I am writing a method to determine if a number is Armstrong for boot camp homework, and I am not allowed to use the Math class. Why is this not working?

public static boolean isArmstrong(int n){

        String strNum = "" + n;
        int pow = strNum.length();
        int sum = 1;
        
       for(int i = 0; i < strNum.length(); i++){
            int eachDigit = Integer.parseInt(strNum.substring(i , i + 1));
           for (int j = 0; j < pow; j++) {
               sum *= eachDigit;
           }
        }

        System.out.println(sum);
        return sum == n;
    }



 public static void main(String[] args) {
    System.out.println(isArmstrong(153));
}

prints:
3375
false