IS437: Fall 2004
Instructor: Dr. Boris Jukic
Object Oriented Programming
Learning Objectives
• Object-oriented concepts
• Implementation of object-oriented concepts in
Visual Basic .Net
Limitations Of Conventional Languages
o
o
o
o
o
o
Small Vocabulary
Highly Procedural
Logic Buried In Long Lines Of Code
Difficult To Re-Use Code
Costly To Build And Modify
Allow Only Simple Data Structures
Object-Oriented Approach
PROGRAMMING LANGUAGES : SMALLTALK, C++,
Java, Visual Basic .Net
Goals
To Achieve Greater Semantic Expressiveness
- Complex Structure
- A Variety Of Relationships
- Natural Representation
To Reduce Use of Procedural Blocks of Code
To Enhance Re-Usability
Objects Correspond to Real World Constructs
student
university
cashier
car
ATM
radio
sales report
….
Key OO Concepts
Object
Encapsulation
Class
Class Hierarchy And Inheritance
Message And Polymorphism
Object & Encapsulation
Everything Is Modeled As Object:
Millie
Buddy Snoopy
Dog
Cashier
A Tax Return
Each Object Has A Name (External Identifier)
An Object Has Two Components :
- Properties (To Store Information)
Can Take On Complex Structure :
E.G. : Widget_A (Acquisition_Date, Quantity On Hand)
(( 3/10/92 $100) ( 3/20/92 $150) ( 3/25/92 $200))
- Methods (Behavior Encapsulation)
Record structure in COBOL
Name
Social Security #
Hobby
John Smith
445-09-2049
Swimming
Mary Scott
670-37-4095
Bridge
Bill Shoemaker
888-92-9104
Dancing
John Smith
123-87-3094
Painting
Records have no common external identifiers.
Attributes are single-valued.
Class Example
instance-of
relationship
MILLE
DOG
PUPPY
DOG(COLOR, SPEED)
SNOOPY
Class Hierarchy Example
IS-A-Kind of
relationship
instance-of
relationship
ANIMAL
BIRD
DOG
FISH
POLLY
MILLIE
MOBY
GENERALIZATION-SPECIALIZATION
RELATIONSHIP
Class Hierarchy: Another Example
IS-A-Kind of
relationship
UNDERGRADUATE
STUDENT
STUDENT
MBA
STUDENT
PH.D.
STUDENT
Inheritance
ANIMAL
(Beak, Fly)
BIRD
POLLY
(COLOR, SPEED)
(Bark, Ears)
DOG
FISH
MILLIE
MOBY
Polymorphism


Ability to take on many shapes and forms
Many classes can provide the same
property or method, without having to worry
what type of class it is:




Dog class (eat() method)
Mosquito class (eat() method)
Of course, same method would be implemented
in a very different way
Same class can have multiple versions of
the method

Overloaded methods
Benefits Of OO Approach:
- Greater Semantic Expressiveness
Can Represent Is_A Relationships
Support Complex Data Structure
- Behavior Encapsulation Facilitates The
Modeling Of Real-World Objects
- Object Library (Re-Use)
- Reduce Procedurality Through An Enlarged
Vocabulary
Difficulties

Different Programming Paradigm


Resistance, Requires a shift in thinking)
Increased Complexity:

Takes time to become acquainted with
the library of objects
Implementation of OO in Visual Basic .Net
 Object
 Encapsulation (property and method)
 Classes: over 6,000 in number
 Class hierarchy and inheritance
 Polymorphism
Visual Basic .Net supports all of the
key OO concepts. It is a full-fledged
OO system.
Object, Class, Encapsulation in VB .Net
class
Textbox
instance-of relationship
object
TextBox1
New keyword: creates
a new instance of an
object class
New Method in VB .Net
• Also called constructor
• It is the method that classes use to
instantiating
objects.
Dim label1 as Label
Label1 = New Label
or
Dim label1 as New Label
Add a control to a form
Me.controls.add(label1)
Represents
this form
The control
to be added
Collections
of controls
on a form
Add to the
collection
A Simplified View of Class Hierarchy in VB .Net
IS-A-Kind of
relationship
Object
Component
Data Adapter
DateTimePicker
Control
Label
PictureBox
Polymorphism in VB .Net
• Functionally equivalent methods can have the
same name
• VB .Net implements polymorphism in various
ways:
- overloading
- overriding
- method hiding
Polymorphism in VB .Net: Overloading
Messagebox.Show(“Enter numeric data.”)
Messagebox.Show(“Enter numeric data.”, “Data
entry error”)
Messagebox.Show(“This is a message.”, “This
is a title bar”, MessageBoxButtons.OK)
…
Overloading: methods
sharing the same name, for
the same object, but with
different signatures
(argument lists)
MessageBox General Form
Messagebox.Show(TextMessage)
Messagebox.Show(TextMessage, TitlebarText)
Messagebox.Show(TextMessage, TitlebarText,
MessageBoxButtons)
Messagebox.Show(TextMessage, TitlebarText,
MessageBoxButtons, MessageBoxIcons)
Polymorphism in VB .Net: Overriding
Animal
Parent class and
child class may
have methods with
the same name.
The method in
child class can
override the
method in parent
class.
Dog
Snoopy
Talk method:“I
cannot talk”
Talk method: “Bark
Bark”
Snoopy.Talk
“Bark Bark”
Polymorphism: method hiding
Button1.Click
CustomerForm.Click
Checkbox1.Click
…
Namespaces




Namespaces are file cabinets for
classes, similar to the concept of
folders.
Namespaces can contain classes, other
namespaces, etc.
Namespaces help organize the vast
number of classes into a neat structure.
To make use of a class, we need to
reference or import the namespace that
contains the class.
Namespace Hierarchy
System namespace
System
Windows.Forms
namespace
Data
namespace
Drawing
namespace
System.Windows.Forms
System.Data
System.Drawing
Button
OleDb namespace
System.Data.OleDb
Label
TextBox
OleDb provides
interaction with MS
Access.