Java Calendar - add

[Sandeep Jindal]

Hi,

I am using the following code:

Calendar calDate = getCalendarFromString("2011/02/28");
System.out.println(calDate.getTime());
calDate.add(Calendar.MONTH, 1);
System.out.println(calDate.getTime());

The output is following:

Mon Feb 28 00:00:00 IST 2011
Mon Mar 28 00:00:00 IST 2011

I was wanting to have output as

Mon Feb 28 00:00:00 IST 2011
Mon Mar [b]31[/b] 00:00:00 IST 2011

which should be in-line with JavaDoc of Calendar:

Usage model. To motivate the behavior of add() and roll(), consider a user interface component with increment and decrement buttons for the month, day, and year, and an underlying GregorianCalendar. If the interface reads January 31, 1999 and the user presses the month increment button, what should it read? If the underlying implementation uses set(), it might read March 3, 1999. A better result would be February 28, 1999. Furthermore, if the user presses the month increment button again, it should read March 31, 1999, not March 28, 1999. By saving the original date and using either add() or roll(), depending on whether larger fields should be affected, the user interface can behave as most users will intuitively expect.

Can anybody please explain the reason for the behaviour and probably the way to get the desired result too.

Regards
Sandeep Jindal

[Henry Wong]

Sandeep Jindal wrote:
which should be in-line with JavaDoc of Calendar:

Usage model. To motivate the behavior of add() and roll(), consider a user interface component with increment and decrement buttons for the month, day, and year, and an underlying GregorianCalendar. If the interface reads January 31, 1999 and the user presses the month increment button, what should it read? If the underlying implementation uses set(), it might read March 3, 1999. A better result would be February 28, 1999. Furthermore, if the user presses the month increment button again, it should read March 31, 1999, not March 28, 1999. By saving the original date and using either add() or roll(), depending on whether larger fields should be affected, the user interface can behave as most users will intuitively expect.

Can anybody please explain the reason for the behaviour and probably the way to get the desired result too.

You kinda ignored the explanation the preceded the quote you posted. The section that explained that for certain fields it will adjust for overflows in order to give you the behavior that you mentioned. In the example, in your quoted text, it overflowed. In your example, it did not.

Anyway, if you want to set to the last day of the month, take a look at the getActualMaximum() and the set() methods.

Henry

[Jesper de Jong]

Well, ofcourse, one month from 28 February is 28 March, so it shouldn't be a surprise that you get 28 March if you add one month.

First, think about what exactly the requirement is. If you have a date X, then what exactly does your method need to produce? The last day of the month that follows the month that X is in? You need to have a clear and detailed description of what you need exactly before you can write any code.

Example:

Calendar cal = Calendar.getInstance();
cal.set(2010, Calendar.FEBRUARY, 28, 12, 0, 0);

// Add one month
cal.add(Calendar.MONTH, 1);

// Set date to last day of the month
cal.set(Calendar.DATE, cal.getActualMaximum(Calendar.DATE));

// Prints: 2010/03/31 12:00:00
System.out.println(new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(cal.getTime()));

[Sandeep Jindal]

Thanks for the replies.

I got my answer/clarification. The behavior if calendar is not same as of my requirement. I need to write the code, similar to written by Jesper.

Thanks again.