("")) {
    System.out.print("Name Required");
}
else {
    // code of try block here ...
}