How to find date range for a given week on Android?

Question

This is driving me nuts!

I have searched everywhere and found for example this question: How to get dates of a week (I know week number)?

However I can't get it to work in my implementation (On ANDROID API19 on NEXUS 7) :

public Pair<String,String> getWeekRange(int year, int week_no) {

    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.WEEK_OF_YEAR, week_no);

    cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
    Date monday = cal.getTime();
    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
    Date sunday = cal.getTime();

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
    return new Pair<String,String>(sdf.format(monday), sdf.format(sunday));
}

For ANY call to getWeekRange(2014, WEEK) it ALWAYS gives me the date range of week 2 (which happens to be the current week number today) ??

Calendar seems to be a very confusing class, and there must be something I haven't understood. However according to the docs, YEAR, WEEK_OF_YEAR and DAY_OF_WEEK should be enough for me to set.

Some test data:
01-10 18:28:54.730: V/JSON(24503): Week 1/2014 is date range:2014-01-06 to 2014-01-12
01-10 18:28:54.730: V/JSON(24503): Week 2/2014 is date range:2014-01-06 to 2014-01-12
01-10 18:28:54.730: V/JSON(24503): Week 3/2014 is date range:2014-01-06 to 2014-01-12
01-10 18:28:54.730: V/JSON(24503): Week 4/2014 is date range:2014-01-06 to 2014-01-12
01-10 18:28:54.740: V/JSON(24503): Week 5/2014 is date range:2014-01-06 to 2014-01-12
01-10 18:28:54.740: V/JSON(24503): Week 1/2013 is date range:2013-01-07 to 2013-01-13
01-10 18:28:54.740: V/JSON(24503): Week 2/2013 is date range:2013-01-07 to 2013-01-13
01-10 18:28:54.740: V/JSON(24503): Week 3/2013 is date range:2013-01-07 to 2013-01-13
01-10 18:28:54.740: V/JSON(24503): Week 4/2013 is date range:2013-01-07 to 2013-01-13
01-10 18:28:54.740: V/JSON(24503): Week 5/2013 is date range:2013-01-07 to 2013-01-13

Can anyone see my mistake? Any help is appreciated.

** EDIT **

Seems that the code works fine on Windows, this is an isolated Android issue.

Your code works perfectly without much change ([link to ideone](http://ideone.com/OfWIVp)). All I did was making the function `static`, and changing it to print the output rather than returning a `Pair`. — Sergey Kalinichenko, Jan 10 '14 at 17:53
I have to agree with dasblinkenlight here. Your code looks ok and works as expected when I test it. Are you sure that you are actually testing the posted code and not something else? Which Java version are you using? — jarnbjo, Jan 10 '14 at 17:57
Yes the java.util.Calendar and Date classes are confusing. Avoid them both. They are so bad that they are being supplanted in Java 8 by the new java.time.* classes defined by JSR 310 and inspired by [Joda-Time](http://www.joda.org/joda-time/) library. Until you can move to Java 8, use Joda-Time. — Basil Bourque, Jan 10 '14 at 18:13
As you see above I have added an edit that this error only occurs on Android / Nexus 7. Should of course have mentioned this in the beginning but I kind of lost track. — Peter Andersson, Jan 10 '14 at 21:58

score 4 · Accepted Answer · answered Jan 10 '14 at 17:51

Writing this question made me read the docs once again, and just on a hunch I swapped the ordering so the function now looks like this:

public Pair<String,String> getWeekRange(int year, int week_no) {

    Calendar cal = Calendar.getInstance();

    cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY);
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.WEEK_OF_YEAR, week_no);
    Date monday = cal.getTime();

    cal.set(Calendar.DAY_OF_WEEK, Calendar.SUNDAY);
    cal.set(Calendar.YEAR, year);
    cal.set(Calendar.WEEK_OF_YEAR, week_no);
    Date sunday = cal.getTime();

    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
    return new Pair<String,String>(sdf.format(monday), sdf.format(sunday));
}

Lo and behold, it now gives me the correct dates.... It must be something with the internal implementation of Calendar that I dont understand.

Still don't know if the redundant lines are necessary, but for now I'm happy that it works!

You could use cal.add(Calendar.Date, 6) to get Sunday. That would save you 3 lines :-). — Sashi, Jan 10 '14 at 18:06

score 2 · Answer 2 · edited Jan 10 '14 at 18:04

2

I think that it's much better to use Joda-Time for such operations:

public Pair<String,String> getWeekRange(int year, int week_no) {
    DateTime startOfWeek = new DateTime().withYear(year).withWeekOfWeekyear(week_no);

    DateTime endOfWeek = startOfWeek.plusDays(6);

    return new Pair<String,String>(startOfWeek.toString(), endOfWeek.toString());
}

edited Jan 10 '14 at 18:04

Basil Bourque

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answered Jan 10 '14 at 17:59

Jakub Kubrynski

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It seems that you are calculating from "today" rather then Monday. If someone would like to calculate from Monday then beside `withYear(year)` he should also add `.withDayOfWeek(1)`. Anyway +1 for Joda. – Pshemo Jan 10 '14 at 18:15
Besides the comment of @Pshemo about adding `.withDayOfWeek(1)` I have to remember that Joda Time is unfortunately only working with ISO-week starting on Monday. For Europe this is quite okay, but in US this is a no-go. Java 8 (and my time library) will do this much better. – Meno Hochschild Jan 10 '14 at 21:26
The problem in this question is actually one of the good reasons *not* to use Joda. Joda has no support for localized week rules, which is not only problematic when the first day of week differs from Monday, but the week-of-year numbering may also be wrong. – jarnbjo Jan 13 '14 at 13:22

score 1 · Answer 3 · edited Mar 08 '18 at 11:07

Do it without importing Pair class

public  void getWeeksRangesDates(int y, int w) {
    Calendar cal = Calendar.getInstance();
    cal.set(Calendar.DAY_OF_MONTH, Calendar.MONDAY);
    cal.set(Calendar.YEAR, y);
    cal.set(Calendar.WEEK_OF_YEAR, w);
    Date date1 = cal.getTime();
    cal.add(Calendar.DATE, 6);
    Date date2 = cal.getTime();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd", Locale.getDefault());
    Log.v("date1",sdf.format(date1));
    Log.v("date2", sdf.format(date2));  
}

How to find date range for a given week on Android?

3 Answers3