Back to Basics: OOP and C# – Part 3 (Polymorphism)

In Part 2, we went into the definition of Inheritance and have shown example of it’s implementation. This week, we’ll be covering one of the OOP Principles that I mentioned in previous posts which is polymorphism.

Also, I realized that there had been a lot of great tutorials in the web already, and since I am delivering this to the Sophomore Class I will be teaching to in a couple of days, I decided to do this a little differently. I am going to ‘experiment’ and mixed some local dialects to it so it would be better understood here in the Philippines (a.k.a. TaglishTagalog/English).

Kung titingnan nyo yung nakaraang posts, makikita nyo dun yung project na ginamit at itutuloy lang natin dito. Pero bago yun, ibigay muna natin yung kahulugan ng Polymorphism sa Taglish:

Mula sa MSDN:

Polymorphism is a Greek word that means “many-shaped” and it has two distinct aspects:

  1. At run time, objects of a derived class may be treated as objects of a base class in places such as method parameters and collections or arrays. When this occurs, the object’s declared type is no longer identical to its run-time type.
  2. Base classes may define and implement virtual methods, and derived classes can override them, which means they provide their own definition and implementation. At run-time, when client code calls the method, the CLR looks up the run-time type of the object, and invokes that override of the virtual method. Thus in your source code you can call a method on a base class, and cause a derived class’s version of the method to be executed.

Ang sabi dito, yung mga objects sa derived class, ay pwedeng ituring na bahagi ng base class sa loob ng method parameters, collections, o sa mga arrays kapag pinatakbo yung program. Pag nangyari yun, iba na yung type ng object sa declaration kumpara kapag pinatakbo mo na sya. Halimbawa (pansinin nyo na itutuloy lang natin yung nakaraang project):

Buksan nyo yung Instructor class, tapos dagdagan nyo ng isang virtual method. (Yun pa yung isang konsepto nya, kapag gumawa ka ng virtual method sa base class, naka deklara na yung pangalan nya at implementasyon, pero pwede mong gamitin yung pangalan sa derived class at magbigay ng panibagong implementasyon (gamit yung override).

Overridable virtual method

Overridable virtual method

Ayun, tapos magdagdag tayo ng tatlo pang derived class na gamit yung Instructor bilang base class. Halimbawa:

Override method on derived class

Override method on derived class

Pansinin nyo, kakalagay ko palang nung override na pangalan tapos lumabas na kaagad na rekomendasyon sa intellisense yung Teach na method.

Ayun, kapag nilagay natin yung kumpleto (pinagsama ko nalang sa isang file yung tatlong class):

Derrived classes with Teach method

Derived classes with Teach method

Ngayon, ilagay naman natin sya sa main program para masubukan natin kung paano sya tatawagin… ang intention nito ay para maipakita na pwedeng magamit yung Programming, SoftwareDesign, at DatabaseDesign kahit saan na ginamit yung Instructor. Hindi narin natin kailangang mag cast sa tamang type kasi kakayanan ng gawin yun nung paggamit ng base class papuntang derived class.

Polymorphism at work

Polymorphism at work

Ang isa pang mapupuna natin sa halimbawa ay yung pagtawag sa method na Teach, na ang implementasyon nila ay hango sa derived class, pero nilagay din nating halimbawa yung pagtawag sa base method ng Teach dun sa Programming class, kaya parehas natin makikita sa resulta yung ginawa ng Teach sa base class at Teach pag tumakbo na yung sa linya ng Programming na class

Polymorphism at runtime

Polymorphism at runtime

Sya nga pala, yung ‘var’ na nakikita nyo, pag-compile nyan, Instructor din na type ang kalalabasan nyan. Kung sinadya ko sya sa code, ganito lang din sya — foreach (Instructor subject in teaches) — malinaw na ba? I hope this work well for you, hanggang sa muli!   (just realized that this is the only Taglish part, and most of it were in Tagalog, hahe) read it, love it, live it 🙂

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Back to Basics: OOP and C#

My older brother has connected me to a student of InfoTech Institute of Arts and Sciences which required a resource speaker for their midterm requirements.

So I chatted with her a little bit and got to an agreement that we are covering ‘building a cloud based solution’ but we need to teach them the fundamentals as pre-requisites since we are bringing it to 2nd year students.

And the best place to start is to brush up their OOP Principles (with C#).

If you quickly pull up your favorite search engine, you’d come by 3 popular terminologies and there is a wealth of resources in the web to help you with its definition – and yes, I am talking about Encapsulation, Inheritance and Polymorphism. Since the intention of my next few series is for the attendees to have a place where they can review my upcoming talk, while this can still be useful to you, this will be a targeted discussion.

Part 1: A quick review on Class and Objects

Supposed we are to treat this activity (activity – referring to ongoing lecture) as a software, and everything we do is part of a computer program, how do we write it? One approach is to try and write a narrative of your observation inside this class.

For instance:

Michael Corpuz is teaching to the 2nd year students Principles of OOP in Room 100 at 9:00am during Tuesdays and Thursdays.

Identify verbs and nouns to form as your objects and methods. i.e. Michael Corpuz, 2nd Year Students, Principles of OOP, Room 100, teaching, 9:00am, Tuesdays and Thursdays.

In some cases, they would treat Instructor (Michael Corpuz) as Class separate to a Student (Students can also be a class that is a collection of Student) and Year Level (2nd year) as a Property. Others would go by defining a Person Class since that is common of an Instructor and Students and adding a property Person Type where you can define if that Person is a Student or an Instructor. Others would go as far as defining Person as a Base Class (note the change ‘base’ from above) and using that as a foundation for Instructor Class and Student Class. That is referred to as Inheritance. Before we dig deeper into that, let us now build the classes for purposes of comparison.

Open Visual Studio 2012 (or equivalent Express Edition) to create a C# Console Project. In my case, I pulled up Express 2012 for Windows Desktop – and click ‘New Project’ shown below:

New Project

New Project

Visual C# > Console Application

Visual C# > Console Application

For the purposes of this demonstration, we are using the 2nd approach above, we are not ready for Inheritance yet. From the ‘Solution Explorer’, right click the project you just created and add new Class and name it Person — by default, the file Person.cs will have a class declaration with the name Person under a namespace which is also by default the name of the project.

 

Person Class

Person Class

 

Quick Tip: typing ‘enum’, you will see the intellisense pull up a code snippet icon aside from the ‘enum’ type itself, hitting ‘tab’ key will use the snippet on your code view for faster construction of your codes. you can do the same for Property by typing ‘prop’ or ‘propa’ then hit ‘tab’ key twice.

Properties and Methods

 

Note that we did not use “Year Level” property yet, that will come in handy discussing Inheritance.

 

Person person = new Person();

 

 

Using the Person class from the main program.

Using the Person class from the main program.

 

 

Program output

Program output

 

Part 2: <<link to be posted here>>.