Programming Primer EncapsulationVB

Programming Primer EncapsulationVB

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  1 A Programme Underthe compumitra Series Programming Primer: Encapsulation and Abstraction LAB WORK GUIDE
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  2 OUTLINE  Encapsulation andAbstraction Using VB in asp.net Creating Example Event Handler. Example Output an Explanation. Home Exercise. Summary Review.
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  3 Encapsulation and Abstraction UsingVB in asp.net
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  4 EncapsulationVB – CreatingButton and Label Template Button with 'Text' Property set to 'Encapsulation'. Two Labels to hold the place for output display with 'text' property set to NULL (blank). • Follow Standard Website Creation Steps and set your path to C:Learner<student-id>ProgrammingPrimerEncapsulationVB • Now Create the Execution Event Handler as a button and output place holders as follows.
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  5 EncapsulationVB –Copy andPaste Code Go to 'Default.aspx.cs' and 'Paste' the Code in 'Button1_Click' handler. Copy this Code Dim emp As New Employee emp.EmployeeID = 100 emp.Salary = 8500.35 Label1.Text = "Employee ID = " & emp.EmployeeID.ToString() Label2.Text = "Employee Salary = " & emp.Salary.ToString() Dim emp As New Employee emp.EmployeeID = 100 emp.Salary = 8500.35 Label1.Text="Employee ID = " & emp.EmployeeID.ToString() Label2.Text="Employee Salary = " & emp.Salary.ToString()
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  6 EncapsulationVB –Copy Code ClassEmployee Private _employeeID As Integer Private _salary As Double Public Property EmployeeID() As Integer Set(ByVal value As Integer) _employeeID = value End Set Get Return _employeeID End Get End Property Public Property Salary() As Double Set(ByVal value As Double) _salary = value End Set Get Return _salary End Get End Property End Class Copy this Code
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  7 EncapsulationVB –Paste Code RunCode By pressing 'F5' Class Employee Private _employeeID As Integer Private _salary As Double Public Property EmployeeID() As Integer Set(ByVal value As Integer) _employeeID = value End Set Get Return _employeeID End Get End Property Public Property Salary() As Double Set(ByVal value As Double) _salary = value End Set Get Return _salary End Get End Property End Class Label1.Text = "Employee ID = " & emp.EmployeeID.ToString() Label2.Text = "Employee Salary = " & emp.Salary.ToString() Paste code after the End of '_Default' class
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  8 Employee emp =new Employee(); emp.EmployeeID = 100; emp.Salary = 8500.30; Label1.Text = emp.EmployeeID.ToString(); Label2.Text = emp.Salary.ToString(); EncapsulationVB –Output Output after executing the handler using the button. This 'output' is generated, because we are trying to fill values in public properties that are accessible outside class even though the values are actually filled in private values such as ' _salary ' '_employeeID'. We are able to change this as this is defined as 'public' in original class. Don't worry we shall soon learn 'private' declaration too.
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  9 Class Employee Private _employeeIDAs Integer Private _salary As Double Public Property EmployeeID() As Integer Set(ByVal value As Integer) _employeeID = value End Set Get Return _employeeID End Get End Property Public Property Salary() As Double Set(ByVal value As Double) _salary = value End Set Get Return _salary End Get End Property End Class EncapsulationVB – Example Explanation This has been defined as 'Private'. This means that only code written inside class Employee can modify it. This is 'Public' as we would like to use a way to change this property from an object based on class Employee. 'Public' and 'Private' declarations are known as access modifiers and they provide the primary technique of ENCAPSULATION. Are there other such modifiers? Surely Yes.
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  10 Class Employee Private _employeeIDAs Integer Private _salary As Double Public Property EmployeeID() As Integer Set(ByVal value As Integer) _employeeID = value End Set Get Return _employeeID End Get End Property Public Property Salary() As Double Set(ByVal value As Double) _salary = value End Set Get Return _salary End Get End Property End Class EncapsulationVB – Example Explanation for ABSTRACTION Lets Focus on this class 'Employee'. Suppose I have to define an additional property 'employ_name' then it is most likely that I shall define it within this class. Means to external world 'Employee' is an abstract representation of all behaviours(methods) and states(properties) of employee and it is supposed to encapsulate everything related to this class. So! Encapsulation helps to attain ABSTRACTION. Abstraction also means that class is just a template or a map. Actual embodiment or physical usage is where we create an object based on a class.
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  11 Dim emp AsNew Employee emp ._employeeID = 100 emp ._salary = 8500.3 Label1.Text = "Employee ID = " & emp ._employeeID.ToString() Label2.Text = "Employee Salary = " & emp._salary.ToString() Dim emp As New Employee emp ._employeeID = 100 emp ._salary = 8500.3 Label1.Text = "Employee ID = " & emp ._employeeID.ToString() Label2.Text = "Employee Salary = " & emp._salary.ToString() EncapsulationCS – Error Trial Make necessary changes here and 'Run' code. Here we shall try to use the same code with a change to try using 'Private' variable _employeeID and _salary.
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  12 EncapsulationVB–Output after changingcode This program will generate a 'Compiler Error Message: BC30390: 'Employee._employeeID' is not accessible as it is 'Private'. Here we see that variable '_employeeID' and '_salary' is actually hidden behind the class ' Employee'. We can not initialize out side the class by using object 'emp' of class 'Employee'. This Error Output Actually proves that the concept of 'ENCAPSULATION' works. Code in Error but we are still very happy.
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  13 EncapsulationVB : HomeExercise  You are required to make a program where you can declare a class 'Mobile'.  Make a public method sendsms( ).  Make a protected method typetext( ).  Call typetext( ) within sendsms( ).  Now write some eventhandler to show functionality if protected could be called outside class or not.  Now further create a class derived from class 'mobile' and name it as 'iphone'.  Try to use the typetext( ) method now. We have told you about 'Private' and 'Public' access modifiers. Another common access modifier used is 'Protected' A 'Protected' access modifier allows access within a derived (child) class, but not outside class. Are there other access modifiers. Try to search internet to find-out and understand. Difficult?. 'Facing Difficulties is the prime goal of a programmer'. Play some music and relax. Next is just a summary slide.
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  14 EncapsulationVB : LearningSummary Review  Concept of Encapsulation  Encapsulation helps to provide controlled access to outside classes.  Encapsulation also helps to bundle similar things together.  Concept of Abstraction  Encapsulation helps to attain Abstraction.  Abstraction also relates to non-physical nature of classes.  Trying to use a 'Private' data outside the class will give an error. For this purpose 'Public' declaration should be done.  A 'Protected' modifier is suitable for neat definition of access restriction for access to derived classes only.  Private properties or methods also serve an additional purpose. If a property or method is private in a class means the property or methods of same name can be freely declared in another class.
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