10 Sep
2012
10 Sep
'12
7:52 p.m.
On Mon, Sep 10, 2012 at 7:23 PM, Vincent Massol <vincent(a)massol.net> wrote:
Hi Jerome,
Hey I didn't really want to awaken this topic again ;) I already gave my
opinion on the other thread (I still need to reply to Sergiu's last mail
BTW). I just wanted to explain how checkstyle computes the class fan out
and share that since it was useful for me to fix one class fan out issue I
had.
See below.
On Sep 10, 2012, at 7:06 PM, Jerome Velociter <jerome(a)velociter.fr> wrote:
I completely agree about that last point. Specific exclusion of specific
rules (not only ClassFanOut) would be a really better practice than
excluding the whole file.
About ClassFanOut in particular, there is something that is not properly
taken into account when measuring this metrics. There is well know or
simple classes, that could be used and depends upon, and other no so well
know one, that will really increase the readability of the code, and its
independence. Since the computation of ClassFanOut metric does not take
that into account, it sometimes consider some code as badly design while it
is simply using many small simple classes, which is usually not a bad
design.
Excluding some custom well-know classes from the count could helps
mitigating that. IMO, classes representing References, Context, Collections
(as you suggest), and ... well this is where we need an expert. So this is
really not an easy topic and it will be very difficult to find a correct
number, and correct exclusions.
One last remark, when you leave a class with a ClassFanOut equal to the
limit, there is a lot of chance that a simple bug fix could exceed the
limit and cause lot of trouble while having not necessarily cause a worse
situation than before. IMO, the priority is to fix the issue first, and to
improve the code quality later if time is available. Of course, it depends
on the details, and it's not always true. This is generally why I am
always skeptical using these metrics as constraints. Could not the dev team
be more responsible without constraint (but keeping an eyes on metrics of
course !) ?
This is just my own ideas and I am not expert ;)
On 09/10/2012 06:17 PM, Vincent Massol wrote:
> With this finding writing a macro requires between 5 to 6 Classes:
>
> * DefaultContentDescriptor (only if there's content)
> * XXXMacroParameters
> * List
> * Block
> * MacroTransformationContext
> * MacroExecutionException
>
> Our checkstyle config fails above 20 which means Macro classes have
about 14
additional deps on external classes allowed before they break.
Which should normally be more than enough.
>
> My understanding is that reading the code is hard when there are too
many
references to external classes (incidentally it also makes the code
more brittle as there are more chances it'll break due to an issue with the
used classes). Apparently 7 (+/- 2) is the magic number (see
http://en.wikipedia.org/wiki/The_Magical_Number_Seven,_Plus_or_Minus_Two)
So this shows "20" was magic to begin with. How do you go from 7 +/-2 to
20 ?
Would be interesting to ask the checkstyle guy why they picked this value.
My guess is that they used something like 7 + standard java classes.
I find it a bit specious to apply the theories
exposed in the article to
a program's class external classes without a pinch of
salt. It would be
saying their is a good match between the notion of "object" as described in
the experiments (so in the sense of an item of input, like a word in a list
of words or a sound in a list of distinct sounds) and the notion of a class
of objects in programming.
Not my choice. All references to Class Fan Out say that the default value
should be around 7 and quote this article.
What I'm trying to say is that maybe we
should rather accept the fact 20
is magic to begin with and try and figure out if
this works for us and
tweak it if necessary
I've already answered to this. I'm -1 to change what we have in a random
manner with another random value. What I said is to show me some code and
we can discuss on this basis. Sergiu has pointed out some code but I didn't
get the time to look at it yet. I need to do that and if the outcome is
that we can't make it pass with a good design then we can discuss either
make an exclude for this special case or decide that the case is generic.
- rather than trying to rationalize it with
bridges to psychology thesis
that are far from obvious (not that the thesis
don't apply to programming ;
just that the impendance of an "input" or "unit of thought" is IMHO
not so
easy to match with programming concepts without making blind guesses).
Maybe I'm wrong, it's just I find this kind of rationalization somehow
naïve.
Hope that made sense.
Well, there's not much point in saying that something is wrong if you
don't provide an alternative… If you're going against the established
standard then you better be an expert in the domain. I know I'm not. But
even if we agree that the study has no meaning, it doesn't change the fact
that to change what we have we need to have a good reason to do so and we
need to define the new value while still ensuring that the check still
makes sense.
Also, a note about ignoring classes that
"don't require effort to
understand" (or to look at their source
code), they would probably span
more than "standard Java classes" like Collections, no ?
Yep, I mentioned that in my mail (I said "Collection" classes).
For example, what about common-langs
(StringUtils, etc.) ?
I wouldn't put those, not everyone know them and again static method calls
**don't count** for the class fan out …
Anyway ATM I don't agree about starting to ignore classes without at least
one good example where we have to do so to make the fan out check pass.
I write new code almost everyday and it's seldom that I have issues with
class fan out and most of the time when it happens it's because I've been
lazy and I can fix the issue in a few minutes. This makes me think that the
current value is good. As I've already said in the other thread for me it
would be much better to agree to do a checkstyle exclude of *only* the
ClassFanOut check for a given class rather than change the default for
everyone.
Thanks
-Vincent
--
Denis Gervalle
SOFTEC sa - CEO
eGuilde sarl - CTO
Jerome
>
> So IMO we have 2 options that could make sense (ie we can rationalize
them):
>
> * Keep this default value of 20 total which includes some standard JDK
classes. 14 deps for Macro should be enough, even if we count, say 2-4 more
for standard Java classes like Collection classes.That still gives us about
10 deps for additional XWiki classes.
> * Decide to exclude some classes that are
basically part of the Java
language (such as Collection classes) since they
don't increase the reading
complexity of the code since everyone knows what they do and we don't need
to look their source code or doc to understand them. However, if we do so
then we should reduce the allowed Fan out to 7 (+/- 2) so let's say to 9.
So that gives us only 9 deps for XWiki classes, compared to about 15 ATM...
>
> IMO the second option is much harder for us than the first one and
that's
why I'd keep the first option...
>
> BTW the reason I wrote about all this is because I made a change to the
ChartMacro and the fan out became 21… In the end I refactored the code and
got a slightly better design (and fixed a bug at the same time…).
>
> Thanks
> -Vincent
>
>
> On Sep 10, 2012, at 4:59 PM, Vincent Massol <vincent(a)massol.net> wrote:
>
>> Hi devs,
>>
>> I wanted to understand how Checkstyle computes the Class Fan out so I
debugged it.
>>
>> Here are my findings:
>>
>> * Some classes are excluded by default:
>>
>> mIgnoredClassNames.add("boolean");
>> mIgnoredClassNames.add("byte");
>> mIgnoredClassNames.add("char");
>> mIgnoredClassNames.add("double");
>> mIgnoredClassNames.add("float");
>> mIgnoredClassNames.add("int");
>> mIgnoredClassNames.add("long");
>> mIgnoredClassNames.add("short");
>> mIgnoredClassNames.add("void");
>> mIgnoredClassNames.add("Boolean");
>> mIgnoredClassNames.add("Byte");
>> mIgnoredClassNames.add("Character");
>> mIgnoredClassNames.add("Double");
>> mIgnoredClassNames.add("Float");
>> mIgnoredClassNames.add("Integer");
>> mIgnoredClassNames.add("Long");
>> mIgnoredClassNames.add("Object");
>> mIgnoredClassNames.add("Short");
>> mIgnoredClassNames.add("String");
>> mIgnoredClassNames.add("StringBuffer");
>> mIgnoredClassNames.add("Void");
>> mIgnoredClassNames.add("ArrayIndexOutOfBoundsException");
>> mIgnoredClassNames.add("Exception");
>> mIgnoredClassNames.add("RuntimeException");
>> mIgnoredClassNames.add("IllegalArgumentException");
>> mIgnoredClassNames.add("IllegalStateException");
>> mIgnoredClassNames.add("IndexOutOfBoundsException");
>> mIgnoredClassNames.add("NullPointerException");
>> mIgnoredClassNames.add("Throwable");
>> mIgnoredClassNames.add("SecurityException");
>> mIgnoredClassNames.add("UnsupportedOperationException");
>>
>> * All classes in java.lang.* are excluded too
>> * Annotation classes are not counted
>> * Classes in the same package are counted (they won't appear in import
since it's in the same package so don't count imports to get class fan out)
>> * Static method calls are not counted. So
for example StringUtils from
Commons Lang never counts for class Fan out
>> * Enums are not counted (no new XXX()
done. That's why static method
calls are not counted too BTW)
>> * Classes used in class extend or
implement are not counted too.
>>
>> Hope it helps
>> -Vincent
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