Exhaustiveness

Switches are considered exhaustive if they have a case label for every possible value of the type of thing they are switching over.

This is important if you try to return from a function within a switch. Since you need to return a value from every possible branch the function may take, you either need to add an extra return after the switch expression or have an exhaustive switch.

String describe(int number) {
    switch (number) {
        case 1 -> {
            return "loneliest";
        }
        case 2 -> {
            return "loneliest since 1";
        }
    }

    // Since no default, need a return here
    return "Its a number";
}

When you have something like an enum you might think you don't need a default case because you can handle every variant explicitly.¹

enum Bird {
    TURKEY,
    EAGLE,
    WOODPECKER
}

boolean isScary(Bird bird) {
    switch (bird) {
        case TURKEY -> {
            return true;
        }
        case EAGLE -> {
            return true;
        }
        case WOODPECKER -> {
            return false;
        }
    }
}

This is, unfortunately, not the case for a switch statement. You either need a default case or to have an explicit case null to handle the possibility that the enum value is null.²

enum Bird {
    TURKEY,
    EAGLE,
    WOODPECKER
}

boolean isScary(Bird bird) {
    switch (bird) {
        case TURKEY -> {
            return true;
        }
        case EAGLE -> {
            return true;
        }
        case WOODPECKER -> {
            return false;
        }
        // Need to handle the possibility of null
        // or give a "default ->"
        case null -> {
            // You might want to return a value or just crash
            return false;
        }
    }
}