Is defining a "ProbableBugException" code smell, paranoia or good practice?

Question

In my Java code, I occasionally run into situations where I have to catch a checked exception from a library function that I'm pretty sure can't occur in my use case.

Also, when coding, I sometimes notice that I'm relying on certain inputs from other modules (my own) to have or not have particular features. For example, I might expect a string to be in a certain format etc. In these situations, I would often put in a verification step, although I control the code that send the input myself.

At the moment, I'm working on a quite complex product that I want to be very reliable. Among other things, I want it to collect information from caught exceptions and automatically file bug reports. For the above two scenarios, I therefore defined an (unchecked) "ProbableBugException", that tells me I made a mistake in the code delivering the input data.

Is that a) stupid, b) paranoid or c) good practice? This is going to be subjective, I'll put up three wiki answers so we can vote away without rep warping.

ETA: Thanks to Svend for pointing out that Java has assertions, I didn't realize that. Assertions are actuall pretty much what my question was about, but I only knew them from C and have never used them there.

Answer 1

It's stupid, because:

• the exception should be much more specific, like InvalidInputException
• you should think harder about the input side, it's likely that it's shaky if you feel you need that kind of exception

Answer 2

It's good practice, because:

• you might have a coworker coding on the input side and the two of you might have misunderstood each other
• if you make a mistake, fixing it becomes trivial
• in situations where the input side is a plugin of some sort, it helps the plugin developers (who might be external) to deliver correct input.

Answer 3

I'm thinking that using an assert is what you really want there ("probably bug").

http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html

Answer 4

I always expect the unexecpected.

I often have code like this : ( $div will never be 0 into my code )

if( $div != 0 ) {
   $var = $var2 / $div;
} else {
    /*
     * It should never happen
     */   
    throw Exception( 'relevant message' );
}

I always protect myself from me and the others