里式转换

    class Program
    {
        static void Main(string[] args)
        {
            //1、里氏转换
            /*1)、子类可以赋值给父类:如果有一个地方需要一个父类作为参数，我们可以给一个子类代替。*/
            //Student s = new Student();
            Person p = new Student();//s;

            /*2)、如果父类中装的是子类对象，那么可以讲这个父类强转为子类对象。*/
            //is的用法
            if (p is Student)
            {
                Student ss = (Student)p;
                ss.StudentSayHello();
            }
            else
            {
                Console.WriteLine("转换失败");
            }
            Console.ReadKey();
            //as的用法
            Student t = p as Student;
            t.StudentSayHello();
            Console.ReadKey();
        }
    }

    public class Person
    {
        public void PersonSayHello()
        {
            Console.WriteLine("我是父类");
        }
    }

    public class Student : Person
    {
        public void StudentSayHello()
        {
            Console.WriteLine("我是学生");
        }
    }

    public class Teacher : Person
    {
        public void TeacherSayHello()
        {
            Console.WriteLine("我是老师");
        }
    }