>In Java, there’s no way to know whether a variable is null.

What? What about `foo == null`?

The author means not knowing it at compile-time. The expression you mention must be evaluated at runtime.

In practice, there are plenty of static analysis programs that will give you the same thing at compile time with @NonNull and similar annotations.

Too bad you need external tools anda lot of boilerplate that you must remember to enforce to achieve this, because it's an after thought and not a language feature.

And there's 7-8 different annotations to mark nullability, all slightly different in some detail.

It's a bloody and messy hell.

Sure, language-support would be better indeed, but in practice the often encountered annotations are supported by every tool, and the only relevant setting is whether everything is nullable by default or nothing is.

It's still not enforced by the language itself, so nothing stops a third party library (that you have to integrate) from not using the annotations, and then the unknown nullability exerts a domino effect on your own code, "infecting" it with uncertainty.

Doesn't help you with third party libraries, but across an org applying that rule (and others!) typically ensures some consistency.