Is it a good or bad idea throwing Exceptions when validating data?

Question

When validating data, I\'ve gotten into a habit of doing the following:

Note: I don\'t really have individual booleans for each check. This is just

Answer 1

In addition to the oft-repeated statement that "exceptions are for exceptional circumstances", here's an additionally clarifying rule I've come to like:

If the user caused it, it's not exceptional.

Exceptions are for system-side things (servers going down, resources being unavailable), not for the user doing odd things, because all users do odd things.

Answer 2

It depends - if you are expecting the data to be there and NOT having the data is unexpected, then throwing an exception is OK. Throwing an exception is very expensive (slow) but is the best way to handle unexpected circumstances.

Answer 3

It really only matters if your data validation is in a tight loop. For most cases, it doesn't matter what you choose as long as you are consistent in your code.

If you have a lot of code that looks like your sample above then you might want to clean it up by introducing a helper method to throw...

private void throwIf( bool condition, String message )
{
    if( condition )
        throw new ApplicationException( message );
}

(also, doing this will help zero in on errors such as "validCheckOne = false" versus "validCheckOne == false" :)

Answer 4

In the title you call it "validating" data. That can happen on several levels. In (near) the GUI where you are checking user entered data, you should be expecting errors and have ways to report the errors back. Exceptions are inappropriate in this case.

But Data Validation can also happen at other boundaries, say between business-rule classes. There, errors in the data are uncommon and unexpected. You should throw when you detect one.

Answer 5

This question is still interesting, mainly because of the answers.

When it comes to exception, there is a lot of arguments involved. We can defend a point to any direction we want to, from performance to exception philosophy. And they all sounds right to me.

But sometimes we have to stick to a direction. In this case, I think it's the validation itself.

When we want to validate something we also want to know (to log, or to show the user) whats wrong when the parameter is invalid. Even thought there are layers of validation such as Business Validation mixed with User Input validations.

For instance, when dealing with user input, a lot of weird cases can happen. A pasted data from a website full of hidden char (\t \n etc), typos, and a really huge kinds of cases that a specific exception could allow further analysis or message to the uses much more precisely than a simple "false" return.

Answer 6

I generally agree with the "exceptions should be exceptional" rule, but I might make an exception (ha!) for Python, where it can be both efficient and considered good practice to use try ... except to control flow.

See Using Exceptions For Other Purposes, for example.