java.util
Class GregorianCalendar

java.lang.Object   
  java.util.Calendar   
      java.util.GregorianCalendar

All Implemented Interfaces:

Serializable , Cloneable , Comparable <Calendar >

public class GregorianCalendar
extends Calendar   

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

GregorianCalendar is a hybrid calendar that supports both the Julian and Gregorian calendar systems with the support of a single discontinuity, which corresponds by default to the Gregorian date when 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 (Julian) was thus followed by October 15, 1582 (Gregorian). 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 to 6. 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.

The clear methods set calendar field(s) undefined. GregorianCalendar uses the following default value for each calendar field if its value is undefined.

Field	Default Value
ERA	AD
YEAR	1970
MONTH	JANUARY
DAY_OF_MONTH	1
DAY_OF_WEEK	the first day of week
WEEK_OF_MONTH	0
DAY_OF_WEEK_IN_MONTH	1
AM_PM	AM
HOUR, HOUR_OF_DAY, MINUTE, SECOND, MILLISECOND	0

Default values are not applicable for the fields not listed above.

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
 

Since:

JDK1.1

See Also:

TimeZone , Serialized Form

Field Summary

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

Fields inherited from class java.util.Calendar

AM , AM_PM , APRIL , areFieldsSet , AUGUST , DATE , DAY_OF_MONTH , DAY_OF_WEEK , DAY_OF_WEEK_IN_MONTH , DAY_OF_YEAR , DECEMBER , DST_OFFSET , ERA , FEBRUARY , FIELD_COUNT , fields , FRIDAY , HOUR , HOUR_OF_DAY , isSet , isTimeSet , JANUARY , JULY , JUNE , MARCH , MAY , MILLISECOND , MINUTE , MONDAY , MONTH , NOVEMBER , OCTOBER , PM , SATURDAY , SECOND , SEPTEMBER , SUNDAY , THURSDAY , time , TUESDAY , UNDECIMBER , WEDNESDAY , WEEK_OF_MONTH , WEEK_OF_YEAR , YEAR , ZONE_OFFSET

Constructor Summary

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

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

GregorianCalendar (int year, int month, int dayOfMonth, int hourOfDay, 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 dayOfMonth, int hourOfDay, int minute, int second)
Constructs a GregorianCalendar with the given date and time set for the default 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 (TimeZone zone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.

GregorianCalendar (TimeZone zone, Locale aLocale)
Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.

Method Summary

void	add (int field, int amount) Adds the specified (signed) amount of time to the given calendar field, based on the calendar's rules.
Object	clone () Creates and returns a copy of this object.
protected void	computeFields () Converts the time value (millisecond offset from the Epoch) to calendar field values.
protected void	computeTime () Converts calendar field values to the time value (millisecond offset from the Epoch).
boolean	equals (Object obj) Compares this GregorianCalendar to the specified Object.
int	getActualMaximum (int field) Returns the maximum value that this calendar field could have, taking into consideration the given time value and the current values of the getFirstDayOfWeek , getMinimalDaysInFirstWeek , getGregorianChange and getTimeZone methods.
int	getActualMinimum (int field) Returns the minimum value that this calendar field could have, taking into consideration the given time value and the current values of the getFirstDayOfWeek , getMinimalDaysInFirstWeek , getGregorianChange and getTimeZone methods.
int	getGreatestMinimum (int field) Returns the highest minimum value for the given calendar field of this GregorianCalendar instance.
Date	getGregorianChange () Gets the Gregorian Calendar change date.
int	getLeastMaximum (int field) Returns the lowest maximum value for the given calendar field of this GregorianCalendar instance.
int	getMaximum (int field) Returns the maximum value for the given calendar field of this GregorianCalendar instance.
int	getMinimum (int field) Returns the minimum value for the given calendar field of this GregorianCalendar instance.
TimeZone	getTimeZone () Gets the time zone.
int	hashCode () Generates the hash code for this GregorianCalendar object.
boolean	isLeapYear (int year) Determines if the given year is a leap year.
void	roll (int field, boolean up) Adds or subtracts (up/down) a single unit of time on the given time field without changing larger fields.
void	roll (int field, int amount) Adds a signed amount to the specified calendar field without changing larger fields.
void	setGregorianChange (Date date) Sets the GregorianCalendar change date.
void	setTimeZone (TimeZone zone) Sets the time zone with the given time zone value.

Methods inherited from class java.util.Calendar

after , before , clear , clear , compareTo , complete , get , getAvailableLocales , getFirstDayOfWeek , getInstance , getInstance , getInstance , getInstance , getMinimalDaysInFirstWeek , getTime , getTimeInMillis , internalGet , isLenient , isSet , set , set , set , set , setFirstDayOfWeek , setLenient , setMinimalDaysInFirstWeek , setTime , setTimeInMillis , toString

Methods inherited from class java.lang.Object

finalize , getClass , notify , notifyAll , wait , wait , wait

Field Detail

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:

Calendar.ERA , Constant Field Values

AD

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:

Calendar.ERA , Constant Field Values

Constructor Detail

GregorianCalendar

public GregorianCalendar()

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

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.

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.

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.

GregorianCalendar

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

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 calendar field in the calendar.

month - the value used to set the MONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.

dayOfMonth - the value used to set the DAY_OF_MONTH calendar field in the calendar.

GregorianCalendar

public GregorianCalendar(int year,
                         int month,
                         int dayOfMonth,
                         int hourOfDay,
                         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 calendar field in the calendar.

month - the value used to set the MONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.

dayOfMonth - the value used to set the DAY_OF_MONTH calendar field in the calendar.

hourOfDay - the value used to set the HOUR_OF_DAY calendar field in the calendar.

minute - the value used to set the MINUTE calendar field in the calendar.

GregorianCalendar

public GregorianCalendar(int year,
                         int month,
                         int dayOfMonth,
                         int hourOfDay,
                         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 calendar field in the calendar.

month - the value used to set the MONTH calendar field in the calendar. Month value is 0-based. e.g., 0 for January.

dayOfMonth - the value used to set the DAY_OF_MONTH calendar field in the calendar.

hourOfDay - the value used to set the HOUR_OF_DAY calendar field in the calendar.

minute - the value used to set the MINUTE calendar field in the calendar.

second - the value used to set the SECOND calendar field in the calendar.

Method Detail

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 (Gregorian). 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.

getGregorianChange