Created method UtcTime.printTimeOfAllClocks().
Created method Clock.getTime().
The field UTC_OFFSET of class Clock must not be static so that all subclasses could have its own UTC_OFFSET. That's the root cause of the bug that the local time of all city clocks are set to the same time.
Removed the static method Clock.toLocalTime().
Expected class Clock to have an interface of setting local time from UTC zero time in method UtcTime.notifyAllClocks().
Created method Clock.setLocalTimeFromUtcZeroTime().