I'm a little confused...

What confuses you?

@Calli "@NonNull @Nullable"

It just tells you that the mehtod is marked up to take in a View that must not be null but can be null etc.. The method itself is marked up like this make(@NonNull @Nullable View view ... )

Its just an informative marker that tells you that the value can't be null. There seems to be an error in that markup for the Snackbar.make(). @NonNull = can't ever be null @Nullable = can be null.

@Gianlu Google dokumentations sure are a mess sometimes.
I once stumbled across a void method that returns if a task was performed successfully. 😂