Exhaustiveness

When a switch is used as an expression it needs to be exhaustive.

void main() {
String name = "bob";

boolean cool = switch (name) {
    case "bob" -> false;
    default -> true;
};

IO.println(cool);
}

If you attempt to make a non-exhaustive switch expression, Java will not let you.

void main() {
String name = "bob";

boolean cool = switch (name) {
    case "bob" -> false;
};

IO.println(cool);
}

Unlike in a switch statement, covering all the enum values in a switch expression is enough for that switch to be considered exhaustive. You do not need an extra default or case null¹.

enum Species {
    ALIEN,
    PREDATOR,
    HUMAN
}

void main() {
    Species species = Species.valueOf(
        IO.readln("What do you see? ").toUpperCase()
    );
    String message = switch (species) {
        case ALIEN -> "Run";
        case PREDATOR -> "Fight Back";
        case HUMAN -> "RUN"
    };

    IO.println(message);
}