Collections.reverse method not reversing entry

My code below is supposed to accept an integer from the user, and then print whatever integer they enter in reverse order. I am getting no errors, but when I run this program the integer is not being printed in reverse. Can someone please help me figure out why?

import java.util.*;public class ReverseDigits {    public static void main(String[] args) {        Scanner sc = new Scanner(System.in);        String response;        System.out.println("Please enter a whole number.");        response = sc.next();        reverseDigit(response);    }    public static void reverseDigit(String digit) {        ArrayList al = new ArrayList();        al.add(digit);        Collections.reverse(al);        System.out.println("Your number in reverse order is: "+ al);    }}