//以下两种方法是在继承Door的同时

　　//MyDoor会出现红色底线

　　//通过Add unimplemented methods

　　//创建的，这也就是体现了抽象类中的抽象方法

　　//当子类要继承是必须重写-//the following two methods are inherited and feel at the same time

The bottom line// MyDoor will appear red

//by the Add unimplemented methods

//created, which is reflected the abstract method in an abstract class

//when a subclass is must be rewritten to inherit