C - the chronology of this datepublic interface ChronoLocalDate<C extends Chrono<C>> extends Temporal, TemporalAdjuster, Comparable<ChronoLocalDate<?>>
Most applications should declare method signatures, fields and variables
as LocalDate, not this interface.
A ChronoLocalDate is the abstract representation of a date where the
Chrono chronology, or calendar system, is pluggable.
The date is defined in terms of fields expressed by TemporalField,
where most common implementations are defined in ChronoField.
The chronology defines how the calendar system operates and the meaning of
the standard fields.
LocalDate rather than this
interface, even in the case where the application needs to deal with multiple
calendar systems. The rationale for this is explored in the following documentation.
The primary use case where this interface should be used is where the generic
type parameter <C> is fully defined as a specific chronology.
In that case, the assumptions of that chronology are known at development
time and specified in the code.
When the chronology is defined in the generic type parameter as ? or otherwise unknown at development time, the rest of the discussion below applies.
To emphasize the point, declaring a method signature, field or variable as this
interface type can initially seem like the sensible way to globalize an application,
however it is usually the wrong approach.
As such, it should be considered an application-wide architectural decision to choose
to use this interface as opposed to LocalDate.
1) Applications using this interface, as opposed to using just LocalDate,
face a significantly higher probability of bugs. This is because the calendar system
in use is not known at development time. A key cause of bugs is where the developer
applies assumptions from their day-to-day knowledge of the ISO calendar system
to code that is intended to deal with any arbitrary calendar system.
The section below outlines how those assumptions can cause problems
The primary mechanism for reducing this increased risk of bugs is a strong code review process.
This should also be considered a extra cost in maintenance for the lifetime of the code.
2) This interface does not enforce immutability of implementations.
While the implementation notes indicate that all implementations must be immutable
there is nothing in the code or type system to enforce this. Any method declared
to accept a ChronoLocalDate could therefore be passed a poorly or
maliciously written mutable implementation.
3) Applications using this interface must consider the impact of eras.
LocalDate shields users from the concept of eras, by ensuring that getYear()
returns the proleptic year. That decision ensures that developers can think of
LocalDate instances as consisting of three fields - year, month-of-year and day-of-month.
By contrast, users of this interface must think of dates as consisting of four fields -
era, year-of-era, month-of-year and day-of-month. The extra era field is frequently
forgotten, yet it is of vital importance to dates in an arbitrary calendar system.
For example, in the Japanese calendar system, the era represents the reign of an Emperor.
Whenever one reign ends and another starts, the year-of-era is reset to one.
4) The only agreed international standard for passing a date between two systems is the ISO-8601 standard which requires the ISO calendar system. Using this interface throughout the application will inevitably lead to the requirement to pass the date across a network or component boundary, requiring an application specific protocol or format.
5) Long term persistence, such as a database, will almost always only accept dates in the ISO-8601 calendar system (or the related Julian-Gregorian). Passing around dates in other calendar systems increases the complications of interacting with persistence.
6) Most of the time, passing a ChronoLocalDate throughout an application
is unnecessary, as discussed in the last section below.
Code that queries the day-of-month and assumes that the value will never be more than 31 is invalid. Some calendar systems have more than 31 days in some months.
Code that adds 12 months to a date and assumes that a year has been added is invalid. Some calendar systems have a different number of months, such as 13 in the Coptic or Ethiopic.
Code that adds one month to a date and assumes that the month-of-year value will increase by one or wrap to the next year is invalid. Some calendar systems have a variable number of months in a year, such as the Hebrew.
Code that adds one month, then adds a second one month and assumes that the day-of-month will remain close to its original value is invalid. Some calendar systems have a large difference between the length of the longest month and the length of the shortest month. For example, the Coptic or Ethiopic have 12 months of 30 days and 1 month of 5 days.
Code that adds seven days and assumes that a week has been added is invalid. Some calendar systems have weeks of other than seven days, such as the French Revolutionary.
Code that assumes that because the year of date1 is greater than the year of date2
then date1 is after date2 is invalid. This is invalid for all calendar systems
when referring to the year-of-era, and especially untrue of the Japanese calendar system
where the year-of-era restarts with the reign of every new Emperor.
Code that treats month-of-year one and day-of-month one as the start of the year is invalid. Not all calendar systems start the year when the month value is one.
In general, manipulating a date, and even querying a date, is wide open to bugs when the calendar system is unknown at development time. This is why it is essential that code using this interface is subjected to additional code reviews. It is also why an architectural decision to avoid this interface type is usually the correct one.
LocalDate.
LocalDate to and from the user's preferred calendar system during
printing and parsing
This approach treats the problem of globalized calendar systems as a localization issue and confines it to the UI layer. This approach is in keeping with other localization issues in the java platform.
As discussed above, performing calculations on a date where the rules of the calendar system are pluggable requires skill and is not recommended. Fortunately, the need to perform calculations on a date in an arbitrary calendar system is extremely rare. For example, it is highly unlikely that the business rules of a library book rental scheme will allow rentals to be for one month, where meaning of the month is dependent on the user's preferred calendar system.
A key use case for calculations on a date in an arbitrary calendar system is producing a month-by-month calendar for display and user interaction. Again, this is a UI issue, and use of this interface solely within a few methods of the UI layer may be justified.
In any other part of the system, where a date must be manipulated in a calendar system other than ISO, the use case will generally specify the calendar system to use. For example, an application may need to calculate the next Islamic or Hebrew holiday which may require manipulating the date. This kind of use case can be handled as follows:
LocalDate being passed to the method
LocalDate
Developers writing low-level frameworks or libraries should also avoid this interface.
Instead, one of the two general purpose access interfaces should be used.
Use TemporalAccessor if read-only access is required, or use Temporal
if read-write access is required.
Additional calendar systems may be added to the system.
See Chrono for more details.
| Modifier and Type | Field and Description |
|---|---|
static Comparator<ChronoLocalDate<?>> |
DATE_COMPARATOR
Comparator for two
ChronoLocalDates ignoring the chronology. |
| Modifier and Type | Method and Description |
|---|---|
ChronoLocalDateTime<C> |
atTime(LocalTime localTime)
Returns a date-time formed from this date at the specified time.
|
int |
compareTo(ChronoLocalDate<?> other)
Compares this date to another date, including the chronology.
|
boolean |
equals(Object obj)
Checks if this date is equal to another date, including the chronology.
|
C |
getChrono()
Gets the chronology of this date.
|
Era<C> |
getEra()
Gets the era, as defined by the chronology.
|
int |
hashCode()
A hash code for this date.
|
boolean |
isAfter(ChronoLocalDate<?> other)
Checks if this date is after the specified date ignoring the chronology.
|
boolean |
isBefore(ChronoLocalDate<?> other)
Checks if this date is before the specified date ignoring the chronology.
|
boolean |
isEqual(ChronoLocalDate<?> other)
Checks if this date is equal to the specified date ignoring the chronology.
|
boolean |
isLeapYear()
Checks if the year is a leap year, as defined by the calendar system.
|
int |
lengthOfMonth()
Returns the length of the month represented by this date, as defined by the calendar system.
|
int |
lengthOfYear()
Returns the length of the year represented by this date, as defined by the calendar system.
|
ChronoLocalDate<C> |
minus(long amountToSubtract,
TemporalUnit unit)
Returns an object of the same type as this object with the specified period subtracted.
|
ChronoLocalDate<C> |
minus(TemporalSubtractor adjuster)
Returns an object of the same type as this object with an amount subtracted.
|
ChronoLocalDate<C> |
plus(long amountToAdd,
TemporalUnit unit)
Returns an object of the same type as this object with the specified period added.
|
ChronoLocalDate<C> |
plus(TemporalAdder adjuster)
Returns an object of the same type as this object with an amount added.
|
long |
toEpochDay()
Converts this date to the Epoch Day.
|
String |
toString()
Outputs this date as a
String. |
String |
toString(DateTimeFormatter formatter)
Outputs this date-time as a
String using the formatter. |
ChronoLocalDate<C> |
with(TemporalAdjuster adjuster)
Returns an adjusted object of the same type as this object with the adjustment made.
|
ChronoLocalDate<C> |
with(TemporalField field,
long newValue)
Returns an object of the same type as this object with the specified field altered.
|
periodUntilget, getLong, isSupported, query, rangeadjustIntostatic final Comparator<ChronoLocalDate<?>> DATE_COMPARATOR
ChronoLocalDates ignoring the chronology.
This comparator differs from the comparison in compareTo(org.threeten.bp.temporal.ChronoLocalDate<?>) in that it
only compares the underlying date and not the chronology.
This allows dates in different calendar systems to be compared based
on the time-line position.
This is equivalent to using Long.compare(date1.toEpochDay(), date2.toEpochDay()).
C getChrono()
The Chrono represents the calendar system in use.
The era and other fields in ChronoField are defined by the chronology.
Era<C> getEra()
The era is, conceptually, the largest division of the time-line.
Most calendar systems have a single epoch dividing the time-line into two eras.
However, some have multiple eras, such as one for the reign of each leader.
The exact meaning is determined by the Chrono.
All correctly implemented Era classes are singletons, thus it
is valid code to write date.getEra() == SomeChrono.ERA_NAME).
boolean isLeapYear()
A leap-year is a year of a longer length than normal. The exact meaning is determined by the chronology with the constraint that a leap-year must imply a year-length longer than a non leap-year.
The default implementation uses Chrono.isLeapYear(long).
int lengthOfMonth()
This returns the length of the month in days.
int lengthOfYear()
This returns the length of the year in days.
The default implementation uses isLeapYear() and returns 365 or 366.
ChronoLocalDate<C> with(TemporalAdjuster adjuster)
Temporal
This adjusts this date-time according to the rules of the specified adjuster.
A simple adjuster might simply set the one of the fields, such as the year field.
A more complex adjuster might set the date to the last day of the month.
A selection of common adjustments is provided in TemporalAdjusters.
These include finding the "last day of the month" and "next Wednesday".
The adjuster is responsible for handling special cases, such as the varying
lengths of month and leap years.
Some example code indicating how and why this method is used:
date = date.with(Month.JULY); // most key classes implement TemporalAdjuster date = date.with(lastDayOfMonth()); // static import from TemporalAdjusters date = date.with(next(WEDNESDAY)); // static import from TemporalAdjusters and DayOfWeek
ChronoLocalDate<C> with(TemporalField field, long newValue)
Temporal
This returns a new object based on this one with the value for the specified field changed.
For example, on a LocalDate, this could be used to set the year, month or day-of-month.
The returned object will have the same observable type as this object.
In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st January, then changing the month to February would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.
ChronoField.
If the field is supported, then the adjustment must be performed.
If unsupported, then a DateTimeException must be thrown.
If the field is not a ChronoField, then the result of this method
is obtained by invoking TemporalField.doWith(Temporal, long)
passing this as the first argument.
Implementations must not alter either this object or the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.
ChronoLocalDate<C> plus(TemporalAdder adjuster)
Temporal
This adjusts this temporal, adding according to the rules of the specified adder.
The adder is typically a Period but may be any other type implementing
the TemporalAdder interface, such as Duration.
Some example code indicating how and why this method is used:
date = date.plus(period); // add a Period instance date = date.plus(duration); // add a Duration instance date = date.plus(MONTHS.between(start, end)); // static import of MONTHS field date = date.plus(workingDays(6)); // example user-written workingDays method
Note that calling plus followed by minus is not guaranteed to
return the same date-time.
ChronoLocalDate<C> plus(long amountToAdd, TemporalUnit unit)
Temporal
This method returns a new object based on this one with the specified period added.
For example, on a LocalDate, this could be used to add a number of years, months or days.
The returned object will have the same observable type as this object.
In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st January, then adding one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.
If the implementation represents a date-time that has boundaries, such as LocalTime,
then the permitted units must include the boundary unit, but no multiples of the boundary unit.
For example, LocalTime must accept DAYS but not WEEKS or MONTHS.
ChronoUnit.
If the unit is supported, then the addition must be performed.
If unsupported, then a DateTimeException must be thrown.
If the unit is not a ChronoUnit, then the result of this method
is obtained by invoking TemporalUnit.doPlus(Temporal, long)
passing this as the first argument.
Implementations must not alter either this object or the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.
ChronoLocalDate<C> minus(TemporalSubtractor adjuster)
Temporal
This adjusts this temporal, subtracting according to the rules of the specified subtractor.
The subtractor is typically a Period but may be any other type implementing
the TemporalSubtractor interface, such as Duration.
Some example code indicating how and why this method is used:
date = date.minus(period); // subtract a Period instance date = date.minus(duration); // subtract a Duration instance date = date.minus(MONTHS.between(start, end)); // static import of MONTHS field date = date.minus(workingDays(6)); // example user-written workingDays method
Note that calling plus followed by minus is not guaranteed to
return the same date-time.
ChronoLocalDate<C> minus(long amountToSubtract, TemporalUnit unit)
Temporal
This method returns a new object based on this one with the specified period subtracted.
For example, on a LocalDate, this could be used to subtract a number of years, months or days.
The returned object will have the same observable type as this object.
In some cases, changing a field is not fully defined. For example, if the target object is a date representing the 31st March, then subtracting one month would be unclear. In cases like this, the field is responsible for resolving the result. Typically it will choose the previous valid date, which would be the last valid day of February in this example.
If the implementation represents a date-time that has boundaries, such as LocalTime,
then the permitted units must include the boundary unit, but no multiples of the boundary unit.
For example, LocalTime must accept DAYS but not WEEKS or MONTHS.
Implementations must not alter either this object or the specified temporal object. Instead, an adjusted copy of the original must be returned. This provides equivalent, safe behavior for immutable and mutable implementations.
ChronoLocalDateTime<C> atTime(LocalTime localTime)
This merges the two objects - this and the specified time -
to form an instance of ChronoLocalDateTime.
This instance is immutable and unaffected by this method call.
localTime - the local time to use, not nulllong toEpochDay()
The Epoch Day count is a simple
incrementing count of days where day 0 is 1970-01-01 (ISO).
This definition is the same for all chronologies, enabling conversion.
int compareTo(ChronoLocalDate<?> other)
The comparison is based first on the underlying time-line date, then
on the chronology.
It is "consistent with equals", as defined by Comparable.
For example, the following is the comparator order:
2012-12-03 (ISO)2012-12-04 (ISO)2555-12-04 (ThaiBuddhist)2012-12-05 (ISO)
If all the date objects being compared are in the same chronology, then the
additional chronology stage is not required and only the local date is used.
To compare the dates of two DateTimeAccessor instances, including dates
in two different chronologies, use ChronoField.EPOCH_DAY as a comparator.
compareTo in interface Comparable<ChronoLocalDate<?>>other - the other date to compare to, not nullboolean isAfter(ChronoLocalDate<?> other)
This method differs from the comparison in compareTo(org.threeten.bp.temporal.ChronoLocalDate<?>) in that it
only compares the underlying date and not the chronology.
This allows dates in different calendar systems to be compared based
on the time-line position.
This is equivalent to using date1.toEpochDay() > date2.toEpochDay().
other - the other date to compare to, not nullboolean isBefore(ChronoLocalDate<?> other)
This method differs from the comparison in compareTo(org.threeten.bp.temporal.ChronoLocalDate<?>) in that it
only compares the underlying date and not the chronology.
This allows dates in different calendar systems to be compared based
on the time-line position.
This is equivalent to using date1.toEpochDay() < date2.toEpochDay().
other - the other date to compare to, not nullboolean isEqual(ChronoLocalDate<?> other)
This method differs from the comparison in compareTo(org.threeten.bp.temporal.ChronoLocalDate<?>) in that it
only compares the underlying date and not the chronology.
This allows dates in different calendar systems to be compared based
on the time-line position.
This is equivalent to using date1.toEpochDay() == date2.toEpochDay().
other - the other date to compare to, not nullboolean equals(Object obj)
Compares this date with another ensuring that the date and chronology are the same.
To compare the dates of two DateTimeAccessor instances, including dates
in two different chronologies, use ChronoField.EPOCH_DAY as a comparator.
int hashCode()
String toString()
String.
The output will include the full local date and the chronology ID.
String toString(DateTimeFormatter formatter)
String using the formatter.formatter - the formatter to use, not nullDateTimeException - if an error occurs during printingCopyright © 2007-2013 ThreeTen.org. All Rights Reserved.