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/