What is the usage of a sealed class in C#?

In C#, the “sealed” keyword is used to restrict the inheritance of a class. When a class is declared as a sealed class, it cannot be inherited by other classes.

The usage of sealed classes is as follows:

1. Prevent other classes from inheriting: When a class does not want to be inherited by other classes, it can be declared as a sealed class.
2. Optimizing performance: Since sealed classes cannot be inherited, the compiler can make optimizations to improve the code’s execution efficiency.
3. Security consideration: Some classes may contain crucial implementation details or security-related logic. Declaring them as sealed classes can prevent other classes from inheriting them and modifying their implementation.
4. By declaring a class as sealed, the designer’s intent is clearly expressed, indicating that the class cannot be inherited, thus helping to better organize and manage the code.

Please note that the sealed keyword can only be applied to classes, and cannot be applied to structures, interfaces, enums, or other types.