I have the week number, its curresponding year and dayOfWeek number(ie 1 for Monday, 2 for Tuesday and so on). Is there a way to find the date with this information in java?
Following is a method I found online.
int week = 51;
LocalDate wkstart = LocalDate.now().with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, week);
LocalDate mon = wks.plusDays(1);
LocalDate tue = wks.plusDays(2);
LocalDate wed = wks.plusDays(3);
LocalDate thu = wks.plusDays(4);
LocalDate fri = wks.plusDays(5);
LocalDate sat = wks.plusDays(6);
LocalDate wkend = wks.plusDays(7);
But then realised that wkstart is storing the current date instead of the start of the week.
Is there a better way of doing this?
Instead of adding a number of days to wkstart
, use with
again to set the day of week. For example:
LocalDate date = LocalDate.now()
.with(WeekFields.ISO.weekBasedYear(), 2018) // year
.with(WeekFields.ISO.weekOfWeekBasedYear(), 51) // week of year
.with(WeekFields.ISO.dayOfWeek(), DayOfWeek.MONDAY.getValue()); // day of week
LocalDate localDate =
YearWeek // Represent an entire week of a week-based year per the ISO 8601 standard definition of a week.
.of( // Instantiate a `YearWeek` object.
2019 , // Specify the week-based year number, NOT the calendar year.
51 // Specify the week number, 1-52 or 1-53.
)
.atDay(
DayOfWeek.of( 1 ) // The value 1 yields a `DayOfWeek.MONDAY` object.
)
;
org.threeten.extra.YearWeek
The Answer by Sweeper looks correct. But there is a more specialized class for this.
If doing much work with weeks of week-based years per the ISO 8601 definition of week , use the YearWeek
class found in the ThreeTen-Extra library. This library adds extra functionality to the java.time classes built into Java 8 and later.
Determine the week.
YearWeek yearWeek = YearWeek.of( 2019 , 51 ) ;
Get a LocalDate
for the day-of-week within that week.
LocalDate localDate = yearWeek.atDay( DayOfWeek.MONDAY ) ;
For the day-of-week, you should be using DayOfWeek
enum objects in your code rather than mere integer numbers. To get a DayOfWeek
from an original number 1-7 for Monday-Sunday, call DayOfWeek.of( x )
.
DayOfWeek dow = DayOfWeek.of( 1 ) ; // 1 = Monday, 7 = Sunday.
Putting that all together we get this one-liner.
LocalDate localDate = YearWeek.of( 2019 , 51 ).atDay( DayOfWeek.of( 1 ) ) ;
To be clear… The ISO 8601 definition of a week is:
Locale
. Note that the first day of the week is Locale
-dependent eg it is Monday in the UK while Sunday in the US. As per the ISO 8601 standards, it is Monday. For comparison, check the US calendar and the UK calendar . Accordingly, the date will vary as shown in the example below:
import java.time.DayOfWeek;
import java.time.LocalDate;
import java.time.temporal.WeekFields;
import java.util.Locale;
public class Main {
public static void main(String[] args) {
// Test
int weekNumber = 34;
int year = 2021;
System.out.println(getLocalDate(weekNumber, DayOfWeek.TUESDAY, year, Locale.UK));
System.out.println(getLocalDate(weekNumber, DayOfWeek.TUESDAY, year, Locale.US));
System.out.println(getLocalDate(weekNumber, DayOfWeek.SUNDAY, year, Locale.UK));
System.out.println(getLocalDate(weekNumber, DayOfWeek.SUNDAY, year, Locale.US));
}
static LocalDate getLocalDate(int weekNumber, DayOfWeek dow, int year, Locale locale) {
return LocalDate.of(year, 2, 1)
.with(dow)
.with(WeekFields.of(locale).weekOfWeekBasedYear(), weekNumber);
}
}
Output:
2021-08-24
2021-08-17
2021-08-29
2021-08-15
Learn more about the modern Date-Time API from Trail: Date Time .
* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project .
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