* Date and time is expressed using fields which partition the time-line into something * meaningful for humans. Implementations of this interface represent those fields. *
* The most commonly used units are defined in {@link ChronoField}. * Further fields are supplied in {@link IsoFields}, {@link WeekFields} and {@link JulianFields}. * Fields can also be written by application code by implementing this interface. *
* The field works using double dispatch. Client code calls methods on a date-time like * {@code LocalDateTime} which check if the field is a {@code ChronoField}. * 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. * Implementations should be {@code Serializable} where possible. * An enum is as effective implementation choice. * * @since 1.8 */ public interface TemporalField { /** * Gets the display name for the field in the requested locale. *
* If there is no display name for the locale then a suitable default must be returned. *
* The default implementation must check the locale is not null * and return {@code toString()}. * * @param locale the locale to use, not null * @return the display name for the locale or a suitable default, not null */ default String getDisplayName(Locale locale) { Objects.requireNonNull(locale, "locale"); return toString(); } /** * Gets the unit that the field is measured in. *
* The unit of the field is the period that varies within the range. * For example, in the field 'MonthOfYear', the unit is 'Months'. * See also {@link #getRangeUnit()}. * * @return the unit defining the base unit of the field, not null */ TemporalUnit getBaseUnit(); /** * Gets the range that the field is bound by. *
* The range of the field is the period that the field varies within. * For example, in the field 'MonthOfYear', the range is 'Years'. * See also {@link #getBaseUnit()}. *
* The range is never null. For example, the 'Year' field is shorthand for * 'YearOfForever'. It therefore has a unit of 'Years' and a range of 'Forever'. * * @return the unit defining the range of the field, not null */ TemporalUnit getRangeUnit(); /** * Gets the range of valid values for the field. *
* All fields can be expressed as a {@code long} integer. * This method returns an object that describes the valid range for that value. * This method is generally only applicable to the ISO-8601 calendar system. *
* Note that the result only describes the minimum and maximum valid values * and it is important not to read too much into them. For example, there * could be values within the range that are invalid for the field. * * @return the range of valid values for the field, not null */ ValueRange range(); //----------------------------------------------------------------------- /** * Checks if this field represents a component of a date. *
* A field is date-based if it can be derived from * {@link ChronoField#EPOCH_DAY EPOCH_DAY}. * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()} * to return false, such as when representing a field like minute-of-week. * * @return true if this field is a component of a date */ boolean isDateBased(); /** * Checks if this field represents a component of a time. *
* A field is time-based if it can be derived from * {@link ChronoField#NANO_OF_DAY NANO_OF_DAY}. * Note that it is valid for both {@code isDateBased()} and {@code isTimeBased()} * to return false, such as when representing a field like minute-of-week. * * @return true if this field is a component of a time */ boolean isTimeBased(); //----------------------------------------------------------------------- /** * Checks if this field is supported by the temporal object. *
* This determines whether the temporal accessor supports this field. * If this returns false, then the temporal cannot be queried for this field. *
* There are two equivalent ways of using this method. * The first is to invoke this method directly. * The second is to use {@link TemporalAccessor#isSupported(TemporalField)}: *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.isSupportedBy(temporal);
* temporal = temporal.isSupported(thisField);
*
* It is recommended to use the second approach, {@code isSupported(TemporalField)},
* as it is a lot clearer to read in code.
* * Implementations should determine whether they are supported using the fields * available in {@link ChronoField}. * * @param temporal the temporal object to query, not null * @return true if the date-time can be queried for this field, false if not */ boolean isSupportedBy(TemporalAccessor temporal); /** * Get the range of valid values for this field using the temporal object to * refine the result. *
* This uses the temporal object to find the range of valid values for the field. * This is similar to {@link #range()}, however this method refines the result * using the temporal. For example, if the field is {@code DAY_OF_MONTH} the * {@code range} method is not accurate as there are four possible month lengths, * 28, 29, 30 and 31 days. Using this method with a date allows the range to be * accurate, returning just one of those four options. *
* There are two equivalent ways of using this method. * The first is to invoke this method directly. * The second is to use {@link TemporalAccessor#range(TemporalField)}: *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.rangeRefinedBy(temporal);
* temporal = temporal.range(thisField);
*
* It is recommended to use the second approach, {@code range(TemporalField)},
* as it is a lot clearer to read in code.
* * Implementations should perform any queries or calculations using the fields * available in {@link ChronoField}. * If the field is not supported an {@code UnsupportedTemporalTypeException} must be thrown. * * @param temporal the temporal object used to refine the result, not null * @return the range of valid values for this field, not null * @throws DateTimeException if the range for the field cannot be obtained * @throws UnsupportedTemporalTypeException if the field is not supported by the temporal */ ValueRange rangeRefinedBy(TemporalAccessor temporal); /** * Gets the value of this field from the specified temporal object. *
* This queries the temporal object for the value of this field. *
* There are two equivalent ways of using this method. * The first is to invoke this method directly. * The second is to use {@link TemporalAccessor#getLong(TemporalField)} * (or {@link TemporalAccessor#get(TemporalField)}): *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.getFrom(temporal);
* temporal = temporal.getLong(thisField);
*
* It is recommended to use the second approach, {@code getLong(TemporalField)},
* as it is a lot clearer to read in code.
* * Implementations should perform any queries or calculations using the fields * available in {@link ChronoField}. * If the field is not supported an {@code UnsupportedTemporalTypeException} must be thrown. * * @param temporal the temporal object to query, not null * @return the value of this field, not null * @throws DateTimeException if a value for the field cannot be obtained * @throws UnsupportedTemporalTypeException if the field is not supported by the temporal * @throws ArithmeticException if numeric overflow occurs */ long getFrom(TemporalAccessor temporal); /** * Returns a copy of the specified temporal object with the value of this field set. *
* This returns a new temporal object based on the specified one with the value for * this field changed. For example, on a {@code LocalDate}, this could be used to * set the year, month or day-of-month. * The returned object has the same observable type as the specified 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 implementation 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. *
* There are two equivalent ways of using this method. * The first is to invoke this method directly. * The second is to use {@link Temporal#with(TemporalField, long)}: *
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.adjustInto(temporal);
* temporal = temporal.with(thisField);
*
* It is recommended to use the second approach, {@code with(TemporalField)},
* as it is a lot clearer to read in code.
* * Implementations should perform any queries or calculations using the fields * available in {@link ChronoField}. * If the field 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 method is invoked during the resolve phase of parsing.
* It is designed to allow application defined fields to be simplified into
* more standard fields, such as those on {@code ChronoField}, or into a date.
*
* Applications should not normally invoke this method directly.
*
* @implSpec
* If an implementation represents a field that can be simplified, or
* combined with others, then this method must be implemented.
*
* The specified map contains the current state of the parse.
* The map is mutable and must be mutated to resolve the field and
* any related fields. This method will only be invoked during parsing
* if the map contains this field, and implementations should therefore
* assume this field is present.
*
* Resolving a field will consist of looking at the value of this field,
* and potentially other fields, and either updating the map with a
* simpler value, such as a {@code ChronoField}, or returning a
* complete {@code ChronoLocalDate}. If a resolve is successful,
* the code must remove all the fields that were resolved from the map,
* including this field.
*
* For example, the {@code IsoFields} class contains the quarter-of-year
* and day-of-quarter fields. The implementation of this method in that class
* resolves the two fields plus the {@link ChronoField#YEAR YEAR} into a
* complete {@code LocalDate}. The resolve method will remove all three
* fields from the map before returning the {@code LocalDate}.
*
* A partially complete temporal is used to allow the chronology and zone
* to be queried. In general, only the chronology will be needed.
* Querying items other than the zone or chronology is undefined and
* must not be relied on.
* The behavior of other methods such as {@code get}, {@code getLong},
* {@code range} and {@code isSupported} is unpredictable and the results undefined.
*
* If resolution should be possible, but the data is invalid, the resolver
* style should be used to determine an appropriate level of leniency, which
* may require throwing a {@code DateTimeException} or {@code ArithmeticException}.
* If no resolution is possible, the resolve method must return null.
*
* When resolving time fields, the map will be altered and null returned.
* When resolving date fields, the date is normally returned from the method,
* with the map altered to remove the resolved fields. However, it would also
* be acceptable for the date fields to be resolved into other {@code ChronoField}
* instances that can produce a date, such as {@code EPOCH_DAY}.
*
* Not all {@code TemporalAccessor} implementations are accepted as return values.
* Implementations that call this method must accept {@code ChronoLocalDate},
* {@code ChronoLocalDateTime}, {@code ChronoZonedDateTime} and {@code LocalTime}.
*
* The default implementation must return null.
*
* @param fieldValues the map of fields to values, which can be updated, not null
* @param partialTemporal the partially complete temporal to query for zone and
* chronology; querying for other things is undefined and not recommended, not null
* @param resolverStyle the requested type of resolve, not null
* @return the resolved temporal object; null if resolving only
* changed the map, or no resolve occurred
* @throws ArithmeticException if numeric overflow occurs
* @throws DateTimeException if resolving results in an error. This must not be thrown
* by querying a field on the temporal without first checking if it is supported
*/
default TemporalAccessor resolve(
Map
* The should be of the format 'BaseOfRange', such as 'MonthOfYear',
* unless the field has a range of {@code FOREVER}, when only
* the base unit is mentioned, such as 'Year' or 'Era'.
*
* @return the name of the field, not null
*/
@Override
String toString();
}