What do you mean by word “Abstract”?

Abstract means (as a noun) summary not a whole story.

"Take vehicle and car, vehicle is an abstract of car."

So in an abstract class we have abstract and non-abstract methods. In the class abstract methods don’t have implementation; we can implement those later in derived classes.

We can create an abstract class through using the abstract keyword. We cannot have an instance of abstract class.

If we try to make an instance of abstract class we get an compile time error "cannot create an instance of abstract class or interface".

So why we need abstract classes? We can have abstract classes just for inheritance. It provides a common pattern to all the derived classes.

Some basic facts about abstract class:

Here is an example code of abstract class and it's output.

  1. using System;
  2. namespace ConsoleApplication1
  3. {
  4. abstract class AbsClass //declaring abstract class
  5. {
  6. //declaring abstract methods
  7. public abstract int MultiplyTwoNumbers(int x, int y);
  8. public abstract int SubtractTwoNumbers(int p, int q);
  9. //declaring non-abstract method
  10. public int AddThreeNumbers(int a, int b, int c)
  11. {
  12. return a + b + c;
  13. }
  14. }
  15. class DerivedClass : AbsClass // derived class inheriting the abstract class
  16. {
  17. // overring the abstract methods in derived class
  18. public override int MultiplyTwoNumbers(int x, int y)
  19. {
  20. return x * y;
  21. }
  22. public override int SubtractTwoNumbers(int p, int q)
  23. {
  24. return p - q;
  25. }
  26. }
  27. class Program
  28. {
  29. static void Main()
  30. {
  31. DerivedClass obj = new DerivedClass(); //created an object of derived class
  32. // calling all methods with signatures
  33. int Addition = obj.AddThreeNumbers(10, 20, 50);
  34. int Multipication = obj.MultiplyTwoNumbers(3, 50);
  35. int Substraction = obj.SubtractTwoNumbers(10, 3);
  36. // not printing the output
  37. Console.Write("Addition of 10, 20 and 50 = " + Addition.ToString() + "\n" + "Mutiplication of 3 and 50 = " + Multipication.ToString() + "\n" + "Subtraction of 10 and 3 = " + Substraction.ToString());
  38. Console.ReadLine();
  39. }
  40. }
  41. }
Output

Output