Single Responsibility Principle java6 principle, the substitution principle in style

Single Responsibility Principle: an interface, a class, a method, a class of only the best thing, of course, in a real project, a series of factors, it is difficult to achieve the principle of single responsibility, but it can be done for the interface , methods and classes to try to make

In the replacement principle: where the parent class appears, replace the subclass can run, but not vice versa (ye do not know the specific use, do not understand)