在C#中基类引用指向派生对象更好还是派生类自己的对象更好

Question

In the following example i have created three object i want to know what is the difference between three object , how it works and which to use and there is error in third object so , why it shows error?

class Base
{

}
class Derived : Base
{

}
class Main
{
    Base base = new Derived();
    Derived derived = new Derived();
    Derived derived_1 = new Base(); 
}

Answer 1

Inheritance is what you are doing in above code.

Base base = new Derived() :

object of type Base class hold object of Derived class in which when you call method which are overridden in your Derived class, it'll call your derived class method. If the method is not overridden, it will call Base class method

Derived derived = new Derived() :

Derived class object holds object of Derived type in which you call method of it, it'll simply call Derived type method. It'll not check any overridden method.

Derived derived_1 = new Base() :

This will not compile as child class can't hold object of base class.

Answer 2

Base base = new Derived();//Here you are referencing the derived object with base reference type, so only base members will be accessed using the base reference  

Derived derived = new Derived();//Here you can access members in base and derived

Derived derived_1 = new Base();//This is a syntax error because you are using a derived reference for the base object(you are referencing a general object with a specific reference you need conversion here )

check this link : https://msdn.microsoft.com/en-us/library/ms173149.aspx