Final variable initialization problem with exhaustive switch

[Brian Goetz]

I'm not seeing this fail on JDK 17.

On 11/29/2021 3:04 PM, Dimitris Paltatzidis wrote:
> Consider the case:
>
> enum Parity {ODD, EVEN}
> Parity p = ...
> final int a;
> switch (p) {
>      case Parity.ODD -> a = 1;
>      case Parity.EVEN -> a = 0;
> }
> int b = a + 1; //Compile time error: variable a might not have been
> initialized
>
> The switch is exhaustive, yet we need to add a default case to compile. The
> same behaviour is observed with instance final fields too.
> Without changing the semantics, the code below compiles:
>
> final int a = switch (p) {
>      case Parity.ODD -> 1;
>      case Parity.EVEN -> 0;
> };
> int b = a + 1; //Compiles
>
> How can the compiler prove that the final variable will be initialized only
> in the second case and not in the first too?
>
> Thanks for your time.