Question

Let say you have a method that checks if the argument (Answer) is correct and check if the question already have answers in the list that is also correct:

public void addAnswer(Answer answer) {
    if (answer.isCorrect()) {
        ...
    }
}

However, I only want one answer to be correct in the list. I have multiple options. I could throw an exception, I could ignore it, I could return some boolean value from the addAnswer that tells me if the operation was ok or not. How are you supposed to think in such scenarios?

Answer 1

This entirely depends on what you want to achieve. Should the caller of your method already have made sure that it doesn’t add two correct answers? Is it a sign of a programming error if that happens? Then throw an exception, but definitely an unchecked exception.

If your method’s purpose is to relieve the caller from enforcing the one-true-answer invariant (I doubt that, though), then you can just arrange to signal via a boolean return value, which makes it only an optional information channel for the caller.

If there is no way to know in advance whether there are other correct answers—for example, the answers are added concurrently from several threads or even processes (via a database)—then it would be meaningful to throw a checked exception.

Bottom line: there is no one-size-fits-all best practice, but there is a best practice for every scenario you want to accomplish.