Re: [xwiki-devs] Call Fan Out computation algorithm

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 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 >