Object-Oriented ProgrammingConcepts and Principles

1. Object-Oriented Programming
Concepts and Principles
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2. Outline
▪ Abstraction
▪ Structured Programming
▪ Procedural vs. Object-Oriented Programming
▪ Goals of Object-Oriented Programming
▪ Principles of Object-Oriented Programming
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3. Abstraction
▪ One of the prime concepts used to simplify programming problems
▪ Mechanism and practice to reduce and factor out details so that one can focus on
a few concepts at a time.
▪ Through the process of abstraction, a programmer hides all but the relevant data
about an object in order to reduce complexity and increase efficiency.
▪ Abstraction is one of the key concepts of object-oriented programming (OOP)
languages.
▪ Its main goal is to handle complexity by hiding unnecessary details from the user.
▪ That enables the user to implement more complex logic on top of the provided
abstraction without understanding or even thinking about all the hidden complexity.
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4. Abstraction

5. Structured Programming
▪ Further refinement of procedural
programming
▪ Formal methods of planning data flow
and functional decomposition
▪ go to is banned

6. Structured Programming
▪ A programming paradigm aimed at improving the clarity, quality, and
development time of a computer program by making extensive use of the
structured control flow constructs
▪ Selection (if/then/else)
▪ Repetition (while and for)
▪ Block structures
▪ Subroutines
▪ A programming paradigm in contrast to using simple tests and jumps such
as the go to statement.
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7. Procedural Programming
▪ A programming model which is derived from structured programming, based
upon the concept of calling procedure.
▪ Procedures, also known as routines, subroutines or functions, simply consist of
a series of computational steps to be carried out.
▪ During a program’s execution, any given procedure might be called at any point,
including other procedures or itself.
▪ Languages
▪ Basic
▪ Pascal
▪ C
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8. Procedural Programming
▪ Routines are grouped into functions
▪ A function can call another function
▪ You don’t have to understand each line, lust what each function did
▪ You could hide data to be accessible to only within a function (encapsulation)
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9. Object-Oriented Programming (OOP)
▪ Takes encapsulation even further by localizing data and associated operations
into a mini-program called an object.
▪ An object-oriented program is an ecosystem of objects that interact with each
other.
▪ “Think of an object-oriented system as a bunch of intelligent animals as objects
inside your machine, talking to each other by sending messages to one
another.” – Alllan Holub
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10. Object-Oriented Programming (OOP)
▪ A programming model which is based upon the concept of objects.
▪ Objects contain data in the form of attributes and code in the form of methods.
▪ In OOP, computer programs are designed using the concept of objects that interact with
real world.
▪ OOP languages are various but the most popular ones are class-based, meaning that
objects are instances of classes, which also determine their types.
▪ OOP takes abstraction farthest by allowing you to group related data and operations into
different types of objects.
▪ You create your own data types, which are types of objects. Each of these data types are
called objects.
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11. Object-Oriented Programming (OOP)
▪ Creating you own classes allows you to design a program so that it is
intuitive to remember how it is organized
▪Example
▪ Creating classes that represent real world entities.
▪ Creating classes to have specific responsibilities so that when you need to update a piece of code,
you know exactly where to look for it
▪ Languages
▪ Java, C++, C#, Python, PHP, JavaScript
▪ Ruby, Perl, Objective-C, Dart, Swift, Scala
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12. Goals of Object-Oriented Programming
▪ Comprehensibility
▪ Make it easier for humans to understand you code
▪ Maintainability
▪ Make code easy to modify
▪ Reusability
▪ Old code should be building blocks for new code
▪ Plugability
▪ You can create interchangeable component that can substitute for one another
just like machine parts.
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13. Class and Objects
▪ A class in Java is a blueprint for objects to follow a specific schema defined in the class.
▪ A class defines the behavior for objects of its type. It represents a collection of properties
(data and functions) for all its objects.
▪ It supports a template for creating objects which bind code and data.
▪ A class acts as a means to define methods and data.
▪It helps in maintaining access specifications for member variables using access specifiers.
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14. Class and Objects
▪ An object is the most fundamental entity in Java
▪ Objects represent real-life entities because each of them could have specific behavior,
identity, and data (attributes).
▪ In Java, the object is an offspring of its class.
▪ The class has properties to reflect the object state and methods to represent the behavior.
▪ The methods also show an object’s response to other objects. Identity is a unique name for
the object assigned by the user, much like variables.
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15. What is a Class and an Instance of a Class?
▪ Class
▪ Definition of an object
▪ Example:
▪ Your car is a 2018 BMW 3-series
▪ Instance
▪ The created object of a class
▪ Example :
▪ There are many other 2018 BMW 3-series out there but there is only one instance of your car.
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16. What is an object?
▪ Has attributes
▪ a property or components
▪ Has methods
▪ behaviours or routines
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17. Example of an Object - Car
▪ Attributes
▪ steering wheel
▪ engine
▪ color
▪ radio
▪ airconditoiner
▪ Methods
▪ go forward
▪ go backward
▪ cool the interior
▪ play music
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18. What is an interface?
▪ An object has an interface
▪ The outward appearance of an object. How other objects see the object
▪ The attributes and methods that the object exposes.
▪ Normally, an object will only expose some of its attributes and methods.
▪ Some attributes and methods are used by the object itself. Therefore, no other object
should have access to those
▪ Some attribute and methods may be made accessible only to certain other objects.
▪ Some attributes and methods may be accessible by any other object
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19. What is an interface?
▪ Normally, only methods are exposed. Objects usually hide their data to
protect then from being changed by other objects without their control
▪ Constants are an exception. These don’t change anyway
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20. Three Core Principles of OOP
▪ Encapsulation
▪ Inheritance
▪ Polymorphism
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21. Encapsulation
▪ It is a mechanism of wrapping the data (variables) and code acting on the
data (methods) together as a single unit.
▪ In encapsulation, the variables of a class will be hidden from other classes,
and can be accessed only through the methods of their current class.
▪ Grouping of data and operations into objects.
▪ Related data and operations should not be separated. They should be found
in a single object.
▪ It is also known as data hiding
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22. Encapsulation
▪To achieve encapsulation in Java
▪ Declare the variables of a class as private.
▪ Provide public setter and getter methods to modify and view the variables values.
▪ Benefits of Encapsulation
▪ The fields of a class can be made read-only or write-only
▪ A class can have total control over what is stored in its fields
▪ Simpler interfaces
▪ Only a few methods are exposed to other objects. Since interactions between objects are simple, system us easier for the
programmer to comprehend.
▪ Data protected from corruption
▪ Easier to modify code or find bugs
▪ Simpler interactions
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23. Examples of Encapsulation
▪ You shouldn’t have to ask someone with radar gun to measure the speed of
your car. Your car should have its own speedometer.
▪ Purchase Order Object
▪ Data for purchase orders should not be lumped in the same objects as data for invoices and receipts
▪ The methods for retrieving data from a purchase order should not be found in a separate class from
the data.
▪ DB Connection Object
▪ The DB Connection object should not need to look up the URL from the database from another
object every time its does an operation.
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24. Examples of Encapsulation
▪ Information Hiding
▪ AN object should expose only what is necessary, and only at the appropriate level.
▪ Think of CIA … “need-to-know”
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25. Examples of Encapsulation
▪ Car
▪ Driver : Only steering wheel, pedals, and stick shift are exposed. Driver should not access engire or
gears or axle to drive the car
▪ Mechanic
▪ Access to engine, gears, etc., but not internals of each part
▪Manufacturer
▪ Access to internals of each part
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26. Examples of Encapsulation
▪ Purchase Order Object
▪ Any object can get into from the object, but only certain objects should have authority to set
information.
▪ Only certain objects should be allowed to create PO object
▪ DB Connection Object
▪ Only the Driver Manager object can create a connection
▪ Users cannot set whether a connection is read-only or not.
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27. Inheritance
▪ It is a way to create a new class by deriving from another class.
▪ It is the mechanism in java by which one class is allowed to inherit the
features(fields and methods) of another class.
▪ Interface Inheritance
▪ The new class acquires the interface of the old class
▪ Implementation Inheritance
▪ The new class often also acquires the implementation of the old class
▪ The new class can change the implementation of the older class or ass its methods and
attributes.
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28. Inheritance
▪ Inheritance is a way to allow objects to share code, preventing code-
duplication
▪ Code supplication is the number sin in OOP
▪ Implementation inheritance is dangerous
▪ The Fragile Base Class Problem
▪ A subclass must inherit all inheritable members of the superclass
▪ No option to disinherit a member
▪ If the subclass inherits members that it doesn’t need, those members might be called by other objects in
a way that the creator of the subclass did not intend (remember you’re working in a tem) causing
undesirable behavior

29. Polymorphism
▪ When a single data type exhibits different behaviours during execution.
▪ Greek : Poly means “many”, morph means “form”
▪ Polymorphism means “existing in many forms”
▪ It is the other side of the same coin as inheritance
▪ Polymorphism is the reason why we want to have inheritance
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30. Polymorphism
▪ Polymorphism allows for “pluggability” or “substitutability”
▪ Types that implement the same interface can substitute for one another
▪ Client code just sees one class, but the actual “concrete” type can be different
in different cases.
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