getTimeInMillis() function of the Calendar class returns wrong values

[16mydream]

i'm using the getTimeInMillis() function from the Calendar class to calculate the number of milliseconds from the epoch to a particular day. however, it seems as if the function is returning wrong values by assuming that every month has 31 days.

a sample code I tested is as follows:

long mili;
Calendar now = new GregorianCalendar();

now.set(2011, 02, 28);
mili = now.getTimeInMillis();
System.out.println(mili);

now.set (2011, 03, 01);
mili = now.getTimeInMillis();
System.out.println(mili);
		
now.set(1970, 1, 1);
mili = now.getTimeInMillis();
System.out.println(mili);

the output i got was 1301280211567 for 2011/02/28 and 1301625811567 for 2011/03/01, there is a four day difference in the milliseconds, when there should only have been one.

also, the output i got for 1970/01/01 is 2688211567. shouldn't this have been zero if getTimeInMilils() calculates starting from the epoch which is exactly 1970/01/01?

is there something i'm not doing correctly or is this really a bug in the function? if it is, is there any other way i can calculate the number of milliseconds to a certain day?

thanks!

[Fubarable]

Don't use numbers for months but instead use the Calendar constants. This way it won't matter that months are 0-based (January is 0, Feb is 1, March is 2, ...), and you won't get tripped up by this.

[Junky]

Nitpick: leading zeros in literal values are pointless.

But as Fubar pointed out if you use the constants this is not an issue.

[16mydream]

thank you both very much!
the difference now matches up =)

[Junky]

By the way, when in doubt read the API:

month - the value used to set the MONTH calendar field. Month value is 0-based. e.g., 0 for January.