Valid Username Regular Expression If You want Explanation Watch the video: 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 Code: 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" ); }