* 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. * *
* 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, not null */ String getName(); /** * 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 period 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 period unit defining the range of the field, not null */ TemporalUnit getRangeUnit(); //----------------------------------------------------------------------- /** * Compares the value of this field in two temporal objects. *
* All fields implement {@link Comparator} on {@link TemporalAccessor}. * This allows a list of date-times to be compared using the value of a field. * For example, you could sort a list of arbitrary temporal objects by the value of * the month-of-year field - {@code Collections.sort(list, MONTH_OF_YEAR)} *
* The default implementation must behave equivalent to this code: *
* return Long.compare(temporal1.getLong(this), temporal2.getLong(this));
*
*
* @param temporal1 the first temporal object to compare, not null
* @param temporal2 the second temporal object to compare, not null
* @throws DateTimeException if unable to obtain the value for this field
*/
public default int compare(TemporalAccessor temporal1, TemporalAccessor temporal2) {
return Long.compare(temporal1.getLong(this), temporal2.getLong(this));
}
/**
* 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 is supported by the temporal object. *
* This determines whether the temporal accessor supports this field. * If this returns false, the 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.doIsSupported(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 doIsSupported(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.doRange(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 a {@code DateTimeException} 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 */ ValueRange doRange(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.doGet(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 a {@code DateTimeException} 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 */ long doGet(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.doWith(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 a {@code DateTimeException} 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 of the builder.
* Implementations should combine the associated field with others to form
* objects like {@code LocalDate}, {@code LocalTime} and {@code LocalDateTime}
*
* @param builder the builder to resolve, not null
* @param value the value of the associated field
* @return true if builder has been changed, false otherwise
* @throws DateTimeException if unable to resolve
*/
boolean resolve(DateTimeBuilder builder, long value);
}