I would like to have your feedback. Please post your feedback, question, or comments about this Sealed Class and Sealed Methods in the C article. Really am impressed with your explanation of all the concepts. 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. The sealed keyword in C language is used to create a sealed class. Sealed classes restricts classes to extend or inherit a class. The code examples of sealed classes in this article demonstrate use of sealed classes in C and.
In this article, I will discuss how to create and use a sealed class using C. We will also see why developers use sealed classes in their libraries and code. Sealed classes are used to restrict the inheritance feature of object oriented programming.
Once a class is defined as a sealed class, this class cannot be inherited. In C , the sealed modifier is used to declare a class as sealed. In Visual Basic. NET, NotInheritable keyword serves the purpose of sealed. If a class is derived from a sealed class, compiler throws an error. Change Language. Related Articles. Table of Contents. Save Article. Improve Article. Like Article. Last Updated : 01 Oct, Add 6, 4 ;. ToString ;.
Previous C Abstract Classes. Next C Object Class. On a class that implements security features, so that the original object cannot be "impersonated". More generally, I recently exchanged with a person at Microsoft, who told me they tried to limit the inheritance to the places where it really made full sense, because it becomes expensive performance-wise if left untreated.
The sealed keyword tells the CLR that there is no class further down to look for methods, and that speeds things up. 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.
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