What weeks are associated with months?

Question

Is there a way in JodaTime to easily determine which weeks belong to that month?

Something that gave the month number returns the weeks of the year associated with it. A week should be associated with a specific month, if it gets 4+ days.

In 2014 for month = 1 then weeks = [1, 2, 3, 4, 5] (note 5 weeks because of 4 days rule) In 2014 for month = 3 then weeks = [10, 11, 12, 13] (note 4 weeks because of same rule) 

I do not want to calculate this "manually" ...

Answer 1

You need to create an instance of the DateTime object for the specified week number, and then just read its month property (using Joda-Time and Google Guava ).

  DateTime dateTime = new DateTime().withWeekOfWeekyear(i).withDayOfWeek(DateTimeConstants.MONDAY); if (dateTime.dayOfMonth().getMaximumValue() - dateTime.dayOfMonth().get() < 3) { dateTime = dateTime.plusMonths(1); } int month = dateTime.monthOfYear().get(); 

We can also use the function below to print all months with their own weeks:

 public static void main(String[] args) { Multimap<Integer, Integer> monthsWithWeeks = LinkedListMultimap.create(); int weeksInYear = new DateTime().withYear(2014).weekOfWeekyear().getMaximumValue(); for (int i = 1; i <= weeksInYear; i++) { DateTime weekDate = new DateTime().withWeekOfWeekyear(i).withDayOfWeek(DateTimeConstants.MONDAY); if (weekDate.dayOfMonth().getMaximumValue() - weekDate.dayOfMonth().get() < 3) { weekDate = weekDate.plusMonths(1); } int month = weekDate.monthOfYear().get(); monthsWithWeeks.put(month, i); } for (Integer month : monthsWithWeeks.keySet()) { System.out.println(String.format("%d => [%s]", month, Joiner.on(',').join(monthsWithWeeks.get(month)))); } } 

Answer 2

An interesting problem, although I have little experience with Joda. I tried to solve it using jata.util Classes with simple calculations, I think it solves your problem - only without Joda.

The method of accumulating all weekly numbers for a month in a year:

 public static Integer[] getWeeksInMonth(int month, int year) { List<Integer> list = new ArrayList<Integer>(); SimpleDateFormat format = new SimpleDateFormat("w"); Calendar startDate = Calendar.getInstance(); Calendar endDate = Calendar.getInstance(); startDate.set(year, month - 1, 1); startDate.setMinimalDaysInFirstWeek(4); endDate.set(year, month, 0); // Iterate between the start and stop days while (startDate.getTimeInMillis() <= endDate.getTimeInMillis()) { Calendar cal = Calendar.getInstance(); cal.setTime(startDate.getTime()); cal.set(Calendar.DAY_OF_WEEK, Calendar.MONDAY); // System.out.println("Here here " + // cal.get(Calendar.DAY_OF_MONTH)); // Start of the week is Monday - check if dates 1, 2, 3 fall after // Wednesday (specified 4 day rule) if ((startDate.get(Calendar.DAY_OF_WEEK) > Calendar.THURSDAY) && (startDate.get(Calendar.DAY_OF_MONTH) < 4)) { // If they do, move the dates to next immediate start of the // week - making it to 4th startDate.add(Calendar.DAY_OF_MONTH, (4 - startDate.get(Calendar.DAY_OF_MONTH))); // Similarly - check if last dates of the month make less than 4 // for that month } else if ((startDate.get(Calendar.DAY_OF_MONTH) > 25) && ((startDate.getActualMaximum(Calendar.DAY_OF_MONTH) - (cal .get(Calendar.DAY_OF_MONTH))) + 1) < 4) { // If they do, move the dates to next immediate start of the // week - making it to next month startDate .add(Calendar.DAY_OF_MONTH, (startDate .getActualMaximum(Calendar.DAY_OF_MONTH) - startDate .get(Calendar.DAY_OF_MONTH)) + 1); } else { // Get the number of the week // System.out.println(startDate.getTime()); int week = Integer.parseInt(format.format(startDate.getTime())); // If December, check if the next year 1st week falls under // the 4 day rule, if it does then ignore if (!(startDate.get(Calendar.MONTH) == Calendar.DECEMBER && week == 1)) list.add(week); startDate.add(Calendar.WEEK_OF_MONTH, 1); } } return list.toArray(new Integer[list.size()]); } 

The main method call:

 public static void main(String... args) { int year = 2014; System.out.println(":::: YEAR " + year + " ::::"); for (int j = 1; j <= 12; j++) { Integer[] array = getWeeksInMonth(j, year); System.out.print("For month : " + j); System.out.print(" [ "); for (int i = 0; i < array.length; i++) { System.out.print(array[i] + " "); } System.out.print("]"); System.out.println(); } } 

Output (possible test cases):

 :::: YEAR 2014 :::: For month : 1 [ 1 2 3 4 5 ] For month : 2 [ 6 7 8 9 ] For month : 3 [ 10 11 12 13 ] For month : 4 [ 14 15 16 17 ] For month : 5 [ 18 19 20 21 22 ] For month : 6 [ 23 24 25 26 ] For month : 7 [ 27 28 29 30 31 ] For month : 8 [ 32 33 34 35 ] For month : 9 [ 36 37 38 39 ] For month : 10 [ 40 41 42 43 44 ] For month : 11 [ 45 46 47 48 ] For month : 12 [ 49 50 51 52 ] 

You can check other test cases and let me know if something is wrong. I know a lot of calculations, but it is flexible with requirements.

Answer 3

This is pretty simple with JodaTime:

 /** returns first and last week in a month (must have at least 4 days of that week) * Warning: The first week might be week 53 */ public static int[] firstAndLastWeeksInMonth(int year, int month) { int firstweek = new LocalDate(year, month, 4).getWeekOfWeekyear(); int lastweek = new LocalDate(year, month, 1).plusMonths(1).minusDays(4).getWeekOfWeekyear(); return new int[] { firstweek, lastweek }; } public static List<Integer> weeksInMonth(int year, int month) { int[] fl = firstAndLastWeeksInMonth(year, month); ArrayList<Integer> weeks = new ArrayList<Integer>(4); weeks.add(fl[0]); for( int w = fl[0] > fl[1] ? 1 : fl[0] + 1; w <= fl[1]; w++ ) weeks.add(w); return weeks; } 

Invalid code to check:

 static void testWeeksInMonth(int year, int month, boolean printdetail) { List<Integer> weeks = weeksInMonth(year, month); System.out.printf("weeks for %d/%d: [%s]\n", year, month, weeks); LinkedHashMap<Integer, Integer> whist = new LinkedHashMap<Integer, Integer>(); LocalDate d1 = new LocalDate(year, month, 1); LocalDate d2 = d1.plusMonths(1); for( LocalDate d = d1; d.isBefore(d2); d = d.plusDays(1) ) { int wd = d.getWeekOfWeekyear(); if( !whist.containsKey(wd) ) whist.put(wd, 0); whist.put(wd, whist.get(wd) + 1); } List<Integer> weeks2 = new ArrayList<Integer>(); for( Integer wd : whist.keySet() ) { if( printdetail ) System.out.printf(" ( %d: %d) ", wd, whist.get(wd)); if( whist.get(wd) >= 4 ) weeks2.add(wd); } if( printdetail ) System.out.println(""); if( !weeks.equals(weeks2) ) { throw new RuntimeException("bad values"); } } public static void main(String[] args) { LocalDate d = new LocalDate(2010, 1, 1); for( int i = 0; i < 60; i++ ) { testWeeksInMonth(d.getYear(), d.getMonthOfYear(), true); d = d.plusMonths(1); } }