Why sealed class is used

In most performance-enhancing tools on the market nowadays, you will find a checkbox that will seal all your classes that aren't inherited. Be careful though, because if you want to allow plugins or assembly discovery through MEF, you will run into problems. An addendum to Louis Kottmann's excellent answer :. On a related note, applicable to unsealed classes only: any method created virtual is an extension point, or at least looks like it should be an extension point. Declaring methods virtual should be a conscious decision as well.

In C this is a conscious decision; in Java it isn't. Also note that Kotlin seals classes by default; its open keyword is the opposite of Java's final or the sealed of C. To be sure, there is no universal agreement that this is a good thing. Marking a class as Sealed prevents tampering of important classes that can compromise security, or affect performance. Many times, sealing a class also makes sense when one is designing a utility class with fixed behaviour, which we don't want to change.

For example, System namespace in C provides many classes which are sealed, such as String. If not sealed, it would be possible to extend its functionality, which might be undesirable, as it's a fundamental type with given functionality. Similarly, structures in C are always implicitly sealed. The reasoning for this is that structures are used to model only stand-alone, atomic, user-defined data types, which we don't want to modify.

Sometimes, when you are building class hierarchies, you might want to cap off a certain branch in the inheritance chain, based on your domain model or business rules. For example, a Manager and PartTimeEmployee are both Employee s, but you don't have any role after part-time employees in your organization.

In this case, you might want to seal PartTimeEmployee to prevent further branching. On the other hand, if you have hourly or weekly part-time employees, it might make sense to inherit them from PartTimeEmployee. I think this post has some good point, the specific case was when trying to cast a non-sealed class to any random interface, compiler doesn't throw error; but when sealed is used the compiler throws error that it can't convert.

Sealed class brings additional code access security. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Even fresher or lay man with out any knowledge also can understand the concepts of your way of explanation, because you have explained concept which is covered the below features. What is the concept. Why is this concept. How this concept will be useful in real world programming.

When this concept can be used. What are all the rules,restrictions and limitations of this concept. Correlating between concept to concept. And more over explanation with practical examples and real time examples. The private method is not inherited whereas sealed method is inherited but cannot be overridden.

So, a private method cannot be called from sub-classes whereas sealed method can be called from sub-classes. You can also use the sealed modifier on a method or a property that overrides a virtual method or property in a base class. This enables you to allow classes to derive from your class and prevent other developers that are using your classes from overriding specific virtual methods and properties.

We just saw how to create and use a sealed class in C. The main purpose of a sealed class is to take away the inheritance feature from the class users so they cannot derive a class from it.

One of the best usage of sealed classes is when you have a class with static members. For example, the Pens and Brushes classes of the System. Drawing namespace. View All. Sealed Class in C. Mahesh Chand Updated date Sep 22, The following class definition defines a sealed class in C :. If you do think so, this is too serious; I would like to see some proof then. Indirect effect on the developers making them to write better performing code? Why not? But performance of sealed class?

Re: My vote of 1 Paulo Zemek Jun There is a difference. But that depends on the use. For example, create a class A with a single virtual method. Then create a class B that inherits from A. Mark B as sealed, and the performance will be difference. The reason is: When B is not sealed, it can, in fact, be another sub-class so a virtual call is made. If you seal it, the call to the method will be non-virtual, because it is guaranteed that it will not be virtual.

Maybe it is a small difference. And I am sure there are a lot of optimizations that may render such techniques obsolete that's why I used SomeNonInlineMethodThatReturnsB, as I think that if you do new B the compiler will notice that B variable has a B instance and will avoid the virtual call [I am not sure]. Also, you may consider the speed difference very insignificant, but there is one. But that's why C does not consider every method virtual to start with.

A class with no virtual methods will really don't have any speed improvement from being sealed. Also, even the arrays have a problem with non-sealed classes, as you can get an B[] as an A[] if B is a sub-class of A.

But each time you want to put a value inside that array it checks to see if it is really a B. Even if you get the array as B[], it may need to check if it is not, in fact, a C[]. If B is sealed, there is no such check. So, sealing the type helps on array accesses too. If you want to check, this is the result in my computer: Reset ; sw.

Stop ; Console. WriteLine sw. Elapsed ; Console. I tried to make it only start counting when the cpu cache is already on that's why it executes 10 times before starting to count. The sealed version always gives better result, but the difference is small.

You can even invert the order of the sealed and the non-sealed version, and the sealed is always faster. My vote of 5 AhsanS May My vote of 4 akosidab May Nice article! Rahul Rajat Singh. My vote of 5.