Class java.util.Calendar

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Class java.util.Calendar

Object
   |
   +----java.util.Calendar

public abstract class Calendar
extends Object
implements Serializable, Cloneable

Calendar is an abstract base class for converting between a Date object and a set of integer fields such as YEAR, MONTH, DAY, HOUR, and so on. (A Date object represents a specific instant in time with millisecond precision. See java.util.Date for information about the Date class.)

Subclasses of Calendar interpret a Date according to the rules of a specific calendar system. The JDK provides one concrete subclass of Calendar: GregorianCalendar. Future subclasses could represent the various types of lunar calendars in use in many parts of the world.

Like other locale-sensitive classes, Calendar provides a class method, getInstance, for getting a generally useful object of this type. Calendar's getInstance method returns a GregorianCalendar object whose time fields have been initialized with the current date and time:

 Calendar rightNow = Calendar.getInstance();

A Calendar object can produce all the time field values needed to implement the date-time formatting for a particular language and calendar style (for example, Japanese-Gregorian, Japanese-Traditional).

When computing a Date from time fields, two special circumstances may arise: there may be insufficient information to compute the Date (such as only year and month but no day in the month), or there may be inconsistent information (such as "Tuesday, July 15, 1996" -- July 15, 1996 is actually a Monday).

Insufficient information. The calendar will use default information to specify the missing fields. This may vary by calendar; for the Gregorian calendar, the default for a field is the same as that of the start of the epoch: i.e., YEAR = 1970, MONTH = JANUARY, DATE = 1, etc.

Inconsistent information. If fields conflict, the calendar will give preference to fields set more recently. For example, when determining the day, the calendar will look for one of the following combinations of fields. The most recent combination, as determined by the most recently set single field, will be used.

 MONTH + DAY_OF_MONTH
 MONTH + WEEK_OF_MONTH + DAY_OF_WEEK
 MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK
 DAY_OF_YEAR
 DAY_OF_WEEK + WEEK_OF_YEAR

For the time of day:

 HOUR_OF_DAY
 AM_PM + HOUR

Note: for some non-Gregorian calendars, different fields may be necessary for complete disambiguation. For example, a full specification of the historial Arabic astronomical calendar requires year, month, day-of-month and day-of-week in some cases.

Note: There are certain possible ambiguities in interpretation of certain singular times, which are resolved in the following ways:

24:00:00 "belongs" to the following day. That is, 23:59 on Dec 31, 1969 < 24:00 on Jan 1, 1970 < 24:01:00 on Jan 1, 1970
Although historically not precise, midnight also belongs to "am", and noon belongs to "pm", so on the same day, 12:00 am (midnight) < 12:01 am, and 12:00 pm (noon) < 12:01 pm

The date or time format strings are not part of the definition of a calendar, as those must be modifiable or overridable by the user at runtime. Use java.text.DateFormat to format dates.

Calendar provides an API for field "rolling", where fields can be incremented or decremented, but wrap around. For example, rolling the month up in the date "September 12, 1996" results in "October 12, 1996".

Calendar also provides a date arithmetic function for adding the specified (signed) amount of time to a particular time field. For example, subtracting 5 days from the date "September 12, 1996" results in "September 7, 1996".

Version:: 1.17 06 Jan 1997
Author:: Mark Davis, David Goldsmith, Chen-Lieh Huang, Alan Liu
See Also:: Date, GregorianCalendar, TimeZone, DateFormat

AM: Useful constant for hour in 12-hour clock.
AM_PM: Useful constant for date and time.
APRIL: Useful constant for month.
AUGUST: Useful constant for month.
DATE: Useful constant for date and time.
DAY_OF_MONTH: Useful constant for date and time.
DAY_OF_WEEK: Useful constant for date and time.
DAY_OF_WEEK_IN_MONTH: Useful constant for date and time.
DAY_OF_YEAR: Useful constant for date and time.
DECEMBER: Useful constant for month.
DST_OFFSET: Useful constant for date and time.
ERA: Useful constant for date and time.
FEBRUARY: Useful constant for month.
FIELD_COUNT: Useful constant for date and time.
FRIDAY: Useful constant for days of week.
HOUR: Useful constant for date and time.
HOUR_OF_DAY: Useful constant for date and time.
JANUARY: Useful constant for month.
JULY: Useful constant for month.
JUNE: Useful constant for month.
MARCH: Useful constant for month.
MAY: Useful constant for month.
MILLISECOND: Useful constant for date and time.
MINUTE: Useful constant for date and time.
MONDAY: Useful constant for days of week.
MONTH: Useful constant for date and time.
NOVEMBER: Useful constant for month.
OCTOBER: Useful constant for month.
PM: Useful constant for hour in 12-hour clock.
SATURDAY: Useful constant for days of week.
SECOND: Useful constant for date and time.
SEPTEMBER: Useful constant for month.
SUNDAY: Useful constant for days of week.
THURSDAY: Useful constant for days of week.
TUESDAY: Useful constant for days of week.
UNDECIMBER: Useful constant for month.
WEDNESDAY: Useful constant for days of week.
WEEK_OF_MONTH: Useful constant for date and time.
WEEK_OF_YEAR: Useful constant for date and time.
YEAR: Useful constant for date and time.
ZONE_OFFSET: Useful constant for date and time.
areFieldsSet: True if the fields are in sync with the currently set time of this Calendar.
fields: The time fields containing values into which the millis is computed.
isSet: The flags which tell if a specified time field for the calendar is set.
isTimeSet: The flag which indicates if the current time is set for the calendar.
time: The current time set for the calendar.

java.util.Calendar(): Constructs a Calendar with the default time zone as returned by TimeZone.getDefault(), and the default locale.
java.util.Calendar(TimeZone, Locale): Constructs a Calendar with the given time zone and locale.

add(int, int): Date Arithmetic function.
after(Object): Compares the time field records.
before(Object): Compares the time field records.
clear(): Clears the values of all the time fields.
clear(int): Clears the value in the given time field.
clone(): Overrides Cloneable
complete(): Fills in any unset fields in the time field list.
computeFields(): Converts UTC as milliseconds to time field values.
computeTime(): Converts Calendar's time field values to UTC as milliseconds.
equals(Object): Compares this calendar to the specified object.
get(int): Gets the value for a given time field.
getAvailableLocales(): Gets the set of locales for which Calendars are installed.
getFirstDayOfWeek(): Gets what the first day of the week is; e.g., Sunday in US, Monday in France.
getGreatestMinimum(int): Gets the highest minimum value for the given field if varies.
getInstance(): Gets a Calendar using the default timezone and locale.
getInstance(TimeZone): Gets a Calendar using the given timezone and default locale.
getInstance(Locale): Gets a Calendar using the default timezone and given locale.
getInstance(TimeZone, Locale): Gets a Calendar using the given timezone and given locale.
getLeastMaximum(int): Gets the lowest maximum value for the given field if varies.
getMaximum(int): Gets the maximum value for the given time field.
getMinimalDaysInFirstWeek(): Gets what the minimal days required in the first week of the year are; e.g., if the first week is defined as one that contains the first day of the first month of a year, getMinimalDaysInFirstWeek returns 1.
getMinimum(int): Gets the minimum value for the given time field.
getTime(): Gets this Calendar's current time.
getTimeInMillis(): Gets this Calendar's current time as a long.
getTimeZone(): Gets the time zone.
internalGet(int): Gets the value for a given time field.
isLenient(): Tell whether date/time interpretation is to be lenient.
isSet(int): Determines if the given time field has a value set.
roll(int, boolean): Time Field Rolling function.
set(int, int): Sets the time field with the given value.
set(int, int, int): Sets the values for the fields year, month, and date.
set(int, int, int, int, int): Sets the values for the fields year, month, date, hour, and minute.
set(int, int, int, int, int, int): Sets the values for the fields year, month, date, hour, minute, and second.
setFirstDayOfWeek(int): Sets what the first day of the week is; e.g., Sunday in US, Monday in France.
setLenient(boolean): Specify whether or not date/time interpretation is to be lenient.
setMinimalDaysInFirstWeek(int): Sets what the minimal days required in the first week of the year are; For example, if the first week is defined as one that contains the first day of the first month of a year, call the method with value 1.
setTime(Date): Sets this Calendar's current time with the given Date.
setTimeInMillis(long): Sets this Calendar's current time from the given long value.
setTimeZone(TimeZone): Sets the time zone with the given time zone value.
toString(): Return a string representation of this calendar.

public static final int AM

Useful constant for hour in 12-hour clock. Used in GregorianCalendar.

AM_PM

public static final int AM_PM

Useful constant for date and time. Used in time fields.

APRIL

public static final int APRIL

Useful constant for month. Used in GregorianCalendar.

AUGUST

public static final int AUGUST

Useful constant for month. Used in GregorianCalendar.

DATE

public static final int DATE

Useful constant for date and time. Used in time fields. This is a synonym for DAY_OF_MONTH.

DAY_OF_MONTH

public static final int DAY_OF_MONTH

Useful constant for date and time. Used in time fields. This is a synonym for DATE.

DAY_OF_WEEK

public static final int DAY_OF_WEEK

Useful constant for date and time. Used in time fields.

DAY_OF_WEEK_IN_MONTH

public static final int DAY_OF_WEEK_IN_MONTH

Useful constant for date and time. Used in time fields.

DAY_OF_YEAR

public static final int DAY_OF_YEAR

Useful constant for date and time. Used in time fields.

DECEMBER

public static final int DECEMBER

Useful constant for month. Used in GregorianCalendar.

DST_OFFSET

public static final int DST_OFFSET

Useful constant for date and time. Used in time fields.

ERA

public static final int ERA

Useful constant for date and time. Used in time fields. ERA is calendar specific.

FEBRUARY

public static final int FEBRUARY

Useful constant for month. Used in GregorianCalendar.

FIELD_COUNT

public static final int FIELD_COUNT

Useful constant for date and time. FIELD_COUNT is used for the time field array creation.

FRIDAY

public static final int FRIDAY

Useful constant for days of week. Used in GregorianCalendar.

HOUR

public static final int HOUR

Useful constant for date and time. Used in time fields. HOUR is used for the 12-hour clock.

HOUR_OF_DAY

public static final int HOUR_OF_DAY

Useful constant for date and time. Used in time fields. HOUR_OF_DAY is used for the 24-hour clock.

JANUARY

public static final int JANUARY

Useful constant for month. Used in GregorianCalendar. Note: Calendar month is now 0-based.

JULY

public static final int JULY

Useful constant for month. Used in GregorianCalendar.

JUNE

public static final int JUNE

Useful constant for month. Used in GregorianCalendar.

MARCH

public static final int MARCH

Useful constant for month. Used in GregorianCalendar.

MAY

public static final int MAY

Useful constant for month. Used in GregorianCalendar.

MILLISECOND

public static final int MILLISECOND

Useful constant for date and time. Used in time fields.

MINUTE

public static final int MINUTE

Useful constant for date and time. Used in time fields.

MONDAY

public static final int MONDAY

Useful constant for days of week. Used in GregorianCalendar.

MONTH

public static final int MONTH

Useful constant for date and time. Used in time fields.

NOVEMBER

public static final int NOVEMBER

Useful constant for month. Used in GregorianCalendar.

OCTOBER

public static final int OCTOBER

Useful constant for month. Used in GregorianCalendar.

public static final int PM

Useful constant for hour in 12-hour clock. Used in GregorianCalendar.

SATURDAY

public static final int SATURDAY

Useful constant for days of week. Used in GregorianCalendar.

SECOND

public static final int SECOND

Useful constant for date and time. Used in time fields.

SEPTEMBER

public static final int SEPTEMBER

Useful constant for month. Used in GregorianCalendar.

SUNDAY

public static final int SUNDAY

Useful constant for days of week. Used in GregorianCalendar.

THURSDAY

public static final int THURSDAY

Useful constant for days of week. Used in GregorianCalendar.

TUESDAY

public static final int TUESDAY

Useful constant for days of week. Used in GregorianCalendar.

UNDECIMBER

public static final int UNDECIMBER

Useful constant for month. Used in GregorianCalendar. UNDECIMBER is an artifical name. This 13th month is for lunar calendars.

WEDNESDAY

public static final int WEDNESDAY

Useful constant for days of week. Used in GregorianCalendar.

WEEK_OF_MONTH

public static final int WEEK_OF_MONTH

Useful constant for date and time. Used in time fields.

WEEK_OF_YEAR

public static final int WEEK_OF_YEAR

Useful constant for date and time. Used in time fields.

YEAR

public static final int YEAR

Useful constant for date and time. Used in time fields.

ZONE_OFFSET

public static final int ZONE_OFFSET

Useful constant for date and time. Used in time fields.

areFieldsSet

protected boolean areFieldsSet

True if the fields are in sync with the currently set time of this Calendar. If false, then the next attempt to get the value of a field will force a recomputation of all fields from the current value of the time field. This should really be named areFieldsInSync, but the old name is retained for backward compatibility.

fields

protected int[] fields

The time fields containing values into which the millis is computed.

isSet

protected boolean[] isSet

The flags which tell if a specified time field for the calendar is set. A new object has no fields set. After the first call to a method which generates the fields, they all remain set after that.

isTimeSet

protected boolean isTimeSet

The flag which indicates if the current time is set for the calendar. The time is made invalid by the user setting an individual field.

time

protected long time

The current time set for the calendar.

Calendar

protected Calendar()

Constructs a Calendar with the default time zone as returned by TimeZone.getDefault(), and the default locale.

See Also:: getDefault

Calendar

protected Calendar(TimeZone zone,
                   Locale aLocale)

Constructs a Calendar with the given time zone and locale.

Parameters:: zone - the given time zone.

add

public abstract void add(int field,
                         int amount)

Date Arithmetic function. Adds the specified (signed) amount of time to the given time field, based on the calendar's rules. For example, to subtract 5 days from the current time of the calendar, you can achieve it by calling:

add(Calendar.DATE, -5).

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

after

public abstract 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.

before

public abstract 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.

clear

public final void clear()

Clears the values of all the time fields.

clear

public final void clear(int field)

Clears the value in the given time field.

Parameters:: field - the time field to be cleared.

clone

public java.lang.Object clone()

Overrides Cloneable

Overrides:: clone in class Object

complete

protected void complete()

Fills in any unset fields in the time field list.

computeFields

protected abstract void computeFields()

Converts UTC as milliseconds to time field values. This allows you to sync up the time field values with a new time that is set for the calendar. The time is not recomputed first; to recompute the time, then the fields, call the complete method.

See Also:: complete

computeTime

protected abstract void computeTime()

Converts Calendar's time field values to UTC as milliseconds.

equals

public abstract 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 Object

get

public final int get(int field)

Gets the value for a given time field.

Parameters:: field - the given time field.
Returns:: the value for the given time field.

getAvailableLocales

public static synchronized java.util.Locale[] getAvailableLocales()

Gets the set of locales for which Calendars are installed.

Returns:: the set of locales for which Calendars are installed.

getFirstDayOfWeek

public int getFirstDayOfWeek()

Gets what the first day of the week is; e.g., Sunday in US, Monday in France.

Returns:: the first day of the week.

getGreatestMinimum

public abstract int getGreatestMinimum(int field)

Gets the highest minimum value for the given field if varies. Otherwise same as getMinimum(). For Gregorian, no difference.

Parameters:: field - the given time field.
Returns:: the highest minimum value for the given time field.

getInstance

public static synchronized java.util.Calendar getInstance()

Gets a Calendar using the default timezone and locale.

Returns:: a Calendar.

getInstance

public static synchronized java.util.Calendar getInstance(TimeZone zone)

Gets a Calendar using the given timezone and default locale.

Parameters:: zone - the given timezone.
Returns:: a Calendar.

getInstance

public static synchronized java.util.Calendar getInstance(Locale aLocale)

Gets a Calendar using the default timezone and given locale.

Parameters:: aLocale - the given locale.
Returns:: a Calendar.

getInstance

public static synchronized java.util.Calendar getInstance(TimeZone zone,
                                                          Locale aLocale)

Gets a Calendar using the given timezone and given locale.

Parameters:: zone - the given timezone.; aLocale - the given locale.
Returns:: a Calendar.

getLeastMaximum

public abstract int getLeastMaximum(int field)

Gets the lowest maximum value for the given field if varies. Otherwise same as getMaximum(). e.g., for Gregorian DAY_OF_MONTH, 28.

Parameters:: field - the given time field.
Returns:: the lowest maximum value for the given time field.

getMaximum

public abstract int getMaximum(int field)

Gets the maximum value for the given time field. e.g. for Gregorian DAY_OF_MONTH, 31.

Parameters:: field - the given time field.
Returns:: the maximum value for the given time field.

getMinimalDaysInFirstWeek

public int getMinimalDaysInFirstWeek()

Gets what the minimal days required in the first week of the year are; e.g., if the first week is defined as one that contains the first day of the first month of a year, getMinimalDaysInFirstWeek returns 1. If the minimal days required must be a full week, getMinimalDaysInFirstWeek returns 7.

Returns:: the minimal days required in the first week of the year.

getMinimum

public abstract int getMinimum(int field)

Gets the minimum value for the given time field. e.g., for Gregorian DAY_OF_MONTH, 1.

Parameters:: field - the given time field.
Returns:: the minimum value for the given time field.

getTime

public final java.util.Date getTime()

Gets this Calendar's current time.

Returns:: the current time.

getTimeInMillis

protected long getTimeInMillis()

Gets this Calendar's current time as a long.

Returns:: the current time as UTC milliseconds from the epoch.

getTimeZone

public java.util.TimeZone getTimeZone()

Gets the time zone.

Returns:: the time zone object associated with this calendar.

internalGet

protected final int internalGet(int field)

Gets the value for a given time field. This is an internal fast time field value getter for the subclasses.

Parameters:: field - the given time field.
Returns:: the value for the given time field.

isLenient

public boolean isLenient()

Tell whether date/time interpretation is to be lenient.

isSet

public final boolean isSet(int field)

Determines if the given time field has a value set.

Returns:: true if the given time field has a value set; false otherwise.

roll

public abstract void roll(int field,
                          boolean up)

Time Field Rolling function. Rolls (up/down) a single unit of time on the given time field. For example, to roll the current date up by one day, you can achieve it by calling:

roll(Calendar.DATE, true). When rolling on the year or Calendar.YEAR field, it will roll the year value in the range between 1 and the value returned by calling getMaximum(Calendar.YEAR). When rolling on the month or Calendar.MONTH field, other fields like date might conflict and, need to be changed. For instance, rolling the month on the date 01/31/96 will result in 03/02/96. When rolling on the hour-in-day or Calendar.HOUR_OF_DAY field, it will roll the hour value in the range between 0 and 23, which is zero-based.

Parameters:: field - the time field.; 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.

set

public final void set(int field,
                      int value)

Sets the time field with the given value.

Parameters:: field - the given time field.; value - the value to be set for the given time field.

set

public final void set(int year,
                      int month,
                      int date)

Sets the values for the fields year, month, and date. Previous values of other fields are retained. If this is not desired, call clear first.

Parameters:: year - the value used to set the YEAR time field.; month - the value used to set the MONTH time field. Month value is 0-based. e.g., 0 for January.; date - the value used to set the DATE time field.

set

public final void set(int year,
                      int month,
                      int date,
                      int hour,
                      int minute)

Sets the values for the fields year, month, date, hour, and minute. Previous values of other fields are retained. If this is not desired, call clear first.

Parameters:: year - the value used to set the YEAR time field.; month - the value used to set the MONTH time field. Month value is 0-based. e.g., 0 for January.; date - the value used to set the DATE time field.; hour - the value used to set the HOUR_OF_DAY time field.; minute - the value used to set the MINUTE time field.

set

public final void set(int year,
                      int month,
                      int date,
                      int hour,
                      int minute,
                      int second)

Sets the values for the fields year, month, date, hour, minute, and second. Previous values of other fields are retained. If this is not desired, call clear first.

Parameters:: year - the value used to set the YEAR time field.; month - the value used to set the MONTH time field. Month value is 0-based. e.g., 0 for January.; date - the value used to set the DATE time field.; hour - the value used to set the HOUR_OF_DAY time field.; minute - the value used to set the MINUTE time field.; second - the value used to set the SECOND time field.

setFirstDayOfWeek

public void setFirstDayOfWeek(int value)

Sets what the first day of the week is; e.g., Sunday in US, Monday in France.

Parameters:: value - the given first day of the week.

setLenient

public void setLenient(boolean lenient)

Specify whether or not date/time interpretation is to be lenient. With lenient interpretation, a date such as "February 942, 1996" will be treated as being equivalent to the 941st day after February 1, 1996. With strict interpretation, such dates will cause an exception to be thrown.

See Also:: setLenient

setMinimalDaysInFirstWeek

public void setMinimalDaysInFirstWeek(int value)

Sets what the minimal days required in the first week of the year are; For example, if the first week is defined as one that contains the first day of the first month of a year, call the method with value 1. If it must be a full week, use value 7.

Parameters:: value - the given minimal days required in the first week of the year.

setTime

public final void setTime(Date date)

Sets this Calendar's current time with the given Date.

Parameters:: date - the given Date.

setTimeInMillis

protected void setTimeInMillis(long millis)

Sets this Calendar's current time from the given long value.

Parameters:: date - the new time in UTC milliseconds from the epoch.

setTimeZone

public void setTimeZone(TimeZone value)

Sets the time zone with the given time zone value.

Parameters:: value - the given time zone.

toString

public java.lang.String toString()

Return a string representation of this calendar.

Returns:: a string representation of this calendar.
Overrides:: toString in class Object

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