02. Sum Digits

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int number = Integer.parseInt(scanner.nextLine()),
            sumDigits = 0;

        while (number > 0) {
            sumDigits += number % 10;
            number /= 10;
        }

        System.out.println(sumDigits);
    }
}

OR:

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String number = scanner.nextLine();
        int sumDigits = 0;

        for (int i = 0; i < number.length(); i++) {
            sumDigits += Character.getNumericValue(number.charAt(i));
        }

        System.out.println(sumDigits);
    }
}