Polymorphism in OOP

"Polymorphism" is a greek word, "poly" means many and "morph" means forms.
In object oriented programming paradigm Polymorphism is expressed as one object behaving as multiple forms. One function behave in different forms.

Inheritance in OOP

Inheritance

One of the most important concepts of object oriented programming is Inheritance. Inheritance is a mechanism of acquiring features and behaviors of one class called as base or parent class into another class called as derived class.

Inheritance implements a IS-A relationship.

Advantages of inheritance

• Code re-usability 
• Reduction in code size
• Improve code readability
• Code extensible support by overriding base class method into derived class  

Disadvantage of inheritance

• Tight coupling between base class and child class
• Performance of your program is affected if inheritance is not implemented properly.
• Many unused data members remain unused & memory is allocated for the same.

Different types of inheritance

• Single Inheritance

When a derived class is created from a single base class.

C# Example

public class Parent

{

    //Definition

}

public class Derived : Parent

{

    //Definition

}

•  Multi-Level Inheritance

When a derived class is created from another derived class is called as multi-level inheritance

C# Example

ppublic class Parent

{

    //Definition

}

public class Derived1 : Parent

{

    //Definition

}

public class Derived2 : Derived1

{

    //Definition

}

• Multiple Inheritance

When a derived class is created from more than one class then it is called as multiple inheritance. This type of inheritance is not supported in C# or .Net

This type of inheritance is not supported in C# or .Net

• Hierarchical Inheritance

When a multiple derived class is created from one single class then it is called as Hierarchical inheritance.

 C# Example

public class Parent

{

    //Definition

}

public class Derived1 : Parent

{

    //Definition

}

public class Derived2 : Parent

{

    //Definition

}

public class Derived3 : Derived1

{

    //Definition

}

public class Derived4 : Derived1

{

    //Definition

}

public class Derived5 : Derived2

{

    //Definition

}

public class Derived6 : Derived2

{

    //Definition

}

• Hybrid Inheritance

This is combination of more than one inheritance. It may be a combination of Multilevel and Multiple inheritance or Hierarchical and Multilevel inheritance or
Hierarchical and Multilevel and Multiple inheritance.

• Why C# does not support multiple inheritance?

C# does not support multiple inheritance because of diamond problem. To know more about diamond problem please refer below link 

https://en.wikipedia.org/wiki/Multiple_inheritance#The_diamond_problem

• As we know multiple inheritance is not supported by C# or .Net what is the other way to achieve multiple inheritance in C# or .Net? 

We can achieve similar functionality using interface in C#.

• Is static class can be inherited ?

Static class can not be inherited. C# complies static class as sealed abstract class hence static class cannot be inherited in c#.

• How to make normal class non inheritable c#?

Using sealed keyword in c# we can stop class from further inheriting it.