About Question enthuware.ocpjp.v21.2.3725 :

[giginar]

A ac = new C();
if (ac instanceof B b1) {
...
}

- ac → at runtime this is a C object.
- instanceof B → evaluates to true because C is a subclass of B.
- If the test is true, the variable b1 is created and bound to the same object that ac is pointing to, but typed as B.

Hello, is this what happens here?

[admin]

Yes, that is correct.

The benefit of getting the variable b1 typed to B is that now you can call methods defined in B on that reference without casting the original reference ac. i.e. instead of doing ((B) ac).b(), you can just do b1.b().