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

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Object-Oriented Programming

(OOP)

Lecture No. 14

Consider the following implementation

of the student class:

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

class Student{

private:

float gpa;

char * name;

int rollNumber;

public:

Student(char * = NULL, int = 0,

float = 0.0);

Student(const Student & st);

const char * GetName() const;

~Student();

…

};

Student::Student(char * _name, int roll, float g){ cout << "Constructor::Student..\n"; if (!_name){ name = new char[strlen(_name)+1]; strcpy(name,_name); } else name = NULL; rollNumber = roll; gpa = g; }

Student::Student(const Student & st){ if(str.name != NULL){ name = new char[strlen(st.name) + 1]; strcpy(name, st.name); } else name = NULL; rollNumber = st.roll; gpa = st.g; }

const char * Student::GetName(){

return name;

}

Student::~Student(){

delete [] name;

}

• C++: “ its all about code reuse”
• Composition:
  • Creating objects of one class inside another class
• “ Has a ” relationship:
  • Bird has a beak
  • Student has a name

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

class String{

private:

char * ptr;

public:

String();

String(const String &);

void SetString(char *);

const char * GetString() const;

~String()

…

};

String::String(){ cout << "Constructor::String..\n"; ptr = NULL; } String::String(const String & str){ if(str.ptr != NULL){ string = new char[strlen(str.ptr)+1]; strcpy(ptr, str.ptr); } else ptr = NULL; }

void String::SetString(char * str){ if(ptr != NULL){ delete [] ptr; ptr = NULL; } if(str != NULL){ ptr = new char[strlen(str)+1]; strcpy(ptr, str); } }

const char * String::GetString()const{

return ptr;

}

String::~String(){

delete [] ptr;

cout <<"Destructor::String..\n";

}

class Student{ private: float gpa; int rollNumber; String name; public: Student(char* =NULL, int=0,float=0.0); Student(const Student &); void SetName(const char *); String GetName() const; const char * GetNamePtr const(); ~Student(); … };

Student Student(char * _name,

int roll, float g){

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

name.SetString(_name);

rollNumber = roll;

gpa = g;

}

Student::Student(const Student & s){

name.Setname(s.name.GetString());

gpa = s.gpa;

rollNo = s.rollNo;

}

const char * Student::GetNamePtr() const{

return name.GetString();

}

void Student::SetName(const char * n){

name.SetString(n);

}

Student::~Student(){

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

}

Main Function:

void main(){

Student aStudent("Fakhir", 899,

3.1);

cout << endl;

cout << “Name:”

<< aStudent.GetNamePtr()

<< “\n”;

}

• Output:

Constructor::String..

Constructor::Student..

Name: Fakhir

Destructor::Student..

Destructor::String..

• Constructors of the sub-objects are always executed before the constructors of the master class
• Example:
  • Constructor for the sub-object

name is executed before the

constructor of Student