IS0514 Lecture Week 5

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IS0514 Lecture Week 5

• Introduction to Object Orientation

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Why Object Oriented?

• Based on domain analysis / subject matter
  analysis
• Close match to real world
• Nearly all Modern Technologies are Object
  Oriented
• Java / C / C / PHP (object extension) / Delphi
• Oracle Object relational database
• gt closer match to end solution
• Widely accepted ( most common approach )
• Extensible / Maintainable
• Reusable

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Today's Lecture

• Introduction to object orientation concepts
• Object
• Class
• Method
• Attribute
• Relationships
• Inheritance

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What is the world?

• The world can be seen to consist
• Things
• Relationships between things
• A thing can be
• Physical / Tangible
• Idea / Concept / Non-Tangible
• In object orientation a thing is called an Object
• Thing-Oriented Analysis!

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Exercise 1

• Think about the objects in this room.
• Try to identify the objects in this room
• What things are here
• Physical
• Conceptual / Ideas
• In groups of 3-4 spend 5 minutes discussing what
  objects there are. At the end of that time you
  will be asked to share your thoughts with the
  rest of the class.

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Exercise 1 - Possible Objects

• Physical
• The lecturer
• Each of the students
• Each of the seats
• The handouts
• Computer
• Projector
• Crisps / Chocolate / Cans
• Each of the Mobile phone switched off or silent!

• Ideas
• The lecture itself
• Exercise 1
• Lecture slide

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Attributes and behaviour

• Objects have properties called attributes
• Attributes are the data associated with an object
• Objects have behaviour we call these methods
• These are the tasks an object will do (typically
  when we ask it to)
• These may also be called operations / member
  functions but we will try and call them methods

• Example A Car
• Attributes
• Make
• Model
• Engine Size
• Current Speed
• Methods
• break()
• accelerate()
• changeGear()
• honkHorn()

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Exercise 2

• Think about the object a student
• Try an identify its
• Attributes
• Methods
• Think about which of these are relevant as regard
  to the university?
• In groups of 3-4 spend 5 minutes discussing this.
  At the end of that time you will be asked to
  share your thoughts with the rest of the class.

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Exercise 2 - Solution

• Attributes
• Name
• Registration Number
• Date of Birth
• Gender
• Address
• Programme
• etc

• Methods
• AttendLecture()
• AttendSeminar()
• CompleteAssignment()
• SitExam()
• etc

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Categories of things

• Things naturally fall into categories (Car,
  Furniture, House)
• In object orientation, a category of things is
  called a class
• an object is an instance of a class
• my car gt object Car gt class
• Objects share behaviour as defined by their class
  respond to the same set of methods
• For example all cars can accelerate
• Some value(s) can affect what a method does
• Objects share Class attributes e.g. every car has
  a colour
• Object attributes will have different values

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Exercise 3

• Think about the objects in the room and try to
  identify what classes these objects belong to.
• In groups of 3-4 spend 5 minutes discussing this.
  At the end of that time you will be asked to
  share your thoughts with the rest of the class.

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Exercise 3 - Possible Classes

• Physical
• Person
• Lecturer
• Student
• Seat
• Furniture
• Handout
• Computer
• Projector

• Ideas
• Lecture
• Exercise

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Classes and Objects more formally

• Class Template to define specific instances or
  objects
• Object Instantiation of a class
• Attributes Describes each object
• Behaviors Specify what each object can do
• Methods (a.k.a. operations)

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Classes and Objects
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Methods and Messages

• Methods implement objects behavior
• Analogous to a function or procedure
• Messages are sent to trigger methods
• Procedure call from one object to another object

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Messages and Methods
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Relationships between Classes

• Classes / Objects can be related
• Student completes Assignment
• Student is registered for a Module
• Student has access to the Blackboard
• Some relationships are stronger than others
• Student is a kind of Person
• Lecturer is a kind of Person
• Inheritance
• Is a generalisation / specialisation relationship
  between two classes
• Is a kind of relationship

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Class Hierarchy
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Exercise 4

• Think about the class hierarchy between Person,
  Student, Lecturer, Full Time Student and Part
  Time Student.
• Draw the class hierarchy
• In groups of 3-4 spend 5 minutes discussing this.
  At the end of that time you will be asked to
  share your thoughts with the rest of the class.

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Exercise 4 - Class Hierarchy
Person
Lecturer
Student
PartTimeStudent
FullTimeStudent
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Inheritance some terms

• Superclasses or general classes are at the top of
  a hierarchy of classes
• Subclasses or specific classes are at the bottom
• Subclasses inherit attributes and methods from
  classes higher in the hierarchy
• In our tree, which are the subclasses and
  superclasses?

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Inheritance
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Basic Characteristics of Object Oriented Systems

• Classes and Objects
• Methods / Messages
• Inheritance
• THE BASICS OF OBJECT ORIENTATION
• Next Week Class Diagrams

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This weeks reading

• ESSENTIAL READING
• Dennis A, Wixom B, and Tegarden D (2005) System
  Analysis and Design with UML version 2 second
  edition, Wiley
• Pages 23-29
• Further reading
• Bennett, S., McRobb, S. and Farmer, R. (2002)
  Object-Oriented Systems Analysis and Design using
  UML, 2nd Edition, McGraw-Hill
• Chapter 4