1. Tonga Institute of Higher Education
Creating Classes
Tonga Institute of Higher Education

2. Current Status The form class contains all of our code
Code is added to the form class
Code may use variables, methods and events
Code may use other objects
When a program is run, the form object is used

3. Custom Classes and Objects
Sometimes, the objects provided by Microsoft do not fit our needs.
We can define custom objects.
We can use custom objects just like normal objects

4. How to Define a Class Access Specifier - Covered later Class Name
Class names should be nouns
One word
The first letter of each internal word is capitalized.
Keep your class names simple and descriptive.
Example:
Customer
SalesOrder

5. Demonstration
Defining a class

6. How to Define a Variable
Access Specifier
Variable Name
Type
Access Specifier – Covered later
Variable Name
One word
The first letter of each internal word is capitalized.
Keep your variable names simple and descriptive.
Example:
FirstName
PhoneNumber
The type can be a primitive or an object
Example: Integer, String, Boolean, Student

7. Demonstration
Defining a variable

8. How to Define a Method (Subroutines and Functions)
Methods - Pieces of code that perform a single function
Subroutine – A method that does not return anything
Function – A method that returns something

9. Difference Between Subroutines and Functions
Access Specifier
Parameter Type
Method Name
Parameter Name
Access Specifier
Method Name
Parameter Type
Parameter Name
Return Type
Return Data

10. Subroutines and Function Names
Verbs
One word
The first letter of each internal word is capitalized.
Keep your method names simple and descriptive.
Example:
RunFast
GetBackground
ShowWelcomeMessage

11. Subroutines and Function Parameters
Parameters are optional
Each parameter that your method accepts must have a name and type
The name should be:
One word
The first letter of each internal word is capitalized.
Keep your parameter names simple and descriptive.
The type can be a primitive or an object
Example: String, Integer, Customer
Example:
Private Sub ShowSummary(ByVal StudentID As Integer)
If multiple parameters are used, separate them with commas
Example: Private Sub ShowSummary(ByVal StudentID As Integer, ByVal StudentName as String)
Use the name inside the method parameter list to access the parameter in your code
StudentID
StudentName

12. Function Return Types
Access Specifier
Method Name
Parameter Type
Parameter Name
Return Type
Return Data
Return Type – Sets the type of data that will be returned from the function.
The type of data can be a primitive or an object
Example: String, Integer, Customer
If you are not returning anything, do not use a function. Use a subroutine.
Do not forget to use the Return keyword in your function

13. Demonstration
Defining a subroutine

14. Demonstration
Defining a function

15. Method Overloading
Overloading - Having multiple methods with the same name but different parameters
To make an overloaded method, create a method with the same name but different parameters.
Return types for functions can be overloaded but it is not a good idea
Same Name
Different Parameters

16. Demonstration
Method Overloading

17. Properties and Code Conventions
Generally, make all class variables private
Use properties to access your variables
Properties – a specialized method used to get and set a class’ variables
This could be done using regular methods, but properties are used more often

18. Regular Methods vs. Properties
Same Thing!

19. Property Features
Read-Only Properties
Write-Only Properties

20. Demonstration
Properties

21. Using the custom class Use custom objects just like normal objects
Declare and instantiate them
Use methods and properties
A class cannot use itself
A different class must use a class
Example: A StudentSystem class would use a Student class

22. Demonstration
Using the custom class

23. Dynamic Link Libraries
Until now, all of our VB.Net programs have been .exe files
This allows us to run a program
Sometimes, we need to share a class that we’ve made
A Dynamic Link Library is a file that contains classes for use by other programs.
They end with .dll
Example: System.dll

24. Seeing DLLs in Action
When a form is run, many different classes are needed. Example: Form class, textbox class, and more.
VS.Net loads dll files when a form is run. The dll files contain the class data for the objects needed to run the program
The loading of dll files can be seen in the Output box

25. Demonstration
Seeing DLLs in Action

26. Creating a DLL File We can create Dynamic Link Libraries
Right click on the project in the Solution Explorer
Select Properties
Select the Class Library Output Type
Click OK button
Compile the project. When the project is compiled, VS.Net creates a .dll file in the Bin directory

27. Demonstration
Creating a DLL File

28. References Many projects use dll files
Many dll files used are listed in the references folder

29. Demonstration
References

30. Adding DLL Files to a Project - 1
To use a dll file in a project, right click on the References folder and select Add Reference
The Add Reference form is displayed

31. Adding DLL Files to a Project - 2
Use the .Net tab to add a .Net dll
Use the COM tab to add a COM dll. (These are dll files made before VB.Net)
Use the Projects tab to add a reference from a project in the same solution

32. Adding DLL Files to a Project
Demonstration
Adding DLL Files to a Project

33. Using DLL Files To use a class defined in a DLL file
Add a reference to the dll file to the project
Write the fully qualified namespace to access the object
Dim x as new ClassLibrary1.Student
Remember: Namespaces are not always the same as the file name!
Class Name
Fully Qualified Namespace

34. Demonstration
Using DLL Files

35. Imports ClassLibrary1.Student
Import Statements
Import Statements allow you to not always type the fully qualified namespace
Imports ClassLibrary1.Student
There are import statements defined at the project level. To see these, go to Project Properties -> Common Properties -> Imports

36. Demonstration
Import Statements

37. .DLL and .EXE File Tips A .Dll file cannot be run. Rather, it is built
Do not use the same name for a .dll and exe file
If the location of a .dll file reference is changed, VS .Net will show a yellow error message. To fix this, remove the incorrect reference and add a new reference
When you make a change in a .dll file, the project must be rebuilt.
When a .dll file is changed in a separate solution from the .exe file, the .exe solution must be reloaded
An .exe project that uses a .dll file will have a copy of the .dll file saved to the bin directory. When giving the program to other people, both the .dll and .exe files must be given to run properly.

38. Demonstration
.DLL and .EXE File Tips

39. What is Scope?
The scope of an element (variable, class, method, etc.) defines what parts of a program can see it
Using Public instead of
Private changes the scope
of this variable.

40. Levels of Scope
Block
Procedure
Class
And others

41. Block Scope
A block is a set of statements terminated by an End, Else, Loop, or Next statement
Example: The code within a For...Next or If...Then...Else...End.
An element declared within a block can be used only inside that block
Use Dim to declare elements with block scope
The Static keyword may also be used (Covered later)
Block

42. Demonstration
Block Scope

43. Procedure Scope A procedure is a subroutine or function
An element declared within a procedure is only usable in the procedure.
Elements at this level are also known as local elements.
Use Dim to declare elements with procedure scope
The Static keyword may also be used (Covered later)
Works like block scope but you must also consider the parameters
Procedure

44. Demonstration
Procedure Scope

45. Class Scope
Declare elements at this level by placing the declaration statement outside of any procedure or block within the class.
These access specifiers can be used
Public
Private
Dim
Friend
Protected
Protected Friend

46. Access Specifiers Public Private Dim Friend Protected Protected Friend
Can be used by everything
Private
Can only be used by code inside the same class
Dim
Same as Private
Friend
Can be used by code inside the same project
Access Specifier
Name
Dim FirstName as String
Type
Protected
Can be used by code that inherits from this class
Protected Friend
Combination of Protected and Friend

47. Demonstration
Access Specifiers

48. Scope: Global Variables vs. Local Variables
Variables defined outside of a procedure or block but inside of a class
Also called member variables
Can be readonly by using the ReadOnly key word
Local Variables
Variables defined inside procedures or blocks
They are only visible by code inside the procedure or block
When looking for a value, start local. Go global if you can’t find the variable

49. Global vs. Local Variables
Demonstration
Global vs. Local Variables
Have global and local variable with same names

50. Element Lifetimes
The lifetime of a declared element is the period of time during which it is available for use.
Local variables declared with Dim exist only while the procedure in which they are declared is executing.
A variable declared in a class exists as a separate copy for each instance of the class in which it is declared; each such variable has the same lifetime as its instance.

51. Demonstration Element Lifetimes
Have global and local variable with same names

52. Controlling Element Lifetimes
We can additionally control the lifetime of a declared element
Code
Setting variables to nothing
Keywords
Shared
Static

53. Setting variables to nothing
Demonstration
Setting variables to nothing
Have global and local variable with same names

54. Shared Lifetime 1
Instance variable - A variable where each instance can have a different value

55. Shared Lifetime 2 Global Variables may be shared
Shared elements are not associated with a specific instance of a class. All instances use the same value.
Access them 2 ways
Use the class name
Use the variable name of a specific instance of the class

56. Demonstration
Shared Lifetime

57. Static Lifetime Local variables may be static
Static variables remain in existence and retain their latest values after termination of the procedure in which they are declared.

58. Demonstration
Static Lifetime

59. Constructors
Constructor – A method that is automatically executed when an object is created.
This allows you to set initial values for the object.
Many objects have multiple constructors. (They are overloaded)
Show Java Doc

60. Default Constructors All classes have a default constructor
The default constructor is a constructor that accepts no parameters
Automatically called when the object is created
Default constructors go away when you define your own constructors

61. Creating Constructors
Constructors do not return anything.
To overload constructors
Define multiple methods with the same name as the class with different parameters
New indicates
that this is
a constructor
Overloaded

62. Creating Constructors
Demonstration
Creating Constructors