java - to get the start date and end date of each week for the given month

Question

Following is the code that I am using to calculate the week start date and end date for the given month. Assume week start day is MONDAY and week end day is SUNDAY. For exa

Answer 1

I get the answer with the following code

List<List<String>> getNumberOfWeeks(int year, int month) {
        SimpleDateFormat format = new SimpleDateFormat("dd-MM-yyyy");
        List<List<String>> weekdates = new ArrayList<List<String>>();
        List<String> dates;
        Calendar c = Calendar.getInstance();
        c.set(Calendar.YEAR, year);
        c.set(Calendar.MONTH, month);
        c.set(Calendar.DAY_OF_MONTH, 1);
        while (c.get(Calendar.MONTH) == month) {
                dates = new ArrayList<String>();
              while (c.get(Calendar.DAY_OF_WEEK) != Calendar.MONDAY) {
                c.add(Calendar.DAY_OF_MONTH, -1);
              }
              dates.add(format.format(c.getTime()));
              c.add(Calendar.DAY_OF_MONTH, 6);
              dates.add(format.format(c.getTime()));
              weekdates.add(dates);
              c.add(Calendar.DAY_OF_MONTH, 1);
        }
        System.out.println(weekdates);
        return weekdates;
      }

Answer 2

A possible solution may be to not reinvent the wheel and use JodaTime or a similar library. For instance, you can use the dayOfWeek() function on a DateTime to get the information you're after.

Answer 3

You are using terrible date-time classes that were supplanted years ago by the modern java.time classes defined in JSR 310. This work is much easier now.

YearMonth

The YearMonth class represents a specific month as a whole. Specify the month using the Month enum.

YearMonth ym = YearMonth.of( 2013 , Month.JANUARY ) ;

LocalDate

Get the first of the month.

LocalDate firstOfMonth = ym.atDay( 1 ) ;

TemporalAdjuster

Get the previous Monday, or stay with this date if it is a Monday.

TemporalAdjuster ta = TemporalAdjusters.previousOrSame( DayOfWeek.MONDAY ) ;
LocalDate previousOrSameMonday = firstOfMonth.with( ta ) ;

Then loop a week at a time.

LocalDate endOfMonth = ym.atEndOfMonth() ;
LocalDate weekStart = previousOrSameMonday ; 
do {
    LocalDate weekStop = weekStart.plusDays( 6 ) ;
    System.out.println( "Week: " + weekStart + " to " + weekStop ) ;
    // Set up the next loop.
    weekStart = weekStart.plusWeeks( 1 ) ;
} while ( ! weekStart.isAfter( endOfMonth ) ) ;

See this code run live at IdeOne.com.

Week: Monday, December 31, 2012 to Sunday, January 6, 2013

Week: Monday, January 7, 2013 to Sunday, January 13, 2013

Week: Monday, January 14, 2013 to Sunday, January 20, 2013

Week: Monday, January 21, 2013 to Sunday, January 27, 2013

Week: Monday, January 28, 2013 to Sunday, February 3, 2013

By the way, you might want to learn about, and consider using, the ISO 860 standard definition of a week. And then use the YearWeek class of the ThreeTen-Extra library.