What are sealed classes and sealed methods

In this article, I will try to explain sealed class and sealed method in a very simple way.

C# Sealed Class

Sealed class is used to define the inheritance level of a class.

The sealed modifier is used to prevent derivation from a class. An error occurs if a sealed class is specified as the base class of another class.

Some points to remember:

1. A class, which restricts inheritance for security reason is declared sealed class.
2. Sealed class is the last class in the hierarchy.
3. Sealed class can be a derived class but can't be a base class.
4. A sealed class cannot also be an abstract class. Because abstract class has to provide functionality and here we are restricting it to inherit.

Practical demonstration of sealed class

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Text;  
namespace sealed_class  
{  
    class Program  
    {  
        public sealed class BaseClass  
        {  
            public void Display()  
            {  
                Console.WriteLine("This is a sealed class which can;t be further inherited");  
            }  
        }  
        public class Derived : BaseClass  
        {  
            // this Derived class can;t inherit BaseClass because it is sealed  
        }  
        static void Main(string[] args)  
        {  
            BaseClass obj = new BaseClass();  
            obj.Display();  
            Console.ReadLine();  
        }  
    }  
}

C# Sealed Methods

Sealed method is used to define the overriding level of a virtual method.

Sealed keyword is always used with override keyword.

Practical demonstration of sealed method.

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Text;  
namespace sealed_method  
{  
    class Program  
    {  
        public class BaseClass  
        {  
            public virtual void Display()  
            {  
                Console.WriteLine("Virtual method");  
            }  
        }  
        public class DerivedClass : BaseClass  
        {  
            // Now the display method have been sealed and can;t be overridden  
            public override sealed void Display()  
            {  
                Console.WriteLine("Sealed method");  
            }  
        }  
        //public class ThirdClass : DerivedClass  
        //{  
        //    public override void Display()  
        //    {  
        //        Console.WriteLine("Here we try again to override display method which is not possible and will give error");  
        //    }  
        //}  
        static void Main(string[] args)  
        {  
            DerivedClass ob1 = new DerivedClass();  
            ob1.Display();  
            Console.ReadLine();  
        }  
    }  
}

Hope this article will give you better view of sealed class and sealed method. Waiting! for your valuable feedback.