Which @NotNull Java annotation should I use?

Question

I\'m looking to make my code more readable as well as use tooling like IDE code inspection and/or static code analysis (FindBugs and Sonar) to avoid NullPointerExceptions.

Answer 1

I very much like the Checker Framework, which is an implementation of type annotations (JSR-308) which is used to implement defect checkers like a nullness checker. I haven't really tried any others to offer any comparison, but I've been happy with this implementation.

I'm not affiliated with the group that offers the software, but I am a fan.

Four things I like about this system:

1. It has a defect checkers for nullness (@Nullable), but also has ones for immutability and interning (and others). I use the first one (nullness) and I'm trying to get into using the second one (immutability/IGJ). I'm trying out the third one, but I'm not certain about using it long term yet. I'm not convinced of the general usefulness of the other checkers yet, but its nice to know that the framework itself is a system for implementing a variety of additional annotations and checkers.

2. The default setting for nullness checking works well: Non-null except locals (NNEL). Basically this means that by default the checker treats everyhing (instance variables, method parameters, generic types, etc) except local variables as if they have a @NonNull type by default. Per the documentation:

   The NNEL default leads to the smallest number of explicit annotations in your code.

   You can set a different default for a class or for a method if NNEL doesn't work for you.

3. This framework allows you to use with without creating a dependency on the framework by enclosing your annotations in a comment: e.g. /*@Nullable*/. This is nice because you can annotate and check a library or shared code, but still be able to use that library/shared coded in another project that doesn't use the framework. This is a nice feature. I've grown accustom to using it, even though I tend to enable the Checker Framework on all my projects now.

4. The framework has a way to annotate APIs you use that aren't already annotated for nullness by using stub files.