nextAfter is probably also including the denormals (an additional 2^23 values near 0).

Yep:

  1,056,964,609 - 1,065,353,216 = 8388607 = 2^23 - 1

because the denormal that is all-zero is already present.

And the author explicitly stated he was excluding the denormals.

Offtopic, but:

Is this not just shorthand, but an actual legitimate Java program these days?

I was curious as well, so I took it for a spin[0]. In short, no. A static initializer still needs to be wrapped in a class that contains a main method.

    public class Main {
    
      static {
        System.out.println("Hello world");
      }
    
      public static void main(String[] args) {}
    }

[0]: https://repl.it/GDZG/1

A bit of both. Code still belongs in a class, not pictured here. `static` blocks are executed when the class is loaded and are usually used to fill `static final` members. In a toy example like this it's shorter than writing the `main()` incantation.

It might depend on the precise representation. This has become increasingly standardized lately which is why those numbers are really close and not wildly off.