Sum of digits of a number in Java public class Main { public static void main(String[] args) { int number = -123456; if(number < 0) number = -number; int sum = 0; while (number > 0) { sum += number % 10; number /= 10; } System.out.println(sum); } } Time Complexity: O(log₁₀N) ; N is the number. Space Complexity: O(1).