DigitReverser.java

Below is the syntax highlighted version of DigitReverser.java from §1.3 Conditionals and Loops.

/******************************************************************************
 *  Compilation:  javac DigitReverser.java
 *  Execution:    java DigitReverser n
 *
 *  Reverses the digits of a positive integer n using arithmetic. Then,
 *  reverse it again using string concatenation.
 *
 *  % java DigitReverser 123456789
 *  987654321
 *  123456789
 *
 ******************************************************************************/

public class DigitReverser {

    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);        // original integer

        // reverse using arithmetic
        int m = 0;
        while (n != 0) {
            m = (10 * m) + (n % 10);
            n = n / 10;
        }
        System.out.println(m);


        // reverse again using string concatenation
        String s = "";
        while (m != 0) {
            int digit = m % 10;
            s = s + digit;
            m = m / 10;
        }
        System.out.println(s);

    }
}