Question

I keep running into slight variations of a problem in Java and it’s starting to get to me, and I can’t really think of a proper way to get around it.

I have an object property that is final, but dynamic. That is, I want the value to be constant once assigned, but the value can be different each runtime. So I declare the class level variable at the beginning of the class – say private final FILE_NAME;. Then, in the constructor, I assign it a value – say FILE_NAME = buildFileName();

The problem begins when I have code in the buildFileName() method that throws an exception. So I try something like this in the constructor:

try{
   FILE_NAME = buildFileName();
}
catch(Exception e){
   ...
   System.exit(1);
}

Now I have an error – “The blank final field FILE_NAME may not have been initialized.” This is where I start to get slightly annoyed at Java’s strict compiler. I know that this won’t be a problem because if it gets to the catch the program will exit… But the compiler doesn’t know that and so doesn’t allow this code. If I try to add a dummy assignment to the catch, I get – “The final field FILE_NAME may already have been assigned.” I clearly can’t assign a default value before the try-catch because I can only assign to it once.

Any ideas…?

Answer 1

On second thought, I think I just came up with a solution! – use an intermediate variable.

String fileName = null;
try{
   fileName = buildFileName();
}
catch(Exception e){
   ...
   System.exit(1);
}
FILE_NAME = fileName;

Don’t know why it took me so long to think of this…