Sealed classes and methods in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a sealed class in C#?

A sealed class is a class that cannot be inherited by any other class. It is used to prevent further extension of the class.

beginner

What happens if you try to inherit from a sealed class?

The compiler will give an error because sealed classes cannot be used as base classes.

intermediate

What is a sealed method in C#?

A sealed method is an override method that cannot be further overridden in derived classes. It stops the method from being changed again.

intermediate

How do you declare a sealed method in C#?

You declare a sealed method by using the 'sealed' keyword along with 'override' in the method signature, like: <br>public sealed override void MethodName() { }

intermediate

Why would you use sealed classes or methods?

To improve security and performance by preventing unwanted inheritance or method overriding, and to clearly define the class or method behavior.

What keyword is used to prevent a class from being inherited in C#?

A static

B abstract

C sealed

D virtual

The 'sealed' keyword prevents a class from being inherited.

Which of the following is true about a sealed method?

A It must be static.

B It can be overridden in derived classes.

C It cannot be called from derived classes.

D It cannot be overridden further once sealed.

A sealed method cannot be overridden further in derived classes.

Can a sealed class have methods that are overridden?

A Yes, if the methods are virtual.

B No, because the class is sealed.

C Yes, but only if the methods are sealed too.

D No, methods cannot be overridden in any class.

A sealed class can have virtual methods, but since the class cannot be inherited, overriding is not possible outside.

How do you declare a method that cannot be overridden further in a derived class?

A Use 'static' keyword.

B Use 'sealed' keyword with 'override'.

C Use 'abstract' keyword.

D Use 'virtual' keyword.

You use 'sealed override' to stop further overriding of a method.

What error occurs if you try to inherit from a sealed class?

A Compiler error

B Logical error

C Runtime exception

D No error

The compiler will show an error because sealed classes cannot be inherited.

Explain what a sealed class is and why you might use it.

Think about stopping others from extending your class.

Describe how to declare a sealed method and what effect it has on inheritance.

Focus on method overriding and stopping it.