public static void main(String args[]){
        char str[] = {'a','1','b','2','c','3','d','4','e','5','f','6','g','7','h','8','i','9','j','A','k','B','l','C','m','D'};
        InPlaceTransformationOfString ip = new InPlaceTransformationOfString();
        ip.inPlaceTransformationImproved(str);
        for(int i=0; i < str.length; i++){
            System.out.print(str[i]);
        }
    }
http://www.geeksforgeeks.org/an-in-place-algorithm-for-string-transformation/
src/com/interview/string/InPlaceTransformationOfString.java