1. Clearly Visual Basic: Programming with Visual Basic 2008 Chapter 27 I Love this Class

2. Clearly Visual Basic: Programming with Visual Basic 2008 Objectives Define a class Instantiate an object from a class that you define Add Property procedures to a class Include data validation in a class Create a default constructor Include methods in a class 2

3. Clearly Visual Basic: Programming with Visual Basic 2008 That’s a Real Classy Object Object-oriented programming language –Allows the programmer to use objects to accomplish a program’s goal Class –Pattern or blueprint that the computer follows when creating an object Object –Instantiated (created) from a class –Referred to as an instance of a class 3

4. Clearly Visual Basic: Programming with Visual Basic 2008 That’s a Real Classy Object (continued) Attributes –Characteristics that describe an object Behaviors –Include methods and events Methods –Operations (actions) that the object is capable of performing Events –Actions to which an object can respond 4

5. Clearly Visual Basic: Programming with Visual Basic 2008 That’s a Real Classy Object (continued) A class –Encapsulates all of the attributes and behaviors of the object it instantiates Class statement –Used to define a class Pascal case –Capitalize the first letter in the name and the first letter in any subsequent words in the name 5

6. Clearly Visual Basic: Programming with Visual Basic 20086

7. Revisiting the Willow Pools Application Willow Pools application –Calculates and displays both the volume of a rectangular pool and the amount of water required to fill the pool –Volume Calculated by multiplying the pool’s length by its width and then multiplying the result by the pool’s depth 7

8. Clearly Visual Basic: Programming with Visual Basic 20088

9. Who Owns that Property? When an application instantiates an object: –Only the Public members of the object’s class are made available to the application Property procedure –Used to create a Public property Figure 27-4 –Code contained in the Get block allows application to retrieve the contents of the Private variable –Code in the Set block allows an application to assign a value to the Private variable 9

10. Clearly Visual Basic: Programming with Visual Basic 200810

11. Clearly Visual Basic: Programming with Visual Basic 200811

12. Clearly Visual Basic: Programming with Visual Basic 2008 Who Owns that Property? (continued) Get statement –Begins with the keyword Get and ends with the keywords End Get Set statement –Begins with the keyword Set and ends with the keywords End Set 12

13. Clearly Visual Basic: Programming with Visual Basic 2008 Constructive Behavior is the Key to Success Constructor –Class method whose instructions are processed by the computer when an object is instantiated –Responsible for creating the object and initializing the class’s Private variables Default constructor –Constructor that has no parameters –A class can have only one 13

14. Clearly Visual Basic: Programming with Visual Basic 200814

15. Clearly Visual Basic: Programming with Visual Basic 2008 Methods Other than Constructors Methods included in a class –Can be either Sub procedures or Function procedures Method name –Should be entered using Pascal case –First word should be a verb, and any subsequent words should be nouns and adjectives 15

16. Clearly Visual Basic: Programming with Visual Basic 200816

17. Clearly Visual Basic: Programming with Visual Basic 2008 Using the Pattern to Create an Object After defining a class: –It can then be used to instantiate one or more objects Figure 27-9 –Shows two versions of the basic syntax to instantiate an object 17

18. Clearly Visual Basic: Programming with Visual Basic 200818

19. Clearly Visual Basic: Programming with Visual Basic 200819

20. Clearly Visual Basic: Programming with Visual Basic 2008 Pool Supplies Application Pool Supplies –Sells a water clarifier designed to combat a common problem in swimming pools: cloudy water –Recommends one ounce of SoClear clarifier per 5000 gallons of water –Manager wants an application that calculates the: Number of gallons of water contained in a pool Required number of ounces of clarifier 20

21. Clearly Visual Basic: Programming with Visual Basic 2008 Summary Objects used in an object-oriented program –Instantiated (created) from classes Class statement –Used to define a class When naming the Private variables in a class: –Begin the name with the underscore character When an object is instantiated in an application: –Public members of the class are exposed to the application 21

22. Clearly Visual Basic: Programming with Visual Basic 2008 Summary (continued) Property procedure –Used to create a Public property –Get block allows an application to access the contents of the Private variable Class –Can have one or more constructors Names of methods in a class –Should be entered using Pascal case 22