Configuring annotations in IntelliJ

To gain compile-time nullability checks in IntelliJ follow this quick guide.

To cut down on the number of problems with NullPointerException nullability annotations are heavily used in Recaf's source. With an IDE's support this can catch problems early on.

Explicit nulls passed to method with parameters marked as Nonnull display warnings.

The Nullable annotation isn't needed here, but is useful for documentation purposes. Even without it IntelliJ will warn that the call to the call to splitNewlineSkipEmpty may be taking in a possible null value.

You'll want to make it so that @Nonnull and @Nullable are recognized by IntelliJ. The settings you'll want to change are highlighted here.

This first image makes it so that method overrides/implementations with missing annotations from their parent types show a warning, and allow you to automatically insert these missing annotations. Plus, when you use IntelliJ to automatically implement methods from a abstract class or interface these interfaces will be copied for you.

This second image makes it so the Jakarta Nonnull and Nullable annotations used in the project are recognized by IntelliJ. This allows us to have a basic system for tracking nullability. You'll also want to ensure the default annotation is the Jakarta one after you add it to the list.

Methods that can return null or parameters that may be null should be marked with Nullable. Any time one of these is used, it will warn you when you do not have an appropriate null check on a value.

Similarly, any method/parameter that should not be null should be marked with Nonnull. We use a plugin that generates null checks at compile time, so the contract for non-null is enforced at runtime.