When to throw an exception?

Question

I have exceptions created for every condition that my application does not expect. UserNameNotValidException, PasswordNotCorrectException etc.

Answer 1

You may use a little bit generic exceptions for that conditions. For e.g. ArgumentException is meant to be used when anything goes wrong with the parameters to a method (with the exception of ArgumentNullException). Generally you would not need exceptions like LessThanZeroException, NotPrimeNumberException etc. Think of the user of your method. The number of the conditions that she will want to handle specifically is equal to the number of the type of the exceptions that your method needs to throw. This way, you can determine how detailed exceptions you will have.

By the way, always try to provide some ways for users of your libraries to avoid exceptions. TryParse is a good example, it exists so that you don't have to use int.Parse and catch an exception. In your case, you may want to provide some methods to check if user name is valid or password is correct so your users (or you) will not have to do lots of exception handling. This will hopefully result in more readble code and better performance.