在控制台应用程序中定义年类、年类的派生类年月类、年月类的派生类年月日类，三个类中均有显示方法。在主程序中声明一个通用的静态显示方法，该方法接受一个年类对象的应用参数，并在Main方法中调用这个通用显示方法，以实现显示年或年月或年月日。-Year class, the class of the years derived class years, years like a derived class date, three classes have display method defined in the console application. A general static display method declared in the main program, the method to accept the parameters of a year class object in the Main method calls this a universal display method, to display year or the year, month or date.