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OOPs

Basic Concepts Of OOPs



Basic Concepts Of OOPs     

What is class?
·       A class is a collection of objects of same type.
·       It is a user defined data type.
·       Class defines basic structure and functionality of an object.
·       It is a collection of data member and data function.
·       Once class is defined any number of objects can be created which belong to that class.
·       It is a set of objects that share a common structure and behavior.
EXAMPLE
class student
{
    private:
             int rollno;
             int marks
    public:
             void getdata();
             void putdata();          
}

  What is object? 
·         Objects are the basic run-time entities in an OOPs.
·         We can create number of object with one class.
·         Object is a variable of user define data type.
·         The data stored within an object represents the current state of the object.
·         Object represents real word entity into a program.

 What is Encapsulation? 
·      The wrapping up of data and functions into a single unit (called class) is known as encapsulation. Class is the best example of it.
·  The data is not accessible to the outside world, and only those functions which are bonded in the class can access it.

What is data abstraction? 
·       Abstraction refers to the act of representing main features without including the background details or explanations.
·     Consider a real life example of driving a car. The man only knows that brakes will stop the car and pressing the accelerators will increase the speed of car but he does not know about the inner mechanism of the car. This is what abstraction is.

       What does polymorphism mean in C++ language?
·       Polymorphism means more than one forms.
·   Real life example of polymorphism, a man at the same time he is a husband, a father, an employee. So the same person performs different roll in different situations. This is called polymorphism.
· There are two types of polymorphism, namely, compile time polymorphism and run time polymorphism.

    How is polymorphism activated at (a) compile time and (b) run time? Or
          How do we carry out compile time polymorphism and run time polymorphism.
a)    Compile time polymorphism:
·     Functions overloading and operator overloading are used to achieve the compile time polymorphism.
·  The overloaded member functions are selected for invoking by matching arguments, both type of argument and number of argument.
·  This information is known to the compiler at the compile time, therefore the compile is able to select the appropriate function for the particular call at the compile time.
· Compile time polymorphism is also known as the static binding, static linking or early binding.
·     In short, an object is bound to its function call at the compile time is known as compile time polymorphism.

b)   Run time polymorphism:
·    Function overriding is used to achieve the run time polymorphism.
 ·    In run time polymorphism appropriate member function is selected while the program is running.
 ·     Using of virtual function C++ supports run time polymorphism.
·   Run time polymorphism is also known as late binding or dynamic binding because the appropriate function is selected dynamically at run time.

 What is function overriding?
Same name different argument is called function overriding.
Example
Class A
{
         Int x;
         Public:
         Void show()
         {
         }      
};

Class B:public A
{
         Int y;
         Public:
         Void show()
         {
         }      
};

What is inheritance? How does it enable reusability?
·  The Procedure of deriving a new class from an old one is called inheritance (or derivation).
·   The old class is referred to as the ‘base class’ and new one is called the ‘derived class’ or ‘subclass’.
·   C++ strongly supports the concepts of reusability, and it is achieved using ‘inheritance’.
·     The derived class inherits some or all of the data from the base class.
·     A class has also inherit properties from more than one class or from more than one level.
·       In inheritance derived class inherits all/some properties of base class and this enable code reusability. So we do not need to define the properties in derived class as in base class again.

What is data hiding?
·     Data hiding means technique of hiding internal details of object.
·      Data hiding is achieved using the encapsulation.
·     In encapsulation the data and functions are wrapped into a single unit (called class).
·    In that the data is not accessible to the outside world, and only those functions which are wrapped in the class can access it.

    Difference between class and object.
Class
Object
By default All the members of a class are private.
All members of a class are not public by default.
Private members cannot be access through any object of that class.
Public members can be access through any object of that class.
We cannot access private data anywhere in the program
We can access public data anywhere in the program
Example class student
               {
                    private:
                      int a;
               }

Example class student
               {
                    public:
                      int a;
               }