Question about type pattern inside record pattern

[Red IO]

This definitely looks wrong. Shouldn't a switch with a pattern matching
against null either have a case or throw an exception?
This behavior seems to differs between a top level match and nested record
pattern match. This doesn't seem intuitive nor intentional to me. Even if
we say that a _ match arm also includes null which to some extent makes
sense because even if it is null it at least has to be of type Number. I
would expect a Double _ arm above to not be taken as the information rather
it's any subtype of Number is not there.
But last but not least the Object _ shouldn't compile because it is in fact
unreachable.

Overall a rather quirky edge case of record pattern matching.
Again I would expect an exception to be thrown because that's the behavior
defined in the switch expression.

Great regards
RedIODev

On Fri, Feb 6, 2026, 17:00 Cay Horstmann <cay.horstmann at gmail.com> wrote:

> Consider this program:
>
> record Amount(Number n) {}
>
> Integer value(Amount p) {
>      return switch (p) {
>          case Amount(Integer value) -> value;
>          case Amount(Number _) -> -1;
>          case Amount(Object _) -> -2;
>      };
> }
>
> void main() {
>      IO.println(value(new Amount(null)));
> }
>
> It prints -1.
>
> I have two questions:
>
> 1. Why does it compile? The case Amount(Object _) does not seem to
> reachable.
> 2. Why does null match case Amount(Number _) and not one of the other?
>
> I tried applying JLS (for Java 25) §14.30, §15.28, and §14.11 but could
> not figure it out. Where should I look?
>
> Thanks,
>
> Cay
>
> --
>
> Cay S. Horstmann | https://horstmann.com
>
>
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