Yes, it's about which exception it throws.

require

throws

IllegalArgumentException

, which makes no sense here, the arguments passed in to my methods were perfectly fine.

So, what exception do you want this function to throw?

In Guava they have a custom class that extends

RuntimeException

, which is the most reasonable thing you can do, I think.

To me it's more like an

AssertionError

— when the returned value doesn't meet the function contract.

Hm, true. However I am not sure if it's "correct" or "a good idea" to re-use

AssertionError

here, since that seems to be only for the

assert

keyword.

I’m curious, why is the exception type important at all? Especially in a super-generic method like

require

. Do you have a exception-type-specific try-catch logic? Limit the

try

scope and you’ll know what failed on your abstraction level. Or use return values instead of data-carrying exceptions. Do you want the exception to explain the error? Let the exception message and stacktrace do it for you.

The exception type is not that important, a generic

Exception

would do. It's just that

IllegalArgumentException

and

IlegalStateException

are not appropriate, just like

IOException

isn't.