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What is the use of virtual, sealed, override, and abstract?

Posted By :Srikanth     Posted Date :April 22, 2011    Points :40   Category :C# 
. The use of virtual keyword is to enable or to allow a class to be overridden in the derived class.
. The use of sealed keyword is to prevent the class from overridden i.e. you can't inherit sealed classes.
. The use of override keyword is to override the virtual method in the derived class.
. The use of abstract keyword is to modify the class, method, and property declaration. You cannot directly make calls to an abstract method and you cannot instantiate an abstract class

You can also find related Interview Question to What is the use of virtual, sealed, override, and abstract?  below: 

What is use of Virtual,sealed,override,abstract keyword?

  
The use of virtual keyword is to enable or to allow a class to be overridden in the derived class.
The use of sealed keyword is to prevent the class from overridden i.e. you can't inherit sealed classes.
The use of override keyword is to override the virtual method in the derived class.
The use of abstract keyword is to modify the class, method, and property declaration. You cannot directly make calls to an abstract method and you cannot instantiate an abstract class. (More...)

Can you override private virtual methods in .NET Framework?

  
No, moreover, you cannot access private methods in inherited classes, have to be protected in the base class to allow any sort of access. (More...)

Expalin one difference between Abstract and virtual methods?

  
Virtual method can be overriden in any of its derived class and abstract method must be overriden in any of the non abstract class. (More...)

Is it possible to modify an abstract class with sealed Modifier?

  
no, Because the two modifier have opposite meanings. (More...)

Can you override private virtual methods?

  
No, private methods are not accessible outside the class. (More...)

What is Method Overriding? How to override a function in C#?

  
Use the override modifier to modify a method, a property, an indexer, or an event. An override method provides a new implementation of a member inherited from a base class. The method overridden by an override declaration is known as the overridden base method. The overridden base method must have the same signature as the override method.
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What is the difference between interface and abstract class ?

  
a class may inherit several interfaces, a class may inherit only one abstract class (More...)

What is web application virtual directory?

  
A virtual directory appears to client browsers as though it were
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What are Abstract base classes?

  
Abstact Class is nothing but a true virtual class..
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What is difference between abstract class and an interface?

  
An Abstract class is a class with some common/certain implementations and defines abstraction for other services which are implemented in its concrete sub classes, whereas interface only have method declaration with zero implementations. An abstract class and Interface both have method only but not have body of method. The difference between Abstract class and An Interface is that if u call Abstract class then u have to call all method of that particular Abstract class but if u call an Interface then it is not necessary that u call all method of that particular interface. An abstract class is a special kind of class that cannot be instantiated. So the question is why we need a class that cannot be instantiated? An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for all the subclasses. In simple words, it is a kind of contract that forces all the subclasses to carry on the same hierarchies or standards.

An interface is not a class. It is an entity that is defined by the word Interface. An interface has no implementation; it only has the signature or in other words, just the definition of the methods without the body. As one of the similarities to Abstract class, it is a contract that is used to define hierarchies for all subclasses or it defines specific set of methods and their arguments. The main difference between them is that a class can implement more than one interface but can only inherit from one abstract class. Since C# doesn't support multiple inheritance, interfaces are used to implement multiple inheritance.


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Explain Virtual Function in C#.

  
Virtual functions implement the concept of polymorphism are the same as in C#, except that you use the override keyword with the virtual function implementaion in the child class.

The parent class uses the same virtual keyword. Every class that overrides the virtual method will use the override keyword.


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What are virtual path providers?

  
Its the path providing facility to provide the virtual content to compiler. For example, a virtual path provider provides a means to supply content from locations other than the file system.

To attain the same following step(s) are required :
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