java.time.Period , dividing the period gives wrong results

问题

i tired using java.time.Period , and the results were different from my manual calculations by three days. The weird thing here is when i divide the period into two periods , the results matches my manual calculations.

the second method is just like how i calculate the period manually.

is there something i missed ? is there a standard method or algorithm of calendar arithmetic ? and what's the algorithm used by java.time.Period ?

import java.time.LocalDate;
import java.time.Period;
import java.time.temporal.ChronoUnit;

public class test2 {

    public static void main(String[] args) {

        LocalDate d1 = LocalDate.of(2014, 2, 14);
        LocalDate d2 = LocalDate.of(2017, 8, 1);

        Period p = Period.between(d1, d2);

        //using period between the two dates directly
        System.out.println("period between " + d1.toString() + " and " + d2.toString() + " is " + p.getYears()
                + " years " + p.getMonths() + " months " + p.getDays() + " Days");

        //dividing the period into two parts 
        p = Period.between(LocalDate.of(2014, 3, 1), d2);

        System.out
                .println("period between " + d1.toString() + " and " + d2.toString() + " is " + p.getYears() + " years "
                        + p.getMonths() + " months " + d1.until(LocalDate.of(2014, 3, 1), ChronoUnit.DAYS) + " Days");

    }
}

回答1:

You perform two different operations here:

Period p = Period.between(d1, d2)

gives you a nicely formated way to output the difference between these dates (you have used the formatting options correctly).

d1.until(d2, ChronoUnit.DAYS)

will give you the same - but not so nicely formated (basically it just gives you the number of days between the LocalDates).

回答2:

The answer (period between 2014-02-14 and 2017-08-01 is 3 years 5 months 18 Days) is what you should expect:

it's 3 years from 2014-02-14 to 2017-02-14
it's 5 months from 2017-02-14 to 2017-07-14
it's 18 days from 2017-07-14 to 2017-08-01

The calculation proceeds from years to months to days. This allows you to calculate the number of years, months and days between 2014-02-14 and 2016-02-29, which gives 2 years and 15 days.

If you try to calculate the days first you have problems determining the number of years, months and days between 2014-02-14 and 2016-02-29, because there is no day 2014-02-29 - 14 days after 2014-02-14 its 2014-02-28, 15 days after 2014-02-14 its 2014-03-01.

来源：https://stackoverflow.com/questions/45905012/java-time-period-dividing-the-period-gives-wrong-results

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java

time

period

localdate