The classes in a package [or subsystem] should be closed together against the same kind of changes.
包（或子系统）中的类应当按照同类的变更封闭在一起。
2
A change that affects a closed package [or subsystem] affects all the classes in that package and no other packages.
对一个封闭包(或系统)的变更影响到包里所有的类，但不影响其他任何包。
3
Currently, the commonly used management system is a closed, single subsystem, control theory does not fully describe the controlled object type of statistical control is not specific;