* Most applications should declare method signatures, fields and variables * as {@link LocalDate}, not this interface. *
* A {@code ChronoLocalDate} is the abstract representation of a date where the * {@code Chronology chronology}, or calendar system, is pluggable. * The date is defined in terms of fields expressed by {@link TemporalField}, * where most common implementations are defined in {@link ChronoField}. * The chronology defines how the calendar system operates and the meaning of * the standard fields. * *
* The primary use case where this interface should be used is where the generic
* type parameter {@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 {@code LocalDate}.
*
*
* 1) Applications using this interface, as opposed to using just {@code 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 {@code ChronoLocalDate} could therefore be passed a poorly or
* maliciously written mutable implementation.
*
* 3) Applications using this interface must consider the impact of eras.
* {@code LocalDate} shields users from the concept of eras, by ensuring that {@code getYear()}
* returns the proleptic year. That decision ensures that developers can think of
* {@code 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 {@code 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 {@code date1} is greater than the year of {@code date2}
* then {@code date1} is after {@code 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.
*
*
* 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:
*
* 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 {@link TemporalAccessor} if read-only access is required, or use {@link Temporal}
* if read-write access is required.
*
*
* Additional calendar systems may be added to the system.
* See {@link Chronology} for more details.
*
* @param
* This comparator differs from the comparison in {@link #compareTo} 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 {@code Long.compare(date1.toEpochDay(), date2.toEpochDay())}.
*
* @see #isAfter
* @see #isBefore
* @see #isEqual
*/
public static final Comparator
* The {@code Chronology} represents the calendar system in use.
* The era and other fields in {@link ChronoField} are defined by the chronology.
*
* @return the chronology, not null
*/
Chronology getChronology();
/**
* Gets the era, as defined by the chronology.
*
* 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 {@code Chronology}.
*
* All correctly implemented {@code Era} classes are singletons, thus it
* is valid code to write {@code date.getEra() == SomeChrono.ERA_NAME)}.
*
* This default implementation uses {@link Chronology#eraOf(int)}.
*
* @return the chronology specific era constant applicable at this date, not null
*/
public default Era getEra() {
return getChronology().eraOf(get(ERA));
}
/**
* Checks if the year is a leap year, as defined by the calendar system.
*
* 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.
*
* This default implementation uses {@link Chronology#isLeapYear(long)}.
*
* @return true if this date is in a leap year, false otherwise
*/
public default boolean isLeapYear() {
return getChronology().isLeapYear(getLong(YEAR));
}
/**
* Returns the length of the month represented by this date, as defined by the calendar system.
*
* This returns the length of the month in days.
*
* @return the length of the month in days
*/
int lengthOfMonth();
/**
* Returns the length of the year represented by this date, as defined by the calendar system.
*
* This returns the length of the year in days.
*
* The default implementation uses {@link #isLeapYear()} and returns 365 or 366.
*
* @return the length of the year in days
*/
public default int lengthOfYear() {
return (isLeapYear() ? 366 : 365);
}
@Override
public default boolean isSupported(TemporalField field) {
if (field instanceof ChronoField) {
return ((ChronoField) field).isDateField();
}
return field != null && field.isSupportedBy(this);
}
//-----------------------------------------------------------------------
// override for covariant return type
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D with(TemporalAdjuster adjuster) {
return (D) getChronology().ensureChronoLocalDate(Temporal.super.with(adjuster));
}
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D with(TemporalField field, long newValue) {
if (field instanceof ChronoField) {
throw new DateTimeException("Unsupported field: " + field.getName());
}
return (D) getChronology().ensureChronoLocalDate(field.adjustInto(this, newValue));
}
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D plus(TemporalAmount amount) {
return (D) getChronology().ensureChronoLocalDate(Temporal.super.plus(amount));
}
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D plus(long amountToAdd, TemporalUnit unit) {
if (unit instanceof ChronoUnit) {
throw new DateTimeException("Unsupported unit: " + unit.getName());
}
return (D) getChronology().ensureChronoLocalDate(unit.addTo(this, amountToAdd));
}
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D minus(TemporalAmount amount) {
return (D) getChronology().ensureChronoLocalDate(Temporal.super.minus(amount));
}
/**
* {@inheritDoc}
* @throws DateTimeException {@inheritDoc}
* @throws ArithmeticException {@inheritDoc}
*/
@Override
public default D minus(long amountToSubtract, TemporalUnit unit) {
return (D) getChronology().ensureChronoLocalDate(Temporal.super.minus(amountToSubtract, unit));
}
//-----------------------------------------------------------------------
/**
* Queries this date using the specified query.
*
* This queries this date using the specified query strategy object.
* The {@code TemporalQuery} object defines the logic to be used to
* obtain the result. Read the documentation of the query to understand
* what the result of this method will be.
*
* The result of this method is obtained by invoking the
* {@link TemporalQuery#queryFrom(TemporalAccessor)} method on the
* specified query passing {@code this} as the argument.
*
* @param
* This returns a temporal object of the same observable type as the input
* with the date changed to be the same as this.
*
* The adjustment is equivalent to using {@link Temporal#with(TemporalField, long)}
* passing {@link ChronoField#EPOCH_DAY} as the field.
*
* In most cases, it is clearer to reverse the calling pattern by using
* {@link Temporal#with(TemporalAdjuster)}:
*
* This instance is immutable and unaffected by this method call.
*
* @param temporal the target object to be adjusted, not null
* @return the adjusted object, not null
* @throws DateTimeException if unable to make the adjustment
* @throws ArithmeticException if numeric overflow occurs
*/
@Override
public default Temporal adjustInto(Temporal temporal) {
return temporal.with(EPOCH_DAY, toEpochDay());
}
/**
* Calculates the period between this date and another date in
* terms of the specified unit.
*
* This calculates the period between two dates in terms of a single unit.
* The start and end points are {@code this} and the specified date.
* The result will be negative if the end is before the start.
* The {@code Temporal} passed to this method must be a
* {@code ChronoLocalDate} in the same chronology.
* The calculation returns a whole number, representing the number of
* complete units between the two dates.
* For example, the period in days between two dates can be calculated
* using {@code startDate.periodUntil(endDate, DAYS)}.
*
* There are two equivalent ways of using this method.
* The first is to invoke this method.
* The second is to use {@link TemporalUnit#between(Temporal, Temporal)}:
*
* The calculation is implemented in this method for {@link ChronoUnit}.
* The units {@code DAYS}, {@code WEEKS}, {@code MONTHS}, {@code YEARS},
* {@code DECADES}, {@code CENTURIES}, {@code MILLENNIA} and {@code ERAS}
* should be supported by all implementations.
* Other {@code ChronoUnit} values will throw an exception.
*
* If the unit is not a {@code ChronoUnit}, then the result of this method
* is obtained by invoking {@code TemporalUnit.between(Temporal, Temporal)}
* passing {@code this} as the first argument and the input temporal as
* the second argument.
*
* This instance is immutable and unaffected by this method call.
*
* @param endDate the end date, which must be a {@code ChronoLocalDate}
* in the same chronology, not null
* @param unit the unit to measure the period in, not null
* @return the amount of the period between this date and the end date
* @throws DateTimeException if the period cannot be calculated
* @throws ArithmeticException if numeric overflow occurs
*/
@Override // override for Javadoc
public abstract long periodUntil(Temporal endDate, TemporalUnit unit);
/**
* Calculates the period between this date and another date as a {@code Period}.
*
* This calculates the period between two dates in terms of years, months and days.
* The start and end points are {@code this} and the specified date.
* The result will be negative if the end is before the start.
*
* The calculation is performed using the the chronology of this date.
* If necessary, the input date will be converted to match.
*
* The result of this method can be a negative period if the end is before the start.
* The negative sign will be the same in each of year, month and day.
*
* This instance is immutable and unaffected by this method call.
*
* @param endDate the end date, exclusive, which may be in any chronology, not null
* @return the period between this date and the end date, not null
* @throws DateTimeException if the period cannot be calculated
* @throws ArithmeticException if numeric overflow occurs
*/
public abstract Period periodUntil(ChronoLocalDate endDate);
//-----------------------------------------------------------------------
/**
* Combines this date with a time to create a {@code ChronoLocalDateTime}.
*
* This returns a {@code ChronoLocalDateTime} formed from this date at the specified time.
* All possible combinations of date and time are valid.
*
* @param localTime the local time to use, not null
* @return the local date-time formed from this date and the specified time, not null
*/
public default ChronoLocalDateTime
* The {@link ChronoField#EPOCH_DAY 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.
*
* This default implementation queries the {@code EPOCH_DAY} field.
*
* @return the Epoch Day equivalent to this date
*/
public default long toEpochDay() {
return getLong(EPOCH_DAY);
}
//-----------------------------------------------------------------------
/**
* Compares this date to another date, including the chronology.
*
* The comparison is based first on the underlying time-line date, then
* on the chronology.
* It is "consistent with equals", as defined by {@link Comparable}.
*
* For example, the following is the comparator order:
*
* 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 {@code TemporalAccessor} instances, including dates
* in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
*
* This default implementation performs the comparison defined above.
*
* @param other the other date to compare to, not null
* @return the comparator value, negative if less, positive if greater
*/
@Override
public default int compareTo(ChronoLocalDate other) {
int cmp = Long.compare(toEpochDay(), other.toEpochDay());
if (cmp == 0) {
cmp = getChronology().compareTo(other.getChronology());
}
return cmp;
}
/**
* Checks if this date is after the specified date ignoring the chronology.
*
* This method differs from the comparison in {@link #compareTo} 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 {@code date1.toEpochDay() > date2.toEpochDay()}.
*
* This default implementation performs the comparison based on the epoch-day.
*
* @param other the other date to compare to, not null
* @return true if this is after the specified date
*/
public default boolean isAfter(ChronoLocalDate other) {
return this.toEpochDay() > other.toEpochDay();
}
/**
* Checks if this date is before the specified date ignoring the chronology.
*
* This method differs from the comparison in {@link #compareTo} 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 {@code date1.toEpochDay() < date2.toEpochDay()}.
*
* This default implementation performs the comparison based on the epoch-day.
*
* @param other the other date to compare to, not null
* @return true if this is before the specified date
*/
public default boolean isBefore(ChronoLocalDate other) {
return this.toEpochDay() < other.toEpochDay();
}
/**
* Checks if this date is equal to the specified date ignoring the chronology.
*
* This method differs from the comparison in {@link #compareTo} 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 {@code date1.toEpochDay() == date2.toEpochDay()}.
*
* This default implementation performs the comparison based on the epoch-day.
*
* @param other the other date to compare to, not null
* @return true if the underlying date is equal to the specified date
*/
public default boolean isEqual(ChronoLocalDate other) {
return this.toEpochDay() == other.toEpochDay();
}
//-----------------------------------------------------------------------
/**
* Checks if this date is equal to another date, including the chronology.
*
* Compares this date with another ensuring that the date and chronology are the same.
*
* To compare the dates of two {@code TemporalAccessor} instances, including dates
* in two different chronologies, use {@link ChronoField#EPOCH_DAY} as a comparator.
*
* @param obj the object to check, null returns false
* @return true if this is equal to the other date
*/
@Override
boolean equals(Object obj);
/**
* A hash code for this date.
*
* @return a suitable hash code
*/
@Override
int hashCode();
//-----------------------------------------------------------------------
/**
* Outputs this date as a {@code String}.
*
* The output will include the full local date and the chronology ID.
*
* @return the formatted date, not null
*/
@Override
String toString();
/**
* Outputs this date as a {@code String} using the formatter.
*
* The default implementation must behave as follows:
* Architectural issues to consider
* These are some of the points that must be considered before using this interface
* throughout an application.
* False assumptions causing bugs in multi-calendar system code
* As indicated above, there are many issues to consider when try to use and manipulate a
* date in an arbitrary calendar system. These are some of the key issues.
* Using LocalDate instead
* The primary alternative to using this interface throughout your application is as follows.
*
*
*
Specification for implementors
* This interface must be implemented with care to ensure other classes operate correctly.
* All implementations that can be instantiated must be final, immutable and thread-safe.
* Subclasses should be Serializable wherever possible.
*
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisLocalDate.adjustInto(temporal);
* temporal = temporal.with(thisLocalDate);
*
*
* // these two lines are equivalent
* amount = start.periodUntil(end, MONTHS);
* amount = MONTHS.between(start, end);
*
* The choice should be made based on which makes the code more readable.
*
*
* Values #2 and #3 represent the same date on the time-line.
* When two values represent the same date, the chronology ID is compared to distinguish them.
* This step is needed to make the ordering "consistent with equals".
*
* return formatter.format(this);
*
*
* @param formatter the formatter to use, not null
* @return the formatted date string, not null
* @throws DateTimeException if an error occurs during printing
*/
public default String toString(DateTimeFormatter formatter) {
Objects.requireNonNull(formatter, "formatter");
return formatter.format(this);
}
}