Re: Uninitialized variables, Java example

[bobduff@world.std.com (Robert A Duff)]

In article <Dv1sME.1u4.0.-s@inmet.camb.inmet.com>,
Arra Avakian <arra@inmet.com> wrote:
>The language spec says the following about this subject:
>
>        4.2.3 Setting Local Variables  
>
>         Methods are rigorously checked to be sure that all local variables 
>        (variables declared inside a method) are set before they are 
>        referenced. Using a local variable before it is initialized is a 
>        compile-time error.  

That's not a language spec, IMHO.  That's a vague description that might
be useful to a person learning Java, but it doesn't tell me exactly
which programs are disallowed at compile time.  Is this feature of Java
precisely defined somewhere (other than in the Java implementation(s))?

The last sentence doesn't say which cases are compile-time errors,
despite the fact that they do NOT use uninit vars.  The halting theorem
tells us that there MUST be some such cases.  And understanding which
cases those are is crucial to deciding whether this is a good rule.

Also, note that this rule explicitly applies to local variables of a
method.  It does not apply to global variables, and it does not apply to
components of objects.  If I remember correctly, Java automatically
initializes those to (null, False, zero, whatever), depending on the
type.  But I could be misremembering my Java.

- Bob