Data encapsulation

DATA ENCAPSULATION:

·        Data encapsulation is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user.

·        C++ supports the properties of encapsulation and data hiding through the creation of user-defined types, called classes. We already have studied that a class can contain private, protected and public members. By default, all items defined in a class are private.

For example:

class Box

{

public:

double getVolume(void)

{

return length * breadth * height;

}

private:

double length; // Length of a box

double breadth;    // Breadth of a box

double height; // Height of a box

};

·        The variables length, breadth, and height are private. This means that they can be accessed only by other members of the Box class, and not by any other part of your program. This is one way encapsulation is achieved.

·        To make parts of a class public (i.e., accessible to other parts of your program), you must declare them after the public keyword. All variables or functions defined after the public specifier are accessible by all other functions in your program.

·        Making one class a friend of another exposes the implementation details and reduces encapsulation. The ideal is to keep as many of the details of each class hidden from all other classes as possible.

Data Encapsulation Example:

Any C++ program where you implement a class with public and private members is an example of data encapsulation and data abstraction. Consider the following example:

#include <iostream.h>

#include<conio.h>

class Adder

{

public:

// constructor

Adder(int i = 0)

{

total = i;

}

// interface to outside world

void addNum(int number)

{

total += number;

}

// interface to outside world

int getTotal()

{

return total;

};

private:

// hidden data from outside world

int total;

};

int main( )

{

Adder a;

 a.addNum(10);

 a.addNum(20);

 a.addNum(30);

cout << "Total " ; cout<< a.getTotal(); cout <<endl;

return 0;

}

When the above code is compiled and executed, it produces the following result: Total 60

Above class adds numbers together, and returns the sum. The public member‟s addNum and getTotal are the interfaces to the outside world and a user needs to know them to use the class. The private member total is something that is hidden from the outside world, but is needed for the class to operate properly.

Designing Strategy:

Most of us have learned through bitter experience to make class members private by default unless we really need to expose them. That's just good encapsulation.

This wisdom is applied most frequently to data members, but it applies equally to all members, including virtual functions.