What are sealed classes and sealed methods

What is sealed class and sealed method?

 

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

 

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();
        }
    }
}

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.