try-catch and final variables [duplicate]

Question

I have a very silly question for you :)

For example, I have following code snippet:

class MyClass {

    public static void main (String[] args) {

        final String status;

        try {
            method1();
            method2();
            method3();
            status = "OK";
        } catch (Exception e) {
            status = "BAD"; // <-- why compiler complains about this line??
        }

    }

    public static void method1() throws Exception {
        // ...
    }

    public static void method2() throws Exception {
        // ...
    }

    public static void method3() throws Exception {
        // ...
    }

}

The question is inside: why compiler complains about this line?

IntelliJ IDEA says, that Variable 'status' might already have been assigned to.

But, as I can see, we don't ever reach line (where we set status = "OK") in case of exceptional situation. So the status variable will be BAD and everything should be ok. And if we don't have any exception, then we get OK. And we will set this variable only ONCE a time.

Any thoughts about this?

Thanks for your help!

compiler is not that smart, and if you are declaring that method could throw an exception compiler wont be struggling to check it, so for the sake of simplicity it does not allow such things to happen — Toumash
– Toumash, Commented Jun 29, 2015 at 18:47

rgettman · Accepted Answer · 2015-06-29 18:47:39Z

12

The Java compiler doesn't see what you and I see -- that either status gets set to "OK" or it gets set to "BAD". It assumes that status can be set and an exception is thrown, in which case it gets assigned twice, and the compiler generates an error.

To workaround this, assign a temporary variable for the try-catch block, and assign the final variable once afterwards.

final String status;
String temp;

try {
    method1();
    method2();
    method3();
    temp = "OK";
} catch (Exception e) {
    temp = "BAD";
}

status = temp;

answered Jun 29, 2015 at 18:47

rgettman

179k30 gold badges282 silver badges365 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Jigar Joshi Over a year ago

I think it is still valid error, what if this thread gets interrupted and throws InterruptedException right after assignment

Sotirios Delimanolis Over a year ago

@JigarJoshi It can't throw InterruptedException (maybe something else, but not that, and probably not in this code).

Jigar Joshi Over a year ago

if this was in separate thread and that got called on interrupt()

Sotirios Delimanolis Over a year ago

@JigarJoshi Then the interrupt flag would be set on the Thread. An InterruptedException will only happen if the thread is blocked on IO (or something similar: locks, etc.).

Vince · Accepted Answer · 2015-06-29 18:58:29Z

2

What if the code that caused the exception occured after status = "OK"? The reason you get the error seems pretty obvious.

Take this for example:

final String status;

try {
    status = "OK":
    causeException();
}catch(Exception e) {
    status = "BAD";
}

void causeException() throws Exception() {
    throw new Exception();
}

This would result in reassigning the variable, which is why you get an error.

edited Jun 29, 2015 at 18:58

answered Jun 29, 2015 at 18:47

Vince

15.2k8 gold badges44 silver badges92 bronze badges

2 Comments

swinkler Over a year ago

The variable is final. Reassigning is forbidden.

Vince Over a year ago

@swinkler That's the point I'm getting across. The error occurs because the code shown above is possible. Man, what's up with StackOverflow now-a-days..

Collectives™ on Stack Overflow

try-catch and final variables [duplicate]

2 Answers 2

4 Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

2 Comments

Linked

Related