Why It is not allowed to inherit sealed class

Question

Hi all! .Net framework doesn't allow us to inherit a Sealed class. I want to know how it restricts us to inherit a sealed class? I mean what is the difference between normal class and a sealed class because of which we can't inherit sealed class? e.g. I am ensuring that I am not going to inherit a class in my application and I am also assured that nobody will use this class as a base class. Then is it makes any difference if I declare it as a sealed class?

Muhammad Fakhr Elden Sami · Answer

About the first question i want to add that the sealed class cannot be used as a base class. For this reason it cannot also be an abstract class. Sealed classes prevent derivation. Because they can never be used as a base class some run-time optimizations can make calling sealed class members slightly faster.

Muhammad Fakhr Elden Sami · Answer

Exactly the keyword sealed for classes in c# is the same as you make a final class in Java. which makes the class not to be extended.

srinath · Answer

I want add to the question of Mr.Jagjit Patil ... Is sealed class is same as final in java?? please anyone give solution to my question. Thanx in advance..

Mahesh Chand · Answer

Compilers are designed to understand keywords. For example if you type keyword class or int or double in C# C# compiler knows what it means. Similarly if a class is sealed compiler knows if there is any inheritance syntax from a base sealed class it needs to throw an error. This is probably a part of parser and lexical analyzer parts of C# Compiler. That's what I think.

Jagjit Patil · Answer

Thanks Shrikanth! But I wanted to know what happens under the hood when we declare any class as sealed which prevents us inheriting it. Do you have any idea?

Shrikanth Hallikhed · Answer

The sealed keyword is used to prevent derivation from a class. You will get an error if a sealed class is specified as the base class of another class. This keyword is also be used for methods. If you are not overriding any methods not inheriting any classes then it is like a normal class.