java.util
Class GregorianCalendar

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

All Implemented Interfaces:

Cloneable, Serializable

public class GregorianCalendar

extends Calendar

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 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.

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:

Calendar, 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 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.

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 time field, based on the calendar's rules.
protected void	computeFields() Converts UTC as milliseconds to time field values.
protected void	computeTime() Overrides Calendar Converts time field values to UTC as milliseconds.
boolean	equals(Object obj) Compares this GregorianCalendar to an object reference.
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.
int	getGreatestMinimum(int field) Returns highest minimum value for the given field if varies.
Date	getGregorianChange() Gets the Gregorian Calendar change date.
int	getLeastMaximum(int field) Returns lowest maximum value for the given field if varies.
int	getMaximum(int field) Returns maximum value for the given field.
int	getMinimum(int field) Returns minimum value for the given field.
int	hashCode() Override hashCode.
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) Add to field a signed amount without changing larger fields.
void	setGregorianChange(Date date) Sets the GregorianCalendar change date.

Methods inherited from class java.util.Calendar

after, before, clear, clear, clone, complete, get, getAvailableLocales, getFirstDayOfWeek, getInstance, getInstance, getInstance, getInstance, getMinimalDaysInFirstWeek, getTime, getTimeInMillis, getTimeZone, internalGet, isLenient, isSet, set, set, set, set, setFirstDayOfWeek, setLenient, setMinimalDaysInFirstWeek, setTime, setTimeInMillis, setTimeZone, 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 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.

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.

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.

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. 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

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.

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.

equals

public boolean equals(Object obj)

Compares this GregorianCalendar to an object reference.

Overrides:

equals in class Calendar

Parameters:

obj - the object reference with which to compare

Returns:

true if this object is equal to obj; false otherwise

hashCode

public int hashCode()

Override hashCode. Generates the hash code for the GregorianCalendar object

Overrides:

hashCode in class Calendar

Returns:

a hash code value for this object.

add

public void add(int field,
                int amount)

Adds the specified (signed) amount of time to the given time field, based on the calendar's rules.

Add rule 1. The value of field after the call minus the value of field before the call is amount, modulo any overflow that has occurred in field. Overflow occurs when a field value exceeds its range and, as a result, the next larger field is incremented or decremented and the field value is adjusted back into its range.

Add rule 2. If a smaller field is expected to be invariant, but it is impossible for it to be equal to its prior value because of changes in its minimum or maximum after field is changed, then its value is adjusted to be as close as possible to its expected value. A smaller field represents a smaller unit of time. HOUR is a smaller field than DAY_OF_MONTH. No adjustment is made to smaller fields that are not expected to be invariant. The calendar system determines what fields are expected to be invariant.

Specified by:

add in class Calendar

Parameters:

field - the time field.

amount - the amount of date or time to be added to the field.

Throws:

IllegalArgumentException - if an unknown field is given.

roll

public 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.

Example: Consider a GregorianCalendar originally set to December 31, 1999. Calling roll(Calendar.MONTH, true) sets the calendar to January 31, 1999. The Year field is unchanged because it is a larger field than MONTH.

Specified by:

roll in class Calendar

Parameters:

up - indicates if the value of the specified time field is to be rolled up or rolled down. Use true if rolling up, false otherwise.

field - the time field.

Throws:

IllegalArgumentException - if an unknown field value is given.

See Also:

add(int, int), Calendar.set(int, int)

roll

public void roll(int field,
                 int amount)

Add to field a signed amount without changing larger fields. A negative roll amount means to subtract from field without changing larger fields.

Example: Consider a GregorianCalendar originally set to August 31, 1999. Calling roll(Calendar.MONTH, 8) sets the calendar to April 30, 1999. Using a GregorianCalendar, the DAY_OF_MONTH field cannot be 31 in the month April. DAY_OF_MONTH is set to the closest possible value, 30. The YEAR field maintains the value of 1999 because it is a larger field than MONTH.

Example: Consider a GregorianCalendar originally set to Sunday June 6, 1999. Calling roll(Calendar.WEEK_OF_MONTH, -1) sets the calendar to Tuesday June 1, 1999, whereas calling add(Calendar.WEEK_OF_MONTH, -1) sets the calendar to Sunday May 30, 1999. This is because the roll rule imposes an additional constraint: The MONTH must not change when the WEEK_OF_MONTH is rolled. Taken together with add rule 1, the resultant date must be between Tuesday June 1 and Saturday June 5. According to add rule 2, the DAY_OF_WEEK, an invariant when changing the WEEK_OF_MONTH, is set to Tuesday, the closest possible value to Sunday (where Sunday is the first day of the week).

Overrides:

roll in class Calendar

Parameters:

field - the time field.

amount - the signed amount to add to field.

Since:

1.2

See Also:

add(int, int), Calendar.set(int, int)

getMinimum

public int getMinimum(int field)

Returns minimum value for the given field. e.g. for Gregorian DAY_OF_MONTH, 1 Please see Calendar.getMinimum for descriptions on parameters and the return value.

Specified by:

getMinimum in class Calendar

Parameters:

field - the given time field.

Returns:

the minimum value for the given time field.

getMaximum

public int getMaximum(int field)

Returns maximum value for the given field. e.g. for Gregorian DAY_OF_MONTH, 31 Please see Calendar.getMaximum for descriptions on parameters and the return value.

Specified by:

getMaximum in class Calendar

Parameters:

field - the given time field.

Returns:

the maximum value for the given time field.

getGreatestMinimum

public int getGreatestMinimum(int field)

Returns highest minimum value for the given field if varies. Otherwise same as getMinimum(). For Gregorian, no difference. Please see Calendar.getGreatestMinimum for descriptions on parameters and the return value.

Specified by:

getGreatestMinimum in class Calendar

Parameters:

field - the given time field.

Returns:

the highest minimum value for the given time field.

getLeastMaximum

public int getLeastMaximum(int field)

Returns lowest maximum value for the given field if varies. Otherwise same as getMaximum(). For Gregorian DAY_OF_MONTH, 28 Please see Calendar.getLeastMaximum for descriptions on parameters and the return value.

Specified by:

getLeastMaximum in class Calendar

Parameters:

field - the given time field.

Returns:

the lowest maximum value for the given time field.

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().

Overrides:

getActualMinimum in class Calendar

Parameters:

field - the field to determine the minimum of

Returns:

the minimum of the given field for the current date of this Calendar

Since:

1.2

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.

Overrides:

getActualMaximum in class Calendar

Parameters:

field - the field to determine the maximum of

Returns:

the maximum of the given field for the current date of this Calendar

Since:

1.2

computeFields

protected void computeFields()

Converts UTC as milliseconds to time field values. The time is not recomputed first; to recompute the time, then the fields, call the complete method.

Specified by:

computeFields in class Calendar

See Also:

Calendar.complete()

computeTime

protected void computeTime()

Overrides Calendar Converts time field values to UTC as milliseconds.

Specified by:

computeTime in class Calendar

Throws:

IllegalArgumentException - if any fields are invalid.