Valid username checker

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  to  characters inclusive. If the username consists of less than  or greater than  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 , uppercase characters , and digits .
• The first character of the username must be an alphabetic character, i.e., either lowercase character  or uppercase character .

For example:

Username	Validity
	INVALID; Username length < 8 characters
	VALID
	VALID
	INVALID; Username begins with non-alphabetic character
	INVALID; '?' character not allowed

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

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Input Format

The first line of input contains an integer , describing the total number of usernames. Each of the next  lines contains a string describing the username. The locked stub code reads the inputs and validates the username.

Constraints

• The username consists of any printable characters.

Output Format

For each of the usernames, the locked stub code prints Valid if the username is valid; otherwise Invalid each on a new line.

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

Explanation 0

Refer diagram in the challenge statement.

Program:

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");

            }           

        }

    }

}

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