HackerRank_UsernameRegEx.java

/*
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

*/
import java.util.Scanner;
class UsernameValidator {
    public static final String regularExpression = "[A-Za-z][A-Za-z0-9_]{7,29}";
}


public class HackerRank_UsernameRegEx {
    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");
            }           
        }
    }
}