C#2008与.NET 3.5 高级程序设计读书笔记(6)--继承和多态

1.基类/派生类的转换规则:

(1)隐式转换:在基类中引用派生类型总是安全的.

Employee employee = new SalesManager();

2.使用C#强制转换运算符进行显示的向下转换

            //隐式转换
            Employee employee = new SalesManager();
            //使用C#强制转换运算符进行显式的向下转换
            SalesManager salesManager = (SalesManager)employee;

(3)关键字as

使用关键字as在运行时检查某个类型是否和另外一个类型兼容

 

            SalesManager salesManager = new SalesManager();
            Employee employee = salesManager as Employee;
            if (employee != null)
            {
                Console.WriteLine("salesManager is a employee");
            }

 (4)关键字is

和关键字as不同,如果类型不兼容,is关键字就返回false而不是null引用.

        static void FireThisPersion(Employee employee)
        {
            if (employee is SalesManager)
            {
            }
        }

 2.超级父类System.Object

在.NET世界中,每一个类都会从System.Object继承,即使没有显示继承改父类,编译器会自动继承Object基类