Java example source code file (TemporalField.java)
The TemporalField.java Java example source code
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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Copyright (c) 2012, Stephen Colebourne & Michael Nascimento Santos
*
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
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package java.time.temporal;
import java.time.DateTimeException;
import java.time.chrono.Chronology;
import java.time.format.ResolverStyle;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
/**
* A field of date-time, such as month-of-year or hour-of-minute.
* <p>
* Date and time is expressed using fields which partition the time-line into something
* meaningful for humans. Implementations of this interface represent those fields.
* <p>
* 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.
* <p>
* 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.
* <p>
* If there is no display name for the locale then a suitable default must be returned.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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()}.
* <p>
* 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();
/**
* Gets the range of valid values for the field.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* This determines whether the temporal accessor supports this field.
* If this returns false, the the temporal cannot be queried for this field.
* <p>
* 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)}:
* <pre>
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.isSupportedBy(temporal);
* temporal = temporal.isSupported(thisField);
* </pre>
* It is recommended to use the second approach, {@code isSupported(TemporalField)},
* as it is a lot clearer to read in code.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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)}:
* <pre>
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.rangeRefinedBy(temporal);
* temporal = temporal.range(thisField);
* </pre>
* It is recommended to use the second approach, {@code range(TemporalField)},
* as it is a lot clearer to read in code.
* <p>
* 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.
* <p>
* This queries the temporal object for the value of this field.
* <p>
* 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)}):
* <pre>
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.getFrom(temporal);
* temporal = temporal.getLong(thisField);
* </pre>
* It is recommended to use the second approach, {@code getLong(TemporalField)},
* as it is a lot clearer to read in code.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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)}:
* <pre>
* // these two lines are equivalent, but the second approach is recommended
* temporal = thisField.adjustInto(temporal);
* temporal = temporal.with(thisField);
* </pre>
* It is recommended to use the second approach, {@code with(TemporalField)},
* as it is a lot clearer to read in code.
* <p>
* 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.
* <p>
* 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 <R> the type of the Temporal object
* @param temporal the temporal object to adjust, not null
* @param newValue the new value of the field
* @return the adjusted temporal object, not null
* @throws DateTimeException if the field cannot be set
* @throws UnsupportedTemporalTypeException if the field is not supported by the temporal
* @throws ArithmeticException if numeric overflow occurs
*/
<R extends Temporal> R adjustInto(R temporal, long newValue);
/**
* Resolves this field to provide a simpler alternative or a date.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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}.
* <p>
* 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.
* <p>
* 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.
* <p>
* 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}.
* <p>
* 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}.
* <p>
* 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<TemporalField, Long> fieldValues,
TemporalAccessor partialTemporal,
ResolverStyle resolverStyle) {
return null;
}
/**
* Gets a descriptive name for the field.
* <p>
* 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();
}
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