Hi Kjetil,
public static final boolean debug
is a constant. This constant will evaluated at compile time. To test this
one can decompile code that uses this. JAD is a good decompiler. That means
a boolean constant used in a if construct means compile time evaluation.
Depending on the value one branch will be included in bytecode and the
other not.
Classloading can not bring "missing" bytecode back.
Regards,
Stephan
Kjetil Valstadsve <[EMAIL PROTECTED]> am 19.12.2001 16:51:02
An: [EMAIL PROTECTED]
Kopie (Blindkopie: Stephan Frind/Duesseldorf/Gebit)
:
Thema Re: [JBoss-dev] use of if(debug) log.debug
:
> Andrew Scherpbier wrote:
>
> Using compile time constants to turn diagnostics on and off is something
> of a hot point for me - it can make it very difficult to diagnose
> problems in typical production environments in the companies I work with
> (rebuilding the app. server to get diagnostics is a no-happen)
I have the same problem with compile-time constants. So I use load-time
constants! I think it works great.
To explain: I have a class Foo (names have been changed etc.) with a
public static final boolean debug. It is set to true or false in the
static initializer, ie. at load-time, by looking up a System property or
something. Note that is final, meaning that a good JIT can remove dead
code after loading. (Or at least hotspot does, from what I can tell after
some profiling.)
Foo has lots of static methods that delegate to my logger object. All
these static methods have an outer if statement around the entire method
body, that checks the debug value before processing the input. Ie. I have:
public static void println(String msg) {
if (debug) {
....
}
}
Then, to log, I say:
Foo.println(my.expensive(statement));
Since the println method, being static, is entirely dependent on Foo.debug,
it will not called if it is false. However, the argument is still
expensive to create, it _will_ still be executed, and I _don't_ want to
write this all the time:
if (Foo.debug) Foo.println(...);
This would obliterate the entire call nicely, but it's not fun, is it, and
I'm bound to miss a few. But, since all the log statements I want compiled
away are static calls to Foo (make it abstract, is my advice), I can simply
add an ant task to my production build target that begins like:
<replace token="Foo.print" value="if (Foo.debug) Foo.print"
... before the javac task. After that, I can still take a lump of
in-production quality byte code, and start it up with the -Dfoo=true
property, upon which all my logging statements are turned back on.
Would this address any of your concerns?
Kjetil
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