Question concerning SimpleDateFormat returning week information

Question

Hello,
I am just trying to get returned a date value with the format 'ww/yyyy' and experience problems in getting the correct value around the turn of the year.
Example:
java.text.SimpleDateFormat df = new java.text.SimpleDateFormat("w/yyyy");
df.getCalendar().setFirstDayOfWeek(java.util.Calendar.MONDAY);
df.getCalendar().setMinimalDaysInFirstWeek(4);
System.out.println(df.format(new java.sql.Date(103,11,31))); //Dez, 31, 2003As output I get "01/2003" which is not correct - I expected "01/2004" instead.
How do I get the correct output?
Do I have miscoded there something or is this a bug?
BTW: when trying the same with Jan, 1, 2004 I get the correct output.
Thank you for any answers
Ralf

Answer 1

From the API documentation for java.util.Calendar:
"The first week of a month or year is defined as the earliest seven day period beginning on getFirstDayOfWeek() and containing at least getMinimalDaysInFirstWeek() days of that month or year."
So, since December 31 2003 was on a Wednesday and you've defined your weeks to start on Monday, there were 3 days of 2003 and 4 days of 2004 in the week containing that date. And since your "minimal days in first week" is defined to be 4, this week is the first week of 2004. In other words, its week number is 1.
So that's why you see week number 1. (A week has only one week number.)
And since December 31 2003 was in 2003, you see 2003 for the year.
If you experiment a bit more with GregorianCalendar and callcal.get(Calendar.WEEK_OF_YEAR)for various dates, you should see what is going on.
If you want the "correct" output (in other words the output you want to see, whatever it is) then you can subclass GregorianCalendar and override its get method.