static private String randomString(String[] values,int length){
  StringBuilder output=new StringBuilder(length);
  for (int i=0; i < length; i++)   output.append(values[rnd.nextInt(values.length)]);
  return output.toString();
}

static private String randomString ( String [ ] values , int length ) { StringBuilder output = new StringBuilder ( length ) ; for ( int i = 0 ; i < length ; i ++ ) output . append ( values [ rnd . nextInt ( values . length ) ] ) ; return output . toString ( ) ; }
get a random , positive whole number
