Understanding Polymorphism, inheritance in C#.

Question

Hello, I am little confused about polymorphism, inheritance in C#.   While learning about polymorphism, I found something like this ParentClass P = new ChildClass(); which is a bit confusing. Why would someone create type of parent class to store the object of child class? However it is valid in c# I just want to understand 3 things:   1. What is the purpose of doing this?   2. What are the advantages of doing this?   3. When we should create object like this?   Below is my code for reference: using  System;   class  ParentClass   {   public   void  Display()   {   Console.WriteLine( "Display method in Parent class" );   }   }   class  ChildClass : ParentClass   {   public   void  Display()   {   Console.WriteLine( "Display method in Child class" );   }   }   public   class  Program   {   public   static   void  Main()   {   ParentClass P =  new  ChildClass();   P.Display();   }   }   The output of the code is:   Display method in Parent class.   Now if someone has to call method in parent class why not simply create   ParentClass P = new ParentClass();   Or if someone has to call method in Child class why not simply create   ChildClass C = new ChildClass();   Have gone through lot of forums, still not found the answer I want. Please if anyone can explain in detail. It would be great. Thanks.

Jaish Mathews · Answer

Your learning path is right as you are thinking :) . I am expecting such queries rather than asking code and how to do kind of questions. Now the answer. The scenario you mentioned is only one of the scenarios of polymorphism. The objects are creating that way if you want all methods of the parent class to access , but some methods you want to execute from your child class by overriding, event though the same method is available in parent . See below example as Maruthi is a parent class and 2 child classes are derived from Maruthi. Then you are creating Maruthi objects to execute methods of Maruthi class except one specific method, which child class will execute.   NB: Please notice the virtual and override keywords there. class  Program      {           static   void  Main( string [] args)          {               //For all Maruthi parent methods + override Alto child method execution               Maruthi alto =  new  Alto();                 Console.WriteLine(alto.GetTotalCarModels());              Console.WriteLine(alto.GetTotalMaruthiCarDealers());                     //For all Maruthi parent methods + override Swift child method execution               Maruthi swift =  new  Swift();                 Console.WriteLine(swift.GetTotalCarModels());              Console.WriteLine(swift.GetTotalMaruthiCarDealers());                 Console.ReadLine();          }              public   class  Maruthi          {               //This method won't execute as of objects created with Ref. to child and             //this method has been overriden inside child
public   virtual   string  GetTotalCarModels()              {                   return   "Total Maruthi Models "  + 100;              }               public   string  GetTotalMaruthiCarDealers()              {                   return   "Total Maruthi Dealers "  + 1000000;              }          }              public   class  Alto : Maruthi          {               public   override   string  GetTotalCarModels()              {                   return   "Total Alto Models "  + 10;              }               public   string  GetAltoSpecification()              {                   return   "All Alto specification" ;              }          }              public   class  Swift : Maruthi          {               public   override   string  GetTotalCarModels()              {                   return   "Total Swift Models "  + 20;              }               public   string  GetSwiftSpecification()              {                   return   "All Swift specification" ;              }          }      }

Mageshwaran R · Answer

Hi, Can you check with the below link: https://www.guru99.com/c-sharp-inheritance-polymorphism.html

Rupesh Kahane · Answer

Check my articles, will help you to understand more 1) https://www.c-sharpcorner.com/UploadFile/a8024d/polymorphism-in-C-Sharp-with-real-life-example/ 2)  https://www.c-sharpcorner.com/UploadFile/a8024d/real-life-example-of-oops/