Calendar instance providing wrong week number when calendar built with basic fields [duplicate]

Question

This question already has answers here:

Why is January month 0 in Java Calendar? (17 answers)

Closed 8 years ago.

I would like to understand why this happens, and how can i solve this small issue. I would like to be able to get the week number from a java calendar instance after providing the day, the month and the year. if i do:

  Calendar cal=Calendar.getInstance();
       cal.set(Calendar.DAY_OF_MONTH, 11);
       cal.set(Calendar.MONTH,2);
       cal.set(Calendar.YEAR, 2013);

11 Feb 2013 is week 7, but if i invoke, in the above calendar instance:

int weekNumber=cal.get(Calendar.week_of_year)

I get the week number 11. Any idea why? I tried setting the locale but no difference, the problem is that i can only build a calendar out of these three fields, since i'm reading them from a xml file with a parser and they are in format dd-mm-yyyy with no more information that that

Answer 1

Months fields in Calendar are zero based. The value 2 corresponds to Calendar.MARCH. To avoid confusion, better to use the Calendar constants. You could use:

cal.set(Calendar.MONTH, Calendar.FEBRUARY);

Answer 2

You have used March, because Java months in Calendar are 0-based: 0 = January, 1 = February, 2 = March.

Use

cal.set(Calendar.MONTH,1);

or

cal.set(Calendar.MONTH, Calendar.FEBRUARY);

if you can use a constant. Else, subtract 1 from the month you received from your parser.