Source Code : Inheritance And Data Abstracion In C++

Inheritance:

  One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.

When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.

Base & Derived Classes:

  A class can be derived from more than one classes, which means it can inherit data and functions from multiple base classes. To define a derived class, we use a class derivation list to specify the base class(es). A class derivation list names one or more base classes and has the form:

class derived-class: access-specifier base-class

  Where access-specifier is one of public, protected, or private, and base-class is the name of a previously defined class. If the access-specifier is not used, then it is private by default.

Access Control and Inheritance:

  A derived class can access all the non-private members of its base class. Thus base-class members that should not be accessible to the member functions of derived classes should be declared private in the base class.

Access	Public	Private	Protected
Same class	Yes	Yes	Yes
Derived Class	Yes	Yes	No
Outside class	Yes	No	No

Access	Public	Private	Protected
Same class	Yes	Yes	Yes
Derived Class	Yes	Yes	No
Outside class	Yes	No	No

A derived class inherits all base class methods with the following exceptions:

Ø Constructors, destructors and copy constructors of the base class.

Ø Overloaded operators of the base class.

Ø The friend functions of the base class.

Type of Inheritance:

  When deriving a class from a base class, the base class may be inherited through public, protected or private inheritance. The type of inheritance is specified by the access-specifier as explained above.

We hardly use protected or private inheritance but public inheritance is commonly used. 

ØPublic Inheritance:

When deriving a class from a public base class, public members of the base class become public members of the derived class and protected members of the base class become protected members of the derived class. A base class's private members are never accessible directly from a derived class, but can be accessed through calls to the publicand protected members of the base class.

ØProtected Inheritance:

When deriving from a protected base class, public and protected members of the base class become protected members of the derived class.

ØPrivate Inheritance:

When deriving from a private base class, public and protected members of the base class become private members of the derived class.

Multiple Inheritances:

A C++ class can inherit members from more than one class and here is the extended Syntax:

class derived-class: access baseA, access baseB....

Polymorphism:

  The word polymorphism means having many forms. C++ polymorphism means that a call to a member function will cause a different function to be executed depending on the type of object that invokes the function.

Virtual Function:

  A virtual function is a function in a base class that is declared using the keyword virtual. Defining in a base class a virtual function, with another version in a derived class, signals to the compiler that we don't want static linkage for this function. What we do want is the selection of the function to be called at any given point in the program to be based on the kind of object for which it is called. This sort of operation is referred to as dynamic linkage, or late binding.

Pure Virtual Functions:

  It's possible that you'd want to include a virtual function in a base class so that it may be redefined in a derived class to suit the objects of that class, but that there is no meaningful definition you could give for the function in the base class.

E.g:

class Shape {

protected:

int width, height;

public:

Shape( int a=0, int b=0)

{

width = a;

height = b;

}

// pure virtual function

virtual int area() = 0;

};

Data Abstraction:

  Data abstraction refers to, providing only essential information to the outside word and hiding their background details, i.e., to represent the needed information in program without presenting the details.

Data abstraction is a programming (and design) technique that relies on the separation of interface and implementation.

E.g:#include

using namespace std;

int main( )

{

cout << "Hello C++" <

return 0;

}

Benefits of Data Abstraction:

Data abstraction provides two important advantages:

· Class internals are protected from inadvertent user-level errors, which might corrupt the state of the object.

· The class implementation may evolve over time in response to changing requirements or bug reports without requiring change in user-level code.

Data Encapsulation:

All C++ programs are composed of the following two fundamental elements:

·Program statements (code): This is the part of a program that performs actions and they are called functions.

·Program data: The data is the information of the program which affected by the program functions.

  Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding.

  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.

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

};