Apr 15, 2013

Some of the terms programmers frequently use. Part one

Classes and Objects
The class represents or defines the common characteristics/attributes of an object of a particular type. For e.g. you might want to define a class of “ Person”. Every person will share some common characteristics/attributes like first name, last name, address etc.. So, a class serves as a blueprint for similar type of object. A class is made up of attributes and behavior. Attributes are defined in terms of member variables and behavior is expressed in terms of function.
An object is an instance of a class. It is a representation of a real world thing. Object can have both attributes/data and behaviors. For e.g. You, me are instance of t he “Person” class. We share some common attributes like we both have a first name, a last name and so on. We have some common behaviors like walking, talking etc.

Abstraction refers to the act of representing essential features without unnecessarily
including the background details or information i.e. representing a complex problem in simple terms. Classes provides a mechanism to abstract the required attributes such as first name, last name in case of “Person” class and functions to operate on these attributes. Classes are also known as “Abstract Data Type or ADT”.

Encapsulation(or Information Hiding)
Encapsulation is a technique where data and its associated behaviors(function) are wrapped in a single unit (Class). The data is hidden fro m the outside word. The purpose is to reveal as little as possible about the inner workings of the class. The only way to access these data is through public interfaces provided by the functions.

Inheritance is a technique with which an object of one class acquires attributes and
behaviors from an object of another class. This is one way to achieve reusability in OOP.
Inheritance models “is -a” relationship . For e.g. a “car” is an automobile. In this case
the “automobile” is called the base class and “car” is called as derived class or inherited class.  This type of reuse is often called  white- box reuse. This term refers to the fact that with inheritance, the parent class implementation is often visible to the subclasses.

When reuse is achieved by composing another object, the technique is known as
composition.  Composition models “has-a” relationship .  This approach requires that the objects have well - defined interfaces since the internals of the objects are unknown. Because objects are treated only as "black boxes," this type of reuse is often called  black-box  reuse.

The ability of different objects to respond to the same message in different ways is called polymorphism.  Polymorphism is also the ability of an object to take more than one forms, for e.g. an operation may exhibit different behavior in different instances. The behavior depends upon the types of data used in the operation. There are basically two types of polymorphism
 static and dynamic polymorphism. Method overloading is an example
of static polymorphism whereas overriding would be an example of dynamic


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