code: public static String uuid(int len, int radix) {
  		if (radix > CHARS.length) {
  			throw new IllegalArgumentException();
  		}
  		char[] uuid = new char[len];
  		// Compact form
  		for (int i = 0; i < len; i++) {
  			uuid[i] = CHARS[(int)(Math.random()*radix)];
  		}
  		return new String(uuid);
  	}
docs: Generate a random uuid of the specified length, and radix. Examples:
  <ul>
  <li>uuid(8, 2) returns "01001010" (8 character ID, base=2)
  <li>uuid(8, 10) returns "47473046" (8 character ID, base=10)
  <li>uuid(8, 16) returns "098F4D35" (8 character ID, base=16)
  </ul>
  
  @param len
  the desired number of characters
  @param radix
  the number of allowable values for each character (must be <=
  62)