date - 如何从 Java 8 Date API 中的回历日期中减去回历年份

Question

我想显示 Ramadan 2017 年开始和结束日期。我尝试使用 HijrahChronology 编写代码内置于 Java 8 及更高版本中，带有 HijrahDate类。

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);
    }

}

但它显然打印出了当年的日期，即 2018 年。

Output

Ramdan 2017

2018-05-16

2018-06-14

我尝试了很多方法，例如减去年份，或进行时间调整，但没有任何帮助。有人可以建议一种很酷的方法来实现它吗？

Answer 1

我不确定这是否是完美的方法，但这对我有用，而且看起来并不太复杂:

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

在转换为 LocalDate 之前插入此行后，您的代码现在将打印:

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?

将舌头伸直放在嘴里:

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 输入到上述方法中，它会给出与之前相同的结果:

    printRamdanDates(2017);

输出:

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

但是尝试一下，例如 2000 年或 2030 年，当斋月在公历/ISO 年份发生两次时。

    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