calendar - Java: Calculate month end date based on timezone

Question

I have method to find month end date based on the timezone.

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("CET"));
calendar.set(
    Calendar.DAY_OF_MONTH, 
    calendar.getActualMaximum(Calendar.DAY_OF_MONTH)
);
System.out.println(calendar.getTime());`

It displays output: Thu Aug 30 18:04:54 PDT 2018.

It should, however, give me an output in CET.

What am I missing?

Answer 1

The Calendar.getTime() method returns a Date object, which you then printed in your code. The problem is that the Date class does not contain any notion of a timezone even though you had specified a timezone with the Calendar.getInstance() call. Yes, that is indeed confusing.

Thus, in order to print a Date object in a specific timezone, you have to use the SimpleDateFormat class, where you must call SimpleDateFormat.setTimeZone() to specify the timezone before you print.

Here's an example:

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

public class TimeZoneTest {

    public static void main(String argv[]){
        Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone("CET"));
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
        System.out.println("calendar.getTime(): " + calendar.getTime());

        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MMM-dd HH:mm:ss z");
        sdf.setTimeZone(TimeZone.getTimeZone("CET"));
        System.out.println("sdf.format(): " + sdf.format(calendar.getTime()));
     }
}

Here is the output on my computer:

calendar.getTime(): Fri Aug 31 01:40:17 UTC 2018
sdf.format(): 2018-Aug-31 03:40:17 CEST