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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 BaiduOpen flight simulator optionCtrl + Alt + A + Option + A Opens the flight simulator dialog box.860010-1119060300　　在Rosewood镇宁静的外表下，隐藏着不少秘密。三年前，镇上四个最漂亮的女生——Aria（露西·海尔 Lucy Hale 饰），Spencer（特莉安·贝利索里奥 Troian Avery Bellisario 饰），Hanna（艾什莉·本森 Ashley Benson 饰）和Emily（薛·米契尔 Shay Mitchell 饰）的朋友、学校最受欢迎的女生Alison（萨莎·皮特丝 Sasha Pieterse 饰）突然失踪，四人发誓保守秘密但关系却渐行渐远。三年之后，四人收到神秘人A发来的短信，知道她们隐藏了很久的、只有Alison才知道的秘密。以为A就是Alison，然而警察在Alison的后院里找到了她的尸体，神秘的A始终是个谜。四个女生将如何面对这一切变故？英王厉声喝道：白凡，敢如此对皇上说话。老鼠拿着剑挑到一顶黄色的帽子,这时猫拿着剑突然出现,他们两个之间开始了搏斗葫芦浑身一震，紧紧地搂着秦淼，眼泪终于流了下来。