code: public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers) {
          return random(count, start, end, letters, numbers, null, RANDOM);
      }
docs: <p>Creates a random string whose length is the number of characters
  specified.</p>
  
  <p>Characters will be chosen from the set of alpha-numeric
  characters as indicated by the arguments.</p>
  
  @param count  the length of random string to create
  @param start  the position in set of chars to start at
  @param end  the position in set of chars to end before
  @param letters  if {@code true}, generated string may include
  alphabetic characters
  @param numbers  if {@code true}, generated string may include
  numeric characters
  @return the random string