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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

* modification, are permitted provided that the following conditions are met:

*

* * Redistributions of source code must retain the above copyright notice,

* this list of conditions and the following disclaimer.

*

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* this list of conditions and the following disclaimer in the documentation

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* * Neither the name of JSR-310 nor the names of its contributors

* may be used to endorse or promote products derived from this software

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*/

package java.time.temporal;

import java.time.DateTimeException;

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.

*

* 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

*/

// 时间量字段，这些字段也包含"单位"的含义

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

*/

// 返回该字段的本地名称(如果有的话)

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

*/

// 返回基础单位

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

*/

// 返回范围上限的单位，比如"月"的范围上限是"年"

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

*/

// 返回当前字段的取值区间

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

*/

// 判断当前字段是否为"日期"字段

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

*/

// 判断当前字段是否为"时间"字段

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

*/

// 判断当前时间量字段是否被指定的时间量所支持

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

*/

// 返回当前时间量字段的取值区间，通常要求当前时间量字段被时间量temporal所支持

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

*/

// 以long形式返回当前时间量字段的值；temporal是当前字段所属的时间量

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 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

*/

/*

* 通过整合当前字段和temporal中的其他类型的字段来构造时间量对象。

*

* 如果整合后的值与temporal中的值相等，则直接返回temporal。

* 否则，需要构造"整合"后的新对象再返回。

*

* newValue: 当前字段的原始值，需要根据字段的类型进行放缩

*/

R adjustInto(R temporal, long newValue);

/**

* Resolves this field to provide a simpler alternative or a date.

*

* 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.

*

* @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

* @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.

*/

// 从fieldValues中解析处字段的值，结合给定的时间量，构造新的时间量对象

default TemporalAccessor resolve(Map fieldValues, TemporalAccessor partialTemporal, ResolverStyle resolverStyle) {

return null;

}

/**

* Gets a descriptive name for the field.

*

* 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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