Coming up: Motivation1 Object-Oriented Analysis Using CRC Cards and Scenarios to Get Started on a Good Object- Oriented Design Slides from Jochen Rick adapted by Dan Fleck

Coming up: Good Object-Oriented Style2 Motivation It’s all very well understanding what an object is, but it’s much harder to decide what kinds of object you should design in order to implement an application in Smalltalk. Indeed given a set of requirements for an application and a development system like Smalltalk, ‘finding the objects’ is easily the most difficult task an experienced OO developer has to face. —Simon Lewis, The Art and Science of Smalltalk

Coming up: Design is a Process, not a Waterfall 3 Good Object-Oriented Style You can hack in any language, but how do you get reusable, maintainable code? Just using Objects doesn’t ensure a good design –Many C++ programs have only have a single class –That’s not good object-oriented style No process can guarantee good results –A good process just makes them more likely

Coming up: OOA vs. OOD4 Design is a Process, not a Waterfall Design is an iterative activity –Start with Object-Oriented Analysis and Design –Move on to OO Programming –Return to OOA/OOD when necessary When creating new functionality To solve problems with the code OO Analysis is just another perspective –Good designers (in any field) shift perspective frequently to create a better design –The boundary between OOA and OOD is fuzzy.

Coming up: Object-Oriented Analysis5 OOA vs. OOD In analysis, we are mostly concerned with the DOMAIN MODEL. What are the objects in the domain and how do they collaborate. In design, we need to integrate an APPLICATION MODEL. What objects do I need to add to get this thing to run on a computer and to be realized in some programming language?

Coming up: OOA Step 1 Brainstorming Candidate Classes 6 Object-Oriented Analysis CRC Cards by Ward Cunningham Goal: Understand the Domain as Objects –Object-Oriented Analysis is Language Independent –Force Developers to “think” in objects Steps 1.Brainstorm Candidate Classes 2.Create Initial Class-Responsibility-Collaboration Cards 3.Come up with scenarios of use in the domain 4.Use Scenarios and role playing to refine CRC Cards When do we do it? –Before we begin coding (to get a good start) –To add new functionality (update CRC cards and scenarios regularly)

Coming up: Brainstorming Tips7 OOA Step 1 Brainstorming Candidate Classes Write down all the objects that relate –Domain Analysis –Focus on the nouns (objects are nouns) –Good objects will have attributes and services Now, filter and refine the candidates –Deal with the interface later (Not part of the domain, that’s the application model) –Are some candidates attributes of others? –Are some subclasses of others? –Are some instances of others?

Coming up: Candidate Class Review8 Brainstorming Tips Two’s only company, Ten’s a crowd Don’t forget the user All ideas are potentially good Analyze – make connections Think fast – ponder later Every voice gets a turn Relax – humor is OK.

Coming up: Filter Candidate Classes9 Candidate Class Review Has clear unambiguous name, recognized by domain experts Has name that fits in with other systems developed by your organization Uses singular noun for name Begins with Uppercase Letter Has responsibilities (what NOT how) Remembers (knowledge) Is needed (collaborates) Actively participates from CRC Card Book

Coming up: OOA Step 2 CRC Cards 10 Filter Candidate Classes Core Classes (pretty sure these are in Analysis model) Undecided Classes (probably not classes – might be attributes) Eliminated Classes – (outside scope of system, Application model classes like UI components tied to implementation)

Coming up: CRC Cards: What Goes Where?11 OOA Step 2 CRC Cards For each core candidate class, create one CRC card What’s a CRC Card? –Class-Responsibility- Collaboration –It’s just a 4x6in index card Analysis vs. Design Information

Coming up: CRC Card Format (Front)12 CRC Cards: What Goes Where?

Coming up: CRC Card Format (Back)13 CRC Card Format (Front) Class Name (OOA) Purpose/Role (OOA): Patterns (OOD): Stereotypes(OOA/OOD):

Coming up: CRC Card Sample14 CRC Card Format (Back) Class Name Superclass: Subclasses: ResponsibilitiesCollaborators

Coming up: CRC Card Sample15 CRC Card Sample Front Document Purpose: A Document acts as a container for graphics and text. Patterns: Composite-Component Stereotypes: Structurer

Coming up: Stereotypes16 CRC Card Sample Back Document Superclass: Subclasses: ResponsibilitiesCollaborators Know Contents Know Storage Location Insert and Removes text, graphics and other elements

Coming up: OOA Step 3 Scenarios with CRC Cards 17 Stereotypes Information Holder –knows and provides information Structurer –Maintains relationships between objects and information about those relationships Service Provider –Performs work for other objects Coordinator –Reacts to events by delegating tasks to others Controller –Makes decisions and closely directs others’ actions Interfacer –Transforms information and requests between different parts of our system

Coming up: Scenario Guidelines18 OOA Step 3 Scenarios with CRC Cards Invent Scenarios –What should these objects do? –What if…? Play the Cards –Assign Roles –Go Through Scenario –Write down new responsibility –Add collaborator objects to help with that responsibility –Team members hold up cards as they participate

Coming up: Scenario Guidelines19 Scenario Guidelines Concrete: –Bob tries to Login to the system with an incorrect password. –Sally creates a new Sorceress character and chooses auto-configuration. Focus on “must do” items first Start easy and move to complex

Coming up: OOA for a Clock20 Scenario Guidelines Keep a record of scenarios played out Explore exception conditions last Separate role-play from analysis

Coming up: OOA for a Clock21 OOA for a Clock We want to make a clock. The clock should: –Have a way to set the current time –Display the time in hours, minutes, and seconds in different formats –Update the time to keep it current

Coming up: OOA for a Clock22 OOA for a Clock Brainstorm (Step 1 – Candidate Classes) –Candidate classes

Coming up: OOA for a Clock23 OOA for a Clock Brainstorm –Face for the clock, internal ticker, hours, minutes, seconds, knob for setting the clock Filter for Core Objects

Coming up: OOA for a Clock24 OOA for a Clock Brainstorm Filter Define the Clock class –Attributes: hours, mins, secs, timezone, state (low bat, etc…), –Services: update, setTime, alarm, setAlarm, display/time, displayDate, setAmPm, getAmPm

Coming up: ALERT!!!!25 OOA for a Clock Brainstorm –Face for the clock, internal ticker, hours, minutes, seconds, knob for setting the clock Filter –Ticker, hours, minutes, seconds Define the Clock class –Attributes: seconds, minutes, hours, displayFormat –Services: get/set, nextSecond, display, setFormat

Coming up: Errors in this Design26 ALERT!!!! Bad OO Design in Progress What did we do wrong? I’m still designing a program thinking – what’s my data and what do I have to do? I need to think about a community of cooperating objects!!!

Coming up: OOA for a Clock: Second Try27 Errors in this Design We assumed there was only one class: Clock –What’s reusable in that? We started with data and not with what the object should be responsible for We were way too focused on the programming from the start Thinking in get/set mode (be aware of your idioms!) –Java/Python does that, but typically not Smalltalk

Coming up: Scenario 1: The Ticker Ticks28 OOA for a Clock: Second Try Brainstorm objects for Clock –Display, Time, Ticker/SecondTimer, Clock, Formatter Filter: CRC Cards –Two scenarios 1.When the ticker pulses the clock, the internal representation of time must increment 2.When a display is requested, the time must be fetched and formatted

Coming up: Scenario 1: The Ticker Ticks29 Scenario 1: The Ticker Ticks The SecondsTicker pulses the Clock

Coming up: Scenario 1: The Ticker Ticks30 Scenario 1: The Ticker Ticks The SecondsTicker pulses the Clock The Clock updates Time

Coming up: Scenario 1: The Ticker Ticks31 Scenario 1: The Ticker Ticks The SecondsTicker pulses the Clock The Clock updates Time Time updates itself

Coming up: Scenario 2: Clock Responds with the Time32 Scenario 1: The Ticker Ticks The SecondsTicker pulses the Clock The Clock updates Time Time updates itself End of Scenario

Coming up: Scenario 2: Clock Responds with the Time33 Scenario 2: Clock Responds with the Time Display the time

Coming up: Scenario 2: Clock Responds with the Time34 Scenario 2: Clock Responds with the Time Display the time Return hours, minutes, & seconds

Coming up: Scenario 2: Clock Responds with the Time35 Scenario 2: Clock Responds with the Time Display the time Return hours, minutes, & seconds Translate the time into the display format

Coming up: OOA for a Clock: Second Try36 Scenario 2: Clock Responds with the Time Display the time Return hours, minutes, & seconds Translate the time into the display format End of Scenario

Coming up: Why CRC Cards?37 OOA for a Clock: Second Try

Coming up: In-class Exercise38 Why CRC Cards? Help you identify objects and their responsibilities Help you understand how the objects interact Cards form a useful record of design activity Cards work well in group situations and are understandable by non-technical stakeholders.

Coming up: In-class Exercise: Handout39 In-class Exercise This application will support the operations of a technical library for an R&D organization. This includes the searching for and lending of technical library materials, including books, videos, and technical journals. Users will enter their company ids in order to use the system; and they will enter material ID numbers when checking out and returning items.Each borrower can be lent up to five items. Each type of library item can be lent for a different period of time (books 4 weeks, journals 2 weeks, videos 1 week). If returned after their due date, the library user's organization will be charged a fine, based on the type of item( books $1/day, journals $3/day, videos $5/day).Materials will be lent to employees with no overdue lendables, fewer than five articles out, and total fines less than $ (Design Constraints)...

Coming up: OO Analysis Exercise: Checkers 40 In-class Exercise: Handout Brainstorm Candidate Classes - Whole Class Candidate Class Review - Whole class Filter Classes - Individual Groups Create the cards - Individual Groups Information Holder - knows and provides information Structurer - Maintains relationships between objects and information about those relationships Service Provider - Performs work for other objects Coordinator - Reacts to events by delegating tasks to others Controller - Makes decisions and closely directs others’ actions Interfacer - Transforms information and requests between different parts of our system Play the cards - Individual Groups –Scenarios - What happens when Johnny Codewarrior returns the book Document, Your job depends on it two days late? He has no other item checked out and no acquired fines. What happens when Ivar Jacobson uses the search feature to look for the book Object-Oriented Software Engineering of which there are 2 copies available? What happens when Grady Booch uses the search feature to look for the book Object-Oriented Analysis and Design with Application of which there is 1 copy available and the database is down? Present Final Card Set - Individual Groups Document Purpose: … Patterns: Stereotypes: … Document Purpose: … Patterns: Stereotypes: …