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- 1. THE BASICS OBJECT ORIENTED PROGRAMMING
- 2. What is Object-Oriented Design? It promotes thinking about software in a way that models how we think about the real world It organises program code into classes of objects
- 3. What is a Class? A class is a collection of things (objects) with similar attributes and behaviours. Attributes: What is looks like Behaviours: What it does
- 4. Classes and Objects Class Object A class is a template or An object is a running blueprint that defines an instance of a class that object’s attributes and consumes memory and operations and created at has a finite lifespan design time
- 5. What is an Object? Every object is an instance of a class Every object has attributes and behaviours Class: Dog Object: Object: Object: Object: Red Setter Labrador Terrier Bulldog
- 6. Class Examples Dogs Attributes: Four legs, a tail Behaviours: Barking Cars Attributes: Four wheels, engine, 3 or 5 doors Behaviours: Acceleration, braking, turning
- 7. In Code The programming constructs of attributes and behaviours are implemented as: Attributes: Properties Behaviours: Methods
- 8. Public Class Dog Public Name As String Public Sub Sleep() MessageBox.Show(“ZZzz”) End Sub End Class
- 9. Class Object Dim GoldenRetriever as New Dog GoldenRetriever.Name = “Rex” GoldenRetriever.Sleep() Property Method
- 10. Another Example Ferrari is an instance of the Car class Attributes (Use properties or fields): Red Rear wheel drive Max speed 330 km/h. Behaviours (Methods): Accelerate Turn Stop
- 11. VB.NET & OOP VB .NET is an object-oriented language. VB.NET Supports: Encapsulation Abstraction Inheritance Polymorphism
- 12. Encapsulation How an object performs its duties is hidden from the outside world, simplifying client development Clients can call a method of an object without understanding the inner workings or complexity Any changes made to the inner workings are hidden from clients
- 13. Example Car Stereo Standard case size and fittings, regardless of features Can be upgraded without affecting rest of car Functionality is wrapped in a self-contained manner
- 14. Encapsulation – In Practice Declare internal details of a class as Private to prevent them from being used outside your class This technique is called data hiding. This is achieved by using property procedures.
- 15. Abstraction Abstraction is selective ignorance Decide what is important and what is not Focus on and depend on what is important Ignore and do not depend on what is unimportant Use encapsulation to enforce an abstraction
- 16. Inheritance Inheritance specifies an “is-a-kind-of” relationship Multiple classes share the same attributes and behaviours, allowing efficient code reuse Base Class Examples: A customer “is a kind of” person Person An employee “is a kind of” person Derived classes Customer Employee
- 17. Inheritance We can create new classes of objects by inheriting attributes and behaviours from existing classes and then extending them We can build hierarchies (family trees) of classes Person Employee Part Time Full Time
- 18. Inheritance Cont’d The existing class is called the base class, and the new class derived from the base class is called the derived class. The derived class inherits all the properties, methods, and events of the base class and can be customized with additional properties and methods.
- 19. Inheritance Example Rally Car Inherits properties of class Car … … and extends class Car by adding a rollcage, racing brakes, fire extinguisher, etc.
- 20. Polymorphism The ability for objects from different classes to respond appropriately to identical method names or operators. Allows you to use shared names, and the system will apply the appropriate code for the particular object. Different code will execute depending on the context!
- 21. FROM THEORY TO PRACTICE DOING IT IN CODE
- 22. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 23. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 24. 1. Add Class to the Project
- 25. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 26. 2. Provide Appropriate Name
- 28. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 29. 3. Create Constructors Sub New replaces Class_Initialize Executes code when object is instantiated Public Sub New( ) 'Perform simple initialization Course = “BIS” End Sub Can overload, but does not use Overloads keyword Public Sub New(ByVal i As Integer) 'Overloaded without Overloads 'Perform more complex initialization intValue = i End Sub
- 30. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 31. 4. Create Destructor Sub Finalize replaces Class_Terminate event Use to clean up resources Code executed when destroyed by garbage collection Important: destruction may not happen immediately Protected Overrides Sub Finalize( ) 'Can close connections or other resources conn.Close End Sub
- 32. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 33. 5. Declare Properties Specify accessibility of variables and procedures Keyword Definition Public Accessible everywhere. Private Accessible only within the type itself. Friend Accessible within the type itself and all namespaces and code within the same assembly. Protected Only for use on class members. Accessible within the class itself and any derived classes. Protected The union of Protected and Friend. Friend
- 34. 5. Cont’d Properties represent a classes attributes Student First Name Last Name StudentID Age Course
- 36. 5. Properties (Property Procedures) To store values for a property you use the SET property procedure To retrieve values from a property you use the GET property procedure You must specify whether the value stored in the property can obtained and changed
- 40. If a procedure can only obtain a property it is Read Only If it can be obtained and changed it is Read-Write
- 43. Creating Classes in Code Add a class to the project Provide appropriate name for the class Create constructors as needed Create a destructor, if appropriate Declare properties Declare methods
- 44. 6. Declare Methods Methods represent a classes behaviours Student Eat Sleep Drink Study Pass Fail Graduate
- 46. FROM THEORY TO PRACTICE USING OUR CLASS
- 48. Instantiating our Class Create the Object Write object attributes Read object attributes Use object behaviours
- 49. Instantiating our Class Create the Object Write object attributes Read object attributes Use object behaviours
- 50. Create the Object Dim myStudent As New Student
- 51. Instantiating our Class Create the Object Write object attributes Read object attributes Use object behaviours
- 52. Write Object Attributes myStudent.FirstName = _ txtFirstName.Text myStudent.LastName = txtLastName.Text myStudent.Age = Val(txtAge.Text) myStudent.StudentID = _ txtStudentID.Text
- 55. Write Object Attributes myStudent.FirstName = _ txtFirstName.Text myStudent.LastName = txtLastName.Text myStudent.Age = Val(txtAge.Text) myStudent.StudentID = _ txtStudentID.Text
- 58. Write Object Attributes myStudent.FirstName = _ txtFirstName.Text myStudent.LastName = txtLastName.Text myStudent.Age = Val(txtAge.Text) myStudent.StudentID = _ txtStudentID.Text
- 61. Write Object Attributes myStudent.FirstName = _ txtFirstName.Text myStudent.LastName = txtLastName.Text myStudent.Age = Val(txtAge.Text) myStudent.StudentID = _ txtStudentID.Text
- 64. FROM THEORY TO PRACTICE EXTENDING OUR CLASS
Editor's Notes
- #18: Every time you create an application in VB.NET you are using inheritance (Forms)