Sealed Method Interview Questions C#

 Sealed Method Interview Questions And Answers C#

 A sealed method is the most common topic for the interview today. Today, we will discuss the most asked interview questions and answers based on the sealed method in C# for experienced developers.

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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. In VB.Net the "NotOverridable" modifier is used for sealing the method.

Please read more about the  sealed class and methods here. 

01. What is a sealed method in C#?

A method modified by the "sealed" keyword is known as a sealed method. A sealed keyword is used for a method to prevent it from being overridden in the derived class. 

The sealed methods in C# cannot be overridden further, but it must be used with an override keyword in the method. If you want to declare a method as sealed, then it has to be declared as virtual in its base class because a non-virtual method cannot be overridden.

Please read more about the sealed method here.

02. What is a final method in C#?

In C# we use the "sealed" keyword for making a method final. The "final" keyword is used in Java for sealing. 

We cannot use the final keyword in C# for making a method as final, but the compiler generates the "final" modifier for the IL code when we use the sealed keyword.

 

03. How can you seal a method in C#?

A method can be marked as sealed by the "sealed" keyword in C#, but it must be used with an override keyword in the method. The sealed keyword can be used before the access modifier, before or after the override keyword.       

If you want to declare a method as sealed, then it has to be declared as virtual in its base class because a non-virtual method cannot be overridden. 

04. Can you use the sealed modifier for any method without override keyword in C#?

No, the "sealed" modifier can only be used with the "override" keyword in C#.     

05. Can an interface define sealed methods in C#?

Yes, an interface can define sealed methods in C# 8. In earlier versions of C#, it was not available.  

Please read more about the sealed interface method here.

06. Can a struct define sealed methods in C#?

No, a struct cannot define sealed methods since a struct cannot inherit from any class or struct in C#. 

Since C# 8 interface contains sealed methods, if an interface containing a sealed method is inherited by a struct, then it can be accessed by the interface reference variables of the struct. 

Please read more about the interface sealed method here.

07. Can a non-child class define sealed methods in C#?

No, a sealed method cannot be defined in the non-child class because a sealed modifier can only be used with the override keyword and an override keyword can be used with a method which is defined as virtual or abstract in the base class.

08. Can a non-sealed class define sealed methods in C#?

Yes, a non-sealed class can also define sealed methods in C#.

09. Can a static method be sealed in C#?

No, a static method cannot be sealed in C#.

10. Can a virtual method be marked as sealed in C#?

No, a sealed method cannot be virtual in C#. 

11. Can a partial method be sealed in C#?

No, a partial method cannot be sealed in C#. 

Please read more about the partial method here.

12. Can a non-virtual method be marked as sealed in C#?

No, because non-virtual methods cannot be overridden in the derived class.

13. Can a non-virtual method be overridden as sealed in C#?

No, because non-virtual methods cannot be overridden in the derived class. But yes an abstract method can also be overridden which is not a virtual method explicitly but implicitly.

14. Can an abstract method be sealed in C#?

We cannot use a sealed modifier with the abstract keyword, but an abstract method can be overridden as sealed in the derived class.

15. Can an abstract method be overridden as sealed in C#?

Yes, an abstract method can be overridden as sealed in the derived class.

16. Can an interface method be overridden as sealed in the derived class C#?

No, an interface method cannot be overridden as sealed directly in C#. But if the interface method is redefined as abstract in the derived class then, it can be overridden in the inheriting class.

Please read more about the virtual interface method here.

17. Can a sealed method be re-defined as abstract or virtual in the derived class?

No, you can only prevent a sealed method from being overridden in the derived class, but you cannot prevent a sealed method from redefining it as new again in the derived class ie derived class can hide the base class sealed method.

 

18. Can a class having all the members as sealed be inherited in C#?

Yes, a class having all the members as sealed can be inherited in C#.

19. Can a property be marked as sealed in C#?

Yes, a property can also be sealed, but you can only seal the property not the underlying setter and getter since C# offers no override syntax for setters or getters.

20. How a sealed property is different from a readonly property in C#?

A sealed property cannot be overridden in the derived class, but the underlying setter and getter can be overridden in the derived class. On the other hand, a readonly property cannot be assigned by any value.

21. What is the difference between a private method and a sealed method?

1. A private method is not inherited whereas a sealed method is inherited but cannot be overridden.
2. A private method cannot be accessed from derived classes while a sealed method can be accessed from derived-classes.
3. Only a virtual member can be sealed in the derived class, but there is no such condition for making a method as private.
4. A sealed method can only be declared in a child class while a private method can be defined in any class.
5. The same private method can be defined in the derived-class and it does not lead to an error or warning.

22. How a sealed class is different from a sealed method in C#?

Sealed classes restrict the users from inheriting the class while a sealed method restricts from overriding. 

A sealed class can be either a stand-alone class or a child class but, a sealed method can only be defined in a child class.

23. When should a method be declared as sealed in C#?

A method should be declared as sealed when we want to restrict the derived class from overriding the method further in C#.

24. What is the difference between sealed override, protected override, and sealed protected override in C#?

A method can be overridden as sealed by using the sealed keyword while protected is the access modifiers for that method. We can specify the sealed modifier anywhere like before the access modifier, after the access modifiers, or after the override keyword. 

25. How a sealed method can prevent the "fragile class problem" in C #?

A sealed method can prevent the fragile class problem in C# by preventing the derived class from overriding the virtual methods.

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Interface Vs Abstract Class in C# 8

Partial Types and Partial Classes in C#
Interface Virtual Method in C# 8

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