* Measurement of time is built on units, such as years, months, days, hours, minutes and seconds. * Implementations of this interface represent those units. *
* An instance of this interface represents the unit itself, rather than an amount of the unit. * See {@link Period} for a class that represents an amount in terms of the common units. *
* The most commonly used units are defined in {@link ChronoUnit}. * Further units are supplied in {@link IsoFields}. * Units can also be written by application code by implementing this interface. *
* The unit works using double dispatch. Client code calls methods on a date-time like * {@code LocalDateTime} which check if the unit is a {@code ChronoUnit}. * If it is, then the date-time must handle it. * Otherwise, the method call is re-dispatched to the matching method in this interface. * * @implSpec * 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. * It is recommended to use an enum where possible. * * @since 1.8 */ public interface TemporalUnit { /** * Gets the duration of this unit, which may be an estimate. *
* All units return a duration measured in standard nanoseconds from this method. * The duration will be positive and non-zero. * For example, an hour has a duration of {@code 60 * 60 * 1,000,000,000ns}. *
* Some units may return an accurate duration while others return an estimate. * For example, days have an estimated duration due to the possibility of * daylight saving time changes. * To determine if the duration is an estimate, use {@link #isDurationEstimated()}. * * @return the duration of this unit, which may be an estimate, not null */ Duration getDuration(); /** * Checks if the duration of the unit is an estimate. *
* All units have a duration, however the duration is not always accurate. * For example, days have an estimated duration due to the possibility of * daylight saving time changes. * This method returns true if the duration is an estimate and false if it is * accurate. Note that accurate/estimated ignores leap seconds. * * @return true if the duration is estimated, false if accurate */ boolean isDurationEstimated(); //----------------------------------------------------------------------- /** * Checks if this unit represents a component of a date. *
* A date is time-based if it can be used to imply meaning from a date. * It must have a {@linkplain #getDuration() duration} that is an integral * multiple of the length of a standard day. * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()} * to return false, such as when representing a unit like 36 hours. * * @return true if this unit is a component of a date */ boolean isDateBased(); /** * Checks if this unit represents a component of a time. *
* A unit is time-based if it can be used to imply meaning from a time. * It must have a {@linkplain #getDuration() duration} that divides into * the length of a standard day without remainder. * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()} * to return false, such as when representing a unit like 36 hours. * * @return true if this unit is a component of a time */ boolean isTimeBased(); //----------------------------------------------------------------------- /** * Checks if this unit is supported by the specified temporal object. *
* This checks that the implementing date-time can add/subtract this unit. * This can be used to avoid throwing an exception. *
* This default implementation derives the value using * {@link Temporal#plus(long, TemporalUnit)}. * * @param temporal the temporal object to check, not null * @return true if the unit is supported */ default boolean isSupportedBy(Temporal temporal) { if (temporal instanceof LocalTime) { return isTimeBased(); } if (temporal instanceof ChronoLocalDate) { return isDateBased(); } if (temporal instanceof ChronoLocalDateTime || temporal instanceof ChronoZonedDateTime) { return true; } try { temporal.plus(1, this); return true; } catch (UnsupportedTemporalTypeException ex) { return false; } catch (RuntimeException ex) { try { temporal.plus(-1, this); return true; } catch (RuntimeException ex2) { return false; } } } /** * Returns a copy of the specified temporal object with the specified period added. *
* The period added is a multiple of this unit. For example, this method * could be used to add "3 days" to a date by calling this method on the * instance representing "days", passing the date and the period "3". * The period to be added may be negative, which is equivalent to subtraction. *
* There are two equivalent ways of using this method. * The first is to invoke this method directly. * The second is to use {@link Temporal#plus(long, TemporalUnit)}: *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisUnit.addTo(temporal);
* temporal = temporal.plus(thisUnit);
*
* It is recommended to use the second approach, {@code plus(TemporalUnit)},
* as it is a lot clearer to read in code.
* * Implementations should perform any queries or calculations using the units * available in {@link ChronoUnit} or the fields available in {@link ChronoField}. * If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown. *
* Implementations must not alter the specified temporal object.
* Instead, an adjusted copy of the original must be returned.
* This provides equivalent, safe behavior for immutable and mutable implementations.
*
* @param
* This calculates the amount in terms of this unit. The start and end
* points are supplied as temporal objects and must be of compatible types.
* The implementation will convert the second type to be an instance of the
* first type before the calculating the amount.
* The result will be negative if the end is before the start.
* For example, the amount in hours between two temporal objects can be
* calculated using {@code HOURS.between(startTime, endTime)}.
*
* The calculation returns a whole number, representing the number of
* complete units between the two temporals.
* For example, the amount in hours between the times 11:30 and 13:29
* will only be one hour as it is one minute short of two hours.
*
* There are two equivalent ways of using this method.
* The first is to invoke this method directly.
* The second is to use {@link Temporal#until(Temporal, TemporalUnit)}:
*
* For example, this method allows the number of days between two dates to
* be calculated:
*
* Implementations should perform any queries or calculations using the units
* available in {@link ChronoUnit} or the fields available in {@link ChronoField}.
* If the unit is not supported an {@code UnsupportedTemporalTypeException} must be thrown.
* Implementations must not alter the specified temporal objects.
*
* @implSpec
* Implementations must begin by checking to if the two temporals have the
* same type using {@code getClass()}. If they do not, then the result must be
* obtained by calling {@code temporal1Inclusive.until(temporal2Exclusive, this)}.
*
* @param temporal1Inclusive the base temporal object, not null
* @param temporal2Exclusive the other temporal object, exclusive, not null
* @return the amount of time between temporal1Inclusive and temporal2Exclusive
* in terms of this unit; positive if temporal2Exclusive is later than
* temporal1Inclusive, negative if earlier
* @throws DateTimeException if the amount cannot be calculated, or the end
* temporal cannot be converted to the same type as the start temporal
* @throws UnsupportedTemporalTypeException if the unit is not supported by the temporal
* @throws ArithmeticException if numeric overflow occurs
*/
long between(Temporal temporal1Inclusive, Temporal temporal2Exclusive);
//-----------------------------------------------------------------------
/**
* Gets a descriptive name for the unit.
*
* This should be in the plural and upper-first camel case, such as 'Days' or 'Minutes'.
*
* @return the name of this unit, not null
*/
@Override
String toString();
}
* // these two lines are equivalent
* between = thisUnit.between(start, end);
* between = start.until(end, thisUnit);
*
* The choice should be made based on which makes the code more readable.
*
* long daysBetween = DAYS.between(start, end);
* // or alternatively
* long daysBetween = start.until(end, DAYS);
*
*