public class ReverseString {

    public static void main(String[] args) {

        String s = "Zack";

        System.out.println("The reverse of " + s + " is " + reverse(s));
        s = null;


        System.out.println("The reverse of " + s + " is " + reverse(s));

    }

    private static String reverse(String s) {

        String reversed = "";


        if (s == null){
            System.out.println("S is null");
            return null;

        }else{


            int i;
            for ( i= s.length()-1; i >= 0; i--){

                if (i != -1){


                    char NextLetter= s.charAt(i);


                    System.out.println (NextLetter);





                }
                else{

                    System.exit (0);
                }

                reversed= reversed + s.charAt(i);

            }
            return reversed;

        }


    }

}