Class java.util.GregorianCalendar 
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Class java.util.GregorianCalendar 

Object
   |
   +----Calendar
           |
           +----java.util.GregorianCalendar
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). This cutover date may be changed by the caller.

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.

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

Version:
1.29 02/02/98
Author:
David Goldsmith, Mark Davis, Chen-Lieh Huang, Alan Liu
See Also:
Calendar, TimeZone

Variable Index

o AD
Useful constant for GregorianCalendar.
o BC
Useful constant for GregorianCalendar.

Constructor Index

o java.util.GregorianCalendar()
Constructs a default GregorianCalendar using the current time in the default time zone with the default locale.
o java.util.GregorianCalendar(TimeZone)
Constructs a GregorianCalendar based on the current time in the given time zone with the default locale.
o java.util.GregorianCalendar(Locale)
Constructs a GregorianCalendar based on the current time in the default time zone with the given locale.
o java.util.GregorianCalendar(TimeZone, Locale)
Constructs a GregorianCalendar based on the current time in the given time zone with the given locale.
o java.util.GregorianCalendar(int, int, int)
Constructs a GregorianCalendar with the given date set in the default time zone with the default locale.
o java.util.GregorianCalendar(int, int, int, int, int)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.
o java.util.GregorianCalendar(int, int, int, int, int, int)
Constructs a GregorianCalendar with the given date and time set for the default time zone with the default locale.

Method Index

o add(int, int)
Overrides Calendar Date Arithmetic function.
o after(Object)
Compares the time field records.
o before(Object)
Compares the time field records.
o computeFields()
Overrides Calendar Converts UTC as milliseconds to time field values.
o computeTime()
Overrides Calendar Converts time field values to UTC as milliseconds.
o equals(Object)
Compares this calendar to the specified object.
o getGreatestMinimum(int)
Returns highest minimum value for the given field if varies.
o getGregorianChange()
Gets the Gregorian Calendar change date.
o getLeastMaximum(int)
Returns lowest maximum value for the given field if varies.
o getMaximum(int)
Returns maximum value for the given field.
o getMinimum(int)
Returns minimum value for the given field.
o hashCode()
Override hashCode.
o isLeapYear(int)
Determines if the given year is a leap year.
o roll(int, boolean)
Overrides Calendar Time Field Rolling function.
o setGregorianChange(Date)
Sets the GregorianCalendar change date.

Variables

o AD 
public static final int AD
Useful constant for GregorianCalendar.

o BC 
public static final int BC
Useful constant for GregorianCalendar.

Constructors

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

o 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.
o 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.
o 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.
o 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.
o 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.
o 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.

Methods

o add 
public void add(int field,
                int amount)
Overrides Calendar Date Arithmetic function. Adds the specified (signed) amount of time to the given time field, based on the calendar's rules.

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.
Overrides:
add in class Calendar
o after 
public boolean after(Object when)
Compares the time field records. Equivalent to comparing result of conversion to UTC.

Parameters:
when - the Calendar to be compared with this Calendar.
Returns:
true if the current time of this Calendar is after the time of Calendar when; false otherwise.
Overrides:
after in class Calendar
o before 
public boolean before(Object when)
Compares the time field records. Equivalent to comparing result of conversion to UTC.

Parameters:
when - the Calendar to be compared with this Calendar.
Returns:
true if the current time of this Calendar is before the time of Calendar when; false otherwise.
Overrides:
before in class Calendar
o computeFields 
protected void computeFields()
Overrides Calendar 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.

Overrides:
computeFields in class Calendar
See Also:
complete
o computeTime 
protected void computeTime()
Overrides Calendar Converts time field values to UTC as milliseconds.

Throws: IllegalArgumentException
if any fields are invalid.
Overrides:
computeTime in class Calendar
o equals 
public boolean equals(Object obj)
Compares this calendar to the specified object. The result is true if and only if the argument is not null and is a Calendar object that represents the same calendar as this object.

Parameters:
obj - the object to compare with.
Returns:
true if the objects are the same; false otherwise.
Overrides:
equals in class Calendar
o 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.

Overrides:
getGreatestMinimum in class Calendar
o getGregorianChange 
public final java.util.Date getGregorianChange()
Gets the Gregorian Calendar change date. This is the point when the switch from Julian dates to Gregorian dates occurred. Default is 00:00:00 local time, October 15, 1582. Previous to this time and date will be Julian dates.

Returns:
the Gregorian cutover time for this calendar.
o 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.

Overrides:
getLeastMaximum in class Calendar
o 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.

Overrides:
getMaximum in class Calendar
o 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.

Overrides:
getMinimum in class Calendar
o hashCode 
public synchronized int hashCode()
Override hashCode. Generates the hash code for the GregorianCalendar object

Overrides:
hashCode in class Object
o 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.
o roll 
public void roll(int field,
                 boolean up)
Overrides Calendar Time Field Rolling function. Rolls (up/down) a single unit of time on the given time field.

Parameters:
field - the time field.
up - Indicates if rolling up or rolling down the field value.
Throws: IllegalArgumentException
if an unknown field value is given.
Overrides:
roll in class Calendar
o 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 00:00:00 local time, October 15, 1582. Previous to this time and date will be Julian dates.

Parameters:
date - the given Gregorian cutover date. 
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