GregorianCalendar

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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.

Week Of Year and Week Year

Values calculated for the WEEK_OF_YEAR field range from 1 to 53. The first week of a calendar 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 (exclusive) are numbered sequentially from 2 to 52 or 53 (except for year(s) involved in the Julian-Gregorian transition).

The getFirstDayOfWeek() and getMinimalDaysInFirstWeek() values are initialized using locale-dependent resources when constructing a GregorianCalendar. The week determination is compatible with the ISO 8601 standard when getFirstDayOfWeek() is MONDAY and getMinimalDaysInFirstWeek() is 4, which values are used in locales where the standard is preferred. These values can explicitly be set by calling setFirstDayOfWeek() and setMinimalDaysInFirstWeek().

A week year is in sync with a WEEK_OF_YEAR cycle. All weeks between the first and last weeks (inclusive) have the same week year value. Therefore, the first and last days of a week year may have different calendar year values.

For example, January 1, 1998 is a Thursday. If getFirstDayOfWeek() is MONDAY and getMinimalDaysInFirstWeek() is 4 (ISO 8601 standard compatible setting), then week 1 of 1998 starts on December 29, 1997, and ends on January 4, 1998. The week year is 1998 for the last three days of calendar year 1997. 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 and their week year is 1997.

Week Of Month

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.

Default Fields Values

The clear method sets 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 Saving 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
 

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

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

Public 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.
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.
String
getCalendarType()
Returns "gregory" as the calendar type.
int
getGreatestMinimum(int field)
Returns the highest minimum value for the given calendar field of this GregorianCalendar instance.
final 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
getWeekYear()
Returns the week year represented by this GregorianCalendar.
int
getWeeksInWeekYear()
Returns the number of weeks in the week year represented by this GregorianCalendar.
int
hashCode()
Generates the hash code for this GregorianCalendar object.
boolean
isLeapYear(int year)
Determines if the given year is a leap year.
final boolean
isWeekDateSupported()
Returns true indicating this GregorianCalendar supports week dates.
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.
void
setWeekDate(int weekYear, int weekOfYear, int dayOfWeek)
Sets this GregorianCalendar to the date given by the date specifiers - weekYear, weekOfYear, and dayOfWeek.

Protected Method Summary

void
computeFields()
Converts the time value (millisecond offset from the Epoch) to calendar field values.
void
computeTime()
Converts calendar field values to the time value (millisecond offset from the Epoch).

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

Public Constructors

public GregorianCalendar ()

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

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.

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 (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.

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.

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.

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.

Public Methods

public void add (int field, int amount)

Adds the specified (signed) amount of time to the given calendar 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.

Parameters
field the calendar field.
amount the amount of date or time to be added to the field.
Throws
IllegalArgumentException if field is ZONE_OFFSET, DST_OFFSET, or unknown, or if any calendar fields have out-of-range values in non-lenient mode.

public Object clone ()

Creates and returns a copy of this object.

Returns
  • a copy of this object.

public boolean equals (Object obj)

Compares this GregorianCalendar to the specified Object. The result is true if and only if the argument is a GregorianCalendar object that represents the same time value (millisecond offset from the Epoch) under the same Calendar parameters and Gregorian change date as this object.

Parameters
obj the object to compare with.
Returns
  • true if this object is equal to obj; false otherwise.

public 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. For example, if the date of this instance is February 1, 2004, the actual maximum value of the DAY_OF_MONTH field is 29 because 2004 is a leap year, and if the date of this instance is February 1, 2005, it's 28.

This method calculates the maximum value of WEEK_OF_YEAR based on the YEAR (calendar year) value, not the week year. Call getWeeksInWeekYear() to get the maximum value of WEEK_OF_YEAR in the week year of this GregorianCalendar.

Parameters
field the calendar field
Returns
  • the maximum of the given field for the time value of this GregorianCalendar

public 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.

For example, if the Gregorian change date is January 10, 1970 and the date of this GregorianCalendar is January 20, 1970, the actual minimum value of the DAY_OF_MONTH field is 10 because the previous date of January 10, 1970 is December 27, 1996 (in the Julian calendar). Therefore, December 28, 1969 to January 9, 1970 don't exist.

Parameters
field the calendar field
Returns
  • the minimum of the given field for the time value of this GregorianCalendar

public String getCalendarType ()

Returns "gregory" as the calendar type.

Returns
  • "gregory"

public int getGreatestMinimum (int field)

Returns the highest minimum value for the given calendar field of this GregorianCalendar instance. The highest minimum value is defined as the largest value returned by getActualMinimum(int) for any possible time value, taking into consideration the current values of the getFirstDayOfWeek, getMinimalDaysInFirstWeek, getGregorianChange and getTimeZone methods.

Parameters
field the calendar field.
Returns
  • the highest minimum value for the given calendar field.

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 (Gregorian). Previous to this, dates will be in the Julian calendar.

Returns
  • the Gregorian cutover date for this GregorianCalendar object.

public int getLeastMaximum (int field)

Returns the lowest maximum value for the given calendar field of this GregorianCalendar instance. The lowest maximum value is defined as the smallest value returned by getActualMaximum(int) for any possible time value, taking into consideration the current values of the getFirstDayOfWeek, getMinimalDaysInFirstWeek, getGregorianChange and getTimeZone methods.

Parameters
field the calendar field
Returns
  • the lowest maximum value for the given calendar field.

public int getMaximum (int field)

Returns the maximum value for the given calendar field of this GregorianCalendar instance. The maximum value is defined as the largest value returned by the get method for any possible time value, taking into consideration the current values of the getFirstDayOfWeek, getMinimalDaysInFirstWeek, getGregorianChange and getTimeZone methods.

Parameters
field the calendar field.
Returns
  • the maximum value for the given calendar field.

public int getMinimum (int field)

Returns the minimum value for the given calendar field of this GregorianCalendar instance. The minimum value is defined as the smallest value returned by the get method for any possible time value, taking into consideration the current values of the getFirstDayOfWeek, getMinimalDaysInFirstWeek, getGregorianChange and getTimeZone methods.

Parameters
field the calendar field.
Returns
  • the minimum value for the given calendar field.

public TimeZone getTimeZone ()

Gets the time zone.

Returns
  • the time zone object associated with this calendar.

public int getWeekYear ()

Returns the week year represented by this GregorianCalendar. The dates in the weeks between 1 and the maximum week number of the week year have the same week year value that may be one year before or after the YEAR (calendar year) value.

This method calls