Question

I want to know whether the Time values of a Calendar object equal the value of a java.sql.Time object.

E.g

Calendar c; //c.getTime().toString() == "Sat Jan 07 09:00:00 GMT 2012"
Time t;     //d.toString() == "09:00:00";

I tried

t.equals(c.getTime())

But because the Calendar has Date information the expression is false.

What would be the best way the compare the two?

Edit:
The Time object is retrieve though Hibernate and come with no date information.

The Calendar object is create by

Calendar c= Calendar.getInstance();
c.set(Calendar.HOUR_OF_DAY, 9);
c.set(Calendar.MINUTE, 0);
c.set(Calendar.SECOND, 0);

Answer 1

The way you use is perfectly fine. The goal is unclear, though. Why do you want c to be equal to d?

Additionally, there’s no way to have d.toString() == "09:00:00" — Date always have, well, the date included.

What’s more important, though, is that Date has no timezone information (well, it used to have, but you’re discouraged to touch this part of Date), so you cannot tell 09:00 UTC from 10:00 BST—that is, unless you specify the timezone. You can get the timezone from Calendar c, and it sort of explains what you need to do:

1. Create a Calendar from your date
2. Copy timezone from the calendar you already use
3. Compare the Calendar fields which are of interest for you. I suppose that will be hour, minute, second, and, perhaps, millisecond.

Update: now that you’ve mentioned it’s actually java.sql.Time, I’m worried. The problem is,

• SQL servers usually store time as a structure containing hours, minutes, seconds, etc. That is, there’s an implied timezone (the SQL Server timezone)
• java.sql.Time stores time as milliseconds since “zero epoch” value of January 1, 1970. The date part is usually stripped to January 1, 1970 — but this class does not contain timezone information. (Well, again, it sort of does, but it’s deprecated.)
• Calendar has an explicitly set timezone

What it means in practice is, that the time from the server gets converted into milliseconds using system default timezone, then you read this value and compare it with a Calendar with its own timezone.

If it sounds confusing and fragile, that’s because it is. So basically you have three timezones:

1. SQL Server TZ
2. JVM’s default TZ
3. Calendar’s TZ

All three must be the same so that any comparison would make any sense.