Programming Primer Encapsulation CS
- 1. 1 A Programme Under the compumitra Series Programming Primer: Encapsulation and Abstraction LAB WORK GUIDE
- 2. 2 OUTLINE Encapsulation and Abstraction Using C# in asp.net Creating Example Event Handler. Example Output an Explanation. Home Exercise. Summary Review.
- 3. 3 Encapsulation and Abstraction Using C# in asp.net
- 4. 4 EncapsulationCS – Creating Button 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 from C# and set your path to C:Learner<student-id>ProgrammingPrimerEncapsulationCS • Now Create the Execution Event Handler as a button and output place holders as follows.
- 5. 5 EncapsulationCS –Copy and Paste Code Go to 'Default.aspx.cs' and 'Paste' the Code in 'Button1_Click' handler. Copy this Code Employee emp = new Employee(); emp.EmployeeID = 100; emp.Salary = 8500.30; Label1.Text = "Employee ID = " + emp.EmployeeID.ToString(); Label2.Text = "Employee Salary = " + emp.Salary.ToString(); Employee emp = new Employee(); emp.EmployeeID = 100; emp.Salary = 8500.30; Label1.Text = "Employee ID = " + emp.EmployeeID.ToString() ; Label2.Text = "Employee Salary = " + emp.Salary.ToString() ;
- 6. 6 EncapsulationCS –Copy Code class Employee { private int _employeeID; private double _salary; public int EmployeeID //Properties { set { _employeeID = value; } get { return _employeeID; } } public double Salary //Properties { set { _salary = value; } get { return _salary; } } } Copy this Code
- 7. 7 EncapsulationCS –Paste Code Run Code By pressing 'F5' Paste code after the End of '_Default' class class Employee { private int _employeeID; private double _salary; public int EmployeeID //Properties { set { _employeeID = value; } get { return _employeeID; } } public double Salary //Properties { set { _salary = value; } get { return _salary; } } } Label1.Text = emp.EmployeeID.ToString(); Label2.Text = emp.Salary.ToString();
- 8. 8 Employee emp = new Employee(); emp.EmployeeID = 100; emp.Salary = 8500.30; Label1.Text = emp.EmployeeID.ToString(); Label2.Text = emp.Salary.ToString(); EncapsulationCS –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.
- 9. 9 class Employee { private int _employeeID; private double _salary; public int EmployeeID //Properties { set { _employeeID = value; } get { return _employeeID; } } public double Salary //Properties { set { _salary = value; } get { return _salary; } } } EncapsulationCS – 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.
- 10. 10 class Employee { private int _employeeID; private double _salary; public int EmployeeID //Properties { set { _employeeID = value; } get { return _employeeID; } } public double Salary //Properties { set { _salary = value; } get { return _salary; } } } EncapsulationCS – 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.
- 11. 11 emp._employeeID = 100; emp._salary = 8500.30; Label1.Text = "Employee ID = " + emp._employeeID.ToString(); Label2.Text = "Employee Salary = " + emp._employeeID.ToString(); emp._employeeID = 100; emp._salary = 8500.30; Label1.Text = "Employee ID = " + emp._employeeID.ToString(); Label2.Text = "Employee Salary = " + emp._employeeID.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.
- 12. 12 EncapsulationCS–Output after changing code This program will generate a 'Compiler Error Message: CS0122: '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.
- 13. 13 EncapsulationCS : Home Exercise 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.
- 14. 14 EncapsulationCS : Learning Summary 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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