Object Orientation

Object:

Object is a real time entity which has real existence in the application.

Ø  Is unique.

Ø  Has an Identity.

Ø  Contains attribute and behavior.

A software object is the representation of the real world object.

Class:

Class is a software template that defines the attribute and behavior to be included in the particular type of object.

Ø  Is used to distinguish one type of object from another.

Ø  Tells how an object looks like.

Ø  Has virtual existence (made for categorize the objects based on their behavior and attribute).

Ø  Does not do anything (Just tells what an object of particular type will do).

Example for object and class: 

 State behavior and identity:

State:  The set of values that an object holds at a particular part of time. State of an object can change in time.

Behavior:  Acts on the object and changes the state. Here the logic of the class is stored.

Identity: A name to the object which will separate it from all the other objects.

Example:

Abstraction:

Abstraction is the representation of a complex system into a general and relevant system

Ø  Hides the complexity.

Ø  Focus on The separation of an object’s essential behavior from its implementation.

Ø  Data abstraction is also known as Data hiding

Ø  Program to an interface, not to an implementation(good abstraction)

Example no. 1:  One does not have to understand how the engine works to drive a car.

Example no. 2: level of Abstraction

Encapsulation:

Encapsulation is a technique of wrapping up of the code and data to a single unit so that it can’t be access by the element outside of the wrapper.

Ø  Provide security to data and function from being misused.

Ø  Implemented using private, protected and public access modifier.

Ø  Typically in a class :

State is private (not accessible externally)

Behavior is public (accessible externally)

Inheritance:

The ability of OOP to organize the classes in hierarchy where one class can acquire the properties of its super class called as inheritance.

Ø  Represents a relationship between classes.

Ø  Hierarchy can be considered as the rank or order of abstraction.

Ø  Implemented in terms of subclass and super class.

Ø  Sub classes have ability to acquire the visible responsibility defined in super class.

Ø  The two most important hierarchies in a complex system are:

Class structure (‘is a’ hierarchy)

Object structure (‘has-a’ and Uses-A hierarchy)

Example:

Relationships among classes:

There are three types of relationships which can exist between classes:

Ø  Is-A (or Kind-Of)

Ø  Has-A (or Part-Of)

Ø  Uses-A

Is-A Relationship (Inheritance):

Ø  A class is a type of another class.

Ø  Acquires the visible responsibility defined in super class.

Ø  Define added responsibilities.

Has-A Relationship (Aggregation):

Ø  Class contains another class (as member)

Ø  Another class is part of the class

Uses-A Relationship (Association):

Ø  Loosely coupled relationship

Ø  A class interacts with another class

Ø  Objects interacting with other objects. It may include

-Creation of another type of object

-Method invocation (Message passing) on already existing object

Polymorphism:

Ability of methods to share same name but different implementation

Ø  Method overloading / Early Binding/ Compile time polymorphism.

Ø  Method overriding /Late Binding/ Run time polymorphism.

Method overloading:

Ø  Function Call mapped at compilation

Ø  Class type and object type are the same

Ø  Here the method call depends on the arguments passed to it.

Method overriding:

Ø  Function Call mapped at run time

Ø  Class type and object type need not to be same

Ø  Here the method call depends on the object who is calling it.