如何从 Java 8 日期 API 中的回历日期中减去回历年份

Question

我要显示 Ramadan 2017 start and end dates. I tried writing code using the HijrahChronology built into Java 8 and later, with HijrahDate class.

import java.time.LocalDate;
import java.time.chrono.HijrahDate;
import java.time.temporal.ChronoField;
import java.time.temporal.TemporalAdjusters;

public class Ramdan {

    public static void main(String[] args) {
        
        HijrahDate ramdanDate = HijrahDate.now().with(ChronoField.DAY_OF_MONTH, 1).with(ChronoField.MONTH_OF_YEAR, 9);
        
        LocalDate ramdanStart = LocalDate.from(ramdanDate);
        LocalDate ramdanEnd = LocalDate.from(ramdanDate.with(TemporalAdjusters.lastDayOfMonth()));
        
        System.out.println("Ramdan 2017");
        System.out.println(ramdanStart);
        System.out.println(ramdanEnd);
    }

}

但它显然打印出当年的日期，即 2018 年。

Output

Ramdan 2017

2018-05-16

2018-06-14

我尝试了很多方法，例如减去年数，或进行时间调整，但都无济于事。有人可以建议一种很酷的实现方式吗？

Answer 1

我不确定这是完美的方法，但这对我有用，而且看起来并不复杂：

    ramdanDate = ramdanDate.with(ChronoField.YEAR, ramdanDate.get(ChronoField.YEAR) - 1);

在转换为 LocalDate 之前插入这一行，您的代码现在打印：

Ramdan 2017
2017-05-27
2017-06-24

编辑：

Suppose even if (in case you got a Gregorian year that overlaps with two instances of Ramadan, finding both) is desired...I cannot think of a way of achieving it. Can you suggest?

舌头伸直：

public static void printRamdanDates(int gregorianYear) {
    LocalDate gregDate = LocalDate.ofYearDay(gregorianYear, 1);
    HijrahDate ramdanDate = HijrahDate.from(gregDate)
            .with(ChronoField.DAY_OF_MONTH, 1)
            .with(ChronoField.MONTH_OF_YEAR, 9);
    LocalDate ramdanStart = LocalDate.from(ramdanDate);
    LocalDate ramdanEnd = LocalDate.from(ramdanDate.with(TemporalAdjusters.lastDayOfMonth()));
    // if in previous Gregorian year, skip
    while (ramdanEnd.getYear() < gregorianYear) {
        ramdanDate = ramdanDate.with(ChronoField.YEAR, ramdanDate.get(ChronoField.YEAR) + 1);
        ramdanStart = LocalDate.from(ramdanEnd);
        ramdanEnd = LocalDate.from(ramdanDate.with(TemporalAdjusters.lastDayOfMonth()));
    }
    if (ramdanStart.getYear() > gregorianYear) { // in following Gregorian year
        System.out.println("No Ramdan in " + gregorianYear);
    } else {
        System.out.println("Ramdan " + gregorianYear);
        do {
            System.out.println(ramdanStart);
            System.out.println(ramdanEnd);
            ramdanDate = ramdanDate.with(ChronoField.YEAR, ramdanDate.get(ChronoField.YEAR) + 1);
            ramdanStart = LocalDate.from(ramdanDate);
            ramdanEnd = LocalDate.from(ramdanDate.with(TemporalAdjusters.lastDayOfMonth()));
        } while (ramdanStart.getYear() == gregorianYear);
    }
}

如果我将 2017 提供给上述方法，它会给出与之前相同的结果：

    printRamdanDates(2017);

输出：

Ramdan 2017
2017-05-27
2017-06-24

但是尝试，例如，2000 年或 2030 年斋月在 Gregorian/ISO 年发生两次。

    printRamdanDates(2000);
    printRamdanDates(2030);

输出：

Ramdan 2000
1999-12-09
2000-01-07
2000-11-27
2000-12-26
Ramdan 2030
2030-01-05
2030-02-03
2030-12-26
2031-01-23

如何从 Java 8 日期 API 中的回历日期中减去回历年份

How to subtract Hijrah year from a Hijrah Date in Java 8 Date API

calendar

date

hijri

java-8

localdate