Why program is not allowing to initialize the static final variable?

Question

I came across the Java code below which looks good at first but never compiles :

public class UnwelcomeGuest {

    public static final long GUEST_USER_ID = -1;
    private static final long USER_ID;

    static {
        try {
            USER_ID = getUserIdFromEnvironment();
        } catch (IdUnavailableException e) {
            USER_ID = GUEST_USER_ID;
            System.out.println("Logging in as guest");
        }
    }

    private static long getUserIdFromEnvironment()
            throws IdUnavailableException {
        throw new IdUnavailableException(); // Simulate an error
    }

    public static void main(String[] args) {
        System.out.println("User ID: " + USER_ID);
    }
}//Class ends here


//User defined Exception
class IdUnavailableException extends Exception {

     IdUnavailableException() { }

}//Class ends here

Below is the error message which comes in the IDE : variable USER_ID might already have been assigned.

Is there any problem with the value assignment to the static final variable ?

Answer 1

Final variables allow at most one assignment in the constructor or the initializer block. The reason this does not compile is that Java code analyzer sees two assignments to USER_ID in branches that do not look mutually exclusive to it.

Working around this problem is simple:

static {
    long theId;
    try {
        theId = getUserIdFromEnvironment();
    } catch (IdUnavailableException e) {
        theId = GUEST_USER_ID;
        System.out.println("Logging in as guest");
    }
    USER_ID = theId;
}