Converting from DateTime to Epoch - and back

Question

I found the question about converting epoch time to normal time, but I'm having two problems:

1. When I run DateTime.newInstance(1391529600 * 1000) I am getting the wrong answer
2. I want to convert normal time to epoch time

1: I have been typing the following into Execute Anonymous:

system.debug(DateTime.newInstance(1391529600 * 1000));

By my calculations (and some websites I found) that should give me 4 Feb, 2014, 16:00:00 GMT.

Apex gives me

1969-12-31 12:56:36

Clearly, this is incorrect (and it's even before 1/1/1970). Can anyone replicate my situation?

2: I also want to change the current datetime (GMT) to epoch time, returning the number of seconds or milliseconds since 1/1/1970. I could break things into parts, but that seems an awful lot of script statements to do something that should be fairly easy, I'd hope.

Thanks for the help!

Answer 1

I can replicate it, and by removing the * 1000 and appending 3 zeros, I got "Invalid Integer". So what I believe is that 1391529600 * 1000 is being evaluated as an integer type and so overflowing.

You can create the Long value using the L notation like so:

system.debug(DateTime.newInstance(1391529600000L));

To get the epoch from a datetime variable you can just call the getTime() instance method:

Datetime dt = Datetime.now();
Long l = dt.getTime();
system.debug(l);
system.debug(DateTime.newInstance(l));

produces:

USER_DEBUG|[7]|DEBUG|1391560453900

USER_DEBUG|[9]|DEBUG|2014-02-05 00:34:13

Answer 2

LaceySnr has a solid answer to #1, but #2 is still unanswered, so I'll note that the DateTime.getTime() method returns the number of milliseconds since Jan 1, 1970, so you'll need to divide by 1000 to get standard unix time, which is the number of seconds since the epoch.

If you want to work with this number you'll need to ensure you store it in a Long, and not an Integer type.