Calender.set() Not working properly

Question

I want to get the last month End date, I am getting the current month and recuding it by one and setting that month value. But Calender.set(Calender.Month, lastMonth) doesnt work for only a specific date.

public static String getLastMonthEndDate(Date nowDate, String dateFormat) 
{
    final String METHOD_NAME = "getLastMonthEndDate" ;


    SimpleDateFormat formatedDate = new SimpleDateFormat(dateFormat);


    Calendar calendar = new GregorianCalendar(2014, Calendar.OCTOBER, 31); // Hard coded as 2014, oct 31st for the sake of example.
    //calendar.setTime(nowDate);
    System.out.println(calendar.getTime());
    if(calendar.get(Calendar.MONTH) == Calendar.JANUARY)
    {
        calendar.set(Calendar.YEAR, calendar.get(Calendar.YEAR) - 1);
    }

    //System.out.println("calendar.get(Calendar.MONTH) -1 : " + (calendar.get(Calendar.MONTH) -1));
    int lastMonth = (calendar.get(Calendar.MONTH) -1);
    System.out.println("Last month : "+lastMonth);
    calendar.set(Calendar.MONTH, lastMonth);
    //System.out.println(calendar.getTime());
    //System.out.println("(calendar.get(Calendar.MONTH) : " + calendar.get(Calendar.MONTH));
    System.out.println("calendar.getActualMaximum(Calendar.DAY_OF_MONTH) : " + calendar.getActualMaximum(Calendar.DAY_OF_MONTH));

    calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
    System.out.println("calendar.getTime() : " + calendar.getTime());

    return formatedDate.format(calendar.getTime());
}



public static void main(String[] args)
{

     Date dCurrentDate = getCurrentDate();
     String strLastMonthEndDateInYYYY = getLastMonthEndDate(dCurrentDate, "MM/dd/yyyy");
     System.out.println("strLastMonthEndDateInYYYY : "+strLastMonthEndDateInYYYY);

}

The Below is the output which i got

output : 


Fri Oct 31 00:00:00 IST 2014

Last month : 8

calendar.getActualMaximum(Calendar.DAY_OF_MONTH) : 31

calendar.getTime() : Wed Oct 01 00:00:00 IST 2014

strLastMonthEndDateInYYYY : 10/01/2014

I don't know what where the mistake is. Please help.

Answer 1

It doesn't work because you are setting the date to "09/31/2014" after your operations on calendar, and there is not day 31 in September 2014. By default, java Calendar is lenient, and will interpret that date as "10/01/2014" (1st October 2014).

Here is the relevant part of the Javadoc:

When a Calendar is in lenient mode, it accepts a wider range of calendar field values than it produces. When a Calendar recomputes calendar field values for return by get(), all of the calendar fields are normalized. For example, a lenient GregorianCalendar interprets MONTH == JANUARY, DAY_OF_MONTH == 32 as February 1.

And here is a commented version of the relevant parts of your code to explain what is going on:

Calendar calendar = new GregorianCalendar(2014, Calendar.OCTOBER, 31); // 10/31/2014
// [...]
int lastMonth = (calendar.get(Calendar.MONTH) -1); // lastMonth will be Calendar.SEPTEMBER
calendar.set(Calendar.MONTH, lastMonth); // internal value of the calendar is now 09/31/2014
// [..]
System.out.println("calendar.getActualMaximum(Calendar.DAY_OF_MONTH) : " + calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); // returns 31 because this is a get() method, so 09/31/2014 will be converted to 10/01/2014, and there are 31 days in October (but the internal representation of the calendar will still be 09/31/2014)
// [...]
calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); // internal representation is still 09/31/2014, so this will not change the value
// [...]
return formatedDate.format(calendar.getTime()); // this is a get() method, so the value will be converted to 10/01/2014

A better solution would be to set your Calendar to the first day of the month, and subtract one day:

Calendar calendar = new GregorianCalendar(2014, 9, 31);
calendar.set(Calendar.DAY_OF_MONTH, 1);
calendar.add(Calendar.DAY_OF_MONTH, -1);
System.out.println((new SimpleDateFormat("MM/dd/yyyy")).format(calendar.getTime())); // 09/30/2014