69. Getting the first and last day of a quarter
Let’s assume that we represent the first and last day of a quarter via this simple class:
public final class Quarter {
private final Date firstDay;
private final Date lastDay;
…
}
Next, we have a java.util.Date and we want the first and the last day of the quarter containing this date. For this, we can use the JDK 8, IsoFields.DAY_OF_QUARTER (we have introduced IsoFields in the previous problem). But, before we can use IsoFields, we have to convert the given java.util.Date to a LocalDate as follows:
LocalDate localDate = date.toInstant()
.atZone(ZoneId.systemDefault()).toLocalDate();
Once we have the given Date as a LocalDate, we can easily extract the first day of the quarter via IsoFields.DAY_OF_QUARTER. Next, we add 2 months to this day to move into the last month of the quarter (a quarter has 3 months, so an year has 4 quarters) and we rely on java.time.temporal.TemporalAdjusters, more precisely on lastDayOfMonth() to obtain the last day of the quarter. Finally, we convert the two obtained LocalDate to Date. Here is the complete code:
public static Quarter quarterDays(Date date) {
LocalDate localDate = date.toInstant()
.atZone(ZoneId.systemDefault()).toLocalDate();
LocalDate firstDay
= localDate.with(IsoFields.DAY_OF_QUARTER, 1L);
LocalDate lastDay = firstDay.plusMonths(2)
.with(TemporalAdjusters.lastDayOfMonth());
return new Quarter(
Date.from(firstDay.atStartOfDay(
ZoneId.systemDefault()).toInstant()),
Date.from(lastDay.atStartOfDay(
ZoneId.systemDefault()).toInstant())
);
}
Of course, these conversions are not needed if you work directly with LocalDate. But, this way, you have a chance to learn more stuff.In the bundled code, you can find more examples including one that relies entirely on the Calendar API.
70. Extracting the months from a given quarter
This problem becomes quite accessible if we are familiar with the JDK 8, java.time.Month. Via this API, we can find the first month (0 for January, 1 for February, …) of a quarter containing the given LocalDate as Month.from(LocalDate).firstMonthOfQuarter().getValue().Once we have the first month is easy to obtain the other two as follows:
public static List<String> quarterMonths(LocalDate ld) {
List<String> qmonths = new ArrayList<>();
int qmonth = Month.from(ld)
.firstMonthOfQuarter().getValue();
qmonths.add(Month.of(qmonth).name());
qmonths.add(Month.of(++qmonth).name());
qmonths.add(Month.of(++qmonth).name());
return qmonths;
}
How about passing as argument the quarter itself? This can be done as a number (1, 2, 3, or 4) or as a string (Q1, Q2, Q3, or Q4). If the given quarter is a number then the first month of the quarter can be obtained as quarter * 3 – 2, where the quarter is 1, 2, 3, or 4. This time, let’s express the code in a functional style:
int qmonth = quarter * 3 – 2;
List<String> qmonths = IntStream.of(
qmonth, ++qmonth, ++qmonth)
.mapToObj(Month::of)
.map(Month::name)
.collect(Collectors.toList());
Of course, if you find it more concise then you can use IntStream.range(qmonth, qmonth+2) instead of IntStream.of(). In the bundled, code you can find more examples.