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* Copyright (c) 2012, 2013 Stephen Colebourne & Michael Nascimento Santos
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package java.time.temporal;
import java.time.DateTimeException;
import java.time.Duration;
import java.time.Period;
import java.util.List;
/**
* Framework-level interface defining an amount of time, such as
* "6 hours", "8 days" or "2 years and 3 months".
*
* This is the base interface type for amounts of time.
* An amount is distinct from a date or time-of-day in that it is not tied
* to any specific point on the time-line.
*
* The amount can be thought of as a {@code Map} of {@link TemporalUnit} to
* {@code long}, exposed via {@link #getUnits()} and {@link #get(TemporalUnit)}.
* A simple case might have a single unit-value pair, such as "6 hours".
* A more complex case may have multiple unit-value pairs, such as
* "7 years, 3 months and 5 days".
*
* There are two common implementations.
* {@link Period} is a date-based implementation, storing years, months and days.
* {@link Duration} is a time-based implementation, storing seconds and nanoseconds,
* but providing some access using other duration based units such as minutes,
* hours and fixed 24-hour days.
*
* This interface is a framework-level interface that should not be widely
* used in application code. Instead, applications should create and pass
* around instances of concrete types, such as {@code Period} and {@code Duration}.
*
* @implSpec
* This interface places no restrictions on the mutability of implementations,
* however immutability is strongly recommended.
*
* @since 1.8
*/
public interface TemporalAmount {
/**
* Returns the value of the requested unit.
* The units returned from {@link #getUnits()} uniquely define the
* value of the {@code TemporalAmount}. A value must be returned
* for each unit listed in {@code getUnits}.
*
* @implSpec
* Implementations may declare support for units not listed by {@link #getUnits()}.
* Typically, the implementation would define additional units
* as conversions for the convenience of developers.
*
* @param unit the {@code TemporalUnit} for which to return the value
* @return the long value of the unit
* @throws DateTimeException if a value for the unit cannot be obtained
* @throws UnsupportedTemporalTypeException if the {@code unit} is not supported
*/
long get(TemporalUnit unit);
/**
* Returns the list of units uniquely defining the value of this TemporalAmount.
* The list of {@code TemporalUnits} is defined by the implementation class.
* The list is a snapshot of the units at the time {@code getUnits}
* is called and is not mutable.
* The units are ordered from longest duration to the shortest duration
* of the unit.
*
* @implSpec
* The list of units completely and uniquely represents the
* state of the object without omissions, overlaps or duplication.
* The units are in order from longest duration to shortest.
*
* @return the List of {@code TemporalUnits}; not null
*/
List getUnits();
/**
* Adds to the specified temporal object.
*
* Adds the amount to the specified temporal object using the logic
* encapsulated in the implementing class.
*
* There are two equivalent ways of using this method.
* The first is to invoke this method directly.
* The second is to use {@link Temporal#plus(TemporalAmount)}:
*
* // These two lines are equivalent, but the second approach is recommended
* dateTime = amount.addTo(dateTime);
* dateTime = dateTime.plus(adder);
*
* It is recommended to use the second approach, {@code plus(TemporalAmount)},
* as it is a lot clearer to read in code.
*
* @implSpec
* The implementation must take the input object and add to it.
* The implementation defines the logic of the addition and is responsible for
* documenting that logic. It may use any method on {@code Temporal} to
* query the temporal object and perform the addition.
* The returned object must have the same observable type as the input object
*
* The input object must not be altered.
* Instead, an adjusted copy of the original must be returned.
* This provides equivalent, safe behavior for immutable and mutable temporal objects.
*
* The input temporal object may be in a calendar system other than ISO.
* Implementations may choose to document compatibility with other calendar systems,
* or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
*
* This method may be called from multiple threads in parallel.
* It must be thread-safe when invoked.
*
* @param temporal the temporal object to add the amount to, not null
* @return an object of the same observable type with the addition made, not null
* @throws DateTimeException if unable to add
* @throws ArithmeticException if numeric overflow occurs
*/
Temporal addTo(Temporal temporal);
/**
* Subtracts this object from the specified temporal object.
*
* Subtracts the amount from the specified temporal object using the logic
* encapsulated in the implementing class.
*
* There are two equivalent ways of using this method.
* The first is to invoke this method directly.
* The second is to use {@link Temporal#minus(TemporalAmount)}:
*
* // these two lines are equivalent, but the second approach is recommended
* dateTime = amount.subtractFrom(dateTime);
* dateTime = dateTime.minus(amount);
*
* It is recommended to use the second approach, {@code minus(TemporalAmount)},
* as it is a lot clearer to read in code.
*
* @implSpec
* The implementation must take the input object and subtract from it.
* The implementation defines the logic of the subtraction and is responsible for
* documenting that logic. It may use any method on {@code Temporal} to
* query the temporal object and perform the subtraction.
* The returned object must have the same observable type as the input object
*
* The input object must not be altered.
* Instead, an adjusted copy of the original must be returned.
* This provides equivalent, safe behavior for immutable and mutable temporal objects.
*
* The input temporal object may be in a calendar system other than ISO.
* Implementations may choose to document compatibility with other calendar systems,
* or reject non-ISO temporal objects by {@link TemporalQueries#chronology() querying the chronology}.
*
* This method may be called from multiple threads in parallel.
* It must be thread-safe when invoked.
*
* @param temporal the temporal object to subtract the amount from, not null
* @return an object of the same observable type with the subtraction made, not null
* @throws DateTimeException if unable to subtract
* @throws ArithmeticException if numeric overflow occurs
*/
Temporal subtractFrom(Temporal temporal);
}