Sealed Classes

Classes can be declared as sealed. This is accomplished by putting the sealed keyword before the keyword class in the class definition. For example:

public sealed class classSealed
{
  // Class members here.
  public string ID;
  public double Price;

}

In the following code listing the implementation of a sealed class has been tested.

classSealed sc=new classSealed();
sc.ID=”C1”;
sc.Price=500.00;
double Samt=sc. CalculatePrice();
Response.Write(“Total Net Price of Product : “ +” “+sc.ID +” “+ “is”+” “+Samt);
Response.Write(“
”);

A sealed class cannot be used as a base class. For this reason, it cannot also be an abstract class. Sealed classes are primarily used to prevent derivation. Because they can never be used as a base class, some run-time optimizations can make calling sealed class members slightly faster. Sealing a class means one can not derive from it. Sealing a method means one can not override it. In C# structs are implicitly sealed; therefore, they cannot be inherited. If we try to inherit from a sealed class in another class we will get compile time error about Inconsistent accessibility (code is shown in following code listing).

public class TestClass : classSealed
{
}

In C# a method can not be declared as sealed. However when we override a method in a derived class, we can declare the overridden method as sealed as shown below. By declaring it as sealed, we can avoid further overriding of this method.

public class testClass

{
  public int x;
  public int y;
  public virtual void testMethod(){

  }

}

public class TestClass: testClass
{
  public override sealed void testMethod()
 {

  }
}