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1. Prerequisites for Nanjing Social Security to Open CA Certificate Online Service:Printed board烈火丽人The Liskov Substitution Principle (LSP) is one of the basic principles of object-oriented design. The Richter substitution principle says that wherever a base class can appear, subclasses can certainly appear. LSP is the cornerstone of inheritance reuse. Only when derivative classes can replace base classes and the functions of software units are not affected can base classes be truly reused, and derivative classes can also add new behaviors to base classes. The Richter substitution principle is a supplement to the "open-close" principle. The key step to realize the "open-close" principle is abstraction. The inheritance relationship between the base class and the subclass is the concrete realization of abstraction, so the Richter substitution principle is the specification of the concrete steps to realize abstraction. --From BaiduSports system diseases, injuries and their sequelae are unqualified.MyDoSth+=new DoSthh (d1);