javaandroidweek-numberdate

Group list of Dates to week number? [Android]

I am working on an android app that will display a list of data. For example, if you start to use app today(28.05.2018)(MO) and I must calculate week number and add 7 days this week or you are starting Friday I must add 2 days this week.

I tried this method https://stackoverflow.com/a/42733001/9259044 but its wrong for me. First of all, I added dates and

 TreeMap<Integer, List<Date>> dateHashMap = new TreeMap<>();
    SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");
    List<Date> spDates = new ArrayList<>();


    try {


        spDates.add(sdf.parse("02/06/2018"));
        spDates.add(sdf.parse("01/06/2018"));
        spDates.add(sdf.parse("31/05/2018"));
        spDates.add(sdf.parse("30/05/2018"));
        spDates.add(sdf.parse("29/05/2018"));

        spDates.add(sdf.parse("28/05/2018"));
        spDates.add(sdf.parse("27/05/2018"));

        spDates.add(sdf.parse("26/05/2018"));
        spDates.add(sdf.parse("25/05/2018"));


    } catch (ParseException e) {
        e.printStackTrace();
    }

I compare weekOfYear to my dates but this is wrong.

for (int i = 0; i < spDates.size(); i++) {
        List<Date> datesList = new ArrayList<>();
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(spDates.get(i));

        int weekOfYear = calendar.get(Calendar.WEEK_OF_YEAR);


        for (Date date : spDates) {
            Calendar c = Calendar.getInstance();
            c.setTime(date);
            if (weekOfYear == c.get(Calendar.WEEK_OF_YEAR)) {
                datesList.add(date);
            }
        }

        dateHashMap.put(weekOfYear, datesList);


    }

   Log.d("DATE",dateHashMap.toString());

Do you have any idea how can I group my Dates to week Number?

Solution

  • I think you want this:

        LocalDate today = LocalDate.now(ZoneId.of("Europe/Istanbul"));
    
    int weekNumber = today.get(WeekFields.ISO.weekOfYear());
    System.out.println("Week no. " + weekNumber);
    
    LocalDate[] days = today.datesUntil(today.with(TemporalAdjusters.next(DayOfWeek.MONDAY)))
            .toArray(LocalDate[]::new);
    System.out.println(Arrays.toString(days));

    Running it today (Monday, May 28) it printed

    Week no. 22
[2018-05-28, 2018-05-29, 2018-05-30, 2018-05-31, 2018-06-01, 2018-06-02, 2018-06-03]

    It gives you all the dates from today, inclusive, until next Monday, exclusive. If Monday is the first day of the week, this means the remaining days of this week.

    I am using and recommending java.time, the modern Java date and time API. I find it much nicer to work with than the old date and time classes that you are using, Date, SimpleDateFormat and Calendar. java.time was introduced in Java 8 exactly because the old classes from Java 1.0 and 1.1 were too troublesome and error-prone.

    Question: Doesn’t java.time require Android API level 26?

    Edit: from the comment:

    Field requires API level 26

    java.time works nicely on both older and newer Android devices including lower API levels than 26.

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