public String reverse( String s ){
  char[] c = s.toCharArray();
  int size = c.length;
  for( int i = 0; i<size/2; i ++ ){
    char temp = c[i];
    c[i] = c[size - i - 1];
    c[size - i - 1] = temp;;
  }
  return new String( c );
}