Is the null type a reference type?

[Stephan Herrmann]

Am 28.01.25 um 17:40 schrieb David Alayachew:
> Isn't null a value and not a type?

null is a value, and null type is a type,
  see https://docs.oracle.com/javase/specs/jls/se23/html/jls-4.html#jls-4.1

> 
> On Tue, Jan 28, 2025, 9:25 AM Stephan Herrmann <stephan.herrmann at berlin.de 
> <mailto:stephan.herrmann at berlin.de>> wrote:
> 
>     Assume this (nonsense) program, which is accepted by javac and ecj:
> 
>     public class X {
>              public static void main(String[] args) {
>                      switch (null) {
>                              case null -> System.out.println("Null");
>                              default-> System.out.println("Default");
>                      }
>              }
>     }
> 
>     14.1.1 Switch Blocks requires (T is the type of the selector expression):
>     * If a null literal is associated with the switch block, then T is a
>     reference type.
> 
>     In our case the selector expression has the null type, which can be assigned to
>     any reference type, but it doesn't seem to be a reference type itself.
> 
>       From this I would conclude that the program is illegal.
> 
> 
>     Next, lets remove the default case from the same program. Now compilers
>     complain, here's how javac puts it:
> 
>     X.java:3: error: the switch statement does not cover all possible input values
>                       switch (null) {
>                       ^
>     1 error
> 
>     In previous discussions I learned that requiring a default label may be
>     justified by requirements of future changes, but here for this reasoning to
>     hold
>     the null type would need to acquire new values, which seems very unlikely :).
>     So, if the initial program would get the blessing from JLS, then also this case
>     (without default) deserves a second look.
> 
>     thanks,
>     Stephan
>