Virtual vs Override vs New Keywords in C#

• Sample Implementation
  
  Here's a simple implementation in C# without using any keywords. Do you think it will run fine, or will it show a runtime or compile-time errors? Let's see:
  
  
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  6. namespace Generics
  7. {
  8. class A
  9. {
  10. public void show()
  11. {
  12. Console.WriteLine("Hello: Base Class!");
  13. Console.ReadLine();
  14. }
  15. }
  17. class B : A
  18. {
  19. public void show()
  20. {
  21. Console.WriteLine("Hello: Derived Class!");
  22. Console.ReadLine();
  23. }
  24. }
  26. class Polymorphism
  27. {
  28. public static void Main()
  29. {
  30. A a1 = new A();
  31. a1.show();
  32. B b1 = new B();
  33. b1.show();
  34. A a2 = new B();
  35. a2.show();
  36. }
  37. }
  38. }

  Output Window
  
  
  
  It is showing some sort of output. That means there is neither a runtime nor a compile-time error. But it will definitely show a warning in Visual Studio. So do you want to know what it is and how to remove it?
  
  Keep reading and you will go through that.
  
  Warning Message
  
  Here's the warning message that you will get:

  
  
  Solution
  
  The solution of this problem is already in the warning. Just read it carefully and you will get that. Yes you got that right, for removing that warning we need to use the new keyword.
  
  In the next sample demo example is showing you a simple demo snippet and implementation of the new keyword. (I hope now you will be getting why we are using the new keyword in here.)

• New keyword | Method Overhiding
  
  Here's a simple snippet of method overriding. So just go through it and guess the output:
  
  
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  6. namespace Generics
  7. {
  8. class A
  9. {
  10. public void show()
  11. {
  12. Console.WriteLine("Hello: Base Class!");
  13. Console.ReadLine();
  14. }
  15. }
  17. class B : A
  18. {
  19. public new void show()
  20. {
  21. Console.WriteLine("Hello: Derived Class!");
  22. Console.ReadLine();
  23. }
  24. }
  26. class Polymorphism
  27. {
  28. public static void Main()
  29. {
  30. A a1 = new A();
  31. a1.show();
  32. B b1 = new B();
  33. b1.show();
  34. A a2 = new B();
  35. a2.show();
  36. }
  37. }
  38. }
  
  Output Window

  
  

  Explanation
  
  The procedure goes something like that:
  
  
  

• Virtual and Override Keywords | Method Overriding
  
  This is a simple example of method overriding. Just go through it and guess the output again and also try to differentiate between the previous snippet and this snippet.
  
  
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  6. namespace Generics
  7. {
  8. class A
  9. {
  10. public virtual void show()
  11. {
  12. Console.WriteLine("Hello: Base Class!");
  13. Console.ReadLine();
  14. }
  15. }
  17. class B : A
  18. {
  19. public override void show()
  20. {
  21. Console.WriteLine("Hello: Derived Class!");
  22. Console.ReadLine();
  23. }
  24. }
  26. class Polymorphism
  27. {
  28. public static void Main()
  29. {
  30. A a1 = new A();
  31. a1.show();
  32. B b1 = new B();
  33. b1.show();
  34. A a2 = new B();
  35. a2.show();
  36. }
  37. }
  38. }
  
  Output Window
  
  
  
  Explanation
  
  The flow goes something like that:
  
  
  
• Overriding + Hiding | Together
  
  This snippet shows how both of these methods can work together in a same snippet. So just go through this and guess the output.
  
  
  1. using System;
  2. using System.Collections.Generic;
  3. using System.Linq;
  4. using System.Text;
  6. namespace Generics
  7. {
  8. class A
  9. {
  10. public virtual void show()
  11. {
  12. Console.WriteLine("Hello: Base Class!");
  13. Console.ReadLine();
  14. }
  15. }
  17. class B : A
  18. {
  19. public override void show()
  20. {
  21. Console.WriteLine("Hello: Derived Class!");
  22. Console.ReadLine();
  23. }
  24. }
  26. class C : B
  27. {
  28. public new void show()
  29. {
  30. Console.WriteLine("Am Here!");
  31. Console.ReadLine();
  32. }
  33. }
  35. class Polymorphism
  36. {
  37. public static void Main()
  38. {
  39. A a1 = new A();
  40. a1.show();
  41. B b1 = new B();
  42. b1.show();
  43. C c1 = new C();
  44. c1.show();
  45. A a2 = new B();
  46. a2.show();
  47. A a3 = new C();
  48. a3.show();
  49. B b3 = new C();
  50. b3.show();
  51. }
  52. }
  53. }
  
  Output Window
  
  
  
  Explanation
  
  The flow goes something like that:
  
  
  

Key Points

I am providing some key points about these keywords by taking a reference of method overloading and overriding concepts, since these keywords are used in these mechanisms.

Virtual and Override

• Used in polymorphism implementation
• Includes same method name and same params
• Used in method overriding
• It is also called runtime polymorphism
• Causes late binding

New

• It is also used in polymorphism concept
• Includes the same method name and different params
• Used in method overriding
• It is compile-time polymorphism
• Causes early binding

Conclusion

So did you like it, I hope you so!

Well I tried to provide just a brief sketch of these keywords, that are very necessary for a beginner in C# as well as in OOP. If you have a good understaind of OOP then you can take any object-oriented language in your pocket.

So just go through OOP first and then C# and if you are facing any problem then feel free to ping or message me.

Happy coding, Cheers!