Recently this question to ask was one of my readers, which inspired me to write this tutorial. There was a usual check to solve this problem using both recursion and iteration. To be frank, calculating the sum of digits of an integral number is not difficult, but I have still seen quite a few programmers fumbles, even after providing hints in terms of division and modules operator. The key point here is to know how to use division and modulus operators in Java. This kind of exercise including reversing a number, where you need to find digits from a number, use division operator to remove right, and use modules operator or % to get rightmost digits.