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The C# library provides a number of generic data structure classes, such as Stack , and Queue , which store and retrieve references to objects as type Object . These classes can be used to create objects that can store and retrieve objects of any class.
I encourage you to copy the code from Listing 7 . Use that code to create a C# console project. Compile and run the project. Experiment with the code, makingchanges, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.
Click here to download a zip file containing my version of the program. Extract the folder named Polymorph04 from the zip file and save it somewhere on your disk. Start Visual C# 2010 Express and select Open Project... from the File menu. Navigate to the project folder and select the file with the extension of .sln . This should cause the project to open and be ready to run or debug as described in the earlier module titled Getting Started .
Polymorphism manifests itself in C# in the form of multiple methods having the same name.
From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in C#:
In this module, I have continued my discussion of the implementation of polymorphism using method overriding through class inheritance, and haveconcentrated on a special case in that category.
More specifically, I have discussed the use of the Object class as a completely generic type for storing references to objects of subclasstypes, and have explained how that results in a very useful form of runtime polymorphism.
I briefly mentioned the default version of the methods defined in the Object class, and explained that in many cases, those default versions are meant to be overridden.
I provided a sample program that illustrates the overriding of the ToString method, which is one of the methods defined in the Object class.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
A complete listing of the program discussed in this module is provided in Listing 7 .
Listing 7 . Project Polymorph04.
/*Project Polymorph04
Copyright 2009, R.G.BaldwinThis program illustrates polymorphic behavior
and the Object classProgram output is:A
ToString in class BToString in class C
*********************************************************/using System;
class A : Object {//This class is empty
}//end class A//======================================================//
class B : A {public override String ToString() {
return "ToString in class B";}//end overridden ToString()
}//end class B//======================================================//
class C : B {public override String ToString() {
return "ToString in class C";}//end overridden ToString()
}//end class B//======================================================//
public class Polymorph04 {public static void Main() {
Object varA = new A();String v1 = varA.ToString();
Console.WriteLine(v1);Object varB = new B();
String v2 = varB.ToString();Console.WriteLine(v2);
Object varC = new C();String v3 = varC.ToString();
Console.WriteLine(v3);//Pause until user presses any key.
Console.ReadKey();}//end Main
}//end class Polymorph04 -end-
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