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Article : - Overriding, Shadowing and Hiding in NET
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From:
Nasha
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Hey Group,
Howz it goin ? I am back after a weeks break. Let me start by wishing all of you A Very Happy & Prosperous NewYear !!!!
Today we will discuss what is overriding , shadowing and hiding ? .
Most of us I guess are familiar with overridering from C++ or Java. Overriding as the term says is to override the base class implementation or provide a new implementation in the derived class. We can override members in the base class in VB.Net using the keyword Overrides and in C# using the key word override. To override a base class member in VB.Net it should be marked as Overridable and in C# they should be marked with virtual. Method signature of the overiddden methods should be same as the base class methods.
Shadowing :- This is a VB.Net Concept by which you can provide a new implementation for the base class member without overriding the member. You can shadow a base class member in the derived class by using the keyword "Shadows". The method signature,access level and return type of the shadowed member can be completely different than the base class member.
Hiding : - This is a C# Concept by which you can provide a new implementation for the base class member without overriding the member. You can hide a base class member in the derived class by using the keyword "new". The method signature,access level and return type of the hidden member has to be same as the base class member.
Comparing the three :-
1) The access level , signature and the return type can only be changed when you are shadowing with VB.NET. Hiding and overriding demands the these parameters as same.
2) The difference lies when you call the derived class object with a base class variable.In class of overriding although you assign a derived class object to base class variable it will call the derived class function. In case of shadowing or hiding the base class function will be called.
Let us create a sample application and this check out :-
1) Create a new solution and three projects to it. One VB.Net Class Library, another C# Class Library and C# Console Application as a Client Application.
2) Name your VB.Net Class Library as Shadowing , C# library as Hiding and Your console application as Client Application.
3) In Shadowing add a class file called Shadow.vb and add the following classes to it.
Public Class BaseShadow
Public Overridable Function OverrideMe() As String
Return "Base Class Override Me"
End Function
Public Function ShadowMe() As String
Return "Base Class Shadow Me"
End Function
End Class
Public Class DerivedShadow
Inherits BaseShadow
Public Overrides Function OverrideMe() As String
Return "Derived Class Override Me"
End Function
Public Shadows Function ShadowMe() As String
Return "Derived Class Shadow Me"
End Function
End Class
4) In Hiding add class file called Hide.cs and add the following classes to it.
using System;
namespace Hiding
{
public class BaseHide
{
public BaseHide()
{
}
public virtual string OverrideMe()
{
return "Base Class Override Me";
}
public string HideMe()
{
return "Base Class Hide Me";
}
}
public class DerivedHide:BaseHide
{
public DerivedHide()
{
}
public override string OverrideMe()
{
return "Derived Class Override Me";
}
public new string HideMe()
{
return "Derived Class Hide Me";
}
}
}
5) Build both the Class Libs and add their refernces to the client console application.
6) Add the following code in the Main of the console Application.
using System;
using Hiding;
using Shadowing;
namespace Client_Application
{
/// <summary>
/// Summary description for Class1.
/// </summary>
class Client
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main(string[] args)
{
Console.WriteLine("// **** Overriding **** //");
// **** Overriding **** //
Shadowing.DerivedShadow derivedShadowOverrideObject = new Shadowing.DerivedShadow();
Console.WriteLine("Accessing thru derived class " + derivedShadowOverrideObject.OverrideMe());
Shadowing.BaseShadow baseShadowOverrideObject = new Shadowing.DerivedShadow();
Console.WriteLine("Accessing thru base class " + baseShadowOverrideObject.OverrideMe());
Hiding.DerivedHide derivedHideOverrideObject = new Hiding.DerivedHide();
Console.WriteLine("Accessing thru derived class " + derivedHideOverrideObject.OverrideMe());
Hiding.BaseHide baseHideOverrideObject = new Hiding.DerivedHide();
Console.WriteLine("Accessing thru base class " + baseHideOverrideObject.OverrideMe());
// **** Hiding **** //
Console.WriteLine("// **** Hiding **** //");
Hiding.DerivedHide derivedHideObject = new Hiding.DerivedHide();
Console.WriteLine("Accessing thru derived class " + derivedHideObject.HideMe());
Hiding.BaseHide baseHideObject = new Hiding.DerivedHide();
Console.WriteLine("Accessing thru base class " + baseHideObject.HideMe());
// **** Shadowing **** //
Console.WriteLine("// **** Shadowing **** //");
Shadowing.DerivedShadow derivedShadowObject = new Shadowing.DerivedShadow();
Console.WriteLine("Accessing thru derived class " + derivedShadowObject.ShadowMe());
Shadowing.BaseShadow baseShadowObject = new Shadowing.DerivedShadow();
Console.WriteLine("Accessing thru base class " + baseShadowObject.ShadowMe());
Console.ReadLine();
}
}
}
7) Execute the code and checkout the differences. You can even go ahead and change the method signature, accesslevel and return type for Shadowing and check it out. -- Please post your queries and comments for my articles in the user group for the benefit of all. I hope this step from my end is helpful to all of us. You can find all articles written by me at my personal Blog http://spaces.msn.com/members/nasha .
Regards,
Namratha (Nasha) <o:p></o:p> <o:p></o:p> |
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