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

Question

I want to display the 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);
    }

}

But it obviously prints out the dates for current year, i.e., 2018.

Output

Ramdan 2017

2018-05-16

2018-06-14

I tried many things like minus years, or doing temporal adjustments but nothing helped. Can someone suggest a cool way of achieving it?

Answer 1

I’m not sure it’s the perfect way to do it, but this works for me and doesn’t seem all too complicated:

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

With this line inserted before you convert to LocalDate your code now prints:

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

Edit:

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?

Keep your tongue straight in your mouth:

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);
    }
}

If I feed 2017 to the above method, it gives the same result as before:

    printRamdanDates(2017);

Output:

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

But try, for example, 2000 or 2030 when Ramadan happens twice in the Gregorian/ISO year.

    printRamdanDates(2000);
    printRamdanDates(2030);

Output:

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