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FlexDoc/Javadoc 2.0 Demo Java Doc |
The class also provides additional fields and methods for implementing a concrete calendar system outside the package. Those fields and methods are defined as protected.
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 Calendar object whose calendar fields have been initialized with the current date and time:
Calendar rightNow = Calendar.getInstance();
A Calendar object can produce all the calendar field values
needed to implement the date-time formatting for a particular language and
calendar style (for example, Japanese-Gregorian, Japanese-Traditional).
Calendar defines the range of values returned by
certain calendar fields, as well as their meaning. For example,
the first month of the calendar system has value MONTH ==
JANUARY
for all calendars. Other values are defined by the
concrete subclass, such as ERA. See individual field
documentation and subclass documentation for details.
The calendar field values can be set by calling the set methods. Any field values set in a Calendar will not be interpreted until it needs to calculate its time value (milliseconds from the Epoch) or values of the calendar fields. Calling the get, getTimeInMillis, getTime, add and roll involves such calculation.
Calendar has two modes for interpreting the calendar fields, lenient and non-lenient. When a Calendar is in lenient mode, it accepts a wider range of calendar field values than it produces. When a Calendar recomputes calendar field values for return by get(), all of the calendar fields are normalized. For example, a lenient GregorianCalendar interprets MONTH == JANUARY, DAY_OF_MONTH == 32 as February 1.
When a Calendar is in non-lenient mode, it throws an exception if there is any inconsistency in its calendar fields. For example, a GregorianCalendar always produces DAY_OF_MONTH values between 1 and the length of the month. A non-lenient GregorianCalendar throws an exception upon calculating its time or calendar field values if any out-of-range field value has been set.
When setting or getting the WEEK_OF_MONTH or
WEEK_OF_YEAR fields, Calendar must determine the
first week of the month or year as a reference point. The first week of a
month or year is defined as the earliest seven day period beginning on
getFirstDayOfWeek() and containing at least
getMinimalDaysInFirstWeek() days of that month or year. Weeks
numbered ..., -1, 0 precede the first week; weeks numbered 2, 3,... follow
it. Note that the normalized numbering returned by get() may be
different. For example, a specific Calendar subclass may
designate the week before week 1 of a year as week n
of
the previous year.
If there is any conflict in calendar field values, Calendar gives priorities to calendar fields that have been set more recently. The following are the default combinations of the calendar fields. The most recent combination, as determined by the most recently set single field, will be used.
For the time of day fields:YEAR + MONTH + DAY_OF_MONTH YEAR + MONTH + WEEK_OF_MONTH + DAY_OF_WEEK YEAR + MONTH + DAY_OF_WEEK_IN_MONTH + DAY_OF_WEEK YEAR + DAY_OF_YEAR YEAR + DAY_OF_WEEK + WEEK_OF_YEAR
HOUR_OF_DAY AM_PM + HOUR
If there are any calendar fields whose values haven't been set in the selected
field combination, Calendar uses their default values. The default
value of each field may vary by concrete calendar systems. For example, in
GregorianCalendar, the default of a field is the same as that
of the start of the Epoch: i.e., YEAR = 1970, MONTH =
JANUARY
, DAY_OF_MONTH = 1, etc.
Note: There are certain possible ambiguities in interpretation of certain singular times, which are resolved in the following ways:
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 DateFormat to format dates.
set(f, value) changes calendar field f to value. In addition, it sets an internal member variable to indicate that calendar field f has been changed. Although calendar field f is changed immediately, the calendar's time value in milliseconds is not recomputed until the next call to get(), getTime(), getTimeInMillis(), add(), or roll() is made. Thus, multiple calls to set() do not trigger multiple, unnecessary computations. As a result of changing a calendar field using set(), other calendar fields may also change, depending on the calendar field, the calendar field value, and the calendar system. In addition, get(f) will not necessarily return value set by the call to the set method after the calendar fields have been recomputed. The specifics are determined by the concrete calendar class.
Example: Consider a GregorianCalendar
originally set to August 31, 1999. Calling set(Calendar.MONTH,
Calendar.SEPTEMBER)
sets the date to September 31,
1999. This is a temporary internal representation that resolves to
October 1, 1999 if getTime() is then called. However, a
call to set(Calendar.DAY_OF_MONTH, 30) before the call to
getTime() sets the date to September 30, 1999, since
no recomputation occurs after set() itself.
add(f, delta) adds delta
to field f. This is equivalent to calling set(f,
get(f) + delta)
with two adjustments:
Add rule 1. The value of field f after the call minus the value of field f before the call is delta, modulo any overflow that has occurred in field f. 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 f is changed or other constraints, such as time zone offset changes, 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.
In addition, unlike set(), add() forces an immediate recomputation of the calendar's milliseconds and all fields.
Example: Consider a GregorianCalendar
originally set to August 31, 1999. Calling add(Calendar.MONTH,
13)
sets the calendar to September 30, 2000. Add rule
1 sets the MONTH field to September, since
adding 13 months to August gives September of the next year. Since
DAY_OF_MONTH cannot be 31 in September in a
GregorianCalendar, add rule 2 sets the
DAY_OF_MONTH to 30, the closest possible value. Although
it is a smaller field, DAY_OF_WEEK is not adjusted by
rule 2, since it is expected to change when the month changes in a
GregorianCalendar.
roll(f, delta) adds delta to field f without changing larger fields. This is equivalent to calling add(f, delta) with the following adjustment:
Roll rule. Larger fields are unchanged after the call. A larger field represents a larger unit of time. DAY_OF_MONTH is a larger field than HOUR.
Example: See GregorianCalendar.roll(int, int).
Usage model. To motivate the behavior of add() and roll(), consider a user interface component with increment and decrement buttons for the month, day, and year, and an underlying GregorianCalendar. If the interface reads January 31, 1999 and the user presses the month increment button, what should it read? If the underlying implementation uses set(), it might read March 3, 1999. A better result would be February 28, 1999. Furthermore, if the user presses the month increment button again, it should read March 31, 1999, not March 28, 1999. By saving the original date and using either add() or roll(), depending on whether larger fields should be affected, the user interface can behave as most users will intuitively expect.
Nested Class Summary |
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static class |
Calendar.Builder is used for creating a Calendar from
various date-time parameters.
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Field Summary |
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static final int |
A style specifier for getDisplayNames indicating names in all styles, such as
"January" and "Jan".
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static final int |
Value of the AM_PM field indicating the
period of the day from midnight to just before noon.
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static final int |
Field number for get and set indicating
whether the HOUR is before or after noon.
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static final int |
Value of the MONTH field indicating the
fourth month of the year in the Gregorian and Julian calendars.
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protected boolean |
True if fields[] are in sync with the currently set time.
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static final int |
Value of the MONTH field indicating the
eighth month of the year in the Gregorian and Julian calendars.
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static final int |
Field number for get and set indicating the
day of the month.
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static final int |
Field number for get and set indicating the
day of the month.
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static final int |
Field number for get and set indicating the day
of the week.
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static final int |
Field number for get and set indicating the
ordinal number of the day of the week within the current month.
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static final int |
Field number for get and set indicating the day
number within the current year.
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static final int |
Value of the MONTH field indicating the
twelfth month of the year in the Gregorian and Julian calendars.
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static final int |
Field number for get and set indicating the
daylight saving offset in milliseconds.
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static final int |
Field number for get and set indicating the
era, e.g., AD or BC in the Julian calendar.
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static final int |
Value of the MONTH field indicating the
second month of the year in the Gregorian and Julian calendars.
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static final int |
The number of distinct fields recognized by get and set.
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protected int[] |
The calendar field values for the currently set time for this calendar.
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static final int |
Value of the DAY_OF_WEEK field indicating
Friday.
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static final int |
Field number for get and set indicating the
hour of the morning or afternoon.
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static final int |
Field number for get and set indicating the
hour of the day.
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protected boolean[] |
The flags which tell if a specified calendar field for the calendar is set.
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protected boolean |
True if then the value of time is valid.
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static final int |
Value of the MONTH field indicating the
first month of the year in the Gregorian and Julian calendars.
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static final int |
Value of the MONTH field indicating the
seventh month of the year in the Gregorian and Julian calendars.
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static final int |
Value of the MONTH field indicating the
sixth month of the year in the Gregorian and Julian calendars.
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static final int |
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a long name used for format.
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a long name used independently,
such as a month name as calendar headers.
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static final int |
Value of the MONTH field indicating the
third month of the year in the Gregorian and Julian calendars.
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static final int |
Value of the MONTH field indicating the
fifth month of the year in the Gregorian and Julian calendars.
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static final int |
Field number for get and set indicating the
millisecond within the second.
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static final int |
Field number for get and set indicating the
minute within the hour.
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static final int |
Value of the DAY_OF_WEEK field indicating
Monday.
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static final int |
Field number for get and set indicating the
month.
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a narrow name used for format.
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a narrow name independently.
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static final int |
Value of the MONTH field indicating the
eleventh month of the year in the Gregorian and Julian calendars.
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static final int |
Value of the MONTH field indicating the
tenth month of the year in the Gregorian and Julian calendars.
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static final int |
Value of the AM_PM field indicating the
period of the day from noon to just before midnight.
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static final int |
Value of the DAY_OF_WEEK field indicating
Saturday.
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static final int |
Field number for get and set indicating the
second within the minute.
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static final int |
Value of the MONTH field indicating the
ninth month of the year in the Gregorian and Julian calendars.
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static final int |
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a short name used for format.
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static final int |
A style specifier for getDisplayName and getDisplayNames indicating a short name used independently,
such as a month abbreviation as calendar headers.
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static final int |
Value of the DAY_OF_WEEK field indicating
Sunday.
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static final int |
Value of the DAY_OF_WEEK field indicating
Thursday.
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protected long |
The currently set time for this calendar, expressed in milliseconds after
January 1, 1970, 0:00:00 GMT.
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static final int |
Value of the DAY_OF_WEEK field indicating
Tuesday.
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static final int |
Value of the MONTH field indicating the
thirteenth month of the year.
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static final int |
Value of the DAY_OF_WEEK field indicating
Wednesday.
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static final int |
Field number for get and set indicating the
week number within the current month.
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static final int |
Field number for get and set indicating the
week number within the current year.
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static final int |
Field number for get and set indicating the
year.
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static final int |
Field number for get and set
indicating the raw offset from GMT in milliseconds.
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Constructor Summary |
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protected |
Calendar()
Constructs a Calendar with the default time zone
and the default FORMAT
locale.
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protected |
Constructs a calendar with the specified time zone and locale.
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Method Summary |
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abstract void |
add(int field, int amount)
Adds or subtracts the specified amount of time to the given calendar field,
based on the calendar's rules.
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boolean |
Returns whether this Calendar represents a time
after the time represented by the specified
Object.
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boolean |
Returns whether this Calendar represents a time
before the time represented by the specified
Object.
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final void |
clear()
Sets all the calendar field values and the time value
(millisecond offset from the Epoch) of
this Calendar undefined.
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final void |
clear(int field)
Sets the given calendar field value and the time value
(millisecond offset from the Epoch) of
this Calendar undefined.
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clone()
Creates and returns a copy of this object.
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int |
Compares the time values (millisecond offsets from the Epoch) represented by two
Calendar objects.
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protected void |
complete()
Fills in any unset fields in the calendar fields.
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protected abstract void |
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protected abstract void |
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boolean |
Compares this Calendar to the specified
Object.
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int |
get(int field)
Returns the value of the given calendar field.
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int |
getActualMaximum(int field)
Returns the maximum value that the specified calendar field
could have, given the time value of this
Calendar.
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int |
getActualMinimum(int field)
Returns the minimum value that the specified calendar field
could have, given the time value of this Calendar.
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Returns an unmodifiable Set containing all calendar types
supported by Calendar in the runtime environment.
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static Locale[] |
Returns an array of all locales for which the getInstance
methods of this class can return localized instances.
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Returns the calendar type of this Calendar.
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getDisplayName(int field, int style, Locale locale)
Returns the string representation of the calendar
field value in the given style and
locale.
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getDisplayNames(int field, int style, Locale locale)
Returns a Map containing all names of the calendar
field in the given style and
locale and their corresponding field values.
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int |
Gets what the first day of the week is; e.g., SUNDAY in the U.S.,
MONDAY in France.
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abstract int |
getGreatestMinimum(int field)
Returns the highest minimum value for the given calendar field
of this Calendar instance.
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static Calendar |
Gets a calendar using the default time zone and locale.
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static Calendar |
getInstance(Locale aLocale)
Gets a calendar using the default time zone and specified locale.
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static Calendar |
getInstance(TimeZone zone)
Gets a calendar using the specified time zone and default locale.
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static Calendar |
Gets a calendar with the specified time zone and locale.
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abstract int |
getLeastMaximum(int field)
Returns the lowest maximum value for the given calendar field
of this Calendar instance.
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abstract int |
getMaximum(int field)
Returns the maximum value for the given calendar field of this
Calendar instance.
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int |
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, this method returns 1.
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abstract int |
getMinimum(int field)
Returns the minimum value for the given calendar field of this
Calendar instance.
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final Date |
getTime()
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long |
Returns this Calendar's time value in milliseconds.
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Gets the time zone.
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int |
Returns the number of weeks in the week year represented by this
Calendar.
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int |
Returns the week year represented by this Calendar.
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int |
hashCode()
Returns a hash code for this calendar.
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protected final int |
internalGet(int field)
Returns the value of the given calendar field.
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boolean |
Tells whether date/time interpretation is to be lenient.
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final boolean |
isSet(int field)
Determines if the given calendar field has a value set,
including cases that the value has been set by internal fields
calculations triggered by a get method call.
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boolean |
Returns whether this Calendar supports week dates.
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abstract 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.
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void |
roll(int field, int amount)
Adds the specified (signed) amount to the specified calendar field
without changing larger fields.
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void |
set(int field, int value)
Sets the given calendar field to the given value.
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final void |
set(int year, int month, int date)
Sets the values for the calendar fields YEAR,
MONTH, and DAY_OF_MONTH.
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final void |
set(int year, int month, int date, int hourOfDay, int minute)
Sets the values for the calendar fields YEAR,
MONTH, DAY_OF_MONTH,
HOUR_OF_DAY, and MINUTE.
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final void |
set(int year, int month, int date, int hourOfDay, int minute, int second)
Sets the values for the fields YEAR, MONTH,
DAY_OF_MONTH, HOUR_OF_DAY, MINUTE, and
SECOND.
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void |
setFirstDayOfWeek(int value)
Sets what the first day of the week is; e.g., SUNDAY in the U.S.,
MONDAY in France.
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void |
setLenient(boolean lenient)
Specifies whether or not date/time interpretation is to be lenient.
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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 this method with value 1.
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final void |
Sets this Calendar's time with the given Date.
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void |
setTimeInMillis(long millis)
Sets this Calendar's current time from the given long value.
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void |
setTimeZone(TimeZone value)
Sets the time zone with the given time zone value.
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void |
setWeekDate(int weekYear, int weekOfYear, int dayOfWeek)
Sets the date of this Calendar with the given date
specifiers - week year, week of year, and day of week.
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final Instant |
Converts this object to an Instant.
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toString()
Return a string representation of this calendar.
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Methods inherited from class java.lang.Object |
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.
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.
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.
protected Calendar |
() |
protected Calendar |
public static Calendar getInstance |
() |
If the locale contains the time zone with "tz" Unicode extension, that time zone is used instead.
public static Calendar getInstance |
(TimeZone zone) |
public static Calendar getInstance |
(Locale aLocale) |
If the locale contains the time zone with "tz" Unicode extension, that time zone is used instead.
public static Calendar getInstance |
public static Locale[] getAvailableLocales |
() |
protected abstract void computeTime |
() |
protected abstract void computeFields |
() |
public final Date getTime |
() |
public final void setTime |
(Date date) |
Note: Calling setTime() with Date(Long.MAX_VALUE) or Date(Long.MIN_VALUE) may yield incorrect field values from get().
public long getTimeInMillis |
() |
public void setTimeInMillis |
(long millis) |
public int get |
(int field) |
field < 0 || field >= FIELD_COUNT
).protected final int internalGet |
(int field) |
public void set |
(int field, int value) |
field < 0 || field >= FIELD_COUNT
).
in non-lenient mode.public final void set |
(int year, int month, int date) |
public final void set |
(int year, int month, int date, int hourOfDay, int minute) |
public final void set |
(int year, int month, int date, int hourOfDay, int minute, int second) |
public final void clear |
() |
public final void clear |
(int field) |
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.
public final boolean isSet |
(int field) |
public String getDisplayName |
For example, if this Calendar is a GregorianCalendar and its date is 2005-01-01, then the string representation of the MONTH field would be "January" in the long style in an English locale or "Jan" in the short style. However, no string representation would be available for the DAY_OF_MONTH field, and this method would return null.
The default implementation supports the calendar fields for which a DateFormatSymbols has names in the given locale.
Narrow names may not be unique due to use of single characters, such as "S" for Sunday and Saturday. In that case narrow names are not included in the returned Map.
The values of other calendar fields may be taken into account to determine a set of display names. For example, if this Calendar is a lunisolar calendar system and the year value given by the YEAR field has a leap month, this method would return month names containing the leap month name, and month names are mapped to their values specific for the year.
The default implementation supports display names contained in a DateFormatSymbols. For example, if field is MONTH and style is ALL_STYLES, this method returns a Map containing all strings returned by DateFormatSymbols.getShortMonths() and DateFormatSymbols.getMonths().
protected void complete |
() |
() |
public String getCalendarType |
() |
The default implementation of this method returns the class name of this Calendar instance. Any subclasses that implement LDML-defined calendar systems should override this method to return appropriate calendar types.
public boolean equals |
(Object obj) |
The Calendar parameters are the values represented by the isLenient, getFirstDayOfWeek, getMinimalDaysInFirstWeek and getTimeZone methods. If there is any difference in those parameters between the two Calendars, this method returns false.
Use the compareTo method to compare only the time values.
public int hashCode |
() |
public boolean before |
(Object when) |
compareTo(when) < 0
if and only if when is a Calendar
instance. Otherwise, the method returns false.
public boolean after |
(Object when) |
compareTo(when) > 0
if and only if when is a Calendar
instance. Otherwise, the method returns false.
public int compareTo |
(Calendar anotherCalendar) |
public abstract void add |
(int field, int amount) |
add(Calendar.DAY_OF_MONTH, -5).
public abstract void roll |
(int field, boolean up) |
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 02/29/96. 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.
public void roll |
(int field, int amount) |
NOTE: This default implementation on Calendar just repeatedly calls the version of roll() that rolls by one unit. This may not always do the right thing. For example, if the DAY_OF_MONTH field is 31, rolling through February will leave it set to 28. The GregorianCalendar version of this function takes care of this problem. Other subclasses should also provide overrides of this function that do the right thing.
public void setTimeZone |
(TimeZone value) |
public TimeZone getTimeZone |
() |
public void setLenient |
(boolean lenient) |
public boolean isLenient |
() |
public void setFirstDayOfWeek |
(int value) |
public int getFirstDayOfWeek |
() |
public void setMinimalDaysInFirstWeek |
(int value) |
public int getMinimalDaysInFirstWeek |
() |
public boolean isWeekDateSupported |
() |
The default implementation of this method returns false.
public int getWeekYear |
() |
The default implementation of this method throws an UnsupportedOperationException.
public void setWeekDate |
(int weekYear, int weekOfYear, int dayOfWeek) |
Unlike the set method, all of the calendar fields and time values are calculated upon return.
If weekOfYear is out of the valid week-of-year range in weekYear, the weekYear and weekOfYear values are adjusted in lenient mode, or an IllegalArgumentException is thrown in non-lenient mode.
The default implementation of this method throws an UnsupportedOperationException.
public int getWeeksInWeekYear |
() |
The default implementation of this method throws an UnsupportedOperationException.
public abstract int getMinimum |
(int field) |
public abstract int getMaximum |
(int field) |
public abstract int getGreatestMinimum |
(int field) |
public abstract int getLeastMaximum |
(int field) |
public int getActualMinimum |
(int field) |
The default implementation of this method uses an iterative algorithm to determine the actual minimum value for the calendar field. Subclasses should, if possible, override this with a more efficient implementation - in many cases, they can simply return getMinimum().
public int getActualMaximum |
(int field) |
The default implementation of this method uses an iterative algorithm to determine the actual maximum value for the calendar field. Subclasses should, if possible, override this with a more efficient implementation.
public Object clone |
() |
public String toString |
() |
public final Instant toInstant |
() |
The conversion creates an Instant that represents the same point on the time-line as this Calendar.
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FlexDoc/Javadoc 2.0 Demo Java Doc |