Can you explain how it works?

Question

It would be awesome if someone could give me a proper explanation of the code :)

Code is working and I like it, however as I am learning Java, need to understand every bit of it.

Thanks!

Checked StringBuilder() - seems fine, However part inside the loop is not quite clear.

    public class SquareDigit {

        public int squareDigits(int n) {
               StringBuilder builder = new StringBuilder();

               while(n > 0) {
                   int digit = n % 10;

                   int square = digit * digit;
                   builder.insert(0, square);

                   n = Math.floorDiv(n, 10);
               }

               return Integer.valueOf(builder.toString());
         }

     }

Answer 1

while(n > 0) {

While the int n is bigger than 0 do the following.

int digit = n % 10;

A new int digit is initialized as n MODULO 10. Modulo returns the remainder of the division n / 10. So for example if n is 21, it will return 1.

int square = digit * digit;
builder.insert(0, square);

A new int square is initialised as the product of digit times itself. The method insert() from class StringBuilder is called with 0 and square as parameters. 0 is the offset and square is the char value to be inserted.

n = Math.floorDiv(n, 10);

Math.floorDiv() returns the largest (closest to positive infinity) integer value that is less than or equal to the algebraic quotient. For example Math.floorDiv(25, 5) will return 5.

return Integer.valueOf(builder.toString());

Finally, you return the value you built before. builder.toString() returns the StringBuilder object as a String. Integer.valueOf(String str) is used to return an Integer object holding the value of the specified String str.