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INTRODUCTION TO OOP
Objective:
• Know the difference between functional programming and OOP• Know basic terminology in OOP• Know the importance of OOP• Know four design principles of OOP• Know OOP programming languages
CSCI N201: Programming Concepts
Copyright ©2005 Department of Computer & Information Science
Introducing Object-Oriented Programming (OOP)
Programming LanguagesProgramming languages allow programmers to code software.The three major families of languages are:
Machine languagesAssembly languagesHigh-Level languages
Machine LanguagesComprised of 1s and 0sThe “native” language of a computerDifficult to program – one misplaced 1 or 0 will cause the program to fail.Example of code:1110100010101 111010101110 10111010110100 10100011110111
Assembly LanguagesAssembly languages are a step towards easier programming. Assembly languages are comprised of a set of elemental commands which are tied to a specific processor.Assembly language code needs to be translated to machine language before the computer processes it.Example:ADD 1001010, 1011010
High-Level LanguagesHigh-level languages represent a giant leap towards easier programming.The syntax of HL languages is similar to English. Historically, we divide HL languages into two groups:
Procedural languagesObject-Oriented languages (OOP)
Procedural LanguagesEarly high-level languages are typically called procedural languages.Procedural languages are characterized by sequential sets of linear commands. The focus of such languages is on structure.Examples include C, COBOL, Fortran, LISP, Perl, HTML, VBScript
Object-OrientationA thinking methodology
Everything is an object.Any system is composed of objects (a system is also an object).The evolution and development of a system is caused by the interactions of the objects inside/outside a system.
Everything is an object
A student, a professorA desk, a chair, a classroom, a buildingA university, a city, a countryThe world, the universeA subject such as CS, IS, Math, History, …
Systems are composed of objects
An educational systemAn economic systemAn information systemA computer system
Object-Oriented Languages
Most object-oriented languages are high-level languages.The focus of OOP languages is not on structure, but on modeling data.Programmers code using “blueprints” of data models called classes.Examples of OOP languages include C++, Visual Basic.NET and Java.
Object Oriented Programming
Object – Unique programming entity that has methods, has attributes and can react to events.Method – Things which an object can do; the “verbs” of objects. In code, usually can be identified by an “action” word -- Hide, Show
Object Oriented Programming
Attribute – Things which describe an object; the “adjectives” of objects. In code, usually can be identified by a “descriptive” word – Enabled, BackColorEvents – Forces external to an object to which that object can react. In code, usually attached to an event procedure
Object Oriented Programming
Class – Provides a way to create new objects based on a “meta-definition” of an object (Example: The automobile class)Constructors – Special methods used to create new instances of a class (Example: A Honda Civic is an instance of the automobile class.)
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STRUCTURED vs. OO PROGRAMMING
STRUCTURED PROGRAMMING:MAIN PROGRAM
FUNCTION 3FUNCTION 2
GLOBAL DATA
FUNCTION 5FUNCTION 4
FUNCTION 1
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Structured Programming
Using functionFunction & program is divided into modulesEvery module has its own data and function which can be called by other modules.
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OBJECT ORIENTED PROGRAMMING
Object 1 Object 2
Data
Function
Data
Function
Object 3
Data
Function
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OBJECT ORIENTED PROGRAMMING
Objects have both data and methods Objects of the same class have the same data
elements and methods Objects send and receive messages to invoke
actions
Key idea in object-oriented:
The real world can be accurately described as a collection of objects that interact.
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Basic terminology
object - usually a person, place or thing (a noun)method
- an action performed by an object (a verb)attribute
- description of objects in a classclass
- a category of similar objects (such as automobiles)- does not hold any values of the object’s attributes
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Example for attributes and methods
Attributes:manufacturer’s namemodel nameyear madecolornumber of doorssize of engineetc.
Methods:Define data items (specify manufacturer’s name, model, year, etc.)Change a data item (color, engine, etc.)Display data itemsCalculate costetc.
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Why OOP?
Save development time (and cost) by reusing code
once an object class is created it can be used in other applications
Easier debuggingclasses can be tested independentlyreused objects have already been tested
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Why OOP (Cont.)Effects of OO methodology on software design
maintenanceextensibilityreusability
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Design Principles of OOP
Four main design principles of Object-Oriented Programming(OOP):
Encapsulation Abstraction Polymorphism Inheritance
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Encapsulation
Also known as data hidingOnly object’s methods can modify
information in the object.
Analogy: ATM machine can only update accounts
of one person or object only.
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AbstractionFocus only on the important facts about the problem at handto design, produce, and describe so that it can be easily used without knowing the details of how it works.
Analogy: When you drive a car, you don’t have to know how the gasoline and air are mixed and ignited. Instead you only have to know how to use the controls.Draw map
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Polymorphism
the same word or phrase can mean different things in different contexts
Analogy: In English, bank can mean side of a river
or a place to put moneymove -
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Function Overloading
The operation of one function depends on the argument passed to it.
Example: Fly(), Fly(low), Fly(150)
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Inheritance
Inheritance—a way of organizing classes Term comes from inheritance of traits like
eye color, hair color, and so on. Classes with properties in common can be
grouped so that their common properties are only defined once. Superclass – inherit its attributes &
methods to the subclass(es). Subclass – can inherit all its superclass
attributes & methods besides having its own unique attributes & methods.
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An Inheritance Hierarchy
Vehicle
Automobile Motorcycle Bus
Sedan Sports Car School BusLuxury Bus
What properties does each vehicle inherit from the types of vehicles above it in the diagram?
Superclass
Subclasses
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Object-Oriented Programming Languages
· Pure OO Languages
Smalltalk, Eiffel, Actor, Java
· Hybrid OO Languages
C++, Objective-C, Object-Pascal
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Review: Introduction to Object Orientation
What are the four basic principles of object orientation? Provide a brief description of each.What is an Object and what is a Class? What is the difference between them?What is an Attribute?What is an Operation?What is inheritance? What is polymorphism? Describe the strengths of object orientation.
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Review: Introduction to Object Orientation
State 2 differences between functional programming and OOP.What are the four basic principles of object orientation? Provide a brief description of each.What is an Object and what is a Class? What is the difference between them?What is an Attribute?What is an Operation?Describe the strengths of object orientation.