Valid Username Regular Expression

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    public static final String regularExpression = "^[a-zA-Z][\w]{7,29}$";

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        public static void main(String[] args) {
            Scanner scanner = new Scanner(System.in);
            int size = scanner.nextInt();
            scanner.nextLine();
            for (int i = 0; i < size; i++) {
                System.out.println(scanner.nextLine().matches("[a-zA-Z][a-zA-Z0-9_]{7,29}") ? "Valid" : "Invalid");
            }
            scanner.close();
        }
    
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    public static final String regularExpression = "[A-Za-z]\\w{7,29}";
    
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    public static final String regularExpression = "^[a-zA-Z][a-zA-Z0-9_]{7,29}$";

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    import java.io.; import java.util.;

    public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner input = new Scanner(System.in);
       int count = input.nextInt();
        input.nextLine();
    
        for(int i=0;i<count;i++){
        String username = input.nextLine();
    
    
        if(checkUsername(username)){
            System.out.println("Valid");
        }
        else{
            System.out.println("Invalid");
        }
        }
    
        input.close();
    
    }
    public static boolean checkUsername(String username){
        int length = username.length();
    
        if(length<8 || length>30){
            return false;
        }
        if(!Character.isLetter(username.charAt(0))){
            return false;
        }
    
        for(int i=1;i<length;i++){
           char ch = username.charAt(i);
           if(!Character.isLetterOrDigit(ch) && ch!='_'){
            return false;
           }
        }
        return true;
    }
    

    }