INTERVIEW QUESTIONS MICROSOFT C# DETAILS

Question: By declaring a base class function as virtual we allow the function to be overridden in subclasses

Answer: The derived class can provide new functionality by overriding the virtual method of the base class.

The method to be called is determined at the run-time depending on the type of the object calling the method, and it does not depend on the type of the variable declared to hold the object. The following example illustrates this point:

Suppose base class B and derived class D provide different implementations of a virtual method V(). Also suppose that there is a non-virtual method NV() of B which is overriden by D.

//In Main(), an object, obj, is declared to be of type B.

B obj;

//An object of D is created for initializing obj

obj = new D;

//Call virtual and non-virtual methods on obj:

obj.V(); //This call would execute D::F() since F() is virtual, and although obj is declared to be of type B, it contains object of type D.

obj.NV(); //This call would execute B::F(), looking at the declaration of obj.

This is the difference between virtual and plain overridable methods. Virtual methods execute slower than non-virtual ones because of run-time resolve of the method to be called. So programmer should be caeful while declaring a method as virtual.

The derived class can provide new functionality by overriding the virtual method of the base class.

The method to be called is determined at the run-time depending on the type of the object calling the method, and it does not depend on the type of the variable declared to hold the object. The following example illustrates this point:

Suppose base class B and derived class D provide different implementations of a virtual method V(). Also suppose that there is a non-virtual method NV() of B which is overriden by D.

//In Main(), an object, obj, is declared to be of type B.

B obj;

//An object of D is created for initializing obj

obj = new D;

//Call virtual and non-virtual methods on obj:

obj.V(); //This call would execute D::F() since F() is virtual, and although obj is declared to be of type B, it contains object of type D.

obj.NV(); //This call would execute B::F(), looking at the declaration of obj.

This is the difference between virtual and plain overridable methods. Virtual methods execute slower than non-virtual ones because of run-time resolve of the method to be called. So programmer should be caeful while declaring a method as virtual.


Source: CoolInterview.com

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