Exception handling in Java - final

Question

If I am catching exceptions separately then why do I need to make the value final ? for e.g. 1. Is this considered a good practice ? If yes why ? If not why ?

catch(final InputOutputException exception) 
{// do stuff 
}

You do not need to make anything final per se, but final is a compile time check that you do not reassign a variable in this block. Some / many people like to declare anything which should not be reassigned as final. — Matthias, Oct 28 '13 at 08:03

score 1 · Answer 1 · answered Oct 28 '13 at 08:06

In Java anything can be declared final - in this case the declaration is akin to declaring a method parameter final.

The effect of this is that you won't be able to reassign the value

catch(final InputOutputException ex) {
    ex = new InputOutputException();
     // ^ compile time error.
}

In practice I have only really ever seen this used if the Exception needs to be used in an anonymous class, as only final local variables are allowed to be referenced in this way:

} catch (final Exception e) {
    SwingUtilities.invokeLater(new Runnable() {

        @Override
        public void run() {
            myLabel.setText(e.getMessage());
        }
    });
}

Robert Simmons Jr in his book Hardcore Java recommends making everything final. The justification for this is that it turns typos and code bugs into compile time errors.

Assigning a `RuntimeException` to a variable of type `InputOutputException` would also result in a compile time error if the variable wasn't final. — Mark Rotteveel, Oct 28 '13 at 08:08
@MarkRotteveel fair point - have changed the example. It was merely illustrative. — Boris the Spider, Oct 28 '13 at 08:09

score 0 · Answer 2 · answered Oct 28 '13 at 08:05

Making it final makes it clear that you haven't changed the field.

IMHO If your handling code is not so short and simple that the reader cannot work this out easily you have done something wrong.

I think you should make fields final as classes can be long, but methods should be simple enough you can work out whether they are final or not.

Exception handling in Java - final

2 Answers2