How to calculate time and space complexity of number

How to calculate time and space complexity of number
0
Hi All,
How to calculate time and space complexity of number.Below id the problem statement and also my solution

Problem Statement:
# Reverse a number using stack
Example :Input : 123 Output : 321

Code:
public class Solution {
 public static void main(String[] args) {
        int number = 39997;
        System.out.println(reverse_number(number));
    }
    static Stack<Integer> st = new Stack<>();
    static void push_digits(int number) {
         while (number != 0) {
            st.push(number % 10);
            number = number / 10;
        }
    }

    static int reverse_number(int number) {
        push_digits(number);
        int reverse = 0;
        int i = 1;
        while (!st.isEmpty()) {
            reverse = reverse + (st.peek() * i);
            st.pop();
            i = i * 10;
        }
        return reverse;
    }
}

Time Complexity : ?
Space Complexity: ?

Could anyone explain me how to calculate above mentioned terms.

Thanks

I think this link will help you: https://www.hackerearth.com/practice/basic-programming/complexity-analysis/time-and-space-complexity/tutorial/

thanks for reply @KittyKora