Re: Uninitialized "out" parameters

[fjh@mundook.cs.mu.OZ.AU (Fergus Henderson)]

mfeldman@seas.gwu.edu (Michael Feldman) writes:

>I think the essence of the discussion is that in a language
>(like Ada) that does not compel initialization, it is undecidable
>whether a given variable has a well-defined (put there by the program)
>value when it is used.

Yes, but remember that if you're willing to accept approximate
solutions, you can solve undecidable problems.

>>[...] I _think_ that
>>Java does not require initialization at the point of declaration,
>>but instead requires that a variable be initialized along all the
>>execution paths leading to a possible use of a that variable;
>>that would mean that if a variable wasn't used, there would be
>>no requirement to initialize it.
>
>And if it _was_ used? How does the JBC interpreter know whether it's 
>been initialized? Possibly in the interpreter, there's a "this space 
>is uninitialized" flag.

I believe that it is done by static checking, not by run-time
checking.  (I think the static checking is done twice, once by the Java
compiler, and then again by the byte-code verifier in the JBC
interpreter when it first loads the JBC code.)

I don't know how Java handles arrays.  But I'm sure there are lots
of Java experts in comp.lang.java.* that would be happy to answer
such questions.

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Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
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