C# Sealed

C# sealed keyword applies restrictions on the class and method. If you create a sealed class, it cannot be derived. If you create a sealed method, it cannot be overridden.

Note: Structs are implicitly sealed therefore they can't be inherited.

C# Sealed class

C# sealed class cannot be derived by any class. Let's see an example of sealed class in C#.

1. using System;  
2. sealed public class Animal{  
3.     public void eat() { Console.WriteLine("eating..."); }  
4. }  
5. public class Dog: Animal  
6. {  
7.     public void bark() { Console.WriteLine("barking..."); }  
8. }  
9. public class TestSealed  
10. {  
11.     public static void Main()  
12.     {  
13.         Dog d = new Dog();  
14.         d.eat();  
15.         d.bark();  
16.   
17.   
18.     }  
19. }  

Output:

Compile Time Error: 'Dog': cannot derive from sealed type 'Animal'

C# Sealed method

The sealed method in C# cannot be overridden further. It must be used with override keyword in method.

Let's see an example of sealed method in C#.

1. using System;  
2. public class Animal{  
3.     public virtual void eat() { Console.WriteLine("eating..."); }  
4.     public virtual void run() { Console.WriteLine("running..."); }  
5.   
6. }  
7. public class Dog: Animal  
8. {  
9.     public override void eat() { Console.WriteLine("eating bread..."); }  
10.     public sealed override void run() {   
11.     Console.WriteLine("running very fast...");   
12.     }  
13. }  
14. public class BabyDog : Dog  
15. {  
16.     public override void eat() { Console.WriteLine("eating biscuits..."); }  
17.     public override void run() { Console.WriteLine("running slowly..."); }  
18. }  
19. public class TestSealed  
20. {  
21.     public static void Main()  
22.     {  
23.         BabyDog d = new BabyDog();  
24.         d.eat();  
25.         d.run();  
26.     }  
27. }  

Output:

Compile Time Error: 'BabyDog.run()': cannot override inherited member 'Dog.run()' because it is sealed

Note: Local variables can't be sealed.

1. using System;  
2. public class TestSealed  
3. {  
4.     public static void Main()  
5.     {  
6.         sealed int x = 10;  
7.         x++;  
8.         Console.WriteLine(x);  
9.     }  
10. }  

Output:

Compile Time Error: Invalid expression term 'sealed'