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POCould a final variable be reassigned in catch, even if assignment is last operation in try?
 

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  1. POCould a final variable be reassigned in catch, even if assignment is last operation in try?
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    <p>I am quite convinced that here</p> <pre><code>final int i; try { i = calculateIndex(); } catch (Exception e) { i = 1; } </code></pre> <p><code>i</code> cannot possibly have already been assigned if control reaches the catch-block. However, Java compiler disagrees and claims <code>the final local variable i may already have been assigned</code>.</p> <p>Is there still some subtlety I am missing here, or is this just a weakness of the model used by the Java Language Specification to identify potential reassignments? My main worry are things like <code>Thread.stop()</code>, which may result in an exception being thrown "out of thin air," but I still don't see how it could be thrown after the assignment, which is apparently the very last action within the try-block.</p> <p>The idiom above, if allowed, would make many of my methods simpler. Note that this use case has first-class support in languages, such as Scala, which consistently employ the <em>Maybe</em> monad:</p> <pre><code>final int i = calculateIndex().getOrElse(1); </code></pre> <p>I think this use case serves as a quite good motivation to allow that one special case where <code>i</code> is <em>definitely unassigned</em> within the catch-block.</p> <h2>UPDATE</h2> <p>After some thought I am even more certain that this is just a weakness of the JLS model: if I declare the axiom "in the presented example, <code>i</code> is definitely unassigned when control reaches the catch-block", it will not conflict with any other axiom or theorem. The compiler will not allow any reading of <code>i</code> before it is assigned in the catch-block, so the fact whether <code>i</code> has been assigned to or not cannot be observed.</p>
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    1. COIf this *were* valid, then adding subsequent statements in the try block, completely unrelated to i, could cause a compile error in the catch block on the assignment to i. I would find that surprising.
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      1. USAndy Thomas
    2. CO@AndyThomas I'd find it quite intuitive that `i` may have been assigned if there are more statements following the assignment.
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      1. USMarko Topolnik
    3. COIf you are looking for a Scala-like construct you cal always use Guava's `Optional`.
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