code: public String toHexString() {
          char[] chars = new char[OBJECT_ID_LENGTH * 2];
          int i = 0;
          for (byte b : toByteArray()) {
              chars[i++] = HEX_CHARS[b >> 4 & 0xF];
              chars[i++] = HEX_CHARS[b & 0xF];
          }
          return new String(chars);
      }
docs: Converts this instance into a 24-byte hexadecimal string representation.
  
  @return a string representation of the ObjectId in hexadecimal format