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java.util

Class GregorianCalendar

Implemented Interfaces:
Cloneable, Comparable<T>, Serializable
public class GregorianCalendar
extends Calendar
This class represents the Gregorian calendar, that is used in most countries all over the world. It does also handle the Julian calendar for dates smaller than the date of the change to the Gregorian calendar. The Gregorian calendar differs from the Julian calendar by a different leap year rule (no leap year every 100 years, except if year is divisible by 400).

This change date is different from country to country, and can be changed with setGregorianChange. The first countries to adopt the Gregorian calendar did so on the 15th of October, 1582. This date followed October the 4th, 1582 in the Julian calendar system. The non-existant days that were omitted when the change took place are interpreted as Gregorian dates.

Prior to the changeover date, New Year's Day occurred on the 25th of March. However, this class always takes New Year's Day as being the 1st of January. Client code should manually adapt the year value, if required, for dates between January the 1st and March the 24th in years prior to the changeover.

Any date infinitely forwards or backwards in time can be represented by this class. A proleptic calendar system is used, which allows future dates to be created via the existing rules. This allows meaningful and consistent dates to be produced for all years. However, dates are only historically accurate following March the 1st, 4AD when the Julian calendar system was adopted. Prior to this, leap year rules were applied erraticly.

There are two eras available for the Gregorian calendar, namely BC and AD.

Weeks are defined as a period of seven days, beginning on the first day of the week, as returned by getFirstDayOfWeek(), and ending on the day prior to this.

The weeks of the year are numbered from 1 to a possible 53. The first week of the year is defined as the first week that contains at least the minimum number of days of the first week in the new year (retrieved via getMinimalDaysInFirstWeek()). All weeks after this are numbered from 2 onwards.

For example, take the year 2004. It began on a Thursday. The first week of 2004 depends both on where a week begins and how long it must minimally last. Let's say that the week begins on a Monday and must have a minimum of 5 days. In this case, the first week begins on Monday, the 5th of January. The first 4 days (Thursday to Sunday) are not eligible, as they are too few to make up the minimum number of days of the first week which must be in the new year. If the minimum was lowered to 4 days, then the first week would instead begin on Monday, the 29th of December, 2003. This first week has 4 of its days in the new year, and is now eligible.

The weeks of the month are numbered from 0 to a possible 6. The first week of the month (numbered 1) is a set of days, prior to the first day of the week, which number at least the minimum number of days in a week. Unlike the first week of the year, the first week of the month only uses days from that particular month. As a consequence, it may have a variable number of days (from the minimum number required up to a full week of 7) and it need not start on the first day of the week. It must, however, be following by the first day of the week, as this marks the beginning of week 2. Any days of the month which occur prior to the first week (because the first day of the week occurs before the minimum number of days is met) are seen as week 0.

Again, we will take the example of the year 2004 to demonstrate this. September 2004 begins on a Wednesday. Taking our first day of the week as Monday, and the minimum length of the first week as 6, we find that week 1 runs from Monday, the 6th of September to Sunday the 12th. Prior to the 6th, there are only 5 days (Wednesday through to Sunday). This is too small a number to meet the minimum, so these are classed as being days in week 0. Week 2 begins on the 13th, and so on. This changes if we reduce the minimum to 5. In this case, week 1 is a truncated week from Wednesday the 1st to Sunday the 5th, and week 0 doesn't exist. The first seven day week is week 2, starting on the 6th.

On using the clear() method, the Gregorian calendar returns to its default value of the 1st of January, 1970 AD 00:00:00 (the epoch). The day of the week is set to the correct day for that particular time. The day is also the first of the month, and the date is in week 0.

See Also:
Calendar, TimeZone, Calendar.getFirstDayOfWeek(), Calendar.getMinimalDaysInFirstWeek(), Serialized Form

Field Summary

static int
AD
Constant representing the era AD (Anno Domini).
static int
BC
Constant representing the era BC (Before Christ).

Fields inherited from class java.util.Calendar

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

Constructor Summary

GregorianCalendar()
Constructs a new GregorianCalender representing the current time, using the default time zone and the default locale.
GregorianCalendar(int year, int month, int day)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
GregorianCalendar(int year, int month, int day, int hour, int minute)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
GregorianCalendar(int year, int month, int day, int hour, int minute, int second)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
GregorianCalendar(Locale locale)
Constructs a new GregorianCalender representing the current time, using the default time zone and the specified locale.
GregorianCalendar(TimeZone zone)
Constructs a new GregorianCalender representing the current time, using the specified time zone and the default locale.
GregorianCalendar(TimeZone zone, Locale locale)
Constructs a new GregorianCalender representing the current time with the given time zone and the given locale.

Method Summary

void
add(int field, int amount)
Adds the specified amount of time to the given time field.
protected void
computeFields()
Converts the milliseconds since the epoch UTC (time) to time fields (fields).
protected void
computeTime()
Converts the time field values (fields) to milliseconds since the epoch UTC (time).
boolean
equals(Object o)
Compares the given calendar with this.
int
getActualMaximum(int field)
Gets the actual maximum value that is allowed for the specified field.
int
getActualMinimum(int field)
Gets the actual minimum value that is allowed for the specified field.
int
getGreatestMinimum(int field)
Gets the greatest minimum value that is allowed for the specified field.
Date
getGregorianChange()
Gets the date of the switch from Julian dates to Gregorian dates.
int
getLeastMaximum(int field)
Gets the smallest maximum value that is allowed for the specified field.
int
getMaximum(int field)
Gets the biggest value that is allowed for the specified field.
int
getMinimum(int field)
Gets the smallest value that is allowed for the specified field.
int
hashCode()
Return a hash code for this object, following the general contract specified by Object.hashCode().
boolean
isLeapYear(int year)
Determines if the given year is a leap year.
void
roll(int field, boolean up)
Rolls the specified time field up or down.
void
roll(int field, int amount)
Rolls the specified time field by the given amount.
void
setGregorianChange(Date date)
Sets the date of the switch from Julian dates to Gregorian dates.

Methods inherited from class java.util.Calendar

add, after, before, clear, clear, clone, compareTo, complete, computeFields, computeTime, equals, get, getActualMaximum, getActualMinimum, getAvailableLocales, getDisplayName, getDisplayNames, getFirstDayOfWeek, getGreatestMinimum, getInstance, getInstance, getInstance, getInstance, getLeastMaximum, getMaximum, getMinimalDaysInFirstWeek, getMinimum, getTime, getTimeInMillis, getTimeZone, hashCode, internalGet, isLenient, isSet, roll, roll, set, set, set, set, setFirstDayOfWeek, setLenient, setMinimalDaysInFirstWeek, setTime, setTimeInMillis, setTimeZone, toString

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

AD
Constant representing the era AD (Anno Domini).
Field Value:
1

BC

public static final int BC
Constant representing the era BC (Before Christ).
Field Value:
0

Constructor Details

GregorianCalendar

public GregorianCalendar()
Constructs a new GregorianCalender representing the current time, using the default time zone and the default locale.

GregorianCalendar

public GregorianCalendar(int year,
                         int month,
                         int day)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
Parameters:
year - corresponds to the YEAR time field.
month - corresponds to the MONTH time field.
day - corresponds to the DAY time field.

GregorianCalendar

public GregorianCalendar(int year,
                         int month,
                         int day,
                         int hour,
                         int minute)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
Parameters:
year - corresponds to the YEAR time field.
month - corresponds to the MONTH time field.
day - corresponds to the DAY time field.
hour - corresponds to the HOUR_OF_DAY time field.
minute - corresponds to the MINUTE time field.

GregorianCalendar

public GregorianCalendar(int year,
                         int month,
                         int day,
                         int hour,
                         int minute,
                         int second)
Constructs a new GregorianCalendar representing midnight on the given date with the default time zone and locale.
Parameters:
year - corresponds to the YEAR time field.
month - corresponds to the MONTH time field.
day - corresponds to the DAY time field.
hour - corresponds to the HOUR_OF_DAY time field.
minute - corresponds to the MINUTE time field.
second - corresponds to the SECOND time field.

GregorianCalendar

public GregorianCalendar(Locale locale)
Constructs a new GregorianCalender representing the current time, using the default time zone and the specified locale.
Parameters:
locale - a locale.

GregorianCalendar

public GregorianCalendar(TimeZone zone)
Constructs a new GregorianCalender representing the current time, using the specified time zone and the default locale.
Parameters:
zone - a time zone.

GregorianCalendar

public GregorianCalendar(TimeZone zone,
                         Locale locale)
Constructs a new GregorianCalender representing the current time with the given time zone and the given locale.
Parameters:
zone - a time zone.
locale - a locale.

Method Details

add

public void add(int field,
                int amount)
Adds the specified amount of time to the given time field. The amount may be negative to subtract the time. If the field overflows it does what you expect: Jan, 25 + 10 Days is Feb, 4.
Overrides:
add in interface Calendar
Parameters:
field - one of the time field constants.
amount - the amount of time to add.
Throws:
IllegalArgumentException - if field is ZONE_OFFSET, DST_OFFSET, or invalid; or if amount contains an out-of-range value and the calendar is not in lenient mode.

computeFields

protected void computeFields()
Converts the milliseconds since the epoch UTC (time) to time fields (fields).
Overrides:
computeFields in interface Calendar

computeTime

protected void computeTime()
Converts the time field values (fields) to milliseconds since the epoch UTC (time).
Overrides:
computeTime in interface Calendar
Throws:
IllegalArgumentException - if any calendar fields are invalid.

equals

public boolean equals(Object o)
Compares the given calendar with this. An object, o, is equivalent to this if it is also a GregorianCalendar with the same time since the epoch under the same conditions (same change date and same time zone).
Overrides:
equals in interface Calendar
Parameters:
o - the object to that we should compare.
Returns:
true, if the given object is a calendar, that represents the same time (but doesn't necessarily have the same fields).
Throws:
IllegalArgumentException - if one of the fields ZONE_OFFSET or DST_OFFSET is specified, if an unknown field is specified or if one of the calendar fields receives an illegal value when leniancy is not enabled.

getActualMaximum

public int getActualMaximum(int field)
Gets the actual maximum value that is allowed for the specified field. This value is dependent on the values of the other fields. Note that this calls complete() if not enough fields are set. This can have ugly side effects. The value given depends on the current time used by this instance; thus, leap years have a maximum day of month value of 29, rather than 28.
Overrides:
getActualMaximum in interface Calendar
Parameters:
field - the time field. One of the time field constants.
Returns:
the actual maximum value.

getActualMinimum

public int getActualMinimum(int field)
Gets the actual minimum value that is allowed for the specified field. This value is dependent on the values of the other fields. Note that this calls complete() if not enough fields are set. This can have ugly side effects. The value given depends on the current time used by this instance.
Overrides:
getActualMinimum in interface Calendar
Parameters:
field - the time field. One of the time field constants.
Returns:
the actual minimum value.
Since:
1.2

getGreatestMinimum

public int getGreatestMinimum(int field)
Gets the greatest minimum value that is allowed for the specified field. This is the largest value returned by the getActualMinimum(int) method.
Overrides:
getGreatestMinimum in interface Calendar
Parameters:
field - the time field. One of the time field constants.
Returns:
the greatest minimum value.
See Also:
getActualMinimum(int)

getGregorianChange

public final Date getGregorianChange()
Gets the date of the switch from Julian dates to Gregorian dates.
Returns:
the date of the change.

getLeastMaximum

public int getLeastMaximum(int field)
Gets the smallest maximum value that is allowed for the specified field. This is the smallest value returned by the getActualMaximum(int). For example, this is 28 for DAY_OF_MONTH (as all months have at least 28 days).
Overrides:
getLeastMaximum in interface Calendar
Parameters:
field - the time field. One of the time field constants.
Returns:
the least maximum value.
Since:
1.2
See Also:
getActualMaximum(int)

getMaximum

public int getMaximum(int field)
Gets the biggest value that is allowed for the specified field.
Overrides:
getMaximum in interface Calendar
Parameters:
field - one of the time field constants.
Returns:
the biggest value.

getMinimum

public int getMinimum(int field)
Gets the smallest value that is allowed for the specified field.
Overrides:
getMinimum in interface Calendar
Parameters:
field - one of the time field constants.
Returns:
the smallest value for the specified field.

hashCode

public int hashCode()
Return a hash code for this object, following the general contract specified by Object.hashCode().
Overrides:
hashCode in interface Calendar
Returns:
the hash code

isLeapYear

public boolean isLeapYear(int year)
Determines if the given year is a leap year. The result is undefined if the Gregorian change took place in 1800, so that the end of February is skipped, and that year is specified. (well...).

To specify a year in the BC era, use a negative value calculated as 1 - y, where y is the required year in BC. So, 1 BC is 0, 2 BC is -1, 3 BC is -2, etc.

Parameters:
year - a year (use a negative value for BC).
Returns:
true, if the given year is a leap year, false otherwise.

roll

public void roll(int field,
                 boolean up)
Rolls the specified time field up or down. This means add one to the specified field, but don't change the other fields. If the maximum for this field is reached, start over with the minimum value. Note: There may be situation, where the other fields must be changed, e.g rolling the month on May, 31. The date June, 31 is automatically converted to July, 1. This requires lenient settings.
Overrides:
roll in interface Calendar
Parameters:
field - the time field. One of the time field constants.
up - the direction, true for up, false for down.
Throws:
IllegalArgumentException - if one of the fields ZONE_OFFSET or DST_OFFSET is specified, if an unknown field is specified or if one of the calendar fields receives an illegal value when leniancy is not enabled.

roll

public void roll(int field,
                 int amount)
Rolls the specified time field by the given amount. This means add amount to the specified field, but don't change the other fields. If the maximum for this field is reached, start over with the minimum value and vice versa for negative amounts. Note: There may be situation, where the other fields must be changed, e.g rolling the month on May, 31. The date June, 31 is automatically corrected to June, 30.
Overrides:
roll in interface Calendar
Parameters:
field - the time field. One of the time field constants.
amount - the amount by which we should roll.
Throws:
IllegalArgumentException - if one of the fields ZONE_OFFSET or DST_OFFSET is specified, if an unknown field is specified or if one of the calendar fields receives an illegal value when leniancy is not enabled.

setGregorianChange

public void setGregorianChange(Date date)
Sets the date of the switch from Julian dates to Gregorian dates. You can use new Date(Long.MAX_VALUE) to use a pure Julian calendar, or Long.MIN_VALUE for a pure Gregorian calendar.
Parameters:
date - the date of the change.
java.util.GregorianCalendar Copyright (C) 1998, 1999, 2001, 2002, 2003, 2004, 2007 Free Software Foundation, Inc. This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.

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