code: private void appendOffsetDigits(StringBuilder buf, int n, int minDigits) {
          assert(n >= 0 && n < 60);
          int numDigits = n >= 10 ? 2 : 1;
          for (int i = 0; i < minDigits - numDigits; i++) {
              buf.append(_gmtOffsetDigits[0]);
          }
          if (numDigits == 2) {
              buf.append(_gmtOffsetDigits[n / 10]);
          }
          buf.append(_gmtOffsetDigits[n % 10]);
      }
docs: Appends localized digits to the buffer.
  <p>
  Note: This code assumes that the input number is 0 - 59
  
  @param buf the target buffer
  @param n the integer number
  @param minDigits the minimum digits width