Java Date year calculation is off by year for two days

Question

This caused a Y2K-style bug in my software if you can imagine. Strange thing is the off-by-one year calculation only occurs for two days in the year, which I'm less sure how to troubleshoot.

The output:

03-Jan-2013
02-Jan-2013
01-Jan-2013
31-Dec-2013 ** strange
30-Dec-2013 ** strange
29-Dec-2012
28-Dec-2012
27-Dec-2012
26-Dec-2012
25-Dec-2012

I am not sure which part of the Java date utilities could cause such an error.

The code (since the test is so small I included a complete working program):

import java.util.Calendar;
import java.util.Date;
import java.text.SimpleDateFormat;

public class DateT {

        private static String getFormattedBackscanStartTime(int days) {

                SimpleDateFormat dateFormat = new SimpleDateFormat("dd-MMM-YYYY");
                Calendar workingDate = Calendar.getInstance();
                workingDate.add(Calendar.DATE, -1 * days);

                String formattedStartTime = dateFormat.format(workingDate.getTime());
                return formattedStartTime;
        }

        public static void main(String args[]) {

                for(int i = 35; i < 45; i++) {
                        System.out.println(getFormattedBackscanStartTime(i));
                }
        }
}

Answer 1

This is the problem:

"dd-MMM-YYYY"

YYYY is the week-year, not the calendar year. You want yyyy instead.

The last two days of calendar year 2012 were in the first week of week-year 2013. You should normally only use the week year in conjunction with the "week of year" specifier (w).