Should a retrieval method return 'null' or throw an exception when it can't produce the return value? [closed]

Answer 1

If the method returns a collection, then return an empty collection (like sayed above). But please not Collections.EMPTY_LIST or such! (in case of Java)

If the method retrives a single object, then You have some options.

1. If the method should always find the result and it's a real exception case not to find the object, then you should throw an exception (in Java: please an unchecked Exception)
2. (Java only) If you can tolerate that the method throws a checked exception, throw a project specific ObjectNotFoundException or the like. In this case the compiler says you if you forget to handle the exception. (This is my preferred handling of not found things in Java.)
3. If you say it's really ok, if the object is not found and your Method name is like findBookForAuthorOrReturnNull(..), then you can return null. In this case it is strongly recomminded to use some sort of static check or compiler check, wich prevents dereferencing of the result without a null check. In case of Java it can be eg. FindBugs (see DefaultAnnotation at http://findbugs.sourceforge.net/manual/annotations.html) or IntelliJ-Checking.

Be careful, if you decide to return a null. If you are not the only programmer in project you will get NullPointerExceptions (in Java or whatever in other Languages) at run time! So don't return nulls which are not checked at compile time.