code: public final synchronized String next() {
          // Increment and capture.
          seq += inc;
          if (seq >= maxSeq) {
              randomizePrefix();
              resetSequential();
          }
  
          // Copy prefix
          char[] b = new char[totalLen];
          System.arraycopy(pre, 0, b, 0, preLen);
  
          // copy in the seq in base36.
          int i = b.length;
          for (long l = seq; i > preLen; l /= base) {
              i--;
              b[i] = digits[(int) (l % base)];
          }
          return new String(b);
      }
docs: Generate the next NUID string from this instance.
  
  @return the next NUID string from this instance.