三三理论

"From then on, the piglet was free from the interference of wolves and lived a happy life."The yellow ticket vending machine shown above is the most versatile. It can be used to buy Manaka, one-day subway tickets, single subway tickets and monthly subway tickets. If it is too troublesome, just identify it when you need to buy tickets.那六胞胎在完全新作剧场版中回来了！This case should be written here. It's not very comfortable.就在这时，张三丰摇摇头，说道：可惜他非要跑来和我比武。……越王宫里早已是一片忙碌，越王尹旭坐在屋子中间。The principle of opening and closing means opening to expansion and closing to modification. When the program needs to be expanded, the original code cannot be modified, but the original code should be expanded to achieve a hot plug effect. Therefore, a summary of one sentence is: in order to make the program scalable, easy to maintain and upgrade. To achieve this effect, we need to use interfaces and abstract classes, etc. We will mention this point in the later specific design.