Re: Uninitialized variables, Java example

[arra@inmet.com (Arra Avakian)]

I find it interesting that the Sun Java compiler warns about POSSIBLE use of
uninitialized variables with a message like

        Variable foo may not have been initialized

This message appears even though all dynamic paths to the use of foo do in 
fact initialize the variable. For example, a switch statement without a 
default initializes the variable in all branches, but the compiler knows that 
if the default case occurs, the variable is not initialized. The programmer 
"knows" that the default case can not occur, but the compiler forces the 
programmer to initialize foo to get a successful compile, i.e. it will not 
produce the class file without the "unnecessary" initialization.

Some may view this as extreme, since the compiler can not know statically the 
"truth", and forces a statically knowable work-around on the programmer. Is 
this what some people want for Ada 0x? It seems to me to be a tradeoff between 
efficiency (an unnecessary initialization to satisfy the compiler) and safety 
(the compiler is then allowed to detect statically known cases of 
uninitialized variables, i.e. true programming errors.) The programmer must 
analyze the error message and determine whether it is a programming error to 
be fixed, or a case where an "unnecessary" initialization is needed to quiet 
the compiler.

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.  


Arra Avakian
Intermetrics, Inc.
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arra@inmet.com