Java Reference
In-Depth Information
Gregorian Calendars
The Gregorian calendar is the calendar generally in use today in the western world, and is represented
by an object of the
GregorianCalendar
class. A
GregorianCalendar
object encapsulates time
zone information, as well as date and time data. There are no less than seven constructors for
GregorianCalendar
objects, from the default that creates a calendar with the current date and time
in the default locale for your machine, through to a constructor where you can specify the year, month,
day, hour, minute, and second. The default suits most situations.
You can create a calendar with a statement such as:
GregorianCalendar calendar = new GregorianCalendar();
This will be set to the current instant in time, and you can retrieve this as a
Date
object by calling the
getTime()
method for the calendar:
Date now = calendar.getTime();
You can create a
GregorianCalendar
object encapsulating a specific date and/or time with the
following constructors:
GregorianCalendar(int year, int month, int day)
GregorianCalendar(int year, int month, int day, int hour, int minute)
GregorianCalendar(int year, int month, int day,
int hour, int minute, int second)
The
day
argument is the day within the month, so the value can be from 1 to 28, 29, 30, or 31,
depending on the month and whether it's a leap year or not. The
month
value is zero-based so January
is 0 and December is 11.
The
GregorianCalendar
class is derived from the abstract
Calendar
class from which it inherits a
large number of methods and static constants for use with these methods. The constants includes month
values with the names
JANUARY
to
DECEMBER
so you could create a calendar object with the statement:
GregorianCalendar calendar = new GregorianCalendar(1967, Calendar.MARCH, 10);
The time zone and locale will be the default for the computer on which this statement executes. If you
want to specify a time zone there is a
GregorianCalendar
constructor that accepts an argument of
type
TimeZone
. The
TimeZone
class is also defined in the
java.util
package. You can get the
default
TimeZone
object by calling the static
getDefault()
method, but if you are going to the
trouble of specifying a time zone, you probably want something other than the default. To create a
particular time zone you need to know its ID. This is a string specifying a region or country plus a
location. For instance, here are some examples of time zone IDs:
Europe/
Stockholm
Asia/Novosibirsk
Pacific/Guam
America/Chicago
Antarctica/
Palmer
Atlantic/
South
_
Georgia
Africa/Accra
Indian/Comoro
