com.ibm.icu.util

Class GregorianCalendar

public class GregorianCalendar extends Calendar

GregorianCalendar is a concrete subclass of {@link 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.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 pdt.setEndRule(Calendar.OCTOBER, -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 {@link com.ibm.icu.util.Calendar#getInstance(ULocale)} passing in a ULocale with the tag "@calendar=gregorian".

Author: David Goldsmith, Mark Davis, Chen-Lieh Huang, Alan Liu

See Also: Calendar TimeZone

UNKNOWN: ICU 2.0

Field Summary
static intAD
Value of the ERA field indicating the common era (Anno Domini), also known as CE.
static intBC
Value of the ERA field indicating the period before the common era (before Christ), also known as BCE.
protected booleaninvertGregorian
Used by handleComputeJulianDay() and handleComputeMonthStart().
protected booleanisGregorian
Used by handleComputeJulianDay() and handleComputeMonthStart().
Constructor Summary
GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone with the default locale.
GregorianCalendar(TimeZone zone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.
GregorianCalendar(Locale aLocale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
GregorianCalendar(ULocale locale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
GregorianCalendar(TimeZone zone, Locale aLocale)
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 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 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 locale.
Method Summary
intgetActualMaximum(int field)
Return the maximum value that this field could have, given the current date.
intgetActualMinimum(int field)
Return the minimum value that this field could have, given the current date.
DategetGregorianChange()
Gets the Gregorian Calendar change date.
StringgetType()
Return the current Calendar type.
protected voidhandleComputeFields(int julianDay)
Override Calendar to compute several fields specific to the hybrid Gregorian-Julian calendar system.
protected inthandleComputeJulianDay(int bestField)
protected inthandleComputeMonthStart(int eyear, int month, boolean useMonth)
Return JD of start of given month/year
protected inthandleGetExtendedYear()
protected inthandleGetLimit(int field, int limitType)
protected inthandleGetMonthLength(int extendedYear, int month)
protected inthandleGetYearLength(int eyear)
inthashCode()
Override hashCode.
booleanisEquivalentTo(Calendar other)
Returns true if the given Calendar object is equivalent to this one.
booleanisLeapYear(int year)
Determines if the given year is a leap year.
voidroll(int field, int amount)
Roll a field by a signed amount.
voidsetGregorianChange(Date date)
Sets the GregorianCalendar change date.

Field Detail

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: ERA

UNKNOWN: ICU 2.0

BC

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: ERA

UNKNOWN: ICU 2.0

invertGregorian

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

UNKNOWN: ICU 2.0

isGregorian

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

UNKNOWN: ICU 2.0

Constructor Detail

GregorianCalendar

public GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone with the default locale.

UNKNOWN: ICU 2.0

GregorianCalendar

public GregorianCalendar(TimeZone zone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.

Parameters: zone the given time zone.

UNKNOWN: ICU 2.0

GregorianCalendar

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.

UNKNOWN: ICU 2.0

GregorianCalendar

public GregorianCalendar(ULocale locale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.

Parameters: locale the given ulocale.

UNKNOWN: ICU 3.2 This API might change or be removed in a future release.

GregorianCalendar

public GregorianCalendar(TimeZone zone, Locale aLocale)
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.

UNKNOWN: ICU 2.0

GregorianCalendar

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.

UNKNOWN: ICU 3.2 This API might change or be removed in a future release.

GregorianCalendar

public GregorianCalendar(int year, int month, int date)
Constructs a GregorianCalendar with the given date set in the default time zone with the default 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.

UNKNOWN: ICU 2.0

GregorianCalendar

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 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.

UNKNOWN: ICU 2.0

GregorianCalendar

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 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.

UNKNOWN: ICU 2.0

Method Detail

getActualMaximum

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.

UNKNOWN: ICU 2.0

getActualMinimum

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().

UNKNOWN: ICU 2.0

getGregorianChange

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.

UNKNOWN: ICU 2.0

getType

public String getType()
Return the current Calendar type.

Returns: type of calendar (gregorian, etc.)

UNKNOWN: ICU 3.0

handleComputeFields

protected void handleComputeFields(int julianDay)
Override Calendar to compute several fields specific to the hybrid Gregorian-Julian calendar system. These are:

UNKNOWN: ICU 2.0

handleComputeJulianDay

protected int handleComputeJulianDay(int bestField)

UNKNOWN: ICU 2.0

handleComputeMonthStart

protected int handleComputeMonthStart(int eyear, int month, boolean useMonth)
Return JD of start of given month/year

UNKNOWN: ICU 2.0

handleGetExtendedYear

protected int handleGetExtendedYear()

UNKNOWN: ICU 2.0

handleGetLimit

protected int handleGetLimit(int field, int limitType)

UNKNOWN: ICU 2.0

handleGetMonthLength

protected int handleGetMonthLength(int extendedYear, int month)

UNKNOWN: ICU 2.0

handleGetYearLength

protected int handleGetYearLength(int eyear)

UNKNOWN: ICU 2.0

hashCode

public int hashCode()
Override hashCode. Generates the hash code for the GregorianCalendar object

UNKNOWN: ICU 2.0

isEquivalentTo

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

UNKNOWN: ICU 2.4

isLeapYear

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.

UNKNOWN: ICU 2.0

roll

public void roll(int field, int amount)
Roll a field by a signed amount.

UNKNOWN: ICU 2.0

setGregorianChange

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.

UNKNOWN: ICU 2.0