2.1 classes and objects

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Introduction To OOP1.0

Classes And Objects

2.0

Inheritance andPolymorphism3.0

Exception handling4.0

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2009 | PN NORHASLIZA BT MUHAMAD NOR


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Define Class1

Define Method2

Access Specifier3

Declare jects

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General format for defining a class :


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class ClassName

{

// Data definition

// Method definition

};

*Keywordclass is a must in defining a class.

* Semicolon (;) must be placed after closing braces each time you define a class.


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class Rectangle

{ int length, width;

public :

void set_data (int x,int y)

{ length=x;

width=y;

}

double calculate_area()

{ return length*width}

};

Definasi metod /

Method definition

NamaKelas/

ClassName

Definasi ahli data /

Data member definition

Katakunci untuk mengisytihar kelas /

Keyword for defining a class

Kawalancapaian /

Access control

Contoh definisi kelas / Example of class definition


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There are two ways of defining method :1. Define it in the class

class Student

{

int ID,age;char name[30];

double mark;

public:

void set_data (int a,int b, char * c, double d)

{

ID=a;age=b;

strcpy(name,c);

mark=d;

}

};


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There are two ways of defining method :2. Define it outside the class by using scope resolution operator (::)

class Student

{

int ID,age;

char name[30];

double mark;

public:

void set_data (int a,int b,char * c,double d);

};

void Student::set_data(int a,int b,char * c,double d)

{

ID=a;age=b;

strcpy(name,c);

mark=d;

}

declare

define


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Three type of access specifier(kawalan capaian) for data members and methods:

1. Public

2. Private

3. Protected

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Class members are private members by default but the situations can be

changed by using another keyword. For example,


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Public: Public members are accessible outside the class (for example in main() function).

Members in the class must be declared in the public section to make it accessible

from outside the class.

Definition of friend does not give any effect to this access control.

class AccessCtrl{

int value1;

void func1 (long);

int value2;

int func2 (char*);

public :

char* value4;

long func4 ( );};

Contoh kawalan capaian public /Example of public access control


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Private: Private members can only be achieved by functional members (ahli-ahli fungsi)

and friends for a class, which has been declared. (Will be explained further later)

Example of the use of this keyword in the real world:

The ATM pin number, password to open an e-mail. This example is more appropriate

if it is declared privately so that it is not accessed by any other unauthorized person.

class AccessCtrl

{

int value1;

int value2;

int func2 (char*);

void func1 (long);};

Contoh kawalan capaian public /Example of public access control

Private Data

Private Method


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Protected: Protected members are accessible in the class where it is declared and also any

other classes, which are inherited from that class.

Definition of friend does not give any effect to this access control.

Example of the use of this keyword in the real world: total savings for a student. Only

certain people knows the actual total savings by a student such as his/her family

members.class A

{ protected:

int valueA;

};

class B : public A

{

public:

void FuncB( );};

class C : public B

{

public:

void FuncC( );

};

Example of protected access control


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Declaring an objects :

`

Example:

Assuming that you have created an object from the class Student.Example ofdeclaration is shown as below:

Student p;

When an object has been declared, it can be manipulated by any function, which is

declared inside the object class. Syntax is used to call a data or method:

ObjectName . MemberName

dot operator


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className objectName;


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Example

2.1 classes and objects

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