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When we create an object, we always new an object. Is there any mistake? Technically, there is nothing wrong with new. After all, it is the basic part of C #. The real prisoner is our old friend "change". And how it affects the use of new.If I were to implement a pizza ordering system, I would definitely write the code like this, because this kind of code can be written subconsciously without consuming our brains. However, take a closer look at this code: the purpose of this method is to order pizza. However, the code for ordering pizza also needs knowledge about the production of pizza. This method must know all pizza. Worse still, if the types of pizza are to be expanded or pizza with poor sales volume are to be deleted in the future, then the code for ordering pizza will be modified. It looks very bad and should be revised. Our first step must be to separate the code for producing Pizza from the code for ordering pizza, because you should not let the code for ordering Pizza know the logic for producing pizza, but should hand over the logic for producing Pizza to a special type. In this way, we can cope with future changes-if we want to add or delete pizza, we can directly modify the producer of pizza without affecting the logic of ordering pizza.20世纪80年代，三个怀有热情和梦想的年轻人在高等学府燕京大学的校园内相遇，从此展开了他们长达三十年的友谊和梦想征途。出生于留学世家的孟晓骏渴望站在美国的土地上改变世界，浪漫自由的王阳尽情享受改革开放初期那蓬勃激昂的青春气息，曾两次高考落榜的农村青年成冬青以晓骏为目标努力求学，并收获了美好的爱情。然而三个好友最终只有晓骏获得美国签证，现实和梦想的巨大差距让冬青和王阳倍受打击。State mode and policy mode are like twins. They both encapsulate a series of algorithms or behaviors. Their class diagrams look almost identical, but their intentions are very different, so they are two very different modes. The policy pattern and the state pattern have in common that they both have a context, policies or state classes to which the context delegates the request to execute此后一路上。23