HackerRank Valid Username Regular Expression solution in java

In this HackerRan Valid Username Regular Expression problem in the java programming language 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].

Update the value of regularExpression field in the UsernameValidator class so that the regular expression only matches with valid usernames.

HackerRank Valid Username Regular Expression problem solution in java.

import java.util.Scanner;
class UsernameValidator {
    /*
     * Write regular expression here.
     */
     public static final String regularExpression =
 "^[a-zA-Z][a-zA-Z0-9_]{7,29}$";
}


public class Solution {
    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");
            }           
        }
    }
}

Second solution

import java.util.Scanner;
class UsernameValidator {
    /*
     * Write regular expression here.
     */
    public static final String regularExpression = "^[A-Za-z_][A-Za-z0-9_]{7,29}$";
}


public class Solution {
    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");
            }           
        }
    }
}