Why GregorianCalendar sets HOUR depending on System time(AM/PM)

Question

I am simply creating a java.util.GregorianCalender

GregorianCalendar calender = new GregorianCalendar();

now setting the hour,min,sec and ms as follows

c.set(Calendar.HOUR, 6);
c.set(Calendar.MINUTE, 45); 
c.set(Calendar.SECOND, 30);         
c.set(Calendar.MILLISECOND, 345);

now printing the output using getTime() method

System.out.println("Date and Time: "+c.getTime());

When System time is in AM, the output is

Date and Time: Tue Feb 09 06:45:23 IST 2016

And When System time is in PM, the output is

Date and Time: Tue Feb 09 18:45:23 IST 2016

Now my question is why the output is changing with the system time?

Answer 1

new GregorianCalendar() fields are set using the current time in your default time zone. The AM/PM flag is therefore set depending on whether the current time in your default time zone is AM or PM.

When you set HOUR to 6, the AM/PM flag is not changed and the resulting calendar is set on 6am or 6pm depending on the current time.

If you set HOUR_OF_DAY to 6, the calendar will be set on 6am, regardless of current time.