At the risk of being too tangential... null pointer analysis is a very
popular static analysis. Tons of Java based static analysis engines
implement it using any off the shelf techniques: abstract
interpretation (execute a piece of the program which carries an
abstract value saying "this is null" or "this is not null"),
constraint based analyses (draw a bunch of constraints from the
program text which correspond to how pointers propagate), or some
simpler ad hoc techniques.
The basic idea is pretty simple: you look at the set of possible
things a reference could point to, and if it's ever possible that
thing can be null, you treat it that way.
E.g.,
if (..) {
x = thing1
}
else {
y = null;
}
p = x;
would mean, if x can be null, then p can be null (so not here, but
would be if the else assigned to x instead). Then you propagate
changes throughout the program, again and again until you cover
everything. Constraint solving does the same thing, but phrased as a
set of constraints which have to be solved.
Since this is wildly imprecise you need to employ some strategies to refine it.
E.g.,
if (some_very_hard_to_solve_arithmetic_formula_that_is_false_here) {
p = null;
}
Will generally cause static analysis to give the wrong answer (saying
p may be null when in fact it never will be)
--
What this means in the real world is that you can take FindBugs and
run it on your program. Findbugs isn't a complete analysis (it will
sometimes fail to report bugs when they *are* there), but it's very
usable and well tuned for production java code.
Kris
On Mon, Jul 15, 2013 at 12:28 AM, TreKing <[email protected]> wrote:
>
> On Sun, Jul 14, 2013 at 10:08 PM, Kristopher Micinski
> <[email protected]> wrote:
>>
>> I think this is probably a valid thing to consider in most APIs,
>> especially if they're statically linked APIs, where you can actually check.
>
>
> Going off topic a bit, but maybe this will be of interest to the OP as well,
> given the subject matter.
>
> I'm curious as to how you check a statically linked library for conditions
> like this. So if I have some statically linked lib "Foo.jar" with some
> method "public void Bar(SomeObject object)", I can do some check to verify
> that "object" may or may not be null when used in my code?
>
>
> -------------------------------------------------------------------------------------------------
> TreKing - Chicago transit tracking app for Android-powered devices
>
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