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Visual C++ Programming: Concepts and Projects Chapter 13A: Object-Oriented Programming (Concepts)

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Presentation on theme: "Visual C++ Programming: Concepts and Projects Chapter 13A: Object-Oriented Programming (Concepts)"— Presentation transcript:

1 Visual C++ Programming: Concepts and Projects Chapter 13A: Object-Oriented Programming (Concepts)

2 Objectives In this chapter, you will: Design class definitions Implement data hiding and encapsulation Use accessor and mutator methods Implement an initializing constructor Use public and private access modes Create and reference a two-dimensional array 2Programming with Visual C++

3 Introduction An abstraction is an idea with varying amounts of definition In computer science, abstractions are class definitions – Examples of system-defined class definitions: Button, TextBox, Label, Form Objects are created from class definitions (abstractions) Objects are implementations of the abstraction 3Programming with Visual C++

4 Introduction (continued) 4Programming with Visual C++

5 Introduction (continued) 5Programming with Visual C++

6 OOP Example Consider a program in which Frog objects are created and made to hop across the screen The Frog class definition is an abstraction The Frogs seen on the interface are objects (instances of the class) Objects exhibit all the properties and methods defined by the class they are derived from 6Programming with Visual C++

7 OOP Example (continued) 7Programming with Visual C++

8 OOP Example (continued) 8Programming with Visual C++

9 The Frog Class Definition A Frog class definition needs: – Class variables (the Frog icons) – Instance variables x and y coordinates of the Frog The assigned icon – Constructor 9Programming with Visual C++

10 The Frog Class Definition (continued) A Frog class definition needs: (continued) – Instance methods Operations that Frog objects can perform Example: showIcon() – Returns the Frog’s assigned icon to the client program so that it can be displayed 10Programming with Visual C++

11 The Frog Class Definition (continued) 11Programming with Visual C++

12 Instantiation and Use Frog objects can be instantiated using gcnew 12Programming with Visual C++

13 Instantiation and Use (continued) 13Programming with Visual C++

14 Initializing Constructors Constructors are used to instantiate objects Initializing constructors use parameters to construct objects with specific properties that can be passed in as actual arguments 14Programming with Visual C++

15 Initializing Constructors (continued) The code for an initializing constructor (from Frog.h) Parameters xcoord and ycoord are assigned to instance variables x and y 15Programming with Visual C++

16 Initializing Constructors (continued) The default constructor assigns every Frog object it makes the same x and y coordinates Initializing constructors may be preferable to default constructors because the client can specify the location for each Frog object created To prevent the client from using the default constructor, it should be placed in the private portion of the Frog class definition 16Programming with Visual C++

17 17Programming with Visual C++

18 Data Hiding Data hiding is the practice of making data members inaccessible by designating them as private Data members that are private can only be accessed by class methods and not by the client 18Programming with Visual C++

19 Data Hiding (continued) In this example, the client constructs a Frog with x and y locations -50, -75 and later assigns other negative coordinate values This could lead to problems, since negative coordinates are off of the interface 19Programming with Visual C++

20 Data Hiding (continued) To make it impossible for the client to place invalid values into instance variables like x and y, these data members can be “hidden” by placing them in the private portion of the class definition – Invalid assignments by the client are no longer allowed – Unfortunately, valid assignments are not allowed either public methods are provided to the client to allow it to change values stored in private data members 20Programming with Visual C++

21 Data Hiding (continued) Hidden data members are not visible to the client The good news – Invalid assignments are no longer possible The bad news – Valid assignments are not allowed either public methods are provided to the client to allow it to change values stored in private data members 21Programming with Visual C++

22 Accessor and Mutator Methods Accessor and mutator methods are public methods that provide access to private data members An accessor method is a public method that returns the value stored in a private data member 22Programming with Visual C++

23 Accessor and Mutator Methods (continued) In this example, public methods getX() and getY() are available to the client, allowing it to retrieve the data stored in private data members x and y 23Programming with Visual C++

24 Accessor and Mutator Methods (continued) The definitions of public methods getX() and getY() are contained in the class definition 24Programming with Visual C++

25 Accessor and Mutator Methods (continued) A mutator method is a public method that changes the value stored in a private data member In this example, setX() is a public mutator method used to change the private x coordinates of each of four Frog objects 25Programming with Visual C++

26 Accessor and Mutator Methods (continued) Mutator methods can be used to screen data before it is assigned to a private data member, as shown in the class definition of setX() 26Programming with Visual C++

27 Accessor and Mutator Methods (continued) 27Programming with Visual C++

28 Utility Methods Utility methods are instance methods that perform operations other than those performed by constructors, destructors, accessors, and mutators (Example: verifyX() ) 28Programming with Visual C++

29 Utility Methods (continued) A Frog class definition might want a public method that the client can call when he or she wants a frog to hop 29Programming with Visual C++

30 Complete Frog Class Definition private data members – x, y, icon private methods – Default constructor ( Frog() ) – Utility methods verifyX() verifyY() 30Programming with Visual C++

31 Complete Frog Class Definition (continued) public methods – Initializing constructor ( Frog(int, int) ) – Accessor methods getX() getY() showIcon() 31Programming with Visual C++

32 Complete Frog Class Definition (continued) public methods – Mutator methods setX() : used to assign a value to x setY() : used to assign a value to y setLeaping() : used to assign the leaping icon setSitting() : used to assign the sitting icon – Utility method hop() : used to add 25 to the x coordinate 32Programming with Visual C++

33 Complete Frog Class Definition (continued) 33Programming with Visual C++

34 Complete Frog Class Definition (continued) 34Programming with Visual C++

35 35Programming with Visual C++

36 Client Code The client needs to instantiate four Frog objects and position them vertically along a starting line Constant STARTX stores the starting x coordinate position Constants START1, START2, START3, and START4 store the starting y coordinate positions 36Programming with Visual C++

37 Client Code (continued) 37Programming with Visual C++

38 Client Code (continued) Using the initializing constructor, each new Frog can be positioned in a different location 38Programming with Visual C++

39 Client Code (continued) To draw a single Frog, you first construct a Rectangle object – Upper-left corner x coordinate is Frog->getX() – Upper-left corner y coordinate is Frog->getY() – Width and height are both 25 pixels The DrawIcon() method displays an icon in a Rectangle – The icon is Frog1->showIcon() 39Programming with Visual C++

40 Client Code (continued) 40Programming with Visual C++

41 Client Code (continued) To reset the interface, all frogs are repositioned back to their starting X location and all frog icons are set to the sitting frog icon 41Programming with Visual C++

42 Client Code (continued) A random number is used to select one of the four frogs; the chosen frog’s icon is set to the leaping icon 42Programming with Visual C++

43 Summary Class definitions are abstractions Objects are instances of the class Initializing constructors are useful if the objects they construct need to have unique values assigned to their attributes public data members and methods are visible to the client private data members and methods are not visible to the client 43Programming with Visual C++

44 Summary (continued) Data hiding is used to restrict client access to data members Accessor methods are public methods that can be used to retrieve a value stored in a private data member Mutator methods are public methods that can be used to assign new values to a private data member 44Programming with Visual C++

45 Summary (continued) Utility methods carry out operations that constructors, destructors, accessors, and mutators do not perform 45Programming with Visual C++


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