Characteristics of an Object-oriented Language

The important elements of an object-oriented language are:

Class

An Object in C++ is an instance of a class. For example, in the following statement:

int iNum1, iNum2, iNum3;

iNum1, iNum2, iNum3 are three variables of type int.

Similarly, you can define many objects of the same class as shown in Figure 10.2

 

Inheritance

Inheritance is the process of creating a new class, called the derived class, from the existing class, called the base class.

Figure 10.3 shows the inheritence of a derived class from the base class.

 

Figure 10.3 Inheritance of a Derived Class From a Base Class

For example, motorcycles, cars and trucks have certain common properties-- all have wheels, engines and breaks. Therefore, they can be grouped under a class called automobiles. Apart from sharing these common features, each subclass has its own particular characteristices--cars use petrol while trucks use diesel.

The derived class has its own characteristics and, in addition, inherits the
properties of the base class.

Reusability

The concept of inheritence provides an important feature to the object-oriented lanuage-reusability. A programmer can take an existing class and, without modifyinh it, and additional features and capabilities to it. This is done by deriving a new class from an existing class.

Polymorphism

The word polymorphism is derived from two Latin words poly (many) and morphos
(forms). The concept of using operators or functions in different ways, depending on what they are operating on, is called polymorphism.

The following program uses an overloaded function to illustrate polymorphism:

//This program uses an overloaded function to display a character or an integer
#include<iostream.h>
void disp(int);
void disp(char);
void main()
{
disp(10);
disp(‘a’);
}
void disp(int iNum1)
{
cout<<”The number is”<<iNum1<<endl;
}
void disp(char cCh)
{
cout<<”The character is”<<oCh<<endl;
}


The output of Program 10.1 is:

The number is 10
The character is a

In Program 10.1, the function disp() is overloaded and, based on the parameter passes, the corresponding message is displayed, therefore exhibiting polymorphism.