clearly visual basic: programming with visual basic 2008 chapter 27 i love this class
DESCRIPTION
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 3TRANSCRIPT
Clearly Visual Basic: Programming with Visual Basic 2008
Chapter 27I Love this Class
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
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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
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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
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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
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Clearly Visual Basic: Programming with Visual Basic 2008 6
Clearly Visual Basic: Programming with Visual Basic 2008
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
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Clearly Visual Basic: Programming with Visual Basic 2008 8
Clearly Visual Basic: Programming with Visual Basic 2008
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
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Clearly Visual Basic: Programming with Visual Basic 2008 10
Clearly Visual Basic: Programming with Visual Basic 2008 11
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
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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
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Clearly Visual Basic: Programming with Visual Basic 2008 14
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
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Clearly Visual Basic: Programming with Visual Basic 2008 16
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
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Clearly Visual Basic: Programming with Visual Basic 2008 18
Clearly Visual Basic: Programming with Visual Basic 2008 19
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
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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
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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
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