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public interface TemporalField
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 ChronoField
.
Further fields are supplied in IsoFields
, WeekFields
and 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
LocalDateTime
which check if the field is a 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.
Serializable
where possible.
An enum is as effective implementation choice.Modifier and Type | Method and Description |
---|---|
<R extends Temporal> |
adjustInto(R temporal,
long newValue)
Returns a copy of the specified temporal object with the value of this field set.
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TemporalUnit |
getBaseUnit()
Gets the unit that the field is measured in.
|
default String |
getDisplayName(Locale locale)
Gets the display name for the field in the requested locale.
|
long |
getFrom(TemporalAccessor temporal)
Gets the value of this field from the specified temporal object.
|
String |
getName()
Gets a descriptive name for the field.
|
TemporalUnit |
getRangeUnit()
Gets the range that the field is bound by.
|
default boolean |
isDateBased()
Checks if this field represents a component of a date.
|
boolean |
isSupportedBy(TemporalAccessor temporal)
Checks if this field is supported by the temporal object.
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default boolean |
isTimeBased()
Checks if this field represents a component of a time.
|
ValueRange |
range()
Gets the range of valid values for the field.
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ValueRange |
rangeRefinedBy(TemporalAccessor temporal)
Get the range of valid values for this field using the temporal object to
refine the result.
|
default Map<TemporalField,Long> |
resolve(TemporalAccessor temporal,
long value,
ResolverStyle resolverStyle)
Resolves this field to provide a simpler alternative.
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String getName()
The should be of the format 'BaseOfRange', such as 'MonthOfYear',
unless the field has a range of FOREVER
, when only
the base unit is mentioned, such as 'Year' or 'Era'.
default String getDisplayName(Locale locale)
If there is no display name for the locale the value of getName
is returned.
locale
- the locale to use, not nullgetName
,
not nullTemporalUnit getBaseUnit()
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 getRangeUnit()
.
TemporalUnit getRangeUnit()
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 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'.
ValueRange range()
All fields can be expressed as a 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.
default boolean isDateBased()
A field is date-based if it can be derived from
EPOCH_DAY
.
The default implementation must return false.
default boolean isTimeBased()
A field is time-based if it can be derived from
NANO_OF_DAY
.
The default implementation must return false.
boolean isSupportedBy(TemporalAccessor temporal)
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 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,
isSupported(TemporalField)
,
as it is a lot clearer to read in code.
Implementations should determine whether they are supported using the fields
available in ChronoField
.
temporal
- the temporal object to query, not nullValueRange rangeRefinedBy(TemporalAccessor temporal)
This uses the temporal object to find the range of valid values for the field.
This is similar to range()
, however this method refines the result
using the temporal. For example, if the field is DAY_OF_MONTH
the
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 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,
range(TemporalField)
,
as it is a lot clearer to read in code.
Implementations should perform any queries or calculations using the fields
available in ChronoField
.
If the field is not supported an UnsupportedTemporalTypeException
must be thrown.
temporal
- the temporal object used to refine the result, not nullDateTimeException
- if the range for the field cannot be obtainedUnsupportedTemporalTypeException
- if the field is not supported by the temporallong getFrom(TemporalAccessor temporal)
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 TemporalAccessor.getLong(TemporalField)
(or 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,
getLong(TemporalField)
,
as it is a lot clearer to read in code.
Implementations should perform any queries or calculations using the fields
available in ChronoField
.
If the field is not supported an UnsupportedTemporalTypeException
must be thrown.
temporal
- the temporal object to query, not nullDateTimeException
- if a value for the field cannot be obtainedUnsupportedTemporalTypeException
- if the field is not supported by the temporalArithmeticException
- if numeric overflow occurs<R extends Temporal> R adjustInto(R temporal, long newValue)
This returns a new temporal object based on the specified one with the value for
this field changed. For example, on a 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 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,
with(TemporalField)
,
as it is a lot clearer to read in code.
Implementations should perform any queries or calculations using the fields
available in ChronoField
.
If the field is not supported an 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.
R
- the type of the Temporal objecttemporal
- the temporal object to adjust, not nullnewValue
- the new value of the fieldDateTimeException
- if the field cannot be setUnsupportedTemporalTypeException
- if the field is not supported by the temporalArithmeticException
- if numeric overflow occursdefault Map<TemporalField,Long> resolve(TemporalAccessor temporal, long value, ResolverStyle resolverStyle)
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 ChronoField
.
The method will only be invoked if the specified temporal supports this field. The value of this field is provided.
The temporal must be queried using the methods of TemporalAccessor
,
not using getFrom
, isSupportedBy
or rangeRefinedBy
.
Before querying any field, implementations must ensure it is supported, as
exceptions of this type would negatively affect the calculation of a parsed result.
If this field can resolve, it must return a map, if not it must return null. The returned map contains the changes to be made to the temporal, expressed as field-value pairs. If the value for a field is null, the field is to be removed from the temporal. A null key must not be added to the result map.
If the result is non-null, this field will be removed from the temporal. This field should not be added to the result map.
The ResolverStyle
should be used by implementations to determine
how to perform the resolve.
The default implementation must return null.
temporal
- the temporal to resolve, not nullvalue
- the value of this fieldresolverStyle
- the requested type of resolve, not nullDateTimeException
- if resolving results in an error. This must not be thrown
by querying a field on the temporal without first checking if it is supportedArithmeticException
- if numeric overflow occurs
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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