GregorianCalendar

public class GregorianCalendar extends Calendar

[icu enhancement] ICU's replacement for GregorianCalendar. Methods, fields, and other functionality specific to ICU are labeled '[icu]'.

GregorianCalendar is a concrete subclass of Calendar and provides the standard calendar used by most of the world.

The standard (Gregorian) calendar has 2 eras, BC and AD.

This implementation handles a single discontinuity, which corresponds by default to the date the Gregorian calendar was instituted (October 15, 1582 in some countries, later in others). The cutover date may be changed by the caller by calling setGregorianChange().

Historically, in those countries which adopted the Gregorian calendar first, October 4, 1582 was thus followed by October 15, 1582. This calendar models this correctly. Before the Gregorian cutover, GregorianCalendar implements the Julian calendar. The only difference between the Gregorian and the Julian calendar is the leap year rule. The Julian calendar specifies leap years every four years, whereas the Gregorian calendar omits century years which are not divisible by 400.

GregorianCalendar implements proleptic Gregorian and Julian calendars. That is, dates are computed by extrapolating the current rules indefinitely far backward and forward in time. As a result, GregorianCalendar may be used for all years to generate meaningful and consistent results. However, dates obtained using GregorianCalendar are historically accurate only from March 1, 4 AD onward, when modern Julian calendar rules were adopted. Before this date, leap year rules were applied irregularly, and before 45 BC the Julian calendar did not even exist.

Prior to the institution of the Gregorian calendar, New Year's Day was March 25. To avoid confusion, this calendar always uses January 1. A manual adjustment may be made if desired for dates that are prior to the Gregorian changeover and which fall between January 1 and March 24.

Values calculated for the WEEK_OF_YEAR field range from 1 to 53. Week 1 for a year is the earliest seven day period starting on getFirstDayOfWeek() that contains at least getMinimalDaysInFirstWeek() days from that year. It thus depends on the values of getMinimalDaysInFirstWeek(), getFirstDayOfWeek(), and the day of the week of January 1. Weeks between week 1 of one year and week 1 of the following year are numbered sequentially from 2 to 52 or 53 (as needed).

For example, January 1, 1998 was a Thursday. If getFirstDayOfWeek() is MONDAY and getMinimalDaysInFirstWeek() is 4 (these are the values reflecting ISO 8601 and many national standards), then week 1 of 1998 starts on December 29, 1997, and ends on January 4, 1998. If, however, getFirstDayOfWeek() is SUNDAY, then week 1 of 1998 starts on January 4, 1998, and ends on January 10, 1998; the first three days of 1998 then are part of week 53 of 1997.

Values calculated for the WEEK_OF_MONTH field range from 0 or 1 to 4 or 5. Week 1 of a month (the days with WEEK_OF_MONTH = 1) is the earliest set of at least getMinimalDaysInFirstWeek() contiguous days in that month, ending on the day before getFirstDayOfWeek(). Unlike week 1 of a year, week 1 of a month may be shorter than 7 days, need not start on getFirstDayOfWeek(), and will not include days of the previous month. Days of a month before week 1 have a WEEK_OF_MONTH of 0.

For example, if getFirstDayOfWeek() is SUNDAY and getMinimalDaysInFirstWeek() is 4, then the first week of January 1998 is Sunday, January 4 through Saturday, January 10. These days have a WEEK_OF_MONTH of 1. Thursday, January 1 through Saturday, January 3 have a WEEK_OF_MONTH of 0. If getMinimalDaysInFirstWeek() is changed to 3, then January 1 through January 3 have a WEEK_OF_MONTH of 1.

Example:

 // get the supported ids for GMT-08:00 (Pacific Standard Time)
 String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
 // if no ids were returned, something is wrong. get out.
 if (ids.length == 0)
     System.exit(0);

  // begin output
 System.out.println("Current Time");

 // create a Pacific Standard Time time zone
 SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);

 // set up rules for daylight savings time
 pdt.setStartRule(Calendar.MARCH, 2, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 pdt.setEndRule(Calendar.NOVEMBER, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);

 // create a GregorianCalendar with the Pacific Daylight time zone
 // and the current date and time
 Calendar calendar = new GregorianCalendar(pdt);
 Date trialTime = new Date();
 calendar.setTime(trialTime);

 // print out a bunch of interesting things
 System.out.println("ERA: " + calendar.get(Calendar.ERA));
 System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 System.out.println("DATE: " + calendar.get(Calendar.DATE));
 System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 System.out.println("DAY_OF_WEEK_IN_MONTH: "
                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 System.out.println("ZONE_OFFSET: "
                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
 System.out.println("DST_OFFSET: "
                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));

 System.out.println("Current Time, with hour reset to 3");
 calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
 calendar.set(Calendar.HOUR, 3);
 System.out.println("ERA: " + calendar.get(Calendar.ERA));
 System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 System.out.println("DATE: " + calendar.get(Calendar.DATE));
 System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 System.out.println("DAY_OF_WEEK_IN_MONTH: "
                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 System.out.println("ZONE_OFFSET: "
        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours
 System.out.println("DST_OFFSET: "
        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours

GregorianCalendar usually should be instantiated using getInstance(ULocale) passing in a ULocale with the tag "@calendar=gregorian".

See Also

Constant Summary

int AD Value of the ERA field indicating the common era (Anno Domini), also known as CE.
int BC Value of the ERA field indicating the period before the common era (before Christ), also known as BCE.

Inherited Constant Summary

Field Summary

protected boolean invertGregorian Used by handleComputeJulianDay() and handleComputeMonthStart().
protected boolean isGregorian Used by handleComputeJulianDay() and handleComputeMonthStart().

Inherited Field Summary

Public Constructor Summary

GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone with the default FORMAT locale.
GregorianCalendar(TimeZone zone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default FORMAT locale.
GregorianCalendar(Locale aLocale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
GregorianCalendar(ULocale locale)
[icu] Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
GregorianCalendar(TimeZone zone, Locale aLocale)
[icu] Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.
GregorianCalendar(TimeZone zone, ULocale locale)
Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.
GregorianCalendar(int year, int month, int date)
Constructs a GregorianCalendar with the given date set in the default time zone with the default FORMAT locale.
GregorianCalendar(int year, int month, int date, int hour, int minute)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default FORMAT locale.
GregorianCalendar(int year, int month, int date, int hour, int minute, int second)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default FORMAT locale.

Public Method Summary

int
getActualMaximum(int field)
Return the maximum value that this field could have, given the current date.
int
getActualMinimum(int field)
Return the minimum value that this field could have, given the current date.
final Date
getGregorianChange()
Gets the Gregorian Calendar change date.
String
getType()
[icu] Returns the calendar type name string for this Calendar object.
int
hashCode()
Override hashCode.
boolean
isEquivalentTo(Calendar other)
Returns true if the given Calendar object is equivalent to this one.
boolean
isLeapYear(int year)
Determines if the given year is a leap year.
void
roll(int field, int amount)
Roll a field by a signed amount.
void
setGregorianChange(Date date)
Sets the GregorianCalendar change date.

Protected Method Summary

void
handleComputeFields(int julianDay)
Override Calendar to compute several fields specific to the hybrid Gregorian-Julian calendar system.
int
handleComputeJulianDay(int bestField)
Subclasses may override this.
int
handleComputeMonthStart(int eyear, int month, boolean useMonth)
Return JD of start of given month/year
int
handleGetExtendedYear()
Returns the extended year defined by the current fields.
int
handleGetLimit(int field, int limitType)
Subclass API for defining limits of different types.
int
handleGetMonthLength(int extendedYear, int month)
Returns the number of days in the given month of the given extended year of this calendar system.
int
handleGetYearLength(int eyear)
Returns the number of days in the given extended year of this calendar system.

Inherited Method Summary

Constants

public static final int AD

Value of the ERA field indicating the common era (Anno Domini), also known as CE. The sequence of years at the transition from BC to AD is ..., 2 BC, 1 BC, 1 AD, 2 AD,...

See Also
Constant Value: 1

public static final int BC

Value of the ERA field indicating the period before the common era (before Christ), also known as BCE. The sequence of years at the transition from BC to AD is ..., 2 BC, 1 BC, 1 AD, 2 AD,...

See Also
Constant Value: 0

Fields

protected boolean invertGregorian

Used by handleComputeJulianDay() and handleComputeMonthStart().

protected boolean isGregorian

Used by handleComputeJulianDay() and handleComputeMonthStart().

Public Constructors

public GregorianCalendar ()

Constructs a default GregorianCalendar using the current time in the default time zone with the default FORMAT locale.

See Also

public GregorianCalendar (TimeZone zone)

Constructs a GregorianCalendar based on the current time in the given time zone with the default FORMAT locale.

Parameters
zone the given time zone.
See Also

public GregorianCalendar (Locale aLocale)

Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.

Parameters
aLocale the given locale.

public GregorianCalendar (ULocale locale)

[icu] Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.

Parameters
locale the given ulocale.

public GregorianCalendar (TimeZone zone, Locale aLocale)

[icu] Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.

Parameters
zone the given time zone.
aLocale the given locale.

public GregorianCalendar (TimeZone zone, ULocale locale)

Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.

Parameters
zone the given time zone.
locale the given ulocale.

public GregorianCalendar (int year, int month, int date)

Constructs a GregorianCalendar with the given date set in the default time zone with the default FORMAT locale.

Parameters
year the value used to set the YEAR time field in the calendar.
month the value used to set the MONTH time field in the calendar. Month value is 0-based. e.g., 0 for January.
date the value used to set the DATE time field in the calendar.
See Also

public GregorianCalendar (int year, int month, int date, int hour, int minute)

Constructs a GregorianCalendar with the given date and time set for the default time zone with the default FORMAT locale.

Parameters
year the value used to set the YEAR time field in the calendar.
month the value used to set the MONTH time field in the calendar. Month value is 0-based. e.g., 0 for January.
date the value used to set the DATE time field in the calendar.
hour the value used to set the HOUR_OF_DAY time field in the calendar.
minute the value used to set the MINUTE time field in the calendar.
See Also

public GregorianCalendar (int year, int month, int date, int hour, int minute, int second)

Constructs a GregorianCalendar with the given date and time set for the default time zone with the default FORMAT locale.

Parameters
year the value used to set the YEAR time field in the calendar.
month the value used to set the MONTH time field in the calendar. Month value is 0-based. e.g., 0 for January.
date the value used to set the DATE time field in the calendar.
hour the value used to set the HOUR_OF_DAY time field in the calendar.
minute the value used to set the MINUTE time field in the calendar.
second the value used to set the SECOND time field in the calendar.
See Also

Public Methods

public int getActualMaximum (int field)

Return the maximum value that this field could have, given the current date. For example, with the date "Feb 3, 1997" and the DAY_OF_MONTH field, the actual maximum would be 28; for "Feb 3, 1996" it s 29. Similarly for a Hebrew calendar, for some years the actual maximum for MONTH is 12, and for others 13.

Parameters
field the field whose maximum is desired
Returns
  • the maximum of the given field for the current date of this calendar

public int getActualMinimum (int field)

Return the minimum value that this field could have, given the current date. For the Gregorian calendar, this is the same as getMinimum() and getGreatestMinimum().

Parameters
field the field whose actual minimum value is desired.
Returns
  • the minimum of the given field for the current date of this calendar

public final Date getGregorianChange ()

Gets the Gregorian Calendar change date. This is the point when the switch from Julian dates to Gregorian dates occurred. Default is October 15, 1582. Previous to this, dates will be in the Julian calendar.

Returns
  • the Gregorian cutover date for this calendar.

public String getType ()

[icu] Returns the calendar type name string for this Calendar object. The returned string is the legacy ICU calendar attribute value, for example, "gregorian" or "japanese".

See type="old type name" for the calendar attribute of locale IDs at http://www.unicode.org/reports/tr35/#Key_Type_Definitions

Returns
  • legacy calendar type name string

public int hashCode ()

Override hashCode. Generates the hash code for the GregorianCalendar object

Returns
  • a hash code value for this object.

public boolean isEquivalentTo (Calendar other)

Returns true if the given Calendar object is equivalent to this one. Calendar override.

Parameters
other the Calendar to be compared with this Calendar

public boolean isLeapYear (int year)

Determines if the given year is a leap year. Returns true if the given year is a leap year.

Parameters
year the given year.
Returns
  • true if the given year is a leap year; false otherwise.

public void roll (int field, int amount)

Roll a field by a signed amount.

Parameters
field the calendar field to roll.
amount the amount by which the field should be rolled.

public void setGregorianChange (Date date)

Sets the GregorianCalendar change date. This is the point when the switch from Julian dates to Gregorian dates occurred. Default is October 15, 1582. Previous to this, dates will be in the Julian calendar.

To obtain a pure Julian calendar, set the change date to Date(Long.MAX_VALUE). To obtain a pure Gregorian calendar, set the change date to Date(Long.MIN_VALUE).

Parameters
date the given Gregorian cutover date.

Protected Methods

protected void handleComputeFields (int julianDay)

Override Calendar to compute several fields specific to the hybrid Gregorian-Julian calendar system. These are:

  • ERA
  • YEAR
  • MONTH
  • DAY_OF_MONTH
  • DAY_OF_YEAR
  • EXTENDED_YEAR

Parameters
julianDay

protected int handleComputeJulianDay (int bestField)

Subclasses may override this. This method calls handleGetMonthLength() to obtain the calendar-specific month length.

Parameters
bestField

protected int handleComputeMonthStart (int eyear, int month, boolean useMonth)

Return JD of start of given month/year

Parameters
eyear the extended year
month the zero-based month, or 0 if useMonth is false
useMonth if false, compute the day before the first day of the given year, otherwise, compute the day before the first day of the given month
Returns
  • the Julian day number of the day before the first day of the given month and year

protected int handleGetExtendedYear ()

Returns the extended year defined by the current fields. This will use the EXTENDED_YEAR field or the YEAR and supra-year fields (such as ERA) specific to the calendar system, depending on which set of fields is newer.

Returns
  • the extended year

protected int handleGetLimit (int field, int limitType)

Subclass API for defining limits of different types. Subclasses must implement this method to return limits for the following fields:

ERA
 YEAR
 MONTH
 WEEK_OF_YEAR
 WEEK_OF_MONTH
 DAY_OF_MONTH
 DAY_OF_YEAR
 DAY_OF_WEEK_IN_MONTH
 YEAR_WOY
 EXTENDED_YEAR

Parameters
field one of the above field numbers
limitType one of MINIMUM, GREATEST_MINIMUM, LEAST_MAXIMUM, or MAXIMUM

protected int handleGetMonthLength (int extendedYear, int month)

Returns the number of days in the given month of the given extended year of this calendar system. Subclasses should override this method if they can provide a more correct or more efficient implementation than the default implementation in Calendar.

Parameters
extendedYear
month

protected int handleGetYearLength (int eyear)

Returns the number of days in the given extended year of this calendar system. Subclasses should override this method if they can provide a more correct or more efficient implementation than the default implementation in Calendar.

Parameters
eyear