(B) What is Object Oriented Programming ?
It is a problem solving technique to develop software systems. It’s a technique to think
real world in terms of objects. Object maps the software model to real world concept. These
objects have responsibilities and provide services to application or other objects.
(B) What’s a Class ?
A class describes all the attributes of objects, as well as the methods that implement the
behavior of member objects.Its a comprehensive data type which represent a blue print
of objects.It’s a template of object.
(B) What’s a Object ?
It’s a basic unit of a system.An object is an entity that has attributes, behavior, and
identity. Objects are members of a class.Attributes and behavior of an object are defined
by the class definition.
(A) What’s the relation between Classes and Objects ?
They look very much same but are not same.Class is a definition , while object is a
instance of the class created.Class is a blue print while objects are actual objects existing
in real world.Example we have class CAR which has attributes and methods like
Speed,Brakes,Type of Car etc.Class CAR is just a prototype , now we can create real time
objects which can be used to provide functionality . Example we can create a Maruti car
object with 100 km speed and urgent brakes.
(B) What are different properties provided by Objectoriented
systems ?
Twist :- Can you explain different properties of Object Oriented Systems?
Note:- Difference between abstraction and encapsulation is one of the favorite interview
question and quiet confusing as both the terminology look alike.Best is if you can
brainstorm with your friends or do a little reading.
Following are characteristic’s of Object Oriented System’s :-
Abstraction
It allows complex real world to be represented in simplified manner.Example color is
abstracted to RGB.By just making the combination of these three colors we can achieve
any color in world.It’s a model of real world or concept. Encapsulation
The process of hiding all the internal details of an object from the outside world. Communication using messages
When application wants to achieve certain task it can only be done using combination of
objects.A single object can not do all the task.Example if we want to make order processing
form. We will use Customer object , Order object , Product object and Payment object to
achieve this functionality.In short these objects should communicate with each other.This
is achieved when objects send messages to each other. Object lifetime
All objects have life time.Objects are created , initialized , necessary functionalities are
done and later the object is destroyed.Every object have there own state and identity,
which differ from instance to instance. Class hierarchies (Inheritance and aggregation)
Twist :- What’s difference between Association , Aggregation and Inheritance relationships?
In object oriented world objects have relation and hierarchies in between them.There are
basically three kind of relationship in Object Oriented world :- Association
This is the simplest relationship between objects.Example every customer has sales.So
Customer object and sales object have a association relation between them. Aggregation
This is also called as composition model.Example in order to make a “Accounts” class it
has use other objects example “Voucher”,”Journal” and “Cash” objects.So accounts class
is aggregation of these three objects. Inheritance
Hierarchy is used to define more specialized classes based on a preexisting generalized
class.Example we have VEHICLE class and we can inherit this class make more specialized
class like CAR, which will add new attributes and use some existing qualities of the
parent class.Its shows more of a parent-child relationship .This kind of hierarchy is called
inheritance. Polymorphism
When inheritance is used to extend a generalized class to a more specialized class,it includes
behavior of the top clas(Generalized class).The inheriting class often implement a behavior
that can be somewhat different than the generalized class, but the name of the behavior
can be same.It is important that a given instance of an object use the correct behavior,
and the property of polymorphism allows this to happen automatically.
(I) What are abstract classes ?
Following are features of a abstract class :-
√ You can not create a object of abstract class
* How would you describe yourself ?
√ Abstract class is designed to act as a base class (to be inherited by other classes).
Abstract class is a design concept in program development and provides a
base upon which other classes are built.
√ Abstract classes are similar to interfaces. After declaring an abstract class, it
cannot be instantiated on it's own, it must be inherited.
√ In VB.NET abstract classes are created using “MustInherit” keyword.In C#
we have “Abstract” keyword.
√ Abstract classes can have implementation or pure abstract methods which
should be implemented in the child class.
(B) What’s a Interface ?
Interface is a contract that defines the signature of the functionality. So if a class is
implementing a interface it says to the outer world , that it provides specific behavior.
Example if a class is implementing Idisposable interface that means it has a functionality
to release unmanaged resources . Now external objects using this class knows that it has
contract by which it can dispose unused unmanaged objects.
√ Single Class can implement multiple interfaces.
√ If a class implements a interface then it has to provide implementation to all
its methods.
Below is the source code “IInterface” is the interface and “ClsDosomething”
implements the “IInterface”. This sample just displays a simple message box.
Public Interface IInterFace
Sub DoSomething()
End Interface
Public Class ClsDoSomething
Implements IInterFace
Public Sub DoSomething() Implements
WindowsInterFace.IInterFace.DoSomething
MsgBox(“Interface implemented”)
End Sub
End Class
