Valid Username Regular Expression Java

Problem Statement :

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  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 [a-z], uppercase characters [A-Z], and [0-9] digits .
 The first character of the username must be an alphabetic character, i.e., either lowercase character [a-z] or uppercase character [A-Z].
For example:

Username	               Validity
  Julia                               INVALID; Username length < 8 characters
  Samantha                     VALID
  Samantha_21               VALID
  1Samantha                   INVALID; Username begins with non-alphabetic character
  Samantha?10_2A        INVALID; '?' character not allowed

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

Input Format

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

Constraints

1<=n<=100
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.