try-with-resources and null resource

[Maurizio Cimadamore]

>> Javac will warn you about this situation.
> Why ? It's a fair code.
> And adding a new warning has a cost. If there is too much
> not-that-useful warnings,
> users will don't care about them or worst deactivate them all.
> If there is a warning, what is the way to fix it ? Introduce a
> t.getClass() ?
>
> try(Transaction t = Transactions.getTransaction()) {
>      t.getClass(); // remove that stupid javac warning
> }
>
> That's exactly what I'm proposing :)
>
Adding a warning has a cost, right - but this particular kind of warning 
can be activated on-demand using -Xlint:twr (and it's disabled by 
default). When do you say that the above code is fair, do you mean that 
it is a legal Java program or that it can actually achieve something 
good? I think the only case in which the above program is interesting is 
if Transaction.getTransactions() has some hidden side-effects. Otherwise 
the whole thing looks like a no-op (modulo Exceptions being thrown at 
runtime).

We currently have some similar warnings in the following case:

switch (xyz) {
case 1: //do something here then fall-thorugh
case 2: //do another thing
}


Which, to some extent, is another fair program... but I think that both 
programs (the one with unused twr variable and the one with 
fall-through) are somewhat suspicious enough to merit a 'style' warning.

Moreover, this kind of warnings can be suppressed with the usual scheme 
- just add @SuppressWarnings("twr") to the enclosing method decl, and 
the warning will go away.

Maurizio