I have a method to view a calendar in Java that calculates the date by year, day of the week and week-number.
Now when I calculates the dates from 2017 everything works. But when I calculates the dates from January 2018 it takes the dates of year 2017.
My code looks like
import java.time.temporal.IsoFields;
import java.time.temporal.ChronoField;
import java.time.LocalDate;
// .....
LocalDate desiredDate = LocalDate.now()
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, 1)
.with(ChronoField.DAY_OF_WEEK, 1)
.withYear(2018);
Which results in 2018-01-02 and it should be 2018-01-01. How is this possible?
The order of invoked methods seems matter.
It you invoke them by descending time-granularity (year, week of week and day of week), you get the correct result :
long weekNumber = 1;
long dayOfWeek = 1;
int year = 2018;
LocalDate desiredDate = LocalDate.now()
.withYear(year)
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, weekNumber)
.with(ChronoField.DAY_OF_WEEK, dayOfWeek );
System.out.println(desiredDate);
2018-01-01
Note that the problem origin comes from :
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, weekNumber)
that sets the week number (1 to 53) according to the current year.
The Java LocalDate API cannot adapt this value if then you change the year with .withYear(year) as the week number information is not kept in the LocalDate instance.
You can indeed see in LocalDate implementation that LocalDate instances are defined by only 3 field : year, month and day.
public final class LocalDate
implements Temporal, TemporalAdjuster, ChronoLocalDate, Serializable {
...
private final int year;
/**
* The month-of-year.
*/
private final short month;
/**
* The day-of-month.
*/
private final short day;
...
}
So to be precise, the important thing is that :
.withYear(year) be invoked before
.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, weekNumber);