Programming Technical Interview Questions

In C#, can you prevent a class from being inherited by another class? If so, how do you do it? And why would you want to do it?

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This can be done by making constructors of the class private and making use of Named constrcutors for the class

In C# the proper way to prevent a class from being inherited is to use the “sealed” modifier.

Sealed classes

try the ’sealed’ keyword on the class definition.

sealed class CantInheritMe {}

The above comment is incorrect. Making a class constructor private will not prevent a class from being inherited by another class, it would simply prevent it from being instantiated. The desired functionality would be accomplished by using the “sealed” keyword in the class declaration. (i.e. public sealed class MyClass).

The sealed modifier is primarily used to prevent unintended derivation, such as when a class contains a concrete implementation of an abstract base. In this case the developer of the sealed class would want other implementations to inherit from the abstract base class and instead of inheriting from the sealed concrete implementation. It also enables certain run-time optimizations. In particular, because a sealed class is known to never have any derived classes, it is possible to transform virtual function member invocations on sealed class instances into non-virtual invocations.

Yes, use the sealed modifier as follows:

sealed class NotInheritable { … }

You would use this to prevent unintential inheritance, or for run-time optimization.

This can be done by declaring the class as a sealed class.

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