Intro. Classes Beginning Objected Oriented Programming. CIS 15 : Spring 2007

Transcription

1 Intro. Classes Beginning Objected Oriented Programming CIS 15 : Spring 2007

2 Functionalia HW 4 Review. HW Out this week. Today: Linked Lists Overview Unions Introduction to Classes

3 // Create a New Node node * n = new node; n->id = id; // some id Adding a Node to the Middle of (an already built) List node * here; // assume that we want to insert after this pointer Start Here 3 End NULL

4 // Create a New Node node * n = new node; n->id = id; // some id Adding a Node to the Middle of (an already built) List node * here; // assume that we want to insert after this pointer n-> = here->; // (1) here-> = n; // (2) Start Here 3 End NULL

5 // Create a New Node node * n = new node; n->id = id; // some id Adding a Node to the Middle of (an already built) List node * here; // assume that we want to insert after this pointer n-> = here->; // (1) here-> = n; // (2) Start Here 3 (1) End NULL

6 // Create a New Node node * n = new node; n->id = id; // some id Adding a Node to the Middle of (an already built) List node * here; // assume that we want to insert after this pointer n-> = here->; // (1) here-> = n; // (2) Start Here 3 (1) End 1 2 (2) 4 5 NULL

7 Delete a Node in the Middle of the List node * del; // node to delete Start Del End NULL

8 Delete a Node in the Middle of the List node * del; // node to delete node * prev; //(need to know the previous node) prev-> = del->; delete del; Start Prev Del End NULL

9 // Create a New Node Delete a Node in the Middle of the List node * n = new node; n->id = id; // some id What about deleting at the Start and End of the list? node * del; // node to delete node * prev; //(need to know the previous node) prev-> = del->; delete del; Start Prev Del End NULL

10 Write a For Loop that print out all of the ids node * start; node * end; Start End NULL

11 Write a For Loop that print out all of the ids node * start; node * end; for(node * n = start; n!= null; n = n->) cout << n->id; Start End NULL

12 Unions Unions are structs where all of the members reside in the same memory space. union Number short little; int bigger; long even_bigger; double with_decimals;

13 Unions Unions are structs where all of the members reside in the same memory space. union Number short little; int bigger; long even_bigger; 1 byte double with_decimals; Number

14 Unions Unions are structs where all of the members reside in the same memory space. union Number short little; int bigger; long even_bigger; double with_decimals; 1 byte 2 bytes Number

15 Unions Unions are structs where all of the members reside in the same memory space. union Number short little; int bigger; long even_bigger; double with_decimals; 1 byte 2 bytes 4 bytes Number

16 Unions Unions are structs where all of the members reside in the same memory space. union Number short little; 1 byte int bigger; long even_bigger; double with_decimals; 2 bytes 4 bytes 8 bytes Number

17 union Number short little; int bigger; long even_bigger; double with_decimals; Unions You can use a Union just like a struct. Just know that you can only use one member at a time. Number mynum; mynum.even_bigger = ; cout << mynum.bigger; //????????????????

18 Unions What s the point? You can be cheap with memory. And (in C) this is a weak form of object-orientation. Example : Palm OS Event Handler

19 Unions What s the point? You can be cheap with memory. And (in C) this is a weak form of object-orientation. Example : Palm OS Event Handler struct EventType eventsenum etype; Boolean pendown; UInt8 tapcount; Int16 screenx; type of data depends on type of Event Int16 screeny; union data...

20 Unions What s the point? You can be cheap with memory. And (in C) this is a weak form of object-orientation. Example : Palm OS Event Handler struct EventType eventsenum etype; Boolean pendown; UInt8 tapcount; Int16 screenx; Int16 screeny; union data... struct keydown WChar chr; UInt16 keycode; UInt16 modifiers; struct pendown UInt16 tapcount; UInt16 screenx; UInt16 screeny;

21 Introduction to Classes and OOP Classes are the basis for Object Oriented Programming in C++. So far, we ve been doing Procedural Programming in C++. Object Oriented Programming provides better organizational structures for your code - classes = data + functionality. Tenants of Object Oriented Programming 1. Encapsulation 2. Data Hiding 3. Polymorphism 4. Inheritance

22 Encapsulation Like structs, classes provide a way to abstract data (and functions) to a higher-level. Encapsulation abstracts the data into an object. Age Name DOG Bark Breed

23 Data Hiding As a result of encapsulation, the actual implementation of the data is hid from the rest of program and becomes only accessible through an interface. DOG char Name[34]; or getname(); setname(char *); string Name; This allows for flexibility and re-usability of the code/objects that you build.

24 Polymorphism Functions (methods) can have differing behavior depending on the context that they are being called in. This is Polymorphism. bark(int volume); bark(); bark(); bark(); Boxer Poodle

25 Inheritance No longer are Classes singularly defined lumped objects. But they can be related to each other through inheritance - which defines is-a-kind-of relationship. (NOT to be confused by the has-a relationship) Dog Greyhound Boxer Poodle AiboRobot

26 Definition of a Class A class is defined in a similar manner as a struct is. Keyword class to indicate that what follows is a struct.

27 Definition of a Class A class is defined in a similar manner as a struct is. The Name (Tag) of the class follows. This becomes the type that you declare instances of the with.

28 Definition of a Class A class is defined in a similar manner as a struct is. Again, customary to capitalize the first letter of the name of the class.

29 Definition of a Class A class is defined in a similar manner as a struct is. Don t forget the semi-colon!

30 Definition of a Class A class is defined in a similar manner as a struct is. Declarations of your data (and functions - as you will shortly see), contained within the curly-braces. NOTE: Unlike structs - by default the data and the functions of a class are Private.

31 Definition of a Class A class is defined in a similar manner as a struct is. Declarations of your data (and functions - as you will shortly see), contained within the curly-braces. NOTE: Unlike structs - by default the data and the functions of a class are Private. Rectange r1; r1.width = 5.555; COMPILE ERROR!

32 Access Specifiers Use and labels to specify the access to the different data and functions. Even through it is by default private - it is a good idea to explicitly label the private components of the class. double getarea();

33 Access Specifiers Set up public member accessor functions to control access to the private members of the class. double getarea(); The interface to manipulating the object.

34 Access Specifiers Set up public member accessor functions to control access to the private members of the class. double getarea(); Called mutators, or setter functions. Called accessor, or getter functions.

35 Read-Only Member Functions The keyword const can be used to specify that the function will not change any of the data stored in the class. This is helpful to guarantee that there is no future code inadvertently overwrites something.

36 Defining Member Functions Once declared in the class, member functions are defined outside of the class definition. Note the use of the :: scope operator. scope operator (used with the class name) void Rectangle::setWidth(double w) width = w; } void Rectangle::setHeight(double h) height = h; }

37 Defining Member Functions Once declared in the class, member functions are defined outside of the class definition. Note the use of the :: scope operator. void Rectangle::setWidth(double w) width = w; } void Rectangle::setHeight(double h) height = h; } Private member variables are accessible from the function definition.

38 Defining Member Functions Once declared in the class, member functions are defined outside of the class definition. Note the use of the :: scope operator. Use of the const operator in the function definition to specify a constant object and read-only access to the class data. double Rectangle::getArea() const return (width * height); }

39 Defining Member Functions Once declared in the class, member functions are defined outside of the class definition. Note the use of the :: scope operator. double Rectangle::getArea() const return (width * height); } Avoids stale data, defining Area as a resulting operation on the two member variables width and height - as opposed to having declared an area member variable.

40 Defining Member Functions Once declared in the class, member functions are defined outside of the class definition. Note the use of the :: scope operator. Notice that the return type comes on the far right-side of the Rectangle::getArea() declaration. double Rectangle::getArea() const return (width * height); }

41 Instantiation of the Class Using the class-name to declare a variable of the class type is called instantiating the class. The variable is called an object. Definition outside of main() and other functions. Rectangle r1; r1.setwidth(1.0); r1.setheight(4.0); cout << r1.getarea() << endl; Use of the Class occurs in main() or other functions.

42 Instantiation of the Class Using the class-name to declare a variable of the class type is called instantiating the class. The variable is called an object. Object r1 is an instance of the Rectangle class. Rectangle r1; r1.setwidth(1.0); r1.setheight(4.0); cout << r1.getarea() << endl;

43 Instantiation of the Class Using the class-name to declare a variable of the class type is called instantiating the class. The variable is called an object. Access the member functions (methods) via dotnotation. Rectangle r1; r1.setwidth(1.0); r1.setheight(4.0); cout << r1.getarea() << endl;

44 Instantiation of the Class Using the class-name to declare a variable of the class type is called instantiating the class. The variable is called an object. Access the member functions (methods) via dotnotation. Rectangle r1; r1.setwidth(1.0); r1.setheight(4.0); cout << r1.getarea() << endl; Expected output?

45 Instantiation of the Class Rectangle r1; r1.setwidth(1.0); r1.setheight(4.0); cout << r1.getarea() << endl; 4.0

46 Instantiation of the Class Rectangle r2; cout << r2.getarea() << endl; Expected output?

47 Instantiation of the Class r2.width =? r2.height =? Rectangle r2; cout << r2.getarea() << endl;

48 Pointer to a Class Like other variables, and structs, an object can have a pointer that references it indirectly. Rectangle r3; Rectangle * rptr. rptr = &r3; rptr->setwidth(0.2);

49 Rectangle r3; Rectangle * rptr. rptr = &r3; rptr->setwidth(0.2); Pointer to a Class Like other variables, and structs, an object can have a pointer that references it indirectly. Use of the & operator to set the pointer to hold the memory address of the object.

50 Pointer to a Class Like other variables, and structs, an object can have a pointer that references it indirectly. Rectangle r3; Rectangle * rptr. rptr = &r3; rptr->setwidth(0.2); Use of the -> reference operator to access the public members of the class.

51 Dynamically Allocated Objects Objects (like structs) can be dynamically allocated as well. Rectangle * rptr. rptr = new Rectangle; new operator allows for the creation of a dynamically allocated Rectangle object. rptr->setwidth(0.2);

52 Dynamically Allocated Objects What gets dynamically allocated must eventually be freed. Rectangle * rptr. rptr = new Rectangle; rptr->setwidth(0.2);... delete rptr; delete operator frees the memory of the dynamically allocated Rectangle object.

53 Private Data Having the data hidden and private allows for more intelligent and safer handling of the object. Additionally it allows for better code evolution. Keep on getting errors! Negative widths. Need to update the setwidth(...) function. void Rectangle::setWidth(double w) width = w; }

54 Private Data Does the rest of the program need to change? void Rectangle::setWidth(double w) if(width >= 0) width = w; else cout << Width is invalid! << endl; exit(exit_failure); // quits the program } }

55 Private Data void Rectangle::setWidth(double w) if(width >= 0) width = w; else cout << Width is invalid! << endl; width = 0; // error handling } } Less heavy handed. But needs to be documented!

56 Inline Member Functions Very small and simple functions can be declared inline to improve code clarity and possible performance enhancements. void setwidth(double w) if(width >= 0) width = w; } void setheight(double h) if(height >= 0) height = h; }

57 Inline Member Functions The actual call of the function gets replaced with a copy inline code. Instead of the normal use of the call stack and jump in the program code. void setwidth(double w) if(width >= 0) width = w; } void setheight(double h) if(height >= 0) height = h; } Code gets copied.

58 Inline Member Functions The actual call of the function gets replaced with a copy inline code. Instead of the normal use of the call stack and jump in the program code. void setwidth(double w) if(width >= 0) width = w; } void setheight(double h) if(height >= 0) height = h; } Inline functions are a request to the compiler. Code size grows considerably with many inline function calls.

59 Rectangle(); Constructors A constructor is a special member function that gets called when the class is instantiated. Name of the constructor is the same as a the class name.

60 Rectangle(); Constructors A constructor is a special member function that gets called when the class is instantiated. Note the absence of a return type!

61 Rectangle(); Constructors A constructor is a special member function that gets called when the class is instantiated. Rectangle::Rectangle() width = 0; height = 0; } Defined like other member functions. Common use: initialization of object data.

62 Rectangle(); Rectangle::Rectangle() width = 0; height = 0; } Constructors A constructor is a special member function that gets called when the class is instantiated. Rectangle r1; cout << r1.getarea() << endl; What is printed?

63 Rectangle(); Rectangle::Rectangle() width = 0; height = 0; } Constructors A constructor is a special member function that gets called when the class is instantiated. Rectangle r1; cout << r1.getarea() << endl; 0

64 Rectangle(); Rectangle::Rectangle() width = 0; height = 0; } Constructors A constructor is called also when an object is dynamically allocated. Rectangle * rptr; rptr = new Rectangle; cout << r1->getarea() << endl;

65 Constructors Constructors also can have function parameters (useful in initializing member data). Rectangle(double w, double h); Rectangle::Rectangle(double w, double h) width = h; height = h; }

66 Constructors Use of parameters in instantiating the object looks similar to a function call. Rectangle(double w, double h); Rectangle::Rectangle(double w, double h) width = h; height = h; } Rectangle r1(0.1, 10.0); cout << r1.getarea() << endl; What is printed?

67 Constructors Use of parameters in instantiating the object looks similar to a function call. Rectangle(double w, double h); Rectangle::Rectangle(double w, double h) width = h; height = h; } Rectangle r1(0.1, 10.0); cout << r1.getarea() << endl; 1.0

68 Constructors Default values can be set in the definition of the Constructor to create a default constructor. Rectangle(double w, double h); Rectangle::Rectangle(double w = 1.0, double h = 1.0) width = h; height = h; }

69 Constructors Default values can be set in the definition of the Constructor to create a default constructor. Rectangle(double w, double h); Rectangle r1; cout << r1.getarea() << endl; What is printed? Rectangle::Rectangle(double w = 1.0, double h = 1.0) width = h; height = h; }

70 Constructors Default values can be set in the definition of the Constructor to create a default constructor. Rectangle(double w, double h); Rectangle r1; cout << r1.getarea() << endl; 1.0 Rectangle::Rectangle(double w = 1.0, double h = 1.0) width = h; height = h; }

71 Passing parameters in Dynamic Objects Dynamically Allocated Objects can also have parameters passed to the Constructor. Rectangle(double w, double h); Rectangle * rptr; rptr = new Rectangle(2.0, 1.0); cout << rptr->getarea() << endl; What is printed? Rectangle::Rectangle(double w = 1.0, double h = 1.0) width = h; height = h; }

72 Passing parameters in Dynamic Objects Dynamically Allocated Objects can also have parameters passed to the Constructor. Rectangle(double w, double h); Rectangle * rptr; rptr = new Rectangle(2.0, 1.0); cout << rptr->getarea() << endl; 2.0 Rectangle::Rectangle(double w = 1.0, double h = 1.0) width = h; height = h; }

73 Destructors Destructors are member functions that are called when the object is de-allocated. Rectangle(double w, double h); ~Rectangle(); Same as a constructor except declaration uses a ~ to indicate that it is a Destructor.

74 Destructors Destructors are member functions that are called when the object is de-allocated. Rectangle(double w, double h); ~Rectangle(); Definition is the same. Note no parameters are ever used. Rectangle::~Rectangle() cout << Bye bye! << endl; }

75 Destructors Rectangle(double w, double h); ~Rectangle(); Rectangle::~Rectangle() cout << Bye bye! << endl; } int main() Rectangle r1(0.1, 10.0); } cout << r1.getarea() << endl; What is printed? Destructor is called at the end of main().

76 Destructors Rectangle(double w, double h); ~Rectangle(); Rectangle::~Rectangle() cout << Bye bye! << endl; } int main() Rectangle r1(0.1, 10.0); } cout << r1.getarea() << endl; 1.0 Bye bye! Destructor is called at the end of main().

77 Destructors Rectangle(double w, double h); ~Rectangle(); Rectangle::~Rectangle() cout << Bye bye! << endl; } Destructors of dynamically allocated objects is called when the delete operator is used. int main() Rectangle * rptr = new Rectangle(0.1, 10.0); } cout << rptr->getarea() << endl; delete rptr;

78 class Cat Design your own class. 3 Member Variables Constructor Destructor Accessor/Mutator Functions.