Sealed Class Interview Questions And Answers C#
Introduction
In C# sealed keyword applies restrictions on the class, method, property, indexer, or event. If you create a sealed class, it cannot be derived. If you create a sealed method, it cannot be overridden. In C#, we can use a sealed keyword before or after the access modifier to define the class as sealed classes.
01. What are the different ways to prevent inheritance in C#?
Normally we use the "sealed" modifier to prevent the inheritance in C#. In VB.Net "NotInheritable" keyword serves the purpose of sealing. In Java "final" keyword serves the same purpose.
02. What is a sealed class in C#?
03. What is a final class?
In C# we use the "sealed" keyword for making a class final. The "final" keyword is used in Java for sealing.
04. How can you define a sealed class in C#?
05. Can an interface be defined as sealed in C#?
06. Can a struct be defined as sealed in C#?
07. Can a sealed class be inherited by any class in C#?
No, a sealed class cannot be inherited by any class or struct.
08. Can a sealed class inherits from a static class in C#?
09. Can a sealed class be used as a base class in C#?
10. A sealed class can be instantiated or not in C#?
11. Can a sealed class define constructors in C#?
12. Can a non-child or stand-alone class can be defined as sealed in C#?
13. Can a sealed class be abstract in C#?
14. Can a sealed class be marked as static in C#?
15. Can a sealed class define a private constructor in C#?
16. Can a constructor be defined as sealed in C#?
17. Is it allowed to define destructor in a sealed class?
18. Can a sealed class implement interface in C#?
19. Can a sealed class have abstract methods in C#?
20. Can a sealed class define virtual methods in C#?
21. Can a sealed class define sealed methods in C#?
22. Can methods defined inside a sealed class be inherited in C#?
No, since a sealed class cannot be inherited, the methods defined inside the sealed class cannot be inherited.
23. Can a partial class be sealed in C#?
24. Can a sealed class be private or a sealed class with all members as private is allowed in C#?
No, a sealed class cannot be declared private explicitly. In fact, any class defined in a namespace cannot be explicitly declared as private, protected, protected internal, or private protected.
25. When should a class be declared as sealed?
26. Can a "sealed" keyword be used in VB.Net also for sealing a class?
No, in VB.Net "NotInheritable" keyword is used for the purpose of sealing a class. For sealing a property "NonOverrideable" keyword is used.
27. What is the difference between abstract class and sealed class in C#?
- An abstract class can only be used as a base class, while a sealed class cannot be used as a base class.
- An abstract class contains abstract methods but a sealed class cannot contain any abstract method.
- An abstract class contains virtual methods but a sealed class cannot contain any virtual method.
- An abstract class cannot be instantiated, but a sealed class can be instantiated.
- An abstract class cannot be the bottom-most level in the inheritance hierarchy but a sealed class may be the bottom-most.
28. How a sealed class is different from a static class in C#?
Although both a sealed class and a static class cannot be inherited by any class or struct but following are the key difference between them:
- A static class cannot be instantiated while a sealed class can be instantiated.
- A static class cannot define any indexer while a sealed class can define the indexers.
- A static class cannot have any destructor while a sealed class can have a destructor.
- Static class cannot have any instance constructor while a sealed class can have both static and instance constructors.
- A static class cannot inherit from any class or interface, but a sealed class can inherit from a class or interface.
- A static class can only contain static members, but a sealed class can have both static and non-static members.
- Members of a static class are accessed by the class name itself while sealed class members can only be accessed by the object of the class.
- Only a single global instance is created by the runtime which remains in the memory for the lifetime of the app domain but, it is not true for the sealed class.
29. How a sealed class is different from a class having a private constructor in C#?
30. What is the difference between sealed class and singleton class in C#?
31. Can you give me some sealed class examples available in the .Net Framework?
- System.String class is a sealed class.
- All the structs are sealed implicitly.
- All the enums are also sealed implicitly.
- All the value types are sealed.
- All the static classes are sealed implicitly.
32. The class containing the Main() method can be sealed or not in C #?
The class containing the main method() can be sealed in C#. The static Main() method is used as the entry point for the Console Application and Windows Application.
33. How a sealed class can solve the "fragile class problem" in C #?
A sealed class can solve the fragile class problem in C# by preventing inheritance.
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