The purpose of the ClassFanOutComplexityCheck is to ensure that classes don't get too complex and stay easy to maintain. Some classes are excluded from computation by default (like java.lang.*) because every java dev know about them and they don't increase the maintenance.

I'd like to propose to add the Java Collections too (Map, HashMap, List, ArrayList, etc) too since they're part of the language and every java dev know about them too (similar to the String class for example).

These classes are causing unnecessary class fan out violations on code.

Could you please consider excluding them?

See https://sourceforge.net/p/checkstyle/feature-requests/607/

The idea is to exclude the following which should be considered as part of the language now by all developers and thus shouldn't be counted as part of the class fan out:

        mIgnoredClassNames.add("Class");

        // java.util.*
        mIgnoredClassNames.add("Map");
        mIgnoredClassNames.add("List");
        mIgnoredClassNames.add("HashMap");
        mIgnoredClassNames.add("ArrayList");
        mIgnoredClassNames.add("Locale");