Java Reference
In-Depth Information
For example, 4, 8, 12, 400, and 800 are known as leap years, and 1, 2, 3, 5, 300, and 100 are known as common
years. Year 0 (1 B. C.) is considered a leap year. With a new definition of a leap year, the average length of a year in
the Gregorian calendar is 365.2425 days, which is very close to the length of a tropical year. The Gregorian calendar
repeats every 400 years. If you save your paper calendar for year 2014, your nth great-grandchildren will be able to
reuse it in year 2414!
The Gregorian calendar was introduced on Friday, October 15, 1582. The day before the Gregorian calendar
started, it was Thursday, October 4, 1582 according to the existing Julian calendar. Note that the introduction of the
Gregorian calendar left the cycle of weekdays unaffected; however, it left a discontinuity of 10 days between the two
calendars that is called the cutover. Dates before the cutover are Julian dates, dates after the cutover are Gregorian
dates, and dates during the cutover do not exist.
Gregorian calendar did not exist before October 15, 1582. How do we assign dates to the events before the start
of the Gregorian calendar? The Gregorian calendar applied to the dates when it was not in effect is called a proleptic
Gregorian calendar. Therefore, October 14, 1582 exists In a proleptic Gregorian calendar, which is the same as
October 4, 1582 in the Julian calendar.
Why was the first day of the Gregorian calendar Friday, October 15, 1582, and not Friday, October 5, 1582?
According to (Doggett, Calendars n.d.), in Julian calendar, the date of Easter, a Christian festival, was computed
based on an assumption that March 21 is the date for vernal equinox. Later, it was realized that vernal equinox had
been drifting from March 21; hence, the date of Easter drifts from the seasonal springtime. To keep the date of Easter
synchronized with springtime, the adjustment of 10 days were made in the start date of the Gregorian calendar, so the
vernal equinox in year 1583 and later occurs approximately on March 21.
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the main difference between the Julian and Gregorian calendar is the rule for determining a leap year. the mean
length of a year in the Gregorian calendar is closer to the length of the tropical year than that of in the Julian calendar.
Tip
ISO-8601 Standards for Datetime
The new Date-Time API has extensive support for ISO-8601 standards. This section is intended to present a brief and
limited overview of the datetime components and their textual representations included in the ISO-8601 standards.
A datetime in ISO 8601 consists of three components: date, time, and zone offset that are combined in the
following format:
[date]T[time][zone offset]
A date component consists of three calendar fields: year, month, and day. Two fields in a date are separated by a
hyphen.
year-month-day
For example, 2012-04-30 represents the 30th day in April of year 2012.
Sometimes humans deal with dates that may not contain complete information to identify a specific day in a
calendar. For example, December 25 makes sense as a Christmas day without specifying the year part of the date. To
identify a specific Christmas day in a calendar, we must also specify the year. A date with some missing parts is known
as a partial. 2012, 2012-05, -----05-29, etc. are examples of partials. ISO-8601 allows omitting parts in a date only from
the right end. That is, it allows omitting day, or month and day. The Date-Time API allows three types of partials: year,
year-month, and month-day.
