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Creating OOP Classes in Code
- 1. DOING IT IN CODE SOME MORE EXAMPLES
- 3. The Problem You are required to create an ATM application using OOP Requirements: User can deposit money User can withdraw money User can view balance
- 4. Example #1
- 5. Creating the Class In Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 6. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Declare Methods Create constructors as needed Create a destructor, if appropriate
- 7. 1. Add Class to the Project
- 8. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 9. 2. Provide Appropriate Name
- 11. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 14. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 15. 4. Property Procedures This property is ReadOnly
- 16. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 18. 5. Deposit
- 19. 5. Withdraw
- 20. Creating Classes in Code Add a class to the project Provide appropriate name for the class Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 23. Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 25. Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 26. 2. _name Retrieve Value Store Value
- 27. 2. _balance
- 29. Static (Shared) Members Data and behaviours that pertain to class as a whole Not just an individual instance of a class You can access static members even if no class exists
- 30. 2. Shared _Rate
- 31. Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 32. Deposit()
- 33. Overloading Methods A method might need different parameter in different circumstances The solution is to define overloaded methods Methods have the same name – common intent Each method can have a unique signature In previous example method takes parameter as a decimal number
- 34. Deposit ()
- 35. Overloading Methods The overloaded method had the same name The parameter list was different Accepts an amount as a String (text) Converts it to a decimal
- 36. Withdraw ()
- 38. IncreaseRate ()
- 39. Declare properties Property Procedures Create Methods Add constructors/destructors if needed
- 41. In Use Dim account as New _ BankAccount()
- 43. In Use Dim account as New _ BankAccount(“Joe”)
- 45. In Use Dim account as New _ BankAccount(“Joe”, 1000)
- 47. Using the Class Instantiating the Object
- 48. Create Object
- 49. Withdrawing Cash
- 50. Method InputBox
- 51. Withdrawing Cash
- 52. Method
- 53. Depositing Cash
- 55. Method Val(txtRate.Text) / 100).ToString( "C"))
- 56. Extending our Example Advanced OOP
- 57. Accessibility Levels Access Level Visual Basic Access Modifier Unrestricted accessibility Public Accessible by containing Private class Accessible in current Friend assembly Accessible by containing Protected class and derived class Accessible in current Protected Friend assembly and by derived classes
- 58. Inheritance Advantages Developer Productivity Real-world modelling Consistency
- 60. Inheritance A base class can define overridable methods and properties Base class provides the default implementation Derived class provides alternative implementations A derived class can: Inherit base class members Override base class members Shadow base class members
- 61. Polymorphism enables an application to use instances of derived classes interchangeably Deposit A SavingsAccount Client application Deposit A CheckingAccount Benefits of polymorphism: Consistency and simplicity Extensibility and resilience
- 67. Derived Class
- 68. Derived Class
- 69. Derived Class
- 70. Shadowing To indicate a derived class member shadows a base class member Use the Shadows Keyword
- 71. Example Public Class BankAccount Protected ReadOnly Property _ Balance() As Decimal End Property Public Class SavingsAccount Public Shadows Sub Balance( _ ByVal amount As Decimal) „Implementation End Sub
Hinweis der Redaktion
- The deposit sub procedure accepts a string value (from our text box) and converts it to a Decimal using the Decimal parse methodThis amount is then added to the balance
- In this example we are getting an amount from the textbox and subtracting it from our balance figureWe could have used the decimal parse method here.If we do not provide a numeric value, we will get a .NET exception error (Unexpected Data Type)
- See: http://visualbasic.about.com/od/learnvbnet/a/sharedinstance.htm
- The SavingsAccount class annotates the Balance method with the Shadows keyword to indicate the Balance method redeclares and hides the Balance property in the base class