Object-Oriented Programming (OOP) Lecture 15: Composition and Aggregation, Slides of Object Oriented Programming

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Object-Oriented Programming

(OOP)

Lecture No. 15

Composition

Conceptual notation:

**String()SetString(char ) : voidGetString() const : const char ~String()…

gpa : floatrollNo : intname : StringStudent(char * = NULL, int = 0,

float = 0.0);

**Student(const Student &)GetName() const : StringGetNamePtr() const : const char SetName(char ) : void~Student()…

Student

**string : char ***

String

Composition

►Output:

Constructor::String..Constructor::Student..Name:

Fakhir

Destructor::Student..Destructor::String..

Composition

Student::Student(char * n,

int

roll, float g){

cout <<"Constructor::

Student..\n";

name.SetString(n);rollNumber = roll;gpa = g; }

Composition

►Add an overloaded constructor to the String

class defined above:

class String{

char

*ptr; public:

String();String(char *);String(const

String

void

SetName(char

~String();…

//String(char * = NULL);

Composition

String::String(char * str){

if(str != NULL){

ptr = new char[strlen(str)+1];strcpy(ptr, str);

} else ptr = NULL;cout << "Overloaded

Constructor::String..\n";

Composition

Student class

continued:^ Student::Student(char * n,int roll,

float g): name(n){

cout << "Constructor::Student..\n";rollNumber = roll;gpa = g;

Composition

Main Function: int main(){

Student aStudent("Fakhir", 899,

cout << endl;cout << “Name:”

<< aStudent.GetNamePtr()<< endl;

return 0;

Composition

Now consider the following case:

String name: char

---

String()String(char )~String()… …Date()Date(int,int,int)*

**…name : StringbirthDate : DateStudent()Student( char *,const Date &, int, float)SetName(char ) : voidGetName() : char ~Student()…

Student

day: intMonth: intyear: int

Date

Composition

►Student class is modified asfollows:

class

Student{ private: … Date

birthDate; String

name; public: Student(char

const

Date

int,

float);

~Student();…

Composition

►Main function:

int main(){ Date _date(31, 12, 1982);Student aStudent("Fakhir",

_date,899,3.5);

return 0;

Composition

►Output:

Overloaded Constructor::Date..Copy Constructor::Date..Overloaded Constructor::String..Constructor::Student..Destructor::Student..Destructor::String..Destructor::Date..Destructor::Date..

Aggregation

►In aggregation, a pointer orreference to an object is createdinside a class ►The sub-object has a life that is NOT

dependant on the life of its

master class ►e.g:

Chairs can be moved inside or outside atanytime When Room is destroyed, the chairs may or

Aggregation class

Room{ private: float

area; Chair

*^

chairs[50];

Public: Room();void

AddChair(Chair

int

chairNo);

Chair

*^

GetChair(int

chairNo);

bool

FoldChair(int

chairNo);