Calendar's add(field, amout) method - is it intuitive?

Question

This may be quite obvious, but my current project relies mainly on the use of this one method.
What I mean by "intuitive" is, if I say:
Calendar c = calendar.getInstance(); //Get current date...
c.add(c.DAY_OF_MONTH, 7); // Add 7 days onto the current date...If we are on, say the 31st of the month, and I add 7 days, will it roll the date correctly? Does Java take into account leap-years and the fact that February only has 28 days (most of the time!)? I'm writing an app that will automatically generate machine maintenance requests on a particular day based on a pre-defined schedule, so it is very important that I can calculate the next date on which a request is to be raised...
Thanks in advance for your help - even if you tell me to go read the API (the reason I'm asking is because I couldn't see anything mentioned about it in the API, and because DAY_OF_WEEK et al are stored as int values, I was concerned it may just be adding to the int value without checking!).

Answer 1

I'd just like to point out, in a vain effort at
defending myself, No need. You're doing fine. We just needed a little clarification on what you're trying to do.
One thing is for sure--you want add(), not roll(). Roll will never change a higher order field then the one you're rolling. For example, if you roll() +1 month in December of 2006, you'll roll to January 2006. What you want to do is add(),n +1 month, which will bump Dec. 06 to Jan. 07.
Now, to clarify your rules--you want to add one month, and then, if the day of the week doesn't match (which it only will in Feb.), add enough days to get to the next occurence of that day of the week.
Does that sound right? This is my interpretation of your clarification a couple of posts ago.
A couple of things to note:
1) This rule will mean that in some months, there will be no service calls. For instance, in your example, service on 3/30, then next service is on 5/5, so no April service call. That's fine, if that's what you're business rules call for. I just want to make sure you noticed that implication of the rules you described.
2) The rules you describe amount to adding 5 weeks in every month except non-leap-year February, in which case it's the same as adding 4 weeks. Therefore, if it's acceptable, I'd recommend just picking either 4 or 5 weeks and always adding that. It will keep it simpler. 4 weeks mean some months get 2 calls, 5 weeks mean some months get none. You have to accept one or the other if you want to always service on the same day of the week, or else you have to complicate your biz rules with something like "...except if it means that a month will get no calls (or two calls), then adjust earlier (or later) to ensure exactly one call each month."
Note that the tricky part here has nothing to do with Java. It's in precisely and completely defining your business rules. Once you have that, the Java part is straightfoward.