Menggunakan Objek Kontrol Gambar Dan Pewaktu

8/12/2019 Menggunakan Objek Kontrol Gambar Dan Pewaktu

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MENGGUNAKAN OBJEK KONTROL GAMBAR DAN PEWAKTUCakupan Materi : Properties, Event, dan Method

Untuk Menampilkan isi file Gambar, kontrol yang dapat digunakan ada 2 (dua) yaitu Image

dan Picture Box. Ekstensi dari file gambar antara lain : BMP, JPG, GIF, PNG, dsbnya.

Untuk pemrograman yang memerlukan pemanfaatan data waktu biasanya menggunakankontrol Timer.


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OOP pada VB.Net

1.1. Pengertian Object Oriented Programming (OOP)

Object Oriented Programming merupakan sebuah sudut pandang pemecahan masalah.

Masalah yang dimaksud di sini merupakan masalah yang berhubungan dengan computer

yang dipandang sebagai kumpulan objek yang saling berhubungan.

1.2. Tujuan OOP

Tujuan utama dari pengembangan pendekatan berorientasi objek adalah untuk

menghilangkan kelemahan-kelemahan yang terdapat pada pendekatan prosedural. Pada

OOP, data dibutuhkan sebagai elemen yang penting dan tidak boleh mengalir secara bebas

dalam sebuah program. Data yang terikat pada function dan harus dilindungi terhadap

kemungkinan perubahan dari luar function.

Catatan :

Anda dapat melihat konsep OOP seperti suatu objek telebisi, dimana sebagai pemakai kita

tidak perlu terlalu pusing dengan komponen apa saja yang bekerja didalam televisetersebut, tetapi sebagi pemakai kita cukup mengerti bagaimana menghidupkan, memilih

channel, mengubah volume suara, dan beberapa setting dasar.

OOP memungkinkan untuk pemecahan masalah kedalam sejumlah entitas yang disebut

sebagai objek dan kemudian mengembangkan data dan fungsi disekitar objek tersebut.

Salah satu manfaat yang terpenting dari OOP adalah pemanfaatan kembali.

Selain kemampuan yang sudah dijabarkan di atas, beberapa kemampuan utama dari OOP

yang lain ialah sebagai berikut:

1. Lebih menekankan pada data daripada prosedur.

2. Program terbagi atas objek-objek.

3. Data disembunyikan dari akses oleh fungsi-fungsi eksternal.4. Melalui function objek dapat berkomunikasi satu dengan yang lain.

5. Mengikuti pendekatan buttom up.

1.3. Konsep Dasar OOP

Konsep dasar suatu program termasuk dalam OOP, apabila terdapat pembungkusan

(Encapsulation), Polymorphisme, turunan (Inheritance) dan abstraction.

1.3.1. Encapsulation (Pembungkusan)

Encapsulation (Pembungkusan) yaitu mengemas suatu objek sehingga pada saat kita akan

memakai objek tersebut kita tidak perlu lagi tahu tentang detail bagaimana suatu action ituterjadi.

Contoh dalam hal ini, misal siswa (suatu object) sedang menulis (method). Maka detail dari

tentang cara siswa itu menulis (bagaimana otot tangan itu bekerja untuk menulis,

bagaimana sistem saraf pusat memerintahkan untuk menulis) kita tidak perlu mengerti.

Kita hanya melihat si siswa sedang menulis.


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Contoh :

class Siswa {

String nama;

String nim;

void isiData ( String namaku,String nimku ) {

nama = namaku;nim = nimku;

}

String ambilNama() {

return nama;

}

String ambilNim() {

return nim;

}

}

public class Mahasiswa {

public static void main ( String [] args)

{

Siswa mahasiswa_itn = new Siswa();

mahasiswa_itn.isiData(Dina Damayanti,0412585);System.out.println( Nama : +mahasiswa_itn.ambilNama());System.out.println( Nim : + mahasiswa_itn.ambilNim());}

}

1.3.2. Polymorphisme

Polimorphisme merupakan suatu object bisa bertindak lain terhadap message/method

yang sama. Misalkan kita punya satu class hewan dan diturunkan menjadi dua class hewan

berkaki dua dan hewan berkaki empat. Ketika hewan berkaki dua melakukan method

makan maka yang dilakukan adalah makan dengan paruhnya, dan ketika hewan berkaki

empat juga makan maka dia akan menggunakan mulutnya. Keduanya melakukan aksi yang

sama yaitu makan akan tetapi perlakuannya lain.

Contoh :

class Binatang{public void info(){

System.out.println( Info tentang Hewan : );}

}


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class Herbivora extends Binatang {

public void info(){

System.out.println (Info pada herbivora: Memakan makanan berupa tumbuh tumbuhan);}

}

class Kelinci extends Herbivora {

public void info(){

System.out.println(Info pada Kelinci: Memakan makanan berupa wortel);}

}

public class Polimorfisme {

public static void main(String[] args) {

Herbivora herbivora;

Kelinci kelinciku;Binatang hewan;

herbivora=new Herbivora();

kelinciku=new Kelinci();

hewan=herbivora;

hewan.info();

hewan=kelinciku;

hewan.info();

}

}

1.3.3. Inheritance (Turunan)Turunan merupakan yaitu salah satu bentuk teknis untuk membuat sebuah class lebih

spesifik lagi. Sebagai contoh dari kasus ini menurut analogi di atas. Misalkan kita akan

membuat class yang lebih spesifik dari ORANG yaitu siswa/student. Maka class ini

mempunyai properti tambahan sekolah tempat dia belajar. Akan tetapi, semua properti

sebagai orang ada juga pada class siswa ini.

Contoh:

Public Class ORANG_TUA

'variabel untuk menampung nama bapak

Private XBapak As String'variabel untuk menampung nama ibu

Private XIbu As String

'property (atribut/informasi) class

Public Property Nama_Bapak() As String

'Get : hanya ijinkan akses data

Get Return XBapak

End Get


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1.4. Keunggulan OOP

Object Oriented Programming memiliki beberapa keunggulan di atas pendekatan

konvensioanal, yaitu sebagai berikut:

1. OOP menyediakan struktur modular yang jelas untuk program, yang mana cocok

untuk mendefinisikan tipe data abstrak yang merupakan detail dari implementasi.2. OOP memudahkan perawatan atau maintenance dan modifikasi terhadap kode yang

telah sebagai objek baru yang dapat dibuat dengan perubahan yang minimal.

3. OOP juga menyediakan suatu kerangka kerja yang baik untuk kode library yang mana

menyediakan komponen software yang secara mudah dapat disesuaikan dan dimodifikasi

oleh programmer. Hal ini khususnya sangat berguna untuk pengembangan user interface

secara grafik.

1.5. OOP pada Visual Basic

1.5.1. Membuat Class

Pemrograman OOP pada Visual Basic dapat dilakukan dengan merancang class dari objekdengan menggunakan struktur class sebagai berikut:

Class nama

'member [variable, property, method and event declarations]

End Class

Contoh :

Misalnya kita ingin membuat program animasi bola pantul yang memanfaatkan GDI+

dengan pendekatan berorientasi objek, maka sebagai langkah awal adalah merancang Class

untuk bola pantul.

Pada tahap rancangan, kita harus dapat mendefinisikan aksi apa saja yang harus dapat

dilakukan oleh objek bola pantul yaitu bergerak (move) yang tentu saja memiliki koordinat

awal (x,y) yang bergerak kearah tertentu (dx, dy). Dalam pergerakan dilayar, tentu sajadibatasi oleh area tertentu (sx,sy).

Kemudian sebagai wujud dari animasi gerakan bola dilayar, kita perlu menyediakan aksi

draw dan clear.

Adapun rancangan class tersebut diatas dalam bentuk terprogram adalah sebagai berikut:

Class Pantul

Protected x As Single 'posisi x dilayar

Protected y As Single 'posisi y dilayar

Private sx As Single 'jumlah kolom x

Private sy As Single 'jumlah baris yPrivate dx As Single 'arah bola terhadap x

Private dy As Single 'arah bola terhadap y

Public Sub New(f as form) 'constructor

sx = f.width \ 30 'lebar form dibagi 30

sy = f.height \ 30 'tinggi form dibagi 30

x = rnd*(sx-2) + 2 'posisi awal random


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y = rnd*(sy-2) + 2

dx = 1 'arah diagonal ke bawah

dy = 1

Draw(f)

End Sub

Public Sub Draw(f as form) 'metoda

'gambar bola ukuran 30x30 dengan warna merah

Dim MyGraphic As Sistem.Drawing.Graphics = f.CreateGraphics

Dim MyPen As New

Sistem.Drawing.Pen(Sistem.Drawing.Color.Red,3)

MyGraphic.DrawEllipse(MyPen,x*30,y*30,30,30)

End Sub

Public Sub Clear(f as form) 'metoda

'gambar bola ukuran 30x30 dengan warna latar belakang formDim MyGraphic As Sistem.Drawing.Graphics = f.CreateGraphics

Dim MyPen As New Sistem.Drawing.Pen(f.BackColor,3)

MyGraphic.DrawEllipse(MyPen, x*30,y*30,30,30)

End Sub

Public Sub Move(f as form) 'metoda

'hapus gambar bola sebelumnya

Clear(f)

'gerakan bola dengan mengubah x, y sesuai dengan arah

x = x + dx

y = y + dy'jika mengenai daerah bingkai

If x < 2 or x > (sx-2) Then dx = -dx

If y < 2 or y > (sy-2) Then dy = -dy

'gambar bola diposisi baru

Draw(f)

End Sub

End Class

Catatan : Jika anda perhatikan perhatikan rancangan class diatas, maka konsep dari data

abstraction akan nampak, dimana sebagai interface keluar hanya terdiri metoda New,Draw, Clear, dan Move, sedangkan pengkodean tersembunyi dari program yang akan

memanfaatkan Objek dari Class Pantul.

Kemudian konsep dari data encapsulation, dimana variable x,y,sx,sy,dx, dan dy disatukan

beserta fungsi New, Draw, Clear, dan Move didalam satu Class Pantul.


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1.5.1.1. Ruang Lingkup member pada suatu class

Pada saat pendeklarasian member pada class anda dapat menggunakan keyword seperti

Friend, Private, Protected, Protected Friend, dan Public, dimana masing- masing memiliki

kendali akses yang berbeda.

Friend, member hanya tersedia bagi kode pada lingkup project yang sama.Private,

membehanya tersedia bagi class itu sendiri Protected, member tersedia bagi class dan class

turunannya.

Protected Friend, member tersedua bagi kode pada lingkup project yang sama, dan class

turunannya. Public, member tersedia bagi semua kode program. Jika anda tidak

menentukan jenis kendali akses bagai suatu member, maka defaultnya adalah Public.

1.5.2. Constructors

Constructor adalah anggota function yang mana memiliki tugas untuk menginisialisasi

objek dari classnya. Suatu constructor akan dijalankan ketika objek dari class tersebut

diciptakan. Kita dapat mengirim data kepada konstruktor dengan mencantumkannya

didalam kurung. Pada Visual Basic suatu konstruktor harus dibuat dengan suatu Sub

procedure dengan nama New pada class. Koding berikut mendemonstrasikan pemakaian

dari konstruktor di Visual Basic.



sy = f.height \ 30 'tinggi form dibagi 30

x = rnd*(sx-2) + 2 'posisi awal random

y = rnd*(sy-2) + 2


dy = 1

Draw(f)

End Sub

Pada contoh diatas, konstruktor digunakan untuk menginisialisasi nilai awal untuk variable

pada Objek seperti sx, sy, x, y, dx, dan dy.

Untuk konstruktor diatas, pada saat kita membuat instance dari Class dengan

Dim Bola As Pantul

Bola = New Pantul(Me)

Dimana Me mengacu pada form yang sedang aktif.

1.5.3. Destructors


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Destructors akan dijalankan ketika suatu objek dimusnahkan. Didalam suatu destructor

kita dapat menempatkan koding untuk membersihkan objek setelah digunakan. Kita

menggunakan metode Finalize di Visual Basic untuk membuat destructor yang otomatis

akan dijalankan ketika runtime. NET menemukan bahwa objek tidak dibutuhkan lagi.

Contoh implementasi pemakaian destructor adalah misalnya pada konstruktor kita

membuka data maupun file, sehingga pada saat destructor kita perlu menutup data

maupun file yang terbuka.

Catatan: Setiap objek didunia nyata memiliki fase awal yaitu kelahiran, dan fase akhir yaitu

kematian. Pada saat suatu objek dilahirkan tentu saja telah memiliki nilai property

bawaan,seperti seorang bayi yang baru dilahirkan telah memiliki jenis kelamin, berat

badan, dan tinggi.

Demikian juga objek dalam konsep OOP, yang kadang-kadang membutuhkan pemberian

nilai awal kepada beberapa property begitu instance dari class dibuat. Tindakan pemberiannilai awal (inisialisasi) ini dapat dilakukan dengan menggunakan metoda khusus yang

dikenal sebagai

Constructor.

1.5.4. Overriding

Pada derived class kadang-kadang kita perlu mendefinisikan ulang fungsi maupun sub

yang ada pada base class, dalam hal inilah istilash Overriding muncul, dimana kita dapat

mendefinisikan ulang fungsi maupun sub pada derived class.

Misalnya pada Class Pantul1 gambar yang ingin kita hasilkan adalah persegi, maka kita

perlu melakukan Overiding terhadap Sub Draw dan Clear yang ada pada base class.

Catatan : Sub maupun Function pada base class harus dideklarasikan sebagai Overridable

baru dapat di Overrides pada derived class.

Pada Class pantul kita perlu mencantumkan keyword Overridable

Overridable Public Sub Draw(f as form) 'metoda



Dim MyPen As New Sistem.Drawing.Pen(Sistem.Drawing.Color.Red,3)


End Sub

Overridable Public Sub Clear(f as form) 'metoda

'gambar bola ukuran 30x30 dengan warna latar belakang form




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Pada class turunannya :

Public Shadows Sub Draw(f as form) 'metoda

'gambar persegi ukuran 30x30 dengan warna merah

Dim MyGraphic As Sistem.Drawing.Graphics = f.CreateGraphicsDim MyPen As New Sistem.Drawing.Pen(Sistem.Drawing.Color.Red,3)

MyGraphic.DrawRectangle(MyPen,x*30,y*30,30,30)

End Sub

Catatan :

Pemakaian cara Shadowing menyebabkan konsep polymorphism tidak dapat berfungsi

sebagaimana pada cara Overriding.

1.6. Contoh Keunggulan OOP (Bagian 1)

Jika sekilas kita melihat uraian yang telah disebutkan diatas seakan-akan segala sesuatu

yang dilakukan dengan pendekatan OOP dapat juga dilakukan dengan teknik pemrograman

biasanya. Tetapi misalnya anda bayangkan kita ingin membuat program bola pantul yang

terdiri dari 15 buah bola pantul dilayar yang masing- masing bergerak tanpa pendekatan

OOP.

Berikut ini saya akan membuat contoh dengan pendekatan OOP, dan anda bandingkan

sendiri.

Pertama kita akan membuat variable array untuk bola pantul sebagai array 15 elemen :

Dim Bola(14) As PantulKemudian kita buat instance dari Class Pantul

For I As Integer = 0 To 14

Bola(I) = New Pantul(Me)

Next I

Selanjutnya kita gerakan masing- masing objek dengan looping :

For I As Integer = 0 To 14

Bola.Move(Me)

Next I

Dari hal ini jelaslah bahwa dengan pendekatan OOP kita tidak melakukan perubahan

terhadap

rancangan Class Pantul sama sekali, melainkan kita membuat 15 instance dari Class Pantul.

Listing lengkap dari program 15 ola pantul dengan pendekatan OOP.


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Option Explicit On

Imports Sistem

Imports Sistem.Windows.Forms

Imports Microsoft.VisualBasic

Public Class MyForm : Inherits Form

Dim WithEvents MyTimer as New Timer

Dim Bola(14) As Pantul

_

Public Shared Sub Main()

Application.Run(New MyForm)

End Sub

Public Sub New() 'Constructor

Me.BackColor = Sistem.Drawing.Color.BlackMe.FormBorderStyle = FormBorderStyle.None

Me.Width = Screen.PrimaryScreen.Bounds.Width

Me.Height = Screen.PrimaryScreen.Bounds.Height

For I As Integer = 0 to 14

Bola(I) = New Pantul(Me)

Next I

MyTimer.Interval = 150 '150 millidetik

MyTimer.Enabled = True

End Sub'Mengerakan objek dengan event tick pada objek MyTimer

Private Sub MyTimer_Tick(sender as object, e as eventargs) _

handles MyTimer.Tick

For I As Integer = 0 to 14

Bola(I).Move(Me)

Next I

End Sub

End Class

Class Pantul

Protected x As Single 'posisi x dilayar

Protected y As Single 'posisi y dilayar

Private sx As Single 'jumlah kolom x

Private sy As Single 'jumlah baris y


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Private dx As Single 'arah bola terhadap x

Private dy As Single 'arah bola terhadap y



sy = f.height \ 30 'tinggi form dibagi 30x = rnd*(sx-2) + 2 'posisi awal random

y = rnd*(sy-2) + 2


dy = 1

Draw(f)

End Sub

Overridable Public Sub Draw(f as form) 'metoda



Dim MyPen As NewSistem.Drawing.Pen(Sistem.Drawing.Color.Red,3)


End Sub

Overridable Public Sub Clear(f as form) 'metoda

'gambar bola ukuran 30x30 dengan warna latar belakang form



MyGraphic.DrawEllipse(MyPen, x*30,y*30,30,30)

End Sub

Public Sub Move(f as form) 'metoda

'hapus gambar bola sebelumnya

Clear(f)

'gerakan bola dengan mengubah x, y sesuai dengan arah

x = x + dx

y = y + dy

'jika mengenai daerah bingkai

If x < 2 or x > (sx-2) Then dx = -dx

If y < 2 or y > (sy-2) Then dy = -dy

'gambar bola diposisi baru

Draw(f)

End Sub


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End Class

Contents Introduction Using the code Lesson 1: Namespaces, Classes & Modules Lesson 2: Access Types Lesson 3: Shared Functions Lesson 4: Overloading Lesson 5: Inheritance Lesson 6: Overriding Lesson 7: Polymorphism

Lesson 8: Constructors & Destructors Lesson 9: Property Routines Lesson 10: A Simple Application

Introduction

VB.NET is completely object oriented. This article uncovers some basic Object Oriented Programming

features of Visual Basic. NET. The whole article is divided into ten lessons. The source code for these

lessons is provided with the article.

This tutorial is designed with the following objectives:

1. To provide a sound knowledge about Object Oriented Programming in VB.NET.2. To educate how Object Oriented techniques are used in VB.NET.3. To explain the following concepts in an easy and simple way:o Creating and using classes and objects in VB.NET.o Encapsulation, Abstraction, Inheritance and Polymorphism.o Overloading and Overriding.o Constructors and Destructors.o Static functions.

Go through this tutorial and you will start making sense of almost any .NET code. Also, Java/CPP

programmers can use this to understand OOPs in VB.NET.

Using the code

The source code for each lesson is available as a .vbsource code file. You need Microsoft .NET

framework SDK installed in your system to compile and execute the exercises in this article. You can
http://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Introductionhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Introductionhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Using%20the%20codehttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Using%20the%20codehttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%201:%20NAMESPACES,%20CLASSES%20AND%20OBJECTS,%20MODULEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%201:%20NAMESPACES,%20CLASSES%20AND%20OBJECTS,%20MODULEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%202:%20ACCESS%20TYPEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%202:%20ACCESS%20TYPEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%203:%20SHARED%20FUNCTIONShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%203:%20SHARED%20FUNCTIONShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%204:%20OVERLOADINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%204:%20OVERLOADINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%205:%20INHERITANCEhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%205:%20INHERITANCEhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%206:%20OVERRIDINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%206:%20OVERRIDINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%207:%20POLYMORPHISMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%207:%20POLYMORPHISMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%208:%20CONSTRUCTORS%20&%20DESTRUCTORShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%208:%20CONSTRUCTORS%20&%20DESTRUCTORShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%209:%20PROPERTY%20ROUTINEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%209:%20PROPERTY%20ROUTINEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%2010:%20A%20SIMPLE%20PROGRAMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%2010:%20A%20SIMPLE%20PROGRAMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%2010:%20A%20SIMPLE%20PROGRAMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%209:%20PROPERTY%20ROUTINEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%208:%20CONSTRUCTORS%20&%20DESTRUCTORShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%207:%20POLYMORPHISMhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%206:%20OVERRIDINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%205:%20INHERITANCEhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%204:%20OVERLOADINGhttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%203:%20SHARED%20FUNCTIONShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%202:%20ACCESS%20TYPEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#LESSON%201:%20NAMESPACES,%20CLASSES%20AND%20OBJECTS,%20MODULEShttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Using%20the%20codehttp://www.codeproject.com/Articles/8825/Object-Oriented-Programming-In-VB-NET#Introduction


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download it from the Microsoft website. The VB.NET compiler (vbc.exe) normally resides in

your FrameworkSDK\binfolder.

To manually compile a source code file, you may use the command prompt to type: vbc filename.vb

/out:"filename.exe" /r:"System.Windows.Forms.dll","System.dll"

Lesson 1: Namespaces, Classes & Objects,

Modules

A NamespaceIn VB.NET, classes and other data structures for a specific purpose are grouped together to form a

namespace. You can use the classes in a namespace, by simply importing the namespace.

The Importskeyword is used to import a namespace to your project. .NET framework provides a

rich set of built in classes, grouped together to various namespaces. In this lesson, we are using

the Systemnamespace. Import the Systemnamespace (already available in .NET).

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ImportsSystem

A ClassProbably, you are already familiar with classes and objects. Simply speaking, a Classis a definition

of a real life object. For example, Humanis a class for representing all human beings. Dogis a class to

represent all Dogs. Classes can contain functions too. Animalsis a namespace.

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NamespaceAnimals

Dogis a class in the namespace Animals:

Collapse |Copy Code

ClassDog

Barkis a function in this Class:

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FunctionBark()Console.Writeline ("Dog is barking")

EndFunction

EndClass

EndNamespace
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An ObjectAn object is an instance of a Class. For example, Jimmyis an object of type Dog. We will create an

object in the next section. Read on.

ModulesYou can use modules to write common functions. A Moduleis a group of functions. Unlike functions

in classes,Publicfunctions in modules can be called directly from anywhere else. VB

provides Functions and Subroutines. Functions and Subroutines are almost the same, but the

difference is that a subroutine can't return a value.

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PublicModulemodMain

Execution will start from the Main()subroutine:

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SubMain()

'Call our function. See belowOurFunction()

Endsub

OurFunction: Our own little function to use the class Dog:

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FunctionOurFunction()'Here is how we declare a variable Jimmy of type Dog.

'We use Animals.Dog because, the class Dog is in the'namespace Animals (see above).

DimJimmy asAnimals.Dog

'Create an object. Unlike in VB 6, it is not required to use

'the 'set' keyword.

Jimmy = newAnimals.Dog()

'Another way to create an object is

'Dim Jimmy as new Dog

'Call Jimmy's Main FunctionJimmy.Bark()

EndFunction

Endmodule

Lesson 2: Access Types
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The major access types are Public, Private, Friendand Protected. A Classmay contain

functions, variables etc., which can be either Publicor Privateor Protectedor Friend. If they

are Public, they can be accessed by creating objects of

the Class. Privateand Protectedmembers can be accessed only by the functions inside

theClass. Protectedmembers are much like Privatemembers, but they have some special use

while inheriting aClass. We will see this later, in Inheritance (Lesson 5). Friendmembers can beaccessed only by elements of the same project, and not by the ones outside the current project. Let

us expand our dogclass.

Import the Systemnamespace (already available in .NET).

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ImportsSystem

Animalsis a namespace.

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NamespaceAnimals

Dogis a class in the namespace Animals.

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PublicClassDog'A public variable

PublicAgeOfDog asInteger

Barkis a function in this class. It is Public:

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PublicFunctionBark()

Console.Writeline ("Dog is barking")

EndFunction

Walkis a function in this class. It is Private.

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PrivateFunctionWalk()Console.Writeline ("Dog is walking")

EndFunctionEndClass

EndNamespace

Our Module:

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PublicModulemodMain

Execution will start from the Main()subroutine:

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SubMain()'Call our function. See below

OurFunction()Endsub

'OurFunction: Called from Main()

FunctionOurFunction()DimJimmy asAnimals.Dog

Jimmy=new Animals.Dog()

'This will work, because Bark & Ageofdog are public

Jimmy.BarkJimmy.AgeOfDog=10

'Calling the Walk function will not work here, because'Walk() is outside the class Dog

'So this is wrong. Uncomment this and try to compile, it will

'cause an error.'Jimmy.Walk

EndFunctionEndModule

Additional Notes:

EncapsulationPutting all the data and related functions in a Classis called Encapsulation.

Data Hiding or Abstraction:Normally, in a Class, variables used to hold data (like the age of a dog) is declared as Private.

Functions or property routines are used to access these variables. Protecting the data of an object

from outside functions is called Abstraction or Data Hiding. This prevents accidental modification of

data by functions outside the class.

Lesson 3: Shared Functions

The shared members in a class (both functions and variables) can be used without creating objects of

a class as shown. The Sharedmodifier indicates that the method does not operate on a specific

instance of a type and may be invoked directly from a type rather than through a particular instance

of a type.

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ImportsSystem

Animalsis a namespace.

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NamespaceAnimals

Dogis a class in the namespace Animals.

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ClassDog

Barkis a now a Public, shared function in this class.

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PublicSharedFunctionBark()

Console.Writeline ("Dog is barking")

EndFunction

Walkis a Publicfunction in this class. It is not shared.

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PublicFunctionWalk()

Console.Writeline ("Dog is walking")

EndFunctionEndClass

EndNamespace

Our Module:

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PublicModulemodMain

Execution will start from the Main()subroutine.

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SubMain()'We can call the Bark() function directly,'with out creating an object of type Dog -

'because it is shared.Animals.Dog.Bark()

'We can call the Walk() function only

'after creating an object, because

'it is not shared.DimJimmy asAnimals.Dog

Jimmy=new Animals.Dog()
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Jimmy.Walk()

'Now Guess? The WriteLine() function we used so far'is a shared function in class Console :)'Also, we can write the Main() function itself as a shared

'function in a class. i.e Shared Sub Main(). Try

'moving Main() from this module to the above class

Endsub

EndModule

Lesson 4: Overloading

Overloading is a simple technique, to enable a single function name to accept parameters of

different type. Let us see a simple Adderclass. Import the Systemnamespace (already available in

.NET).

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ImportsSystem

ClassAdder

Here, we have two Add()functions. This one adds two integers. Convert.ToString is equivalent

to the good oldCStr.

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OverloadsPublicSubAdd(A asInteger, B asInteger)

Console.Writeline ("Adding Integers: "+ Convert.ToString(a + b))

EndSub

This one adds two strings.

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OverloadsPublicSubAdd(A asString, B asString)Console.Writeline ("Adding Strings: "+ a + b)

EndSub

'And both have the same name. This is possible because, we used the'Overloads keyword, to overload them.

'Here, we have the Main Function with in this class. When you write.'your main function inside the class, it should be a shared function.

SharedSubMain()

DimAdderObj asAdder

'Create the object

AdderObj=new Adder'This will invoke first function

AdderObj.Add(10,20)'This will invoke second function

AdderObj.Add("hello"," how are you")

EndSub

EndClass

Lesson 5: Inheritance


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Inheritance is the property in which, a derived class acquires the attributes of its base class. In simple

terms, you can create or 'inherit' your own class (derived class), using an existing class (base class).

You can use the Inheritskeyword for this.

Let us see a simple example. Import the Systemnamespace (already available in .NET).

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ImportsSystem

Our simple base class:

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ClassHuman'This is something that all humans do

PublicSubWalk()

Console.Writeline ("Walking")

EndSub

EndClass

Now, let us derive a class from Human.

A Programmeris a Human.

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ClassProgrammerInheritsHuman

'We already have the above Walk() function'This is something that all programmers do ;)

PublicSubStealCode()

Console.Writeline ("Stealing code")EndSub

EndClass

Just a MainClass.

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ClassMainClass

'Our main functionSharedSubMain()

DimTom asProgrammer

Tom=new Programmer

'This call is okie because programmer got this function

'from its base classTom.Walk()

'This is also correct because Tom is a programmerTom.StealCode()

EndSub

EndClass


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Additional Notes:

MustInheritThe MustInheritkeyword specifies that a class cannot be instantiated and can be used only as a

base class. I.e., if you declare our Humanclass as "MustInherit Class Human", then you can'tcreate objects of typeHumanwithout inheriting it.

NotInheritableThe NotInheritable keyword specifies that a class cannot be inherited. I.e., if you specify

'NotInheritableClass Human', no derived classes can be made from the Humanclass.

Lesson 6: Overriding

By default, a derived class Inheritsmethods from its base class. If an inherited property or methodneeds to behave differently in the derived class it can be overridden; that is, you can define a new

implementation of the method in the derived class. The Overridablekeyword is used to mark a

function as overridable. The keyword Overridesis used to mark that a function is overriding some

base class function. Let us see an example.


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ImportsSystem


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ClassHuman'Speak() is declared Overridable

OverridablePublicSubSpeak()

Console.Writeline ("Speaking")EndSub

EndClass

Now, let us derive a class from Human:

An Indianis a Human:

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ClassIndianInheritsHuman

'Let us make Indian speak Hindi, the National Language

'in India

'Speak() is overriding Speak() in its base class (Human)


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OverridesPublicSubSpeak()Console.Writeline ("Speaking Hindi")

'Important: As you expect, any call to Speak() inside this class'will invoke the Speak() in this class. If you need to

'call Speak() in base class, you can use MyBase keyword.

'Like this

'Mybase.Speak()EndSub

EndClass

Just a class to put our Main().

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ClassMainClass


'Tom is a generic HumanDimTom asHuman

Tom=new Human

'Tony is a human and an IndianDimTony asIndian

Tony=new Indian'This call will invoke the Speak() function'in class Human

Tom.Speak()

'This call will invoke the Speak() function

'in class Indian

Tony.Speak()EndSub

EndClass

Lesson 7: Polymorphism

Polymorphism is the property in which a single object can take more than one form. For example, if

you have a base class named Human, an object of Humantype can be used to hold an object of any

of its derived type. When you call a function in your object, the system will automatically determine

the type of the object to call the appropriate function. For example, let us assume that you have a

function named speak()in your base class. You derived a child class from your base class and

overloaded the function speak(). Then, you create a child class object and assign it to a base class

variable. Now, if you call the speak()function using the base class variable, the speak()function

defined in your child class will work. On the contrary, if you are assigning an object of the base class

to the base class variable, then thespeak()function in the base class will work. This is achieved

through runtime type identification of objects. See the example.


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ImportsSystem
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This example is exactly the same as the one we saw in the previous lesson. The only difference is in

the Shared SubMain()in the class MainClass. So scroll down and see an example:


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'Speak() is declared Overridable

OverridablePublicSubSpeak()

Console.Writeline ("Speaking")

EndSub

EndClass

Now, let us derive a class from Human.

An Indianis a Human.

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ClassIndianInheritsHuman

'Let us make Indian speak Hindi, the National Language'in India

'Speak() is overriding Speak() in its base class (Human)

OverridesPublicSubSpeak()Console.Writeline ("Speaking Hindi")

'Important: As you expect, any call to Speak() inside this class

'will invoke the Speak() in this class. If you need to'call Speak() in base class, you can use MyBase keyword.

'Like this'Mybase.Speak()

EndSub

EndClass

Carefully examine the code in Main():

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ClassMainClass


'Let us define Tom as a human (base class)

DimTom asHuman

'Now, I am assiging an Indian (derived class)Tom=new Indian

'The above assignment is legal, because'Indian IS_A human.

'Now, let me call Speak as

Tom.Speak()

'Which Speak() will work? The Speak() in Indian, or the

'Speak() in human?'The question arises because, Tom is declared as a Human,

'but an object of type Indian is assigned to Tom.

'The Answer is, the Speak() in Indian will work. This is because,

'most object oriented languages like Vb.net can automatically

'detect the type of the object assigned to a base class variable.


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'This is called PolymorphismEndSub

EndClass

Lesson 8: Constructors & Destructors


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ImportsSystem

A Constructor is a special function which is called automatically when a class is created. In VB.NET,

you should useuseNew()to create constructors. Constructors can be overloaded (see Lesson 4), but

unlike the functions, theOverloadskeyword is not required. A Destructor is a special function which

is called automatically when a class is destroyed. In VB.NET, you should use useFinalize()routine

to create Destructors. They are similar toClass_Initializeand Class_Terminatein VB 6.0.

Dogis a class:

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ClassDog

'The age variable

PrivateAge asinteger

The default constructor:

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PublicSubNew()

Console.Writeline ("Dog is Created With Age Zero")

Age=0

EndSub

The parameterized constructor:

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PublicSubNew(val asInteger)

Console.Writeline ("Dog is Created With Age "+ Convert.ToString(val))

Age=val

EndSub

This is the destructor:

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OverridesProtectedSubFinalize()

Console.Writeline ("Dog is Destroyed")

EndSub

'The Main Function
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SharedSubMain()DimJimmy, Jacky asDog

'Create the objects'This will call the default constructor

Jimmy=new Dog

'This will call the parameterized constructor

Jacky=new Dog(10)EndSub

'The Destruction will be done automatically, when'the program ends. This is done by the Garbage

'Collector.

EndClass

Lesson 9: Property Routines

You can use both properties and fields to store information in an object. While fields are

simply Publicvariables, properties use property procedures to control how values are set or

returned. You can use the Get/Setkeywords for getting/setting properties. See the following

example. Import the Systemnamespace (already available in .NET).

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ImportsSystem

Dogis a class.

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PublicClassDog

'A private variable to hold the value

PrivatemAgeOfDog asInteger

This is our property routine:

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PublicPropertyAge() AsInteger

'Called when someone tries to retreive the value

GetConsole.Writeline ("Getting Property")

ReturnmAgeOfdog

EndGetSet(ByValValue AsInteger)

'Called when someone tries to assign a valueConsole.Writeline ("Setting Property")

mAgeOfDog=ValueEndSet

EndProperty

EndClass

Another class:

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ClassMainClass

'Our main function. Execution starts here.SharedSubMain()'Let us create an object.

DimJimmy asDog

Jimmy=new Dog

'We can't access mAgeofDog directly, so we should

'use Age() property routine.'Set it. The Age Set routine will workJimmy.Age=30

'Get it back. The Age GEt routine will work

DimcurAge=Jimmy.Age()

EndSub

EndClass

Lesson 10: A simple program

Let us analyze a simple program. First, let us import the required namespaces:

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ImportsSystemImportsSystem.ComponentModel

ImportsSystem.Windows.Forms

ImportsSystem.Drawing

'We are inheriting a class named SimpleForm, from the

'class System.Windows.Forms.Form''i.e, Windows is a namespace in system, Forms is a

'namespace in Windows, and Form is a class in Forms.

PublicClassSimpleForm

InheritsSystem.Windows.Forms.Form

'Our constructorPublicSubNew()

'This will invoke the constructor of the base'class

MyBase.New()

Set the textproperty of this class. We inherited this property from the base class:

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Me.Text = "Hello, How Are You?"

EndSub

EndClass

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PublicClassMainClassSharedSubMain()

'Create an object from our SimpleForm classDimsf asSimpleFormsf=new SimpleForm

'Pass this object to the Run() function to start

System.Windows.Forms.Application.Run(sf)EndSub

EndClass


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That is it. Now you can atleast read and understand most of those VB.NET source code, and probably

implement more OOP features in your VB.NET programs. Now, in my next article, I'll try to cover the

patterns and practices in VB.NET.

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