mark dixon, socce soft 131page 1 22 – object oriented analysis, design, and programming

Mark Dixon, SoCCE SOFT 131

22 – Object Oriented Analysis, Design, and Programming


Session Aims & Objectives• Aims

– To introduce the fundamental ideas of object orientation

• Objectives,by end of this week’s sessions, you should be able to:

– create and use an object class


Evolution of SoftwarePressman (1992) page 5:


Software CrisisCustomer (User) dissatisfaction:

• Over budget

• Late delivery

• Does not do what is required

• Poor quality– accuracy– reliability– maintainability– ease of use and learning

Pressman (1992) p. 18


Example: Counter v1Option ExplicitDim tmpCount As Long

Private Sub Form_Load() tmpCount = 0 Me.lblCounter.Caption = tmpCountEnd Sub

Private Sub btnUp_Click() tmpCount = tmpCount + 1 Me.lblCounter.Caption = tmpCountEnd Sub

Private Sub btnDown_Click() tmpCount = tmpCount - 1 Me.lblCounter.Caption = tmpCountEnd Sub

Private Sub btnReset_Click() tmpCount = 0 Me.lblCounter.Caption = tmpCountEnd SubCounter v1


Structured Paradigm• Program made up of

– data structures, and – routines (procedures and functions) that

process the data within those structures.

• Each routine should perform a single, clearly identifiable operation.

• Each routine should be self-contained

• Go to statements replaced by structures

• Abstract data type = structure + procedures


Example: Counter v2Private Sub Form_Load() CounterReset CounterDisplayEnd Sub

Private Sub btnUp_Click() CounterUp CounterDisplayEnd Sub

Private Sub btnDown_Click() CounterDown CounterDisplayEnd Sub

Private Sub btnReset_Click() CounterReset CounterDisplayEnd Sub

Counter v2

Option ExplicitDim tmpCount As Long

Sub CounterDisplay() Me.lblCounter.Caption = tmpCountEnd Sub

Sub CounterReset() tmpCount = 0End Sub

Sub CounterUp() tmpCount = tmpCount + 1End Sub

Sub CounterDown() tmpCount = tmpCount - 1End Sub


Object-Oriented Paradigm• A program is made up of a number of objects that

communicate with each other by passing messages

• Each object contains– attributes/properties that represent its state, and– operations/methods that represent its behaviour

• Objects often mirror the real world– Customers– Students– Patients


Classes and Instances• Object Classes

– general descriptions of types of objects,e.g. student, product, customer, lecturer, and room.

• Object Instances– specific items of a given class, e.g.

• each of you could be an instance of the student class• Room 214 could be an instance of the room class• I could be an instance of the lecturer class• Bolt could be an instance of the part class


Object Concepts - Implementation

• Properties – implemented as– data structures (variables, arrays, and types).

• Methods – implemented as either– a procedure (to perform some processing), or– a function (to return a value).

• Object oriented paradigm builds on (rather than replaces) the structured paradigm


Class Diagrams• Used to describe structure of object classes:

Module

Code: stringTitle: string

GetTitle(): stringSetTitle(t: string)Count(): integer

Class Attributes/Properties

Class Operations/Methods

Class Name


Implementation in VB• class module – special type of module that

defines an object class– Project menu, Add Class Module item

• Extends the record / structure / user defined data type,– which is used to store related data which may

be of different types.

• An object stores– data – but also provides methods for accessing and

manipulating that data.

Animation


OOP: Animation


Modules/Units• 1 Class per Module

– keeps logically related things together– makes programming easier– less errors

• Example: Counter– Counter class put in separate module– main (form) module uses counter module


Example: Counter v3Option ExplicitDim tmpCounter As Counter

Private Sub Form_Load() Set tmpCounter = New Counter tmpCounter.Reset tmpCounter.Display Me.lblCounterEnd Sub

Private Sub btnUp_Click() tmpCounter.Up tmpCounter.Display Me.lblCounterEnd Sub

Private Sub btnDown_Click() …

Private Sub btnReset_Click() tmpCounter.Reset tmpCounter.Display Me.lblCounterEnd Sub

Private Sub Form_Unload(Cancel As Integer) Set tmpCounter = NothingEnd Sub

Counter v3

Option Explicit

Private mCount As Long

Public Sub Display(tmpLabel As Label) tmpLabel.Caption = mCountEnd Sub

Public Sub Reset() mCount = 0End Sub

Public Sub Up() mCount = mCount + 1End Sub

Public Sub Down() mCount = mCount - 1End Sub

Counter (class module)


Things to Note• The dot notation is the same for both

records and objects.• A record variable may be accessed

immediately after definition whereas an object must first be ‘created’: Set tmpCounter = New Counter


Benefits of OOP in code• Procedures and Functions are part of object

– encapsulation

• Related Data and Operations together

• Private keyword – restrict access to data

• Clearer code

• Less prone to error


Why change?• It’s well established that program quality

improves as the semantic distance between the programming language and the real world problem language is diminished.

• It’s believed that the concept of communicating objects provides a better general framework for programming since it is closer to the real world situation than the structured paradigm.


Public Code As StringPublic Title As String

Public Function GetTitle() As string Public Sub SetTitle(t As String) Public Function Count() As Integer

Implementing Class Diagrams

Module

Code: String[7]Title: String[25]

GetTitle(): stringSetTitle(t: string)Count(): integer


Object Oriented Analysis• Look for nouns in text, either

– object classes, or– object properties

• Look for verbs in text,– object methods

The students' Union bar needs a computer system for recording the purchase of drinks. Typically, a student will stagger to the bar and describe their order, consisting of one or (usually) more drinks.The bar staff will then prepare the drinks and calculate the cost of the order.


Identify all nouns and verbs

• Nouns: student's Union bar, computer system, drinks, student, bar, order, bar staff, cost.

• Verbs: recording the purchase, stagger, describe, prepare drinks, calculate cost

The students' Union bar needs a computer system for recording the purchase of drinks. Typically, a student will stagger to the bar and describe their order, consisting of one or (usually) more drinks.The bar staff will then prepare the drinks and calculate the cost of the order.


Identify relevant nouns and verbs• What is relevant?

– depends on project scope, duration, budget

• Scenario 1: small project, limited automation– Nouns: drinks, order, cost– Verbs: describe, calculate cost

• Scenario 2: large project, high automation– Nouns: student's Union bar, drinks, student,

bar, order, bar staff, cost.– Verbs: recording the purchase, describe,

prepare drinks, calculate cost


Scenario 1: detail• Nouns: drinks, order, cost

• Verbs: describe, calculate cost


Tutorial Exercise: Counter• Learning Objective: The important thing to understand from

this exercise is that using classes allows you to make data private, and therefore prevents it being accidentally changed by other modules.

• Task 1: Get the Counter examples (1, 2, and 3) from the lecture working.

• Task 2: Modify your code (for v3) – add code to prevent the counter going below zero.

• Task 3: Modify your code (for v3) – add code to prevent the counter going above ten.

• Task 4: Modify your code (for v3) – add code for two additional properties max and min, that are used by the above limits.


Tutorial Exercise: Bar• Task 1: Continue the analysis of the bar

example in the lecture, and implement a simple object oriented bar drinks calculation program.

mark dixon, socce soft 131page 1 22 – object oriented analysis, design, and programming

Documents

end sub sub counterup

end sub slide

socce soft

mark dixon

long sub counterdisplay

load tmpcount

object class slide

counter v2 private sub