A Java recursive program

First of all, I searched some interview questions to do, including one: enter an integer and find the sum of each number in the integer?

Thinking: 1 How to or get each digit: if it is 1234, 1234% 10 = 4, get a digit; (1234 / 10)% 10 = 3 gets ten bits, (1234 / 100)% 10 = 2 gets a hundred bits, (1234 / 1000)% 10 = 1 gets a thousand bits.

2. Since a number is entered, the number of digits is uncertain. We can't use meaning judgment to remove 10, 100 or 1000,

At this time, my brain suggested that I use recursion, so I wrote the following code:

Operation result: 10. Done