Week numbers in Java
To do week number calculations in Java, you need configure a GregorianCalendar instance.
import java.util.GregorianCalendar; GregorianCalendar calendar = new GregorianCalendar(); calendar.setFirstDayOfWeek(GregorianCalendar.MONDAY); calendar.setMinimalDaysInFirstWeek(4); calendar.setTime(date);
The variable date is a java.util.Date instance.
How to get the week number from a date
To get the ISO week number (1-53), configure a GregorianCalendar instance as shown above and call
To get the corresponding four-digit year (e.g. 2023), use
Read more about GregorianCalendar in the Java documentation.
How to get the date from a week number
To get the date from a year and week number, configure a GregorianCalendar instance as shown above
calendar.setWeekDate(year, week, GregorianCalendar.MONDAY).
The variable year is a four-digit year, and week is an ISO week number (1-53).
calendar.getTime() to get a java.util.Date instance.
Read more about setWeekDate() in the Java documentation.
How to get the number of weeks in a year
To get the number of ISO weeks (i.e. the number of the last week) in a year, configure a
GregorianCalendar instance as shown above with date referencing a some date in the year
in question, and then call
If the variable year is an integer four-digit year, set the reference date to e.g. June 1, i.e.
date = Date(year, 6, 1).
Read more about getActualMaximum() in the Java documentation.