Mark Dixon SOFT 131Page 1 12 – Object Oriented Analysis, Design, and Programming

Mark Dixon SOFT 131Page 2 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 a class definition, which includes properties, and methods –create an object instance, for the class –use the object instance, by assigning values to its properties, and calling its methods

Mark Dixon SOFT 131Page 3 Example: Ball Bounce v1 Ball Bounce Option Explicit Dim x Dim y Dim xInc Dim yInc Sub window_onLoad() window.setinterval "Main", 20 xInc = 5 yInc = 3 End Sub Sub Main() x = imgBall.style.pixelLeft + xInc If x = document.body.clientWidth - imgBall.width Then xInc = -xInc Else imgBall.style.pixelLeft = x End If y = imgBall.style.pixelTop + yInc If y = document.body.clientHeight - imgBall.height Then yInc = -yInc Else imgBall.style.pixelTop = y End If End Sub

Mark Dixon SOFT 131Page 4 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

Mark Dixon SOFT 131Page 5 Example: Ball Bounce v2 Option Explicit Dim x Dim y Dim xInc Dim yInc Sub Init(tmpXInc, tmpYInc) xInc = tmpXInc yInc = tmpYInc End Sub Sub Move(img) x = img.style.pixelLeft + xInc If x = document.body.clientWidth - img.width Then xInc = -xInc Else img.style.pixelLeft = x End If y = img.style.pixelTop + yInc If y = document.body.clientHeight - img.height Then yInc = -yInc Else img.style.pixelTop = y End If End Sub Ball Bounce Option Explicit Sub window_onLoad() window.setinterval "Main", 20 Init 5, 3 End Sub Sub Main() Move imgBall End Sub BallBounce.htm Sprit.vbs

Mark Dixon SOFT 131Page 6 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

Mark Dixon SOFT 131Page 7 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

Mark Dixon SOFT 131Page 8 Object Concepts - Implementation Properties – implemented as –data structures (variables, and arrays) 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

Mark Dixon SOFT 131Page 9 Properties: Animals Class: Animal Properties: Name, Species, Gender Instances: myPet, yourPet

Mark Dixon SOFT 131Page 10 Example: Ball Bounce v3 Option Explicit Class Sprite Dim x Dim y Dim xInc Dim yInc End Class Sub Init(spr, tmpXInc, tmpYInc) spr.xInc = tmpXInc spr.yInc = tmpYInc End Sub Sub Move(spr, img) spr.x = img.style.pixelLeft + spr.xInc If spr.x = document.body.clientWidth - img.width Then spr.xInc = -spr.xInc Else img.style.pixelLeft = spr.x End If spr.y = img.style.pixelTop + spr.yInc If spr.y = document.body.clientHeight - img.height Then spr.yInc = -spr.yInc Else img.style.pixelTop = spr.y End If End Sub … Option Explicit Dim ball Sub window_onLoad() window.setinterval "Main", 20 Set ball = New Sprite Init ball, 5, 3 End Sub Sub Main() Move ball, imgBall End Sub BallBounce.htm Sprit.vbs Class Definition

Mark Dixon SOFT 131Page 11 Methods: Students Method: Clear

Mark Dixon SOFT 131Page 12 Example: Ball Bounce v4 Option Explicit Class Sprite Dim x Dim y Dim xInc Dim yInc Sub Init(tmpXInc, tmpYInc) xInc = tmpXInc yInc = tmpYInc End Sub Sub Move(img) x = img.style.pixelLeft + xInc If x = document.body.clientWidth - img.width Then xInc = -xInc Else img.style.pixelLeft = x End If y = img.style.pixelTop + yInc If y = document.body.clientHeight - img.height Then yInc = -yInc Else img.style.pixelTop = y End If End Sub End Class … Option Explicit Dim ball Sub window_onLoad() window.setinterval "Main", 20 Set ball = New Sprite ball.Init 5, 3 End Sub Sub Main() ball.Move imgBall End Sub BallBounce.htm Sprit.vbs

Mark Dixon SOFT 131Page 13 Example: Ball Bounce v5 Multiple instances:

Mark Dixon SOFT 131Page 14 Example: Ball Bounce v5 Ball Bounce Option Explicit Dim ball Dim face Sub window_onLoad() window.setinterval "Main", 20 Set ball = New Sprite ball.Init 5, 3 Set face = New Sprite face.Init 1, 12 End Sub Sub Main() ball.Move imgBall face.Move imgFace End Sub Now have easy way of: –creating & using multiple sprites –each with own identity (separate characteristics) –only a few (4) lines of code

Mark Dixon SOFT 131Page 15 Questions: OOP Name a –class –property –method –instance Class House Dim number Dim road Dim district Sub ChangeDist(newDist) district = newDist End Sub End Class Dim h Set h = New House

Mark Dixon SOFT 131Page 16 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 Reduces chance of accidental interference Less prone to error

Mark Dixon SOFT 131Page 17 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.

Mark Dixon SOFT 131Page 18 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.

Mark Dixon SOFT 131Page 19 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

Mark Dixon SOFT 131Page 20 Scenario 1: detail Nouns: drinks, order, cost Verbs: describe, calculate cost

Mark Dixon SOFT 131Page 21 Tutorial Exercise: Ball Bounce Learning Objective: To create and use your own class. Task 1: Get the Ball Bounce examples (1, 2, and 5) from the lecture working. Task 2: Add a hit method to the sprite class, which detects the collision with another sprite. Task 3: Modify your page to count the number of hits between the two sprites. Task 4: Modify your page to make sprites bounce off each other. Task 5: Add another sprite.

Mark Dixon SOFT 131Page 22 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 SOFT 131Page 23 Tutorial Exercise: Interceptor Learning Objective: To create and use your own classes. Task 1: Re-write your Interceptor example (from last week) to use object oriented concepts (classes, properties, methods, and instances)