12429_basics of oops

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Copyright ©2005 Department of Computer & Information Science

Object Oriented Concepts




Goals

• Understand objects, their attributesand their methods.

• Understand the pillars of object-oriented programming asencapsulation, inheritance &

polymorphism.




OOP Concepts

• Objects

• Attributes

• Methods• Events

• Abstraction & Classes• Constructors




What is an object?

• An object is a unique programmingentity that has attributes to describe

it (like adjectives in grammar) andmethods to retrieve/set attributevalues (like verbs in grammar).




Attributes

• Programmers store an object’s data inattributes, also called properties.

• Attributes provide us a way todescribe an object, similar toadjectives in grammar.

• We can read property values orchange properties, assigning values.




Methods

• Whereas attributes describe anobject, methods allow us to access

object data. Methods are like verbs ingrammar.

• We can manipulate object data,

stored in attributes, using methods.




Events

• Object-oriented programming isinherently tied to user interaction.

Programs record interaction in theform of events.

• Events are changes in an object’s

environment to which it can react.




Abstraction

• One of the chief advantages ofobject-oriented programming is the

idea that programmers can essentiallyfocus on the “big picture” and ignorespecific details regarding the inner-

workings of an object. This concept iscalled abstraction .




Classes

• How do programmers get byimplementing abstraction? They use a

programming structure called a class .• A class presents a blueprint of an

object, its properties and its methods.




Instantiation

• To create an object based on a class,we create an instance of that class.

This process is called instantiation.• In Java, JavaScript and other

languages, we use a special method

called a constructor method to createan instance of an object.




Encapsulation

• Abstraction in OOP is closely relatedto a concept called encapsulation .

• Data and the ways to get at that dataare wrapped in a single package, aclass. The only way to access such

data is through that package. Thisidea translates to information hiding.




Inheritance

• Another of the main tenets of OOP isinheritance . Inheritance allows

programmers to create new classesfrom existing ones.

• A child class inherits its properties

and attributes from its parents, whichprogrammers can change.




Polymorphism

• Polymorphism describes howprogrammers write methods to do

some general purpose function.• Different objects might perform

polymorphic methods differently.




Summary

• Programming objects are comprisedof attributes and methods.

• Classes provide programmers withblueprints of objects.

• To create an object from a class, weuse constructor methods to create aclass instance.

12429_basics of oops

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