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