1. Mark Dixon Page 1 13 – Object Oriented Programming

2. Mark Dixon Page 2 Admin: Coursework 3 – Test In class test –26 Jan 2009: teaching week 15 50 mins short answer (5 - 6 words max) 25% of coursework mark

3. Mark Dixon Page 3 Questions: Functions Consider the following code: Function Smallest(num1, num2) If num1 < num2 Then Smallest = num1 Else Smallest = num2 End If End Function name a function. what is left in small after the following is executed? Dim small small = Smallest(23, 15) 15 Smallest

4. Mark Dixon Page 4 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

5. Mark Dixon Page 5 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

6. Mark Dixon Page 6 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 Abstract data type = structure + procedures

7. Mark Dixon Page 7 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 Sprite.vbs

8. Mark Dixon Page 8 Object-Oriented Paradigm program made up 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

9. Mark Dixon Page 9 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

10. Mark Dixon Page 10 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

11. Mark Dixon Page 11 Example: Animals Class: Animal Properties: Name, Species, Gender Instances: myPet, yourPet

12. Mark Dixon Page 12 Question: Objects Consider the following code: Class FetalBloodSample Dim Time Dim Acidity Dim Reactivity End Class Dim fbs1 Set fbs1 = New FetalBloodSample Name all: –classes –properties –instances FetalBloodSample Time, Acidity, Reactivity fbs1

13. Mark Dixon Page 13 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 Sprite.vbs Class Definition

14. Mark Dixon Page 14 Example: Students Method: Clear

15. Mark Dixon Page 15 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 Sprite.vbs procedures are now methods inside the class

16. Mark Dixon Page 16 Example: Ball Bounce v5 Multiple instances:

17. Mark Dixon Page 17 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

18. Mark Dixon Page 18 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 House number, road, district ChangeDist h

19. Mark Dixon Page 19 OOP: Errors Object doesn't support this property or method: Class Animal Dim name Dim species End Class Dim a Set a = New Animal a.name = "Skippy" a.specys = "Kangaroo"

20. Mark Dixon Page 20 Private make properties and methods invisible outside class: Class Counter Private value Sub Reset() value = 0 End Sub Sub Increase() value = value + 1 End Sub Function GetValue() GetValue = value End Function End Class Dim c Set c = New Counter c.Reset c.Increase parRes.innerText = c.GetValue() c.value = -6

21. Mark Dixon Page 21 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

22. Mark Dixon Page 22 Example: Balloon Shoot Question: –what objects? –what classes? –what properties? –what methods

23. Mark Dixon Page 23 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.

24. Mark Dixon Page 24 Tutorial Exercise: Balloon Shoot Learning Objective: To create and use your own classes. Task 1: Create the Balloon Shoot example (from the lecture) using object oriented concepts (classes, properties, methods, and instances) hint: use some of the code from your Interceptor example (from last week)