Richter transformational grammar

Original link: http://www.cnblogs.com/zwj-199306231519/p/11027038.html

1. Richter transformational grammar:

　　1) subclass can be assigned to the parent class: If there is a need to place a parent class as an argument, we can give instead of a subclass

　　Person p = new Student();

　　2). If the parent class is loaded with subclass object, then this can be converted to the parent subclass object

　　Student stu = (Student)p

And as 2.is

　　1) is: indicates the type of conversion, if the conversion can be successful, returns true, otherwise returns false;

　　　　Person p = new Student();

　　　　if (p is Teacher)
　　　　{
　　　　　　Student stu = (Student)p;
　　　　　　stu.StudentPrint();
　　　　}
　　　　else
　　　　{
　　　　　　Console.WriteLine("转换失败");
　　　　}

 　2) as: indicates the type of conversion, if the object can be converted to the corresponding return, otherwise it returns a null;

　　　　Teacher tea = p as Teacher;
　　　　if (tea == null)
　　　　{
　　　　　　Console.WriteLine("转换失败");
　　　　}
　　　　else
　　　　{
　　　　　　tea.TeacherPrint();
　　　　}　　

Reproduced in: https: //www.cnblogs.com/zwj-199306231519/p/11027038.html