HackerRank: Valid Username Regular Expression

You are updating the username policy on your company's internal networking platform. According to the policy, a username is considered valid if all the following constraints are satisfied:

The username consists of 8 to 30 characters inclusive. If the username consists of less than 8 or greater than 30 characters, then it is an invalid username.

The username can only contain alphanumeric characters and underscores (_). 

Alphanumeric characters describe the character set consisting of lowercase characters [a-z], uppercase characters [A-Z], and digits [0-9].

The first character of the username must be an alphabetic character, i.e., either lowercase character [a-z] or uppercase character [A-Z].

Sample Input 0

8

Julia

Samantha

Samantha_21

1Samantha

Samantha?10_2A

JuliaZ007

Julia@007

_Julia007

Sample Output 0

Invalid

Valid

Valid

Invalid

Invalid

Valid

Invalid

Invalid

Java Code:

import java.util.Scanner;

class UsernameValidator

{

    public static final String regularExpression="^[A-Za-z][A-Za-z0-9_]{7,29}$";

}

public class validUsernameRegularExpression

{

    private static final Scanner scan = new Scanner(System.in);

    public static void main(String[] args) {

        int n = Integer.parseInt(scan.nextLine());

        while (n-- != 0) {

            String userName = scan.nextLine();

            if (userName.matches(UsernameValidator.regularExpression)) {

                System.out.println("Valid");

            } else {

                System.out.println("Invalid");

            }          

        }

    }

}