OOAD Adapted from Object Oriented Analysis and Design Methodology A Tech Talk by Ed Sullivan

Today’s Discussion n Background – Why OO is hot n OO Methodology – Java Factory Approach n Hands on application of CRC Methodology

Object Oriented Headlines “Object-Oriented Technology Ventures Into the Real World” “IBM unveils new object-oriented middleware” “Expo to serve up object-oriented products” “Object-Oriented is Here to Stay”

Motivation For OOAD Traditional Methodologies are broken because… n They haven’t solved problems of quality and timeliness. n They separates data from procedures making software reusability more difficult. n They don’t work well in our non-linear world.

Linear vs. Non-linear LinearNon-Linear Step 1 Step 2 Step 3 Page 1 Page 2 Page 3 Page 4

OOAD Vs. Traditional Approach n Process is less rigorous –Analysis Paralysis n Process is more fluid –Waterfall vs. Onion n No definitive stopping point –How many iterations? n More Trial and Error… “I failed my way to success.” Thomas Edison

OOAD Methodology Roots n Unified Modeling Language(UML) –Use Cases –Class Diagrams n Sun Microsystems Java factory –CRC Methodology n Class n Responsibility n Collaboration

Defining the Process n Determine the Requirements n Identify the Classes and Objects n Describe the Object Collaborations and the classes n Sketch the User Interface

Diagram of OOAD Class Diagram Determine Requirements Identify Classes & Objects Describe Collaboration Sketch Interface SummaryCRC Cards Colloboration Diagrams Interface Sketch

Determining Requirements n Summary Paragraph –Define general approach to solving problem –Emphasize the what and not the how –Describe all major functions(operations/methods) –Define boundaries

Sample Problem Summary

Identifying Classes and Objects n CRC Card Preparation –Class(data attributes) –Responsibility(Message response) –Collaboration(Class interaction)

Class Definition n Classes are the templates or blueprints for objects n Classes define the attributes and behavior(methods) for objects n Objects contain the data and the methods n Objects are the nouns of the Object Oriented world

So how do you define Classes?? 1) Read Problem Summary statement for nouns and noun phrases which may be physical objects, concepts, categories of objects or attributes of other objects. Create a list of all of these items. 2) Review list for Class candidates. Transfer classes to CRC card.

Sample Problem Summary

Noun Phrases n Renter Application n Bugs n Inventory n User n Message

Transitioning Nouns to Classes n Not always easy n Iterative n Experience n Steps… –Logical Groupings and Leveling –Identify Implied Classes –Eliminate noise(primitives, attributes, messages) “Design Decisions have no obvious right and wrong answers.”

Noun Phrases Class Steps n Renter Application n Bugs n Inventory n User n Message n Logical Groupings/Leveling n Implied Classes n Noise elimination

So what are the Classes of the Bug Rental Application?? n Renter n Lender n Inventory

CRC Card - Front Class: Renter Responsibilities:Collaborations: (Front of Card)

Defining Responsibilities n Use Problem Statement to identify verbs n Logical group and organize action items n Match Method to Class n Adjust for any omissions

Method Verbs Identification Method Verbs Identification n Track Inventory n Rent Bug n Decrease Inventory n Return Bug n Increase Inventory n Display Message n Logical Grouping n Leveling n Match Method to Class

Bug Rental Methods n Renter –Rent Bug –Return Bug –Display Message n Lender –Rent Bug –Return Bug –Supply Message

Describing Collaboration n Develop Use-case scenarios –Sequence of related events n Walk Through Use-cases –Identify message exchanges –Identify missed Classes

Identify Use-Case Scenarios n Customer Rents a Bug 1) Customer enters request for bug 2) Lender checks inventory for bug availability 3) If inventory is greater than zero Inventory is decreased by one Inventory is decreased by one Bug is made available to Customer Bug is made available to Customer Message is sent to Customer from Lender Message is sent to Customer from Lender 4) If inventory is zero, error message is sent to customer from Lender

Now it’s your turn… Develop Use-Case for Bug Returns Ê Customer returns bug Ë Lender increases inventory ¸ Lender sends message to Customer

CRC Card - Front Class: Renter Responsibilities: Collaborations: (Front of Card) Rent Bug Return Bug Display Message Lender N/A

Identifying Attributes n Characteristics of Class n Adjectives of the Object Oriented World n Inventory Example –Bug ID –Bug Description –Bug Version

Your turn again… Develop some common attributes for the Renter n Customer Name n Customer Address n Customer Status n Customer Rentals n Customer Balance

CRC Card - Back Attributes:

Developing a Class Diagram Class Name Attributes Methods

CRC Adjustments n Create new CRC cards n Trash invalid CRC cards n Challenge yourself –Not a cookbook –Process is not magic;requires critical thinking skills n Iterate!