better way to determine quarter boundaries dates

Question

I have this code that works :

    private fun getCycleBoundaries(cycleNumber: Int, year: Int): Array<Date> {

        return when (cycleNumber) {
            1 -> arrayOf(DATE_FORMATER.parse("$year-01-01T00:00:00"), DATE_FORMATER.parse("$year-03-31T23:59:59"))
            2 -> arrayOf(DATE_FORMATER.parse("$year-04-01T00:00:00"), DATE_FORMATER.parse("$year-06-30T23:59:59"))
            3 -> arrayOf(DATE_FORMATER.parse("$year-07-01T00:00:00"), DATE_FORMATER.parse("$year-09-30T23:59:59"))
            4 -> arrayOf(DATE_FORMATER.parse("$year-10-01T00:00:00"), DATE_FORMATER.parse("$year-12-31T23:59:59"))
            else -> throw IllegalArgumentException("$cycleNumber is nor a valid cycle number")
        }
    }

This code takes a cycle number : 1 or 2 or 3 or 4 and a year And it returns an arrays of 2 dates (the start and the end of the quarter)

For example if i call :

 getCycleBoundaries(1, 2019)

I expect :

2019-01-01T00:00:00 and 2019-03-31T23:59:59

As said it works but i'm not happy with the code and was trying to do it better. Is there a better way to achieve this ?

Thanks

Answer 1

The IsoFields class of java.time may be a bit overlooked. It’s our friend when it comes to manipulating quarters. Sorry that I can write only Java code.

public static LocalDate[] getCycleBoundaries(int cycleNumber, int year) {
    YearMonth firstMonthOfQuarter = YearMonth.of(year, 1)
            .with(IsoFields.QUARTER_OF_YEAR, cycleNumber);
    return new LocalDate[] { firstMonthOfQuarter.atDay(1),
            firstMonthOfQuarter.plusMonths(2).atEndOfMonth() };
}

Let’s try it out:

    System.out.println(Arrays.toString(getCycleBoundaries(4, 2019)));

Output in this case:

[2019-10-01, 2019-12-31]

Tip: use half-open intervals. While users usually prefer to have a period in the calendar given as first and last day, in a computer program it’s generally more convenient to represent a period as a from date inclusive and a to date exclusive. So a quarter as the first day of the quarter and the first day of the following quarter. And if you know already that the period is a quarter, then just the first day of the quarter and nothing more. The rest can be easily calculated as needed.