Constant expression required error in switch statement with strings

Question

I get a JSON response which roughly looks like this.

{
  "status": "success",
  "data": [
    {
      ....
    }
  ]
}

The status field can have two values: success or fail.

So in my code, I have the following enum.

private enum Status {
    SUCCESS("success", 0),
    FAIL("fail", 1);

    private String stringValue;
    private int intValue;
    private Status(String toString, int value) {
        stringValue = toString;
        intValue = value;
    }

    @Override
    public String toString() {
        return stringValue;
    }
}

What I want to do is in a switch statement, I need to check for the status value and execute code in each condition.

String status = jsonObj.getString("status");

switch (status) {
    case Status.SUCCESS.toString():
        Log.d(LOG_TAG, "Response is successful!");
    case Status.FAIL.toString():
        Log.d(LOG_TAG, "Response failed :(");
    default:
        return;
}

But I get the Constant expression required error at each case.

I checked the value returned by Status.SUCCESS.toString() and Status.FAIL.toString() which indeed return strings.

Any idea why this error still occur?

Do not forget the `break`. `switch(Status.fromValue(status)) { case Success:` — Joop Eggen, Aug 10 '15 at 09:21
I didn't downvote, but I guess you got that response because a Java switch statement is a basic language feature, and information is readily available via Google. — Andrew Fielden, Aug 10 '15 at 09:25
Why wouldn't you simply write `case "success":` and `case "failure":`? — Dawood ibn Kareem, Aug 10 '15 at 09:29
@DavidWallace: I suppose doing that would mean typing "success" in more than one place, breaking https://en.wikipedia.org/wiki/Don%27t_repeat_yourself — Bathsheba, Aug 10 '15 at 09:30
Yes, but the alternative is to use the `valueOf` method, and `switch` on an `Enum` then; which is problematic because of the exception that it throws if the `String` is wrong. — Dawood ibn Kareem, Aug 10 '15 at 09:38
@Bathsheba Sorry, I didn't mean to change that AFTER you replied to it. — Dawood ibn Kareem, Aug 10 '15 at 09:40

score 33 · Accepted Answer · answered Aug 10 '15 at 09:20

33

case statements have to be compile-time evaluable.

Something like Status.SUCCESS.toString() doesn't satisfy that. A string literal, on the other hand, does.

The obvious fix is to use an an if block.

answered Aug 10 '15 at 09:20

Bathsheba

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I though the same. using if-else will suffice – Murtaza Khursheed Hussain Aug 10 '15 at 09:25
1

Thank you. That works! `if` statements are not the most elegant thing but well, what to do. Thanks again. – Isuru Aug 10 '15 at 10:06
.....but why tho? – Philip Rego Mar 04 '18 at 01:01

Constant expression required error in switch statement with strings

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