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Polymorphism

By tusharkant.agarwal
Polymorphism is reflected in the ability to write one routine that can operate on objects from more than one class-treating different objects from different classes in exactly the same way. For instance, if both Customer and Vendor objects have a Name property, and we can write a routine that calls the Name property regardless of whether we’re using a Customer or Vendor object, then we have polymorphism.

A vehicle is a good example of polymorphism. A vehicle interface would only have those properties and methods that all vehicles have, a few of which might include paint color, number of doors, accelerator, and ignition. These properties and methods would apply to all types of vehicles including cars, trucks, and semi-trucks.

Polymorphism will not implement code behind the vehicle’s properties and methods. Instead, polymorphism is the implementation of an interface. If the car, truck, and semitruck all implement the same vehicle interface, then the client code for all three classes can be exactly the same.

C# gives us polymorphism through inheritance. C# provides a keyword virtual that is used in the definition of a method to support polymorphism.

Child class are now free to provide their own implementation of this virtual method, that is called overriding. The following points are important regarding virtual keyword:-

If the method is not virtual, the compiler simply uses the reference type to invoke the appropriate method.

If the method is virtual, the compiler will generate code to checkup the reference type at runtime it is actually denoting to, then the appropriate method is called from the class of the reference type.

When a virtual method is called, runtime check (late method binding) is made to identify the object and appropriate method is invoked, all this is done at runtime.

In case of non-virtual methods, this information is available at compile time, so no runtime check to identify the object is made, so slightly efficient in the way non-virtual methods are called. But the behavior of virtual method is useful in many ways; the functionality they provide is fair enough to bear this slight loss of performance.

Implementing Polymorphism

The key factor here is the ability to dynamically invoke methods in a class based on their type. Essentially, a program would have a group of objects, examine the type of each one, and execute the appropriate method. Here’s an example:

using System;
public class WebSite
{
public string SiteName;
public string URL;
public string Description;
public WebSite()
{
}
public WebSite( string strSiteName, string strURL, string strDescription )
{
SiteName = strSiteName;
URL = strURL;
Description = strDescription;
}
public override string ToString()
{
return SiteName + “, ” +URL + “, ” +Description;
}
}

When we inherit above class, we have two choices to invoke constructor of the class. So this is an example of design time polymorphism. Here at design time we have to decide which method we need to invoke while inheriting the class.

Polymorphism is the capability of a program to carry out dynamic operations by implementing methods of multiple derived classes through a common base class reference. Another definition of polymorphism is the ability to treat different objects the same way. This means that the runtime type of an object determines its behavior rather than the compile-time type of its reference.

Summery:

It was a long trip, but I tried to explain all the basics of Object Orientation in C# with some practical examples.

http://www.c-sharpcorner.com/UploadFile/tusharkantagarwal/objectorientedcsharp11162005070743AM/objectorientedcsharp.aspx