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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 Baidu　　文洁的妈妈为了照顾女儿也硬是挤了进来，于是，两个老太太睡进了主卧，躺在了一张大床上，开始了斗智、斗勇、斗法、相互较量，小吵大闹，战事不断，夫妻之间，婆媳之间，母女之间，母子之间，父女之间，以及两个老太之间，矛盾重重，争吵撕扯，搅成了一锅滚烫的热粥。Class Program外层空间的不明飞行物体将降落地球，专家们正在搜寻飞碟的降落地点。此时，一名电力公司的电线工人李察德瑞佛斯，在户外检查电力问题时， 竟发觉自己受到天空中异光的包围，从此他的心中就不停的出现怪异的景像、与5个奇怪的音符，为了解开这个不可思议的谜 ，他像着了魔一样，亲自与外星人作了第一次面对面的接触，并展开了一段外层空间之旅。Knowing在整理父亲的遗物时，宁文源发现了一个放有书信、半块犀角佩、还有一幅双龙绘制图的秘藏匣子。在大家的努力下，双龙的秘密解开了。