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13 – Object Oriented Programming

13 – Object Oriented Programming. 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. Questions: Functions.

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13 – Object Oriented Programming

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  1. 13 – Object Oriented Programming

  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. 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) Smallest 15

  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. Example: Ball Bounce v1 <html> <head><title>Ball Bounce</title></head> <body style="margin: 0;"> <img id="imgBall" src="Ball.gif" style="position: absolute;" /> </body> </html> <script language="vbscript"> 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 <= 0 Or x >= document.body.clientWidth - imgBall.width Then xInc = -xInc Else imgBall.style.pixelLeft = x End If y = imgBall.style.pixelTop + yInc If y <= 0 Or y >= document.body.clientHeight - imgBall.height Then yInc = -yInc Else imgBall.style.pixelTop = y End If End Sub </script>

  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. Example: Ball Bounce v2 Sprite.vbs 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 <= 0 Or x >= document.body.clientWidth - img.width Then xInc = -xInc Else img.style.pixelLeft = x End If y = img.style.pixelTop + yInc If y <= 0 Or y >= document.body.clientHeight - img.height Then yInc = -yInc Else img.style.pixelTop = y End If End Sub BallBounce.htm <html> <head><title>Ball Bounce</title></head> <body style="margin: 0;"> <img id="imgBall" src="Ball.gif" style="position: absolute;" /> </body> </html> <script language="vbscript" src="Sprite.vbs"></script> <script language="vbscript"> Option Explicit Sub window_onLoad() window.setinterval "Main", 20 Init 5, 3 End Sub Sub Main() Move imgBall End Sub </script>

  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. 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. 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. Example: Animals • Class: Animal • Properties: Name, Species, Gender • Instances: myPet, yourPet

  12. Question: Objects • Consider the following code: Class FetalBloodSample Dim TimeDim Acidity Dim ReactivityEnd ClassDim fbs1Set fbs1 = New FetalBloodSample • Name all: • classes • properties • instances FetalBloodSample Time, Acidity, Reactivity fbs1

  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 <= 0 Or 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 <= 0 Or spr.y >= document.body.clientHeight - img.height Then spr.yInc = -spr.yInc Else img.style.pixelTop = spr.y End If End Sub Sprite.vbs Class Definition BallBounce.htm <html> … </html> <script language="vbscript" src="Sprite.vbs"></script> <script language="vbscript"> 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 </script>

  14. Example: Students • Method: Clear

  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 <= 0 Or x >= document.body.clientWidth - img.width Then xInc = -xInc Else img.style.pixelLeft = x End If y = img.style.pixelTop + yInc If y <= 0 Or y >= document.body.clientHeight - img.height Then yInc = -yInc Else img.style.pixelTop = y End If End Sub End Class Sprite.vbs • procedures are now methods inside the class BallBounce.htm <html> … </html> <script language="vbscript" src="Sprite.vbs"></script> <script language="vbscript"> 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 </script>

  16. Example: Ball Bounce v5 • Multiple instances:

  17. Example: Ball Bounce v5 <html> <head><title>Ball Bounce</title></head> <body style="margin: 0;"> <img id="imgBall" src="Ball.gif" style="position: absolute;" /> <img id="imgFace" src="BallChar2.GIF" style="position: absolute;" /> </body> </html> <script language="vbscript" src="Sprite.vbs"></script> <script language="vbscript"> 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 </script> • Now have easy way of: • creating & using multiple sprites • each with own identity (separate characteristics) • only a few (4) lines of code

  18. Questions: OOP Class House Dim number Dim road Dim district Sub ChangeDist(newDist) district = newDist End Sub End Class Dim h Set h = New House • Name a • class • property • method • instance House number, road, district ChangeDist h

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

  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 Counterc.Reset c.Increase parRes.innerText = c.GetValue() c.value = -6

  21. Benefits of OOP in code • Procedures and Functions are part of object • encapsulation • RelatedData and Operationstogether • Private keyword – restrict access to data • Clearer code • Reduces chance of accidental interference • Less prone to error

  22. Example: Balloon Shoot • Question: • what objects? • what classes? • what properties? • what methods

  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. 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)

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