GregorianCalendar

[Navi Lock]

Hi Guys,
I am using GregorianCalendar to compare 2 dates to see it they are equal.
I create 1 gc object, set the yyyy , mm , dd then the same for the second gc object.

GregorianCalendar gregorianCalendar1 = new GregorianCalendar();
gregorianCalendar1.set(2006,2,1,0, 0, 0);
step**",
GregorianCalendar gregorianCalendar2 = new GregorianCalendar();
gregorianCalendar2.set(2006,2,1,0, 0, 0);

System.out.println("TIMEAAAA 2 "+gregorianCalendar2.getTimeInMillis());
System.out.println("TIMEAAAAA 1 "+gregorianCalendar1.getTimeInMillis());
System.out.println("COMPARE "+gregorianCalendar1.getTime().equals (gregorianCalendar2.getTime()));
------------------->>>>> THis is ALWAYS TRUE..

BUT if i have a "Delay / for Loop" of more than 250 at "step**",between the creation of first GC object instance and the second GC object, then the result of the comparison is always FALSE...



GregorianCalendar gregorianCalendar1 = new GregorianCalendar();

gregorianCalendar1.set(Calendar.YEAR,2006);
for(int h = 0; h < 20000 ; )
{
h++;
}

GregorianCalendar gregorianCalendar2 = new GregorianCalendar();
gregorianCalendar2.set(Calendar.YEAR,2006);

try {

System.out.println("TIME 2 "+gregorianCalendar2.getTimeInMillis());
System.out.println("TIME 1 "+gregorianCalendar1.getTimeInMillis());
System.out.println("COMPARE "+gregorianCalendar1.getTime().equals(gregorianCalendar2.getTime()));

} catch (IllegalArgumentException iae) {
iae.printStackTrace(System.out);
}

}



DUNNO why..... Can anybody help me out...

Thanks,
Navi.
[ April 01, 2006: Message edited by: Navi Navi ]

[Jason Moors]

The set method only sets the year, month, date, hour and minute fields of the GregorianCalendar. Therefore seconds, milliseconds will be retained from when you created the object, you need to clear all the time fields first.

Sets the values for the fields year, month, date, hour, and minute. Previous values of other fields are retained. If this is not desired, call clear first.

However it is probably easier to just use the GregorianCalendar constructor.

    
GregorianCalendar gregorianCalendar1 = new GregorianCalendar(2006,2,1);

Jason

[Navi Lock]

Hi Jason, Thanks a bunch. Your explaination helped.

-Navi

[Marilyn de Queiroz]

A related question:
If I use the default GregorianCalendar constructor, I get the current date and the current time. What is the simplest way to get the current date at the previous midnight? For example, today is April 2, 2006, and it is about 7 pm. But I want today at 12:01 am minus one minute, in other words the beginning of today.

[ak pillai]

something like:

Calendar cal = GregorianCalendar.getInstance();
        cal.setTime(new Date());
        
        //prints the current time day etc i.e now
        System.out.println(cal.getTime());
        
        
        //reset teh time to beginning of the day
        cal.set(Calendar.HOUR_OF_DAY, 00);//midnight
        cal.set(Calendar.MINUTE, 00);
        cal.set(Calendar.SECOND, 00);
        
        System.out.println(cal.getTime());
        
        
        //add a day
        cal.add(Calendar.DAY_OF_MONTH, 1);
        
        System.out.println(cal.getTime());

[Jim Yingst]

Don't forget

cal.set(Calendar.MILLISECOND, 0);

Depending how you're displaying the result, this may or may not be noticeable, but milliseconds are part of the state of the GregorianCalendar, which probably should be zeroed out with the rest of them. The fields AM_PM and HOUR are redundant, their values implied by HOUR_OF_DAY, so you can safely skip them.

However,

Calendar cal = GregorianCalendar.getInstance();

This is misleading - getInstance() is in the Calendar class, and static. In my opinion it's clearer to either use Calendar.getInstance(), or just use new GregorianCalendar().

        cal.setTime(new Date());

Should be unnecessary - a newly created Calendar is already at the current time.

        //add a day
        cal.add(Calendar.DAY_OF_MONTH, 1);

This appears to be for some problem other than the one Marilyn described.

[Marilyn de Queiroz]

Ok, thanks. It just seems like there should be a simpler way than calling set() four times, but if there isn't, there isn't.

[Jim Yingst]

Simpler? Sure, but not from Sun. Calendar and GregorianCalendar are among the more API's they've created. You seek Joda:

ReadableDateTime dateTime = new DateMidnight();

[ April 03, 2006: Message edited by: Jim Yingst ]

[Marilyn de Queiroz]

Thanks, Jim.