Android 7.x (API24) WEEK_OF_MONTH Calendar Bug?

Question

We've got some strange behavior in Android 7 (API 24/25) using Calendar.

Given this fairly simple code:

SimpleDateFormat month_date = new SimpleDateFormat("dd.MM.YYYY");
Calendar cal = new GregorianCalendar(TimeZone.getTimeZone("Europe/Berlin"), Locale.GERMANY);
cal.setFirstDayOfWeek(Calendar.MONDAY);

for (int month = Calendar.JANUARY; month <= Calendar.DECEMBER; month++) {
    Calendar start = ((Calendar) cal.clone());
    start.set(2017, month, 1);

    Calendar end = ((Calendar) start.clone());
    end.set(Calendar.DAY_OF_MONTH, end.getActualMaximum(Calendar.DAY_OF_MONTH));

    Log.d("CAL", "\n    Date Start: " + month_date.format(start.getTime()) + " " +
        " WEEK_OF_MONTH: " + start.get(Calendar.WEEK_OF_MONTH)
    );
    Log.d("CAL", "\n    Date End: " + month_date.format(end.getTime()) +
        " WEEK_OF_MONTH: " + end.get(Calendar.WEEK_OF_MONTH)
       );
}

Running on Android 4.0x, 5.x and 6.x showing the right value for WEEK_OF_MONTH:

 Date Start: 01.01.2016  WEEK_OF_MONTH: 1
 Date End: 31.01.2017 WEEK_OF_MONTH: 6
 Date Start: 01.02.2017  WEEK_OF_MONTH: 1
 Date End: 28.02.2017 WEEK_OF_MONTH: 5
 Date Start: 01.03.2017  WEEK_OF_MONTH: 1
 Date End: 31.03.2017 WEEK_OF_MONTH: 5
 Date Start: 01.04.2017  WEEK_OF_MONTH: 1
 Date End: 30.04.2017 WEEK_OF_MONTH: 5
 Date Start: 01.05.2017  WEEK_OF_MONTH: 1
 Date End: 31.05.2017 WEEK_OF_MONTH: 5
 Date Start: 01.06.2017  WEEK_OF_MONTH: 1
 Date End: 30.06.2017 WEEK_OF_MONTH: 5
 Date Start: 01.07.2017  WEEK_OF_MONTH: 1
 Date End: 31.07.2017 WEEK_OF_MONTH: 6
 Date Start: 01.08.2017  WEEK_OF_MONTH: 1
 Date End: 31.08.2017 WEEK_OF_MONTH: 5
 Date Start: 01.09.2017  WEEK_OF_MONTH: 1
 Date End: 30.09.2017 WEEK_OF_MONTH: 5
 Date Start: 01.10.2017  WEEK_OF_MONTH: 1
 Date End: 31.10.2017 WEEK_OF_MONTH: 6
 Date Start: 01.11.2017  WEEK_OF_MONTH: 1
 Date End: 30.11.2017 WEEK_OF_MONTH: 5
 Date Start: 01.12.2017  WEEK_OF_MONTH: 1
 Date End: 31.12.2017 WEEK_OF_MONTH: 5

Running on Android 7.x broken WEEK_OF_MONTH:

 Date Start: 01.01.2016  WEEK_OF_MONTH: 0
 Date End: 31.01.2017 WEEK_OF_MONTH: 5
 Date Start: 01.02.2017  WEEK_OF_MONTH: 1
 Date End: 28.02.2017 WEEK_OF_MONTH: 5
 Date Start: 01.03.2017  WEEK_OF_MONTH: 1
 Date End: 31.03.2017 WEEK_OF_MONTH: 5
 Date Start: 01.04.2017  WEEK_OF_MONTH: 0
 Date End: 30.04.2017 WEEK_OF_MONTH: 4
 Date Start: 01.05.2017  WEEK_OF_MONTH: 1
 Date End: 31.05.2017 WEEK_OF_MONTH: 5
 Date Start: 01.06.2017  WEEK_OF_MONTH: 1
 Date End: 30.06.2017 WEEK_OF_MONTH: 5
 Date Start: 01.07.2017  WEEK_OF_MONTH: 0
 Date End: 31.07.2017 WEEK_OF_MONTH: 5
 Date Start: 01.08.2017  WEEK_OF_MONTH: 1
 Date End: 31.08.2017 WEEK_OF_MONTH: 5
 Date Start: 01.09.2017  WEEK_OF_MONTH: 0
 Date End: 30.09.2017 WEEK_OF_MONTH: 4
 Date Start: 01.10.2017  WEEK_OF_MONTH: 0
 Date End: 31.10.2017 WEEK_OF_MONTH: 5
 Date Start: 01.11.2017  WEEK_OF_MONTH: 1
 Date End: 30.11.2017 WEEK_OF_MONTH: 5
 Date Start: 01.12.2017  WEEK_OF_MONTH: 0
 Date End: 31.12.2017 WEEK_OF_MONTH: 4

We couldn't find any documented changes for Calendar in API 24.

Any clue how to solve this issue?

We already implemented our own method for WEEK_OF_MONTH returning the same values as Android 6.x but by the looks of it set(WEEK_OF_MONTH) is also broken. Rewriting the code using Joda is not an option.

score 2 · Accepted Answer · answered Jun 30 '17 at 17:17

You can use the setMinimalDaysInFirstWeek() method to change how the weeks are counted:

Calendar cal = new GregorianCalendar(TimeZone.getTimeZone("Europe/Berlin"), Locale.GERMANY);
cal.setFirstDayOfWeek(Calendar.MONDAY);
cal.setMinimalDaysInFirstWeek(1);

This will produce the correct values for week of month.

You told that rewriting the code with Joda-Time is not an option, but what about another API?

In Android you can use the ThreeTen Backport, a great backport for Java 8's new date/time classes, together with the ThreeTenABP (more on how to use it here).

^{BTW, Joda-Time is in maintainance mode and is being replaced by the new APIs, so I don't recommend start a new project with it. Even in joda's website it says: "Note that Joda-Time is considered to be a largely “finished” project. No major enhancements are planned. If using Java SE 8, please migrate to java.time (JSR-310).".}

The classes below are under the org.threeten.bp package. The code will be like this:

import java.util.Locale;
import org.threeten.bp.DayOfWeek;
import org.threeten.bp.LocalDate;
import org.threeten.bp.Month;
import org.threeten.bp.format.DateTimeFormatter;
import org.threeten.bp.format.DateTimeFormatterBuilder;
import org.threeten.bp.temporal.TemporalAdjusters;
import org.threeten.bp.temporal.WeekFields;

DateTimeFormatter fmt = new DateTimeFormatterBuilder()
    // day and month
    .appendPattern("dd.MM.")
    // week based year (equivalent to YYYY in SimpleDateFormat)
    .appendValue(WeekFields.ISO.weekBasedYear())
    // create formatter
    .toFormatter(Locale.GERMANY);

// week starting at monday, consider week=1 even if it has 1 day (default is 4)
WeekFields wf = WeekFields.of(DayOfWeek.MONDAY, 1);
for (Month month : Month.values()) {
    LocalDate start = LocalDate.of(2017, month, 1);
    LocalDate end = start.with(TemporalAdjusters.lastDayOfMonth());

    System.out.println("Date Start: " + fmt.format(start) + " " + " WEEK_OF_MONTH: " + start.get(wf.weekOfMonth()));
    System.out.println("Date End: " + fmt.format(end) + " WEEK_OF_MONTH: " + end.get(wf.weekOfMonth()));
}

The output will be:

Date Start: 01.01.2016  WEEK_OF_MONTH: 1
Date End: 31.01.2017 WEEK_OF_MONTH: 6
Date Start: 01.02.2017  WEEK_OF_MONTH: 1
Date End: 28.02.2017 WEEK_OF_MONTH: 5
Date Start: 01.03.2017  WEEK_OF_MONTH: 1
Date End: 31.03.2017 WEEK_OF_MONTH: 5
Date Start: 01.04.2017  WEEK_OF_MONTH: 1
Date End: 30.04.2017 WEEK_OF_MONTH: 5
Date Start: 01.05.2017  WEEK_OF_MONTH: 1
Date End: 31.05.2017 WEEK_OF_MONTH: 5
Date Start: 01.06.2017  WEEK_OF_MONTH: 1
Date End: 30.06.2017 WEEK_OF_MONTH: 5
Date Start: 01.07.2017  WEEK_OF_MONTH: 1
Date End: 31.07.2017 WEEK_OF_MONTH: 6
Date Start: 01.08.2017  WEEK_OF_MONTH: 1
Date End: 31.08.2017 WEEK_OF_MONTH: 5
Date Start: 01.09.2017  WEEK_OF_MONTH: 1
Date End: 30.09.2017 WEEK_OF_MONTH: 5
Date Start: 01.10.2017  WEEK_OF_MONTH: 1
Date End: 31.10.2017 WEEK_OF_MONTH: 6
Date Start: 01.11.2017  WEEK_OF_MONTH: 1
Date End: 30.11.2017 WEEK_OF_MONTH: 5
Date Start: 01.12.2017  WEEK_OF_MONTH: 1
Date End: 31.12.2017 WEEK_OF_MONTH: 5

Android 7.x (API24) WEEK_OF_MONTH Calendar Bug?

1 Answers1