1. Object Oriented Analysis and Design
Agenda
Object basics (continued)
Encapsulation & Information Hiding
Class Hierarchy
Inheritance
Polymorphism
Associations
Aggregations

2. Encapsulation & Information Hiding:
Object basics:
Encapsulation & Information Hiding:
An object is said to encapsulate the data & a program
No object can operate directly on another object’s data
Object’s internal format is insulated from other object’s
Private Protocol
Public Protocol
Massages
Data
Permissible operations

3. Encapsulation & Information Hiding:
Object basics:
Encapsulation & Information Hiding:
Encapsulation & Information Hiding:
Very general encapsulation mechanisms are private, public & protected
Public members may be accessed from anywhere
Private members are accessible only from within a class
Protected members can be accessed only from subclasses

4. Encapsulation & Information Hiding:
Object basics:
Encapsulation & Information Hiding:
An important factor in achieving encapsulation is the design of different classes of objects that operate using common protocol
Protocol is an interface to the object
TV contains many complex components, but you do not need to know about them to use it
Data abstraction is a benefit of the object oriented concepts that incorporates encapsulation & polymorphism

5. Object basics: Class Hierarchy:
An object oriented system organize classes into a super class – subclass hierarchy
Different properties and behaviors are used as the basis for making distinction between super & subclasses
A subclass inherits all of the properties & methods defined in a super class
Eliminates duplication by allowing classes to share & reuse behaviors

6. Object basics: Inheritance:
A relationship between classes where one class is the parent of another class
It allows classes to share & reuse behavior & attributes
We can “build on what we already have” & “reuse what we already have”

7. Multiple Inheritance:
Object basics:
Multiple Inheritance:
OO systems permit a class to inherit from more than one superclass
This kind of inheritance is referred to as multiple inheritance
For example utility vehicle inherits from Car and Truck classes

8. Object basics: Polymorphism: Poly means “many” & morph means “form”
Same operation may behave differently on different objects
Draw message can be sent to many objects like triangle, circle or line & each object could act differently
Polymorphism is the main difference between a message and a subroutine call
It allows us write generic, reusable code more easily, because we can specify general instructions & delegate the implementation details to the object involved

9. Object basics: Associations: Represents relationship between objects
For example a pilot can fly planes.
Associations are Bidirectional
An important issue in association is cardinality

10. Object basics: Associations: Client server association:
A special form of association is a client-server relationship.
This relationship can be viewed as one-way interaction: one object (client) requests the service of another object (server).
PrintServer
Item
Request for printing

11. Object basics: Aggregations: Aggregation is a form of association
Objects are composed of & may contain other objects
One object’s attributes can reference to other objects, where an attribute can be object itself
Example
Category
Book
Publication
Author

12. Object basics:
Aggregations:
Example