2. Pemrograman VisualMinggu …3… Page 1 MINGGU Ke Tiga Pemrograman Visual Pokok Bahasan: Class, Objects, Methods and Instance Variable Tujuan Instruksional Khusus: Mahasiswa dapat menjelaskan dan mengaplikasikan konsep class dan object pada Visual Basic 2008 Referensi: Deitel Deitel, Visual Basic 2008 (2009), How to Program, Prentice Hall. Chapter 4

3. Pemrograman VisualMinggu …3… Page 2 Agenda Declare class with a method and instantiating an object of class Declare a method with parameter Instance variable and properties Value Types and Reference Types Initializing Objects with constructors Validating data with set accessors in properties

4. Pemrograman VisualMinggu …3… Page 3 Declare class with a method and instantiating an object of class Adding a class to a Visual Basic Project –Right click the project name in the solution explorer and select add > class from the menu that appears Example of Class GradeBook

5. Pemrograman VisualMinggu …3… Page 4 Declare class with a method and instantiating an object of class (Continued …) Using Class GradeBook –You’ll now use class GradeBook in an apllication. A Visual Basic project that contains only class GradeBook is not an application that can be exceuted, because GradeBook does not contain main. If you try to compile such a project, you’ll get an error message like: ‘Sub Main’ was not found in ‘GradeBook.GradeBookTest’ So How we can fixed the Problem??? –We must declare a separate class or module that contains main, or we must place main in class GradeBook

6. Pemrograman VisualMinggu …3… Page 5 Example Using Class GradeBook

7. Pemrograman VisualMinggu …3… Page 6 Declare a Method With Parameter What is a Parameter ??? Example parameter of Class GradeBook

8. Pemrograman VisualMinggu …3… Page 7 Example execution Class GradeBook using parameter

9. Pemrograman VisualMinggu …3… Page 8 Instance Variables and Properties In Previous discussion, we declare all of an application’s variable in the main method. Variables declared in the body of a particular method are known as local variables and can be used only in that method. When a method terminates, the values of its local variables are lost. So How we can fixed the Problem??? –We must create attributes exist before a method is called on the object, while the method is executing and after the method completes execution.

10. Pemrograman VisualMinggu …3… Page 9 Example using instance variables and properties

11. Pemrograman VisualMinggu …3… Page 10 Example execution Class GradeBook using instance variables and properties

12. Pemrograman VisualMinggu …3… Page 11 Value Type and Reference Type Data type in Visual Basic are divided into two categories – value types and reference type Dim count as Integer = 7 A variable (count) of a value type (Integer) Contains a value (7) of that type

13. Pemrograman VisualMinggu …3… Page 12 Value Type and Reference Type (Continued …) A variable of a reference type (sometimes called a reference) contains the address of a location in memory where an object is stored Reference type instance variables are initialized by default to the value nothing A client of an object must use a reference to the object to invoke (i.e.,call) the object’s methods and access the object’s properties Is a object

14. Pemrograman VisualMinggu …3… Page 13 Initializing Objects with Constructors Each class you declare can provide a constructor that can be used to initialize an object of the class when the object is created Keyword new calls the class’s constructor to perform the initialization By default, the compiler provides a default constructor with no parameter in any class that does not explicitly include a constructor When you declare a class, you can provide your own constructor to specify custom initialization for objects of your class

15. Pemrograman VisualMinggu …3… Page 14 Initializing Objects with Constructors (Continued …) A constructor must have the name New Constructor declarations cannot return values A class’s instance variables are initialized to their default values if no constructor is provided

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18. Pemrograman VisualMinggu …3… Page 17 Validating Data with Set Accessors in Properties Properties can be used to keep an object in a consistent state, that is a state in which the object’s instance variables contains valid data A class’s set accessors cannot return values indicating a failed attempt to assign invalid data to objects of the class In Visual basic, it is possible to declare the get and set accessors of a property with different access modifiers. In this case, one of the accessors must have the same access as the property and the other must be more restrictive than the property. Private is more restrictive than public.

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21. Pemrograman VisualMinggu …3… Page 20 Questions & Answers

22. Pemrograman VisualMinggu …3… Page 21 Thank You