java.util
public class GregorianCalendar extends Calendar
This class represents the Gregorian calendar, that is used in most countries all over the world. It does also handle the Julian calendar for dates smaller than the date of the change to the Gregorian calendar. The Gregorian calendar differs from the Julian calendar by a different leap year rule (no leap year every 100 years, except if year is divisible by 400).
This change date is different from country to country, and can be changed with
setGregorianChange. The first countries to adopt the Gregorian
calendar did so on the 15th of October, 1582. This date followed October
the 4th, 1582 in the Julian calendar system. The non-existant days that were
omitted when the change took place are interpreted as Gregorian dates.
Prior to the changeover date, New Year's Day occurred on the 25th of March. However, this class always takes New Year's Day as being the 1st of January. Client code should manually adapt the year value, if required, for dates between January the 1st and March the 24th in years prior to the changeover.
Any date infinitely forwards or backwards in time can be represented by this class. A proleptic calendar system is used, which allows future dates to be created via the existing rules. This allows meaningful and consistent dates to be produced for all years. However, dates are only historically accurate following March the 1st, 4AD when the Julian calendar system was adopted. Prior to this, leap year rules were applied erraticly.
There are two eras available for the Gregorian calendar, namely BC and AD.
Weeks are defined as a period of seven days, beginning on the first day
of the week, as returned by getFirstDayOfWeek(), and ending
on the day prior to this.
The weeks of the year are numbered from 1 to a possible 53. The first week
of the year is defined as the first week that contains at least the minimum
number of days of the first week in the new year (retrieved via
getMinimalDaysInFirstWeek()). All weeks after this are numbered
from 2 onwards.
For example, take the year 2004. It began on a Thursday. The first week of 2004 depends both on where a week begins and how long it must minimally last. Let's say that the week begins on a Monday and must have a minimum of 5 days. In this case, the first week begins on Monday, the 5th of January. The first 4 days (Thursday to Sunday) are not eligible, as they are too few to make up the minimum number of days of the first week which must be in the new year. If the minimum was lowered to 4 days, then the first week would instead begin on Monday, the 29th of December, 2003. This first week has 4 of its days in the new year, and is now eligible.
The weeks of the month are numbered from 0 to a possible 6. The first week of the month (numbered 1) is a set of days, prior to the first day of the week, which number at least the minimum number of days in a week. Unlike the first week of the year, the first week of the month only uses days from that particular month. As a consequence, it may have a variable number of days (from the minimum number required up to a full week of 7) and it need not start on the first day of the week. It must, however, be following by the first day of the week, as this marks the beginning of week 2. Any days of the month which occur prior to the first week (because the first day of the week occurs before the minimum number of days is met) are seen as week 0.
Again, we will take the example of the year 2004 to demonstrate this. September 2004 begins on a Wednesday. Taking our first day of the week as Monday, and the minimum length of the first week as 6, we find that week 1 runs from Monday, the 6th of September to Sunday the 12th. Prior to the 6th, there are only 5 days (Wednesday through to Sunday). This is too small a number to meet the minimum, so these are classed as being days in week 0. Week 2 begins on the 13th, and so on. This changes if we reduce the minimum to 5. In this case, week 1 is a truncated week from Wednesday the 1st to Sunday the 5th, and week 0 doesn't exist. The first seven day week is week 2, starting on the 6th.
On using the clear() method, the Gregorian calendar returns
to its default value of the 1st of January, 1970 AD 00:00:00 (the epoch).
The day of the week is set to the correct day for that particular time.
The day is also the first of the month, and the date is in week 0.
See Also: Calendar TimeZone getFirstDayOfWeek getMinimalDaysInFirstWeek
| Field Summary | |
|---|---|
| static int | AD
Constant representing the era AD (Anno Domini). |
| static int | BC
Constant representing the era BC (Before Christ). |
| Constructor Summary | |
|---|---|
| GregorianCalendar()
Constructs a new GregorianCalender representing the current
time, using the default time zone and the default locale. | |
| GregorianCalendar(TimeZone zone)
Constructs a new GregorianCalender representing the current
time, using the specified time zone and the default locale.
| |
| GregorianCalendar(Locale locale)
Constructs a new GregorianCalender representing the current
time, using the default time zone and the specified locale.
| |
| GregorianCalendar(TimeZone zone, Locale locale)
Constructs a new GregorianCalender representing the current
time with the given time zone and the given locale.
| |
| GregorianCalendar(int year, int month, int day)
Constructs a new GregorianCalendar representing midnight on the
given date with the default time zone and locale.
| |
| GregorianCalendar(int year, int month, int day, int hour, int minute)
Constructs a new GregorianCalendar representing midnight on the
given date with the default time zone and locale.
| |
| GregorianCalendar(int year, int month, int day, int hour, int minute, int second)
Constructs a new GregorianCalendar representing midnight on the
given date with the default time zone and locale.
| |
| Method Summary | |
|---|---|
| void | add(int field, int amount)
Adds the specified amount of time to the given time field. |
| protected void | computeFields()
Converts the milliseconds since the epoch UTC
( time) to time fields
(fields). |
| protected void | computeTime()
Converts the time field values ( fields) to
milliseconds since the epoch UTC (time).
|
| boolean | equals(Object o)
Compares the given calendar with this. |
| int | getActualMaximum(int field)
Gets the actual maximum value that is allowed for the specified field.
|
| int | getActualMinimum(int field)
Gets the actual minimum value that is allowed for the specified field.
|
| int | getGreatestMinimum(int field)
Gets the greatest minimum value that is allowed for the specified field.
|
| Date | getGregorianChange()
Gets the date of the switch from Julian dates to Gregorian dates.
|
| int | getLeastMaximum(int field)
Gets the smallest maximum value that is allowed for the
specified field. |
| int | getMaximum(int field)
Gets the biggest value that is allowed for the specified field.
|
| int | getMinimum(int field)
Gets the smallest value that is allowed for the specified field.
|
| int | hashCode()
Return a hash code for this object, following the general contract
specified by {@link Object#hashCode()}. |
| boolean | isLeapYear(int year) Determines if the given year is a leap year. |
| void | roll(int field, boolean up)
Rolls the specified time field up or down. |
| void | roll(int field, int amount)
Rolls the specified time field by the given amount. |
| void | setGregorianChange(Date date)
Sets the date of the switch from Julian dates to Gregorian dates.
|
Parameters: zone a time zone.
Parameters: locale a locale.
Parameters: zone a time zone. locale a locale.
Parameters: year corresponds to the YEAR time field. month corresponds to the MONTH time field. day corresponds to the DAY time field.
Parameters: year corresponds to the YEAR time field. month corresponds to the MONTH time field. day corresponds to the DAY time field. hour corresponds to the HOUR_OF_DAY time field. minute corresponds to the MINUTE time field.
Parameters: year corresponds to the YEAR time field. month corresponds to the MONTH time field. day corresponds to the DAY time field. hour corresponds to the HOUR_OF_DAY time field. minute corresponds to the MINUTE time field. second corresponds to the SECOND time field.
Parameters: field one of the time field constants. amount the amount of time to add.
Throws: IllegalArgumentException if field is
ZONE_OFFSET, DST_OFFSET, or invalid; or
if amount contains an out-of-range value and the calendar
is not in lenient mode.
time) to time fields
(fields).fields) to
milliseconds since the epoch UTC (time).
Throws: IllegalArgumentException if any calendar fields are invalid.
GregorianCalendar
with the same time since the epoch under the same conditions
(same change date and same time zone).
Parameters: o the object to that we should compare.
Returns: true, if the given object is a calendar, that represents the same time (but doesn't necessarily have the same fields).
Throws: IllegalArgumentException if one of the fields
ZONE_OFFSET or DST_OFFSET is
specified, if an unknown field is specified or if one
of the calendar fields receives an illegal value when
leniancy is not enabled.
complete() if not enough fields are set. This
can have ugly side effects. The value given depends on the current time
used by this instance; thus, leap years have a maximum day of month value of
29, rather than 28.
Parameters: field the time field. One of the time field constants.
Returns: the actual maximum value.
complete() if not enough fields are set. This
can have ugly side effects. The value given depends on the current
time used by this instance.
Parameters: field the time field. One of the time field constants.
Returns: the actual minimum value.
Since: 1.2
getActualMinimum(int)
method.
Parameters: field the time field. One of the time field constants.
Returns: the greatest minimum value.
See Also: GregorianCalendar
Returns: the date of the change.
getActualMaximum(int). For example,
this is 28 for DAY_OF_MONTH (as all months have at least
28 days).
Parameters: field the time field. One of the time field constants.
Returns: the least maximum value.
Since: 1.2
See Also: GregorianCalendar
Parameters: field one of the time field constants.
Returns: the biggest value.
Parameters: field one of the time field constants.
Returns: the smallest value for the specified field.
Returns: the hash code
Determines if the given year is a leap year. The result is undefined if the Gregorian change took place in 1800, so that the end of February is skipped, and that year is specified. (well...).
To specify a year in the BC era, use a negative value calculated as 1 - y, where y is the required year in BC. So, 1 BC is 0, 2 BC is -1, 3 BC is -2, etc.
Parameters: year a year (use a negative value for BC).
Returns: true, if the given year is a leap year, false otherwise.
Parameters: field the time field. One of the time field constants. up the direction, true for up, false for down.
Throws: IllegalArgumentException if one of the fields
ZONE_OFFSET or DST_OFFSET is
specified, if an unknown field is specified or if one
of the calendar fields receives an illegal value when
leniancy is not enabled.
Parameters: field the time field. One of the time field constants. amount the amount by which we should roll.
Throws: IllegalArgumentException if one of the fields
ZONE_OFFSET or DST_OFFSET is
specified, if an unknown field is specified or if one
of the calendar fields receives an illegal value when
leniancy is not enabled.
new Date(Long.MAX_VALUE) to use a pure
Julian calendar, or Long.MIN_VALUE for a pure Gregorian
calendar.
Parameters: date the date of the change.