This service uses {@link JsonHttpRequestInitializer} to initialize global parameters via its{@link Builder}. Sample usage:
public class CalendarRequestInitializer implements JsonHttpRequestInitializer { public void initialize(JsonHttpRequest request) { CalendarRequest calendarRequest = (CalendarRequest)request; calendarRequest.setPrettyPrint(true); calendarRequest.setKey(ClientCredentials.KEY); } }@since 1.3.0 @author Google, Inc.
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 {@link Date}for information about the Date
class.) Note: This class is similar, but not identical, to the class java.util.Calendar
. Changes are detailed below.
Subclasses of Calendar
interpret a Date
according to the rules of a specific calendar system. ICU4J contains several subclasses implementing different international calendar systems.
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 of a type appropriate to the locale, whose time fields have been initialized with the current date and time:
Calendar rightNow = Calendar.getInstance()
When a ULocale
is used by getInstance
, its 'calendar
' tag and value are retrieved if present. If a recognized value is supplied, a calendar is provided and configured as appropriate. Currently recognized tags are "buddhist", "chinese", "coptic", "ethiopic", "gregorian", "hebrew", "islamic", "islamic-civil", and "japanese". For example:
will return an instance of JapaneseCalendar (using en_US conventions for minimum days in first week, start day of week, et cetera).Calendar cal = Calendar.getInstance(new ULocale("en_US@calendar=japanese"));
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). Calendar
defines the range of values returned by certain fields, as well as their meaning. For example, the first month of the year has value MONTH
== JANUARY
for all calendars. Other values are defined by the concrete subclass, such as ERA
and YEAR
. See individual field documentation and subclass documentation for details.
When a Calendar
is lenient, it accepts a wider range of field values than it produces. For example, a lenient GregorianCalendar
interprets MONTH
== JANUARY
, DAY_OF_MONTH
== 32 as February 1. A non-lenient GregorianCalendar
throws an exception when given out-of-range field settings. When calendars recompute field values for return by get()
, they normalize them. For example, a GregorianCalendar
always produces DAY_OF_MONTH
values between 1 and the length of the month.
Calendar
defines a locale-specific seven day week using two parameters: the first day of the week and the minimal days in first week (from 1 to 7). These numbers are taken from the locale resource data when a Calendar
is constructed. They may also be specified explicitly through the API.
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.
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.
For the time of day: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
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:
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 {@link DateFormat}to format dates.
Field manipulation methods
Calendar
fields can be changed using three methods: set()
, add()
, and roll()
.
set(f, value)
changes field f
to value
. In addition, it sets an internal member variable to indicate that field f
has been changed. Although field f
is changed immediately, the calendar's milliseconds is not recomputed until the next call to get()
, getTime()
, or getTimeInMillis()
is made. Thus, multiple calls to set()
do not trigger multiple, unnecessary computations. As a result of changing a field using set()
, other fields may also change, depending on the field, the field value, and the calendar system. In addition, get(f)
will not necessarily return value
after the 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 calendar 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 calendar 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 fieldf
before the call isdelta
, modulo any overflow that has occurred in fieldf
. 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, 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 thanDAY_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 thanHOUR
.
Example: Consider a GregorianCalendar
originally set to August 31, 1999. Calling roll(Calendar.MONTH, 8)
sets the calendar to April 30, 1999. Add rule 1 sets the MONTH
field to April. Using a GregorianCalendar
, the DAY_OF_MONTH
cannot be 31 in the month April. Add rule 2 sets it to the closest possible value, 30. Finally, the roll rule maintains the YEAR
field value of 1999.
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).
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.
Note: You should always use {@link #roll roll} and {@link #add add} ratherthan attempting to perform arithmetic operations directly on the fields of a Calendar. It is quite possible for Calendar subclasses to have fields with non-linear behavior, for example missing months or days during non-leap years. The subclasses' add and roll methods will take this into account, while simple arithmetic manipulations may give invalid results.
Calendar Architecture in ICU4J
Recently the implementation of Calendar
has changed significantly in order to better support subclassing. The original Calendar
class was designed to support subclassing, but it had only one implemented subclass, GregorianCalendar
. With the implementation of several new calendar subclasses, including the BuddhistCalendar
, ChineseCalendar
, HebrewCalendar
, IslamicCalendar
, and JapaneseCalendar
, the subclassing API has been reworked thoroughly. This section details the new subclassing API and other ways in which com.ibm.icu.util.Calendar
differs from java.util.Calendar
.
Changes
Overview of changes between the classic Calendar
architecture and the new architecture.
fields[]
array is private
now instead of protected
. Subclasses must access it using the methods {@link #internalSet} and{@link #internalGet}. Motivation: Subclasses should not directly access data members.time
long word is private
now instead of protected
. Subclasses may access it using the method {@link #internalGetTimeInMillis}, which does not provoke an update. Motivation: Subclasses should not directly access data members.Calendar
base class. As a result, it is much easier to subclass Calendar
. Motivation: Subclasses should not have to reimplement common code. Certain behaviors are common across calendar systems: The definition and behavior of week-related fields and time fields, the arithmetic ( {@link #add(int,int) add} and {@link #roll(int,int) roll}) behavior of many fields, and the field validation system.Calendar
base class contains some Gregorian calendar algorithmic support that subclasses can use (specifically in {@link #handleComputeFields}). Subclasses can use the methods getGregorianXxx()
to obtain precomputed values. Motivation: This is required by all Calendar
subclasses in order to implement consistent time zone behavior, and Gregorian-derived systems can use the already computed data.FIELD_COUNT
constant has been removed. Use {@link #getFieldCount}. In addition, framework API has been added to allow subclasses to define additional fields. Motivation: The number of fields is not constant across calendar systems.Date(Long.MIN_VALUE)
or Date(Long.MAX_VALUE)
. Instead, the Calendar
constants {@link #MIN_DATE}, {@link #MAX_DATE}, {@link #MIN_MILLIS}, {@link #MAX_MILLIS}, {@link #MIN_JULIAN}, and {@link #MAX_JULIAN} should be used. Motivation: Withthe addition of the {@link #JULIAN_DAY} field, Julian daynumbers must be restricted to a 32-bit int
. This restricts the overall supported range. Furthermore, restricting the supported range simplifies the computations by removing special case code that was used to accomodate arithmetic overflow at millis near Long.MIN_VALUE
and Long.MAX_VALUE
.Calendar
.DateFormat
.Subclass API
The original Calendar
API was based on the experience of implementing a only a single subclass, GregorianCalendar
. As a result, all of the subclassing kinks had not been worked out. The new subclassing API has been refined based on several implemented subclasses. This includes methods that must be overridden and methods for subclasses to call. Subclasses no longer have direct access to fields
and stamp
. Instead, they have new API to access these. Subclasses are able to allocate the fields
array through a protected framework method; this allows subclasses to specify additional fields.
More functionality has been moved into the base class. The base class now contains much of the computational machinery to support the Gregorian calendar. This is based on two things: (1) Many calendars are based on the Gregorian calendar (such as the Buddhist and Japanese imperial calendars). (2) All calendars require basic Gregorian support in order to handle timezone computations.
Common computations have been moved into Calendar
. Subclasses no longer compute the week related fields and the time related fields. These are commonly handled for all calendars by the base class.
Subclass computation of time => fields
The {@link #ERA}, {@link #YEAR}, {@link #EXTENDED_YEAR}, {@link #MONTH}, {@link #DAY_OF_MONTH}, and {@link #DAY_OF_YEAR} fields arecomputed by the subclass, based on the Julian day. All other fields are computed by Calendar
.
Calendar
, they must also be computed. These are the only fields that the subclass should compute. All other fields are computed by the base class, so time and week fields behave in a consistent way across all calendars. The default version of this method in Calendar
implements a proleptic Gregorian calendar. Within this method, subclasses may call getGregorianXxx()
to obtain the Gregorian calendar month, day of month, and extended year for the given date.Subclass computation of fields => time
The interpretation of most field values is handled entirely by Calendar
. Calendar
determines which fields are set, which are not, which are set more recently, and so on. In addition, Calendar
handles the computation of the time from the time fields and handles the week-related fields. The only thing the subclass must do is determine the extended year, based on the year fields, and then, given an extended year and a month, it must return a Julian day number.
Other methods
limitType
. This method only needs to handle the fields {@link #ERA}, {@link #YEAR}, {@link #MONTH}, {@link #WEEK_OF_YEAR}, {@link #WEEK_OF_MONTH}, {@link #DAY_OF_MONTH}, {@link #DAY_OF_YEAR}, {@link #DAY_OF_WEEK_IN_MONTH}, {@link #YEAR_WOY}, and {@link #EXTENDED_YEAR}. Other fields are invariant (with respect to calendar system) and are handled by the base class.IllegalArgumentException
. The method may call super.validateField(field)
to handle fields in a generic way, that is, to compare them to the range getMinimum(field)
..getMaximum(field)
.int[]
array large enough to hold the calendar's fields. This is only necessary if the calendar defines additional fields beyond those defined by Calendar
. The length of the result must be at least {@link #BASE_FIELD_COUNT} and no more than{@link #MAX_FIELD_COUNT}.DateFormat
appropriate to this calendar. This is only required if a calendar subclass redefines the use of a field (for example, changes the {@link #ERA} field from a symbolic fieldto a numeric one) or defines an additional field.Normalized behavior
The behavior of certain fields has been made consistent across all calendar systems and implemented in Calendar
.
Calendar
and to maintain basic correpsondences between calendar systems. Affected fields: {@link #AM_PM}, {@link #HOUR}, {@link #HOUR_OF_DAY}, {@link #MINUTE}, {@link #SECOND}, {@link #MILLISECOND}, {@link #ZONE_OFFSET}, and {@link #DST_OFFSET}.GregorianCalendar
fields: the {@link #YEAR}, {@link #MONTH}, and {@link #DAY_OF_MONTH}. As a result, Calendar
always computes these fields, even for non-Gregorian calendar systems. These fields are available to subclasses.WEEK_OF_YEAR, WEEK_OF_MONTH
, {@link #DAY_OF_WEEK_IN_MONTH}, {@link #DOW_LOCAL}, {@link #YEAR_WOY} are all computed ina consistent way in the base class, based on the {@link #EXTENDED_YEAR}, {@link #DAY_OF_YEAR}, {@link #MONTH}, and {@link #DAY_OF_MONTH}, which are computed by the subclass.Supported range
The allowable range of Calendar
has been narrowed. GregorianCalendar
used to attempt to support the range of dates with millisecond values from Long.MIN_VALUE
to Long.MAX_VALUE
. This introduced awkward constructions (hacks) which slowed down performance. It also introduced non-uniform behavior at the boundaries. The new Calendar
protocol specifies the maximum range of supportable dates as those having Julian day numbers of -0x7F000000
to +0x7F000000
. This corresponds to years from ~5,000,000 BCE to ~5,000,000 CE. Programmers should use the constants {@link #MIN_DATE} (or{@link #MIN_MILLIS} or {@link #MIN_JULIAN}) and {@link #MAX_DATE} (or {@link #MAX_MILLIS} or{@link #MAX_JULIAN}) in Calendar
to specify an extremely early or extremely late date.
General notes
GregorianCalendar
class supports dates before the historical onset of the calendar by extending the calendar system backward in time. Similarly, the HebrewCalendar
extends backward before the start of its epoch into zero and negative years. Subclasses do not throw exceptions because a date precedes the historical start of a calendar system. Instead, they implement {@link #handleGetLimit} to return appropriate limits on{@link #YEAR}, {@link #ERA}, etc. fields. Then, if the calendar is set to not be lenient, out-of-range field values will trigger an exception.ERA==AD ? YEAR : 1-YEAR
. Another example is the Mayan long count, which has years (KUN
) and nested cycles of years (KATUN
and BAKTUN
). The Mayan {@link #EXTENDED_YEAR} is computed as TUN + 20 * (KATUN+ 20 * BAKTUN)
. The Calendar
base class uses the {@link #EXTENDED_YEAR} field to compute the week-relatedfields.Abstraction of a calendar interface for tracking working/non-working days, such as Bank Holidays. This is used in conjunction with DayCount and BusinessDayConvention to calculate settlement dates.
User: Zhang Kaitao
Date: 13-11-4
Version: 1.0
CalendarEvents
Events are represented as ordinary JavaScript Objects (see {@link com.smartgwt.client.widgets.calendar.CalendarEvent}). The Calendar expects to be able to read and write a basic set of properties on events: name, startDate, endDate, description, etc, which can be stored under configurable property names (see eg {@link com.smartgwt.client.widgets.calendar.Calendar#getStartDateField startDateField}.
Much like a {@link com.smartgwt.client.widgets.grid.ListGrid} manages it's ListGridRecords, the Calendar can either be passed an ordinaryArray of CalendarEvents or can fetch data from a DataSource.
If the calendar is bound to a DataSource, event changes by user action or by calling methods will be saved to the DataSource.
Navigation
The calendar supports a {@link com.smartgwt.client.widgets.calendar.Calendar#getWeekView WeekView}, {@link com.smartgwt.client.widgets.calendar.Calendar#getDayView DayView} and {@link com.smartgwt.client.widgets.calendar.Calendar#getMonthView MonthView} by default. The user can navigate using back andforward buttons or via an attached {@link com.smartgwt.client.widgets.calendar.Calendar#getDateChooser DateChooser}.
Event Manipulation
Events can be created via clicking on the day, week or month views, or via the "Add Event" button. In the day and week views, the user may click and drag to create an event of a specific duration.
Creating an event via click or click and drag pops up the {@link com.smartgwt.client.widgets.calendar.Calendar#getEventDialog EventDialog}, which provides a simple form for quick event entry (only one field, the description, is required by default).
A separate editor called the {@link com.smartgwt.client.widgets.calendar.Calendar#getEventEditor EventEditor} provides an interface for editing allpossible properties of an event, including custom properties. The EventEditor is used whenever a pre-existing event is being edited, and can also be invoked by the user wherever the simpler EventDialog appears.
Events can also be programmatically {@link com.smartgwt.client.widgets.calendar.Calendar#addEvent added}, {@link com.smartgwt.client.widgets.calendar.Calendar#removeEvent removed}, or {@link com.smartgwt.client.widgets.calendar.Calendar#updateEvent updated}.
Vaadin Calendar is for visualizing events in a calendar. Calendar events can be visualized in the variable length view depending on the start and end dates.
Calendar
class is an abstract class that provides methods for converting between a specific instant in time and a set of {@link #fields calendar fields} such as YEAR
, MONTH
,DAY_OF_MONTH
, HOUR
, and so on, and for manipulating the calendar fields, such as getting the date of the next week. An instant in time can be represented by a millisecond value that is an offset from the Epoch, January 1, 1970 00:00:00.000 GMT (Gregorian). 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.
Calendar
defines a locale-specific seven day week using two parameters: the first day of the week and the minimal days in first week (from 1 to 7). These numbers are taken from the locale resource data when a Calendar
is constructed. They may also be specified explicitly through the methods for setting their values. 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.
Calendar
will resolve calendar field values to determine the date and time in the following way. 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 {@link DateFormat}to format dates.
set()
, add()
, and roll()
. 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 fieldf
before the call isdelta
, modulo any overflow that has occurred in fieldf
. 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 thanDAY_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 thanHOUR
.
Example: See {@link java.util.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.
Copyright (C) 2011-2013 Carlos Eduardo Leite de Andrade
This library is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License along with this program. If not, see www.gnu.org/licenses/
For more information, contact: www.japura.org
@author Carlos Eduardo Leite de Andrade
A calendar should be defined for specific exchange holiday schedule or for general country holiday schedule. Legacy city holiday schedule calendars will be moved to the exchange/country convention. @author Richard Gomes
An interface to be implemented by objects that define spaces of time during which an associated {@link Trigger}
may fire. Calendars do not define actual fire times, but rather are used to limit a Trigger
from firing on its normal schedule if necessary. Most Calendars include all times by default and allow the user to specify times to exclude. As such, it is often useful to think of Calendars as being used to exclude a block of time — as opposed to include a block of time. (i.e. the schedule "fire every five minutes except on Sundays" could be implemented with a SimpleTrigger
and a WeeklyCalendar
which excludes Sundays)
Implementations MUST take care of being properly Cloneable
and Serializable
.
Default {@link #getZclass}: z-calendar. (since 3.5.0) @author tomyeh
Default {@link #getZclass}: z-calendar. (since 3.5.0) @author tomyeh @since 3.5.2
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