Using an unchecked exception to alter flow control inside a class

Question

Best-practice question:
Is it wrong to use an unchecked exception in an if-like manner?
For example, instead of using:
if (condition) {
-----------a lot of code-----------------
} else {
----------some more code--------------
Is it wrong to do it like this?
try {
if (!condition) throw new IllegalArgumentException();
-------------a lot of code---------------
} catch (IllegalArgumentException e) {
--------------some more code-----------
I'm asking because I used this kind of practice recently in a piece of code i wrote (actually i used it to validate an argument I received from a html-form and post an error message in the catch block) and a colleague told me it was bad practice.
If it IS bad practice, when should you actually use unchecked exceptions like IllegalArgumentException?
I already posted this question in the newbie forum, but didn't get any answers. Anybody here can explain this to me please?

Answer 1

It is fine to use IllegalArgumentException, but typically it is used when the code generating the exception and the client who is using the code that generates the exception are two different pieces of code.
If you were writing some kind of library for others to use. It would make sense to throw this exception out of your library if the user gave you wrong data.
But you shouldn't use exceptions as normal program logic.