code: public static Clock parseClock(String str) {
          if(str == null || str.length() == 0) {
              return Clock.ZERO;
          }
          
          String[] parts = str.split(":");
          long[] values = new long[parts.length];
          for(int i = 0; i < values.length; i++) {
              values[i] = Long.parseLong(parts[i]);
          }
          return new Clock(values);
      }
docs: Parses a Clock value from its string representation.
  
  @param str - the string representation of Clock
  @return A Clock object.
  <code>Clock.ZERO</code> is returned <code>upon</code> null or zero-length string.