How to determine the first day of the week in Java

Especially in English-speaking countries, the use of the calendar week is very common. The calculation and conversion are done with the class LocalDate in Java 8 and with Calendar in Java before version 8.

The date for a specific calendar week is calculated by creating any date in the year and then setting the calendar week. To get the first day of the week, set DayOfWeek.MONDAY.
 

Example :

import java.time.*;
import java.util.Locale;
import java.time.temporal.*;

public class WeekNumber {

 public static void main(String []args)
 {
    int year = 2020;
    int weekN = 22;
    LocalDate ldate = LocalDate.of(year, Month.JANUARY, 3);
    LocalDate day = ldate.with(IsoFields.WEEK_OF_WEEK_BASED_YEAR, weekN);
    LocalDate start = day.with(DayOfWeek.MONDAY);
    System.out.println(start);
 }
}

Output:

2020-05-25

As shown above, you can of course use another locale.
 

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