This article explains how to create and use a sealed class using C#. We will also review why programming gurus use sealed classes in their code and products.
Sealed classes are used to restrict the inheritance feature of object oriented programming. Once a class is defined as a sealed class, the class cannot be inherited.
In C#, the sealed modifier is used to define a class as sealed. In Visual Basic .NET the NotInheritable keyword serves the purpose of sealed. If a class is derived from a sealed class then the compiler throws an error.
If you have ever noticed, structs are sealed. You cannot derive a class from a struct.
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
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.
