Classes and Objects. Types and Classes. Example. Object Oriented Programming

Transcription

1 Classes and Objects Types and Classes Chapter 6 Object Oriented program development. Read this Chapter 7 Classes Read this Chapter 8 More About Classes Some sections will be assigned later Chapter 9 Inheritance. Not covered in this course Standard Types Classes, Objects Object Oriented Programming Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring Example Object Oriented Programming class Time int hour; int minute; int second; ; int main() Time t1; t1.hour = 10; t1.minute = 30; t1.second = 25; Object-oriented Programming (OOP) encapsulates data (attributes) and functions (behavior) into packages called classes; the data and functions of a class are intimitely tied together. A class is like a blueprint. Out of a blueprint, a builder can build a house. Out of a class, a programmer can create an object. One blueprint can be reused many times to make many houses. One class can be reused many times to make many objects of the same class. return 0; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring

2 Object Oriented Programming Example I Information Hiding Interfaces Classes User/Programmer defined types Data Members Functions class Temperature void set(double newdegrees, char newscale); double degrees; char scale; ; Temperature t1; Temperature t2; t1.set(53.2, F ); t2.set(57.4, F ); cout << "Today it is: " << t1.degrees << t1.scale; cout << "Tomorrow will be: " << t2.degrees << t2.scale; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring Example I (continued) Example II void Temperature::set(double newdegrees, char newscale) class Bicycle char getcolor(); int numberofspeeds(); void set(int thespeeds, char thecolor); int speeds; char color; ; Bicycle mybike; Bicycle yourbike; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring

3 Example II: Methods Example III char Bicycle::getColor() char Bicycle::numberOfSpeeds() void Bicycle::set(int thespeeds, char thecolor) #include <iostream> using std::cout; using std::endl; class Time Time(); void settime( int, int, int ); void printmilitary(); void printstandard(); int hour; // 0-23 int minute; // 0-59 int second; // 0-59 ; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring Example: Constructor Example: Methods Time::Time() hour = 0; minute = 0; second = 0; void Time::setTime( int h, int m, int s ) if ( h >= 0 && h < 24 ) hour = h; hour = 0; if ( m >= 0 && m < 24 ) minute = m; minute = 0; if ( h >= 0 && h < 24 ) second = s; second = 0; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring

4 Example: Methods Example: Methods void Time::printMilitary() if (hour < 10) cout << "0" << hour << ":" cout << hour << ":"; if (minute < 10) cout << "0" << minute << ":" cout << minute; void Time::printStandard() if ( hour == 0 hour == 12 ) cout << 12; cout << hour % 12; cout << ":"; if ( minute < 10? "0" : "" ) cout "0"; cout << minute; cout << ":"; if ( second < 10 ) cout "0"; cout : << second; if ( hour < 12 ) cout << " AM"; cout << " PM"; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring Driver int main() Time t; cout << "The initial military time is "; cout << "\nthe initial std time is "; t.settime( 13, 27, 6 ); cout << "\n\nmilitary time now is "; cout << "\nstandard time now is is "; t.settime( 99, 99, 99 ); cout << "\n\nafter invalid settings:" << "\nmilitary time: "; cout << "\nstandard time: "; cout << endl; return 0; Program Devel/Intro Alg Lang CS501b/275 Spring Exercise class Automobile void setprice(double newprice); void setprofit(double newprofit); double getprice(); double price: double profit; double getprofit();; Automobile hyundai, jaguar; hyundai.price = ; jaguar.setprice( ); double aprice, aprofit; aprice = jaguar.getprice(); aprofit = jaguar.getprofit(); aprofit = hyundai.getprofit(); hyundai = jaguar; Program Devel/Intro Alg Lang CS501b/275 Spring

5 Separating Inferface from Implementation Separating Interface from Implementation (cont) One of the fundamental principles of good software engineering is to separate interface from implementation. this makes it easier to modify programs. As far as clients of a class are concerned, changes in the class implementation do not affect the client as long as the class interface priginally provided to the client is unchanged (the class functionality could be expanded beyond the original interface). myclass.h file #include "myclass.h" Put method definitions in source file myclass.cpp Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring time.h time.cpp #include <iostream> using std::cout; using std::endl; class Time Time(); void settime( int, int, int ); void printmilitary(); void printstandard(); int hour; // 0-23 int minute; // 0-59 int second; // 0-59 ; Time::Time() hour = 0; minute = 0; second = 0; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring

6 time.cpp (cont) time.cpp void Time::setTime( int h, int m, int s ) if ( h >= 0 && h < 24 ) hour = h; hour = 0; if ( m >= 0 && m < 24 ) minute = m; minute = 0; if ( h >= 0 && h < 24 ) second = s; second = 0; void Time::printMilitary() if (hour < 10) cout << "0" << hour << ":" cout << hour << ":"; if (minute < 10) cout << "0" << minute << ":" cout << minute; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring time.cpp void Time::printStandard() if ( hour == 0 hour == 12 ) cout << 12; cout << hour % 12; cout << ":"; if ( minute < 10? "0" : "" ) cout "0"; cout << minute; cout << ":"; if ( second < 10 ) cout "0"; cout : << second; if ( hour < 12 ) cout << " AM"; cout << " PM"; Program Devel/Intro Alg Lang CS501b/275 Spring testtime.cpp #include <iostream> #include "time.h" int main() Time t; cout << "The initial military time is "; cout << "\nthe initial std time is "; t.settime( 13, 27, 6 ); cout << "\n\nmilitary time now is "; cout << "\nstandard time now is is "; t.settime( 99, 99, 99 ); cout << "\n\nafter invalid settings:" << "\nmilitary time: "; cout << "\nstandard time: "; cout << endl; return 0; Program Devel/Intro Alg Lang CS501b/275 Spring

7 Compiling Constructors g++ time.cpp test.cpp g++ -o test time.cpp test.cpp g++ -c time.cpp g++ -o test test.cpp time.o When a class object is created, its members can be initialized by that class constructor function. A constructor is a class member function with the same name as the class. The programmer provides the constructor, which is then invoked automatically each time an object of that class is created (instantiated). Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring Constructor Overloading Find the error Time(int, int, int); Time::Time(int h, int m, int s) settime(h, m, s); Time t1; Time t2(3, 20, 55); The following is a partial definition of class Time: class Time // function prototypes int hour = 0; int minute = 0; int second = 0; ; Program Devel/Intro Alg Lang CS501b/275 Spring Program Devel/Intro Alg Lang CS501b/275 Spring

8 Find the error Assume the following is declared in class Employee: int Employee(int, char[]); Program Devel/Intro Alg Lang CS501b/275 Spring