1 public class Test 2 { 3     final static int[] sizeTable = { 9, 99, 999, 9999, 99999, 999999, 9999999, 99999999, 999999999, Integer.MAX_VALUE }; 4  5     static int sizeOfInt(int x) 6     { 7         for (int i = 0;; i++) 8             if (x <= sizeTable[i]) 9                 return i + 1;10     }11 12     public static String reverse(String originStr)13     {14         if (originStr == null || originStr.length() <= 1)15             return originStr;16         return reverse(originStr.substring(1)) + originStr.charAt(0);17     }18 19     public static Integer reverse(int value)20     {21         if (value < 10)22         {23             return value;24         }25         return (value % 10) * (int)Math.pow(10, sizeOfInt(value) - 1) + reverse(value / 10);26     }27 28     public static void main(String[] args)29     {30         System.out.println(reverse("helloworld"));31         System.out.println(reverse(123456789));32 33     }34 }