Aggregation, Composition - Object Oriented Programming - Lecture Slides, Slides of Object Oriented Programming

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Object-Oriented Programming

(OOP)

Lecture No. 15

Conceptual notation:

*String() SetString(char ) : void GetString() const : const char * ~String() …

*gpa : float rollNo : int name : String Student(char * = NULL, int = 0, float = 0.0); Student(const Student &) GetName() const : String GetNamePtr() const : const char * SetName(char ) : void ~Student() …

Student

**string : char ***

String

• Output:

Constructor::String..

Constructor::Student..

Name: Fakhir

Destructor::Student..

Destructor::String..

Student::Student(char * n,

int roll, float g){

cout <<"Constructor::

Student..\n";

name.SetString(n);

rollNumber = roll;

gpa = g;

}

• 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);

String::String(char * str){

if(str != NULL){

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

strcpy(ptr, str);

else ptr = NULL;

cout << "Overloaded

Constructor::String..\n";

• Student class continued:

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

float g): name(n){

cout << "Constructor::Student..\n";

rollNumber = roll;

gpa = g;

Main Function:

int main(){

Student aStudent("Fakhir", 899,

cout << endl;

cout << “Name:”

<< aStudent.GetNamePtr()

<< endl;

return 0;

Now consider the following case:

*String name: char * String() String(char ) ~String() …

… Date() Date(int,int,int) Date(const Date &) …

**Student() Student( char , const Date &, int, float) SetName(char ) : void GetName() : char * ~Student() …

… name : String birthDate : Date

Student

day: int Month: int year: int

Date

• Student class is modified as

follows:

class Student{ private: … Date birthDate; String name; public: Student(char *, const Date &, int, float); ~Student(); … };

• Main function:

int main(){

Date _date(31, 12, 1982);

Student aStudent("Fakhir",

_date,899,3.5);

return 0;

}

• 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 or reference

to an object is created inside 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 at

anytime

• When Room is destroyed, the chairs may or

may not be destroyed

Aggregation

class Room{

private:

float area; Chair * chairs[50];

Public:

Room();

void AddChair(Chair *, int chairNo);

Chair * GetChair(int chairNo); bool FoldChair(int chairNo);

…

};