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
|
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
GregorianCalendar using the current time
in the default time zone with the default locale.GregorianCalendar based on the current time
in the given time zone with the default locale.GregorianCalendar based on the current time
in the default time zone with the given locale.GregorianCalendar based on the current time
in the given time zone with the given locale.GregorianCalendar with the given date set
in the default time zone with the default locale.GregorianCalendar with the given date
and time set for the default time zone with the default locale.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,...get and set indicating
whether the HOUR is before or after noon.
E.g., at 10:04:15.250 PM the AM_PM is PM.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,...get and set indicating the
day of the month. This is a synonym for DAY_OF_MONTH.
The first day of the month has value 1.get and set indicating the
day of the month. This is a synonym for DATE.
The first day of the month has value 1.get and set indicating the day
of the week. This field takes values SUNDAY,
MONDAY, TUESDAY, WEDNESDAY,
THURSDAY, FRIDAY, and SATURDAY.get and set indicating the
ordinal number of the day of the week within the current month. Together
with the DAY_OF_WEEK field, this uniquely specifies a day
within a month. Unlike WEEK_OF_MONTH and
WEEK_OF_YEAR, this field's value does not depend on
getFirstDayOfWeek() or
getMinimalDaysInFirstWeek(). DAY_OF_MONTH 1
through 7 always correspond to DAY_OF_WEEK_IN_MONTH
1; 8 through 14 correspond to
DAY_OF_WEEK_IN_MONTH 2, and so on.
DAY_OF_WEEK_IN_MONTH 0 indicates the week before
DAY_OF_WEEK_IN_MONTH 1. Negative values count back from the
end of the month, so the last Sunday of a month is specified as
DAY_OF_WEEK = SUNDAY, DAY_OF_WEEK_IN_MONTH = -1. Because
negative values count backward they will usually be aligned differently
within the month than positive values. For example, if a month has 31
days, DAY_OF_WEEK_IN_MONTH -1 will overlap
DAY_OF_WEEK_IN_MONTH 5 and the end of 4.get and set indicating the day
number within the current year. The first day of the year has value 1.get and set indicating the
daylight savings offset in milliseconds.
This field reflects the correct daylight saving offset value of
the time zone of this Calendar if the
TimeZone implementation subclass supports
historical Daylight Saving Time schedule changes.
get and set indicating the
era, e.g., AD or BC in the Julian calendar. This is a calendar-specific
value; see subclass documentation.get and set.
Field numbers range from 0..FIELD_COUNT-1.get and set indicating the
hour of the morning or afternoon. HOUR is used for the
12-hour clock (0 - 11). Noon and midnight are represented by 0, not by 12.
E.g., at 10:04:15.250 PM the HOUR is 10.get and set indicating the
hour of the day. HOUR_OF_DAY is used for the 24-hour clock.
E.g., at 10:04:15.250 PM the HOUR_OF_DAY is 22.get and set indicating the
millisecond within the second.
E.g., at 10:04:15.250 PM the MILLISECOND is 250.get and set indicating the
minute within the hour.
E.g., at 10:04:15.250 PM the MINUTE is 4.get and set indicating the
month. This is a calendar-specific value. The first month of the year is
JANUARY which is 0; the last depends on the number of months in a year.get and set indicating the
second within the minute.
E.g., at 10:04:15.250 PM the SECOND is 15.GregorianCalendar
does not use this value, lunar calendars do.get and set indicating the
week number within the current month. The first week of the month, as
defined by getFirstDayOfWeek() and
getMinimalDaysInFirstWeek(), has value 1. Subclasses define
the value of WEEK_OF_MONTH for days before the first week of
the month.get and set indicating the
week number within the current year. The first week of the year, as
defined by getFirstDayOfWeek() and
getMinimalDaysInFirstWeek(), has value 1. Subclasses define
the value of WEEK_OF_YEAR for days before the first week of
the year.get and set indicating the
year. This is a calendar-specific value; see subclass documentation.get and set
indicating the raw offset from GMT in milliseconds.
This field reflects the correct GMT offset value of the time
zone of this Calendar if the
TimeZone implementation subclass supports
historical GMT offset changes.
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.
Calendar represents a time
after the time represented by the specified
Object. This method is equivalent to:
if and only ifcompareTo(when) > 0
when is a Calendar
instance. Otherwise, the method returns false.Calendar represents a time
before the time represented by the specified
Object. This method is equivalent to:
if and only ifcompareTo(when) < 0
when is a Calendar
instance. Otherwise, the method returns false.Calendar undefined. This means that isSet()
will return false for all the
calendar fields, and the date and time calculations will treat
the fields as if they had never been set. A
Calendar implementation class may use its specific
default field values for date/time calculations. For example,
GregorianCalendar uses 1970 if the
YEAR field value is undefined.Calendar undefined. This means that isSet(field)
will return false, and
the date and time calculations will treat the field as if it
had never been set. A Calendar implementation
class may use the field's specific default value for date and
time calculations.
The #HOUR_OF_DAY
, #HOUR
and #AM_PM
fields are handled independently and the the resolution rule for the time of
day is applied. Clearing one of the fields doesn't reset
the hour of day value of this Calendar. Use set(Calendar.HOUR_OF_DAY, 0)
to reset the hour
value.
Calendar objects.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.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.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.
getInstance
methods of this class can return localized instances.
The array returned must contain at least a Locale
instance equal to Locale.US
.SUNDAY in the U.S.,
MONDAY in France.GregorianCalendar instance. The highest
minimum value is defined as the largest value returned by
for any possible time value,
taking into consideration the current values of the
getFirstDayOfWeek
,
getMinimalDaysInFirstWeek
,
getGregorianChange
and
getTimeZone
methods.Calendar returned is based on the current time
in the default time zone with the default locale.Calendar returned is based on the current time
in the default time zone with the given locale.Calendar returned is based on the current time
in the given time zone with the default locale.Calendar returned is based on the current time
in the given time zone with the given locale.GregorianCalendar instance. The lowest
maximum value is defined as the smallest value returned by
for any possible time value,
taking into consideration the current values of the
getFirstDayOfWeek
,
getMinimalDaysInFirstWeek
,
getGregorianChange
and
getTimeZone
methods.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.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.GregorianCalendar object.true if
the given year is a leap year. To specify BC year numbers,
1 - year number must be given. For example, year BC 4 is
specified as -3.get method call.wait methods.
The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:
synchronized statement
that synchronizes on the object.
Class, by executing a
synchronized static method of that class.
Only one thread at a time can own an object's monitor.
wait methods.
The awakened threads will not be able to proceed until the current thread relinquishes the lock on this object. The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.
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.
This method calls
before adding the
amount so that all the calendar fields are normalized. If there
is any calendar field having an out-of-range value in non-lenient mode, then an
IllegalArgumentException is thrown.
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).
SUNDAY in the U.S.,
MONDAY in France.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).
Date.
Note: Calling setTime() with
Date(Long.MAX_VALUE) or Date(Long.MIN_VALUE)
may yield incorrect field values from get().
null.
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until another thread
notifies threads waiting on this object's monitor to wake up
either through a call to the notify method or the
notifyAll method. The thread then waits until it can
re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) {
while (<condition does not hold>)
obj.wait();
... // Perform action appropriate to condition
}
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.The current thread must own this object's monitor.
This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. Thread T becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:
synchronized (obj) {
while (<condition does not hold>)
obj.wait(timeout);
... // Perform action appropriate to condition
}
(For more information on this topic, see Section 3.2.3 in Doug Lea's
"Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
2000), or Item 50 in Joshua Bloch's "Effective Java Programming
Language Guide" (Addison-Wesley, 2001).
If the current thread is interrupted by another thread while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.
Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.
This method is similar to the wait method of one
argument, but it allows finer control over the amount of time to
wait for a notification before giving up. The amount of real time,
measured in nanoseconds, is given by:
1000000*timeout+nanos
In all other respects, this method does the same thing as the method of one argument. In particular, wait(0, 0) means the same thing as wait(0).
The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until either of the following two conditions has occurred:
notify method
or the notifyAll method.
timeout
milliseconds plus nanos nanoseconds arguments, has
elapsed.
The thread then waits until it can re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) {
while (<condition does not hold>)
obj.wait(timeout, nanos);
... // Perform action appropriate to condition
}
This method should only be called by a thread that is the owner
of this object's monitor. See the notify method for a
description of the ways in which a thread can become the owner of
a monitor.