why is there a compalation error to my solution? do you have it too?

class UsernameValidator { Scanner scan = new Scanner (System.in);

for(int i=0;i<scan.nextInt();i++){
    String s=scan.nextLine();
    if(s.length()<8 || s.length()>30)
        System.out.println("Invalid");
    else{
        if(s.matches("^[a-zA-Z_]+$"))
            System.out.println("Valid");
        else
            System.out.println("Invalid");

    }
}