9 March 2007

Oh, well done Sun

You know how DST rules for the USA have been changed this year, and every OS needs patches?

You know how Java doesn’t use the OS’s info, so you have to patch all your Java VMs separately?

Well, it turns out that Sun’s “fix” was broken, in that it changed the behavior of the (deprecated) 3-letter time zones EST, MST and HST so that they now no longer reflect daylight saving time at all.

So, chances are you need to check every Java runtime again, and maybe delete 3 files, or run the fix again with a -bc flag.

But hey, you’ve got until 1am on Sunday to fix all your production systems. No big deal, right?

While I’m on the subject of Java’s date/time handling being a confusing mess, let’s talk about a few of the other things wrong with it…

Java.util.Date represents a date/time, i.e. an instant in time.

Java.sql.Time represents a date/time as well. It is a subclass of Java.util.Date, yet you can’t cast a Date to a Time. Instead, you have to get the epoch time in milliseconds from your Date, and use that long value to construct a Time.

To get the epoch time/date from your Date, you use the getTime() method, which gives you a long rather than a Time. Java.util.Calendar also represents a date/time. It also has a getTime() method. However, that getTime() method returns a Date object, not a Time object or a long epoch time.

Next: Calendar numbers months from zero, so January is month 0, February is month 1. This makes it unlike any calendar in human history.

Next: If you read a Time value from a database, you can’t examine it (e.g. check the hour is AM or PM) until you convert it into a Calendar. You can’t do that by simply constructing a Calendar with the Time value. The only way to create a Calendar with a particular time value is to construct an empty Calendar, then call setTime(). And of course, setTime takes a Date, not a Time. So you have to convert your Time to a long, convert the long to a Date, create a Calendar, then call setTime() on the Calendar with the Date as argument.

In fact Date objects are pretty much a useless relic, almost all date and time handling is done with Calendar objects. For example, SimpleDateFormat allows you to convert String objects to and from date/time values. However, it only returns Date objects. So your String gets parsed into fields, which are then converted by Java to a Calendar-like representation, which is then converted to a Date object passed back to you; you then convert the Date object back into fields in a Calendar so you can work with it.

Still, it’s a much more enterprisey way to do things.

© mathew 2017