Spring 2008

Mark Fontenotmfonten@engr.smu.edu

CSE 2341 - HonorsPrinciples of Computer Science I

Note Set 61

Quick Look

2

Object Composition

Relationships

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Different kinds of relationships can exist between classes“is a” (inheritance – more on this later)“has a” (composition/aggregation)“uses a” (association)

Object Composition

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Object composition occurs when a class contains an instance of another class

Creates a “has a” relationship between classes

Object Composition

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class Date{private: //private //memberspublic: //public //members};

class Employee{private: char lName[25]; char fName[25]; Date birthDate; Date hireDate;public: //public members};

Date Class

6

#ifndef DATE1_H#define DATE1_Hclass Date{public:

Date(int = 1, int = 1, int = 1900); void print ( ) const; ~Date( );

private:int month; // 1-12int day; // 1-31 based on monthint year; // any yearint checkDay(int);

};#endif

Date Class

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Date::Date(int mn, int dy, int yr) { if (mn > 0 && mn <= 12) month = mn; else { month = 1; cout << “Month 1” << mn << “ invalid.Set to month 1.”

<< endl; } year = yr; // could also check day = checkDay(dy); // validate the day cout << “Date object constructor for date ”; print( ); cout << endl;}

Date Class

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int Date::checkDay(int testDay){ static int daysPerMonth[13] = {0, 31, 28, 31, 30

31, 30, 31, 31, 30, 31, 30, 31}; if (testDay > 0 && testDay <= daysPerMonth[month]) return testDay;

if (month == 2 && testDay == 29 && (year % 400 == 0||(year % 4 == 0 && year % 100 !=0)))

return testDay;

cout << “Day” << testDay << “ invalid. Set to day 1.”<<endl; return 1; }

Date Class

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// Print Date object in form month/day/yearvoid Date::print() const{ cout << month << ‘/’ << day << ‘/’ << year;}

Date::~Date(){ cout << “Date object destructor for date ”; print(); cout << endl;}

Employee Class

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// emply1.h#ifndef EMPLY1_H#define EMPLY1_H#include "date1.h“class Employee {public: Employee(char *, char *, int, int, int, int, int, int ); void print() const; ~Employee(); private: char firstName[ 25 ]; char lastName[ 25 ]; const Date birthDate; const Date hireDate;};#endif

Employee Class

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// Member function definitions for Employee class.#include <iostream>using namespace std;#include <cstring>#include "emply1.h"#include "date1.h”Employee::Employee( char *fname, char *lname, int bmonth, int bday, int byear, int hmonth, int hday, int hyear ) : birthDate( bmonth, bday, byear ), hireDate( hmonth, hday, hyear ) // constructor of date class called twice: // once for the birthDate object // once for the hireDate object{ // body of constructor

Employee Constructor

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Employee::Employee( char *fname, char *lname, int bmonth, int bday, int byear, int hmonth, int hday, int hyear ) :birthDate( bmonth, bday, byear ), hireDate( hmonth, hday, hyear ) { int length = strlen( fname ); length = ( length < 25 ? length : 24 ); strncpy( firstName, fname, length ); length = strlen( lname ); length = ( length < 25 ? length : 24 ); strncpy( lastName, lname, length ); cout << "Employee object constructor: “ << firstName << ' ' << lastName << endl;}

Employee Class

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void Employee::print() const{ cout << lastName << ", " << firstName << "\nHired: "; hireDate.print(); cout << " Birth date: "; birthDate.print(); cout << endl;}Employee::~Employee(){ cout << "Employee object destructor: " << lastName << ", " << firstName << endl;}

Sample Driver

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#include <iostream>using namespace std;

#include "emply1.h“int main(){ Employee e( "Bob", "Jones", 7, 24, 1949, 3, 12, 1988 ); e.print(); Date d( 14, 35, 1994 ); cout << endl; return 0;}

for birthDate for hireDate

has - a

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Aggregation/Compositionone object contains another object

car has a motorhuman has a brainRobot has an arm

aggregation

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class car{ public://stuff private: Motor myMotor;};

class human{ public://stuff private: Brain myBrain;};

is – a

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is a - relationship that represents inheritance/generalization (class derivation)

For example:Helicopter is a vehicleTrain is a vehicleTruck is a vehiclePlane is a vehicleMotorcycle is a vehicle

Inheritance Diagram

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CAR HELICOPTER

Vehicle

TRAIN

Uses A Relationship

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An operation of class A receives or returns an object of class B

In the process of an operation of class A, an object of class B must be inspected or created

Objects of class A contain a reference to objects of class B

Identify Relationships

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Sun, Planet __________Elevator, Rider __________Date, Person __________Person, Employee __________Circle, Point __________Manager, Employee __________Triangle, Rectangle__________Computer, Keyboard __________Computer, Person __________Computer, Laptop __________

Two Types of Inheritance

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BASE1 BASE2 BASE3

DerivedA DerivedC

DerivedB

DerivedD

Single Multiple

Draw an Inheritance Diagram

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PersonStudentNameAddressProfessor