Enum: difference of behaviour between exhaustive switch vs. using default:

[Jean-Noël Rouvignac (ForgeRock)]

Hello amber-dev experts!

I am modernizing our codebase by making it use enhanced / exhaustive
switches.

In several places, I replaced `default: ` by `case
THE_ONLY_UNUSED_ENUM_VALUE:`, except that I am hitting an unexpected
difference in behaviour, at least from my point of view.

I have reduced the code to the following reproducer (tested on the
https://dev.java/playground/), where `main1()` compiles, but `main2()` does
not. And yet, I am under the impression both should be equivalent?

What do you think?
Thanks a lot.



import java.io.IOException;

class Main {
    public enum Action { IGNORE, REJECT }

    public static void main(String[] args) {
        main1();
        main2();
    }

    private static void main1() {
        String s;
        try {
            s = getValue();
        } catch (IOException e) {
            switch (getAction()) {
                case IGNORE:
                    return;
                default:
                    throw new RuntimeException("REJECTED");
            }
        }

        System.out.println(s);
    }

    private static void main2() {
        String s;
        try {
            s = getValue();
        } catch (IOException e) {
            switch (getAction()) {
                case IGNORE:
                    return;
                case REJECT: // <------------------- Fails compilation
                    throw new RuntimeException("REJECTED");
            }
        }

        System.out.println(s); // <------- Main.java:40: error: variable s
might not have been initialized
    }

    static Action getAction() {
        return Action.IGNORE;
    }

    static String getValue() throws IOException {
        return "SUCCESS";
    }
}

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