1. Object-Oriented Analysis
Barb Ericson
Jan 2005
Georgia Institute of Technology

2. Georgia Institute of Technology
Learning Goals
Understand at a practical level
How to identify objects and classes
How to record potential classes
How to record responsibilities
How to record fields and methods
How to record the relationships between classes
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Identifying Classes
As you go through a scenario
Write down each noun you hear (or underline each noun if the scenario is written)
Put each one at the top of an index card
Write down what objects of this class are responsible for
Write down what other classes this object has to work with to accomplish it’s responsibilities
What type of thing is each item? For example popcorn is a type of food (or snack). For each snack we would need to know at least the name and price.
Georgia Institute of Technology

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CRC Cards
Class Responsibility Collaborators
Developed by Ward Cunningham and Kent Beck at Tektronix in the late 1980’s
Analysis technique
Classname
Responsibilities
Collaborators
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Use and Advantages
Used to
Record classes as they are identified
Record the purpose (responsibility) of each class
Record and experiment with relationships (collaborators) between classes
Advantages
cheap, portable, readily available, and familiar
focus on analysis, not on a diagram
good in a group discussion
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CRC Cards Example
Do an analysis of a hotel room reservation system.
The system must allow clerks to assign rooms to customers. It must also allow clerks to assign maids to clean the rooms.
Clerk
Customer
Maid
Room
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CRC Cards Example
Clerk
Customer
Customer
Maid
Stays in hotel
Room
Clerk
Checks customer in and out
Manages maids
Maid
Room
Customer
Maid
Cleans room
Room
Clerk
Place for customer to stay
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CRC Card Example
Clerk
Customer
Customer
Maid
Stays in hotel
Check in
Check out
Pay for room
Use phone
Room
Clerk
Checks customer in and out
Assigns room
Handles payment
Manages maids
Maid
Room
Customer
Maid
Cleans room
Assigned room
Room
Clerk
Place for customer to stay
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Abstraction
Pull out only the important details about the thing we are simulating
Maids have hobbies but we don’t need to know about them
What is important in the context of the problem?
What data will objects of the class need
What things will they need to be able to do?
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10. CRC Card Practice Ideas
Do CRC cards for the movie scenario
Do CRC cards for a game of blackjack
Do CRC cards for a game of solitaire
Do CRC cards for a game of war
Do CRC cards for a drawing program
Do CRC cards for airplane flights
Do CRC cards for a soccer game
Do CRC cards for an ATM
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11. Drawing Editor Exercise
Identify the classes for a simple drawing editor. Also show the data and operations for the classes.
The editor can draw rectangles, circles, and triangles. It can show connections between shapes with a a line. The shapes can be erased, moved, and rotated.
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12. Record Class Information
Can use a UML Class Diagram
Unified Modeling Language
Standard way to documents OO analysis, design, and implementations
UML Specification
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UML Tools
Popular Tools
Rational Rose –
Market leader but expensive
Visio –
Poseidon -
Free community edition
ArgoUML -
Links to sites that list UML Tools is at
IBM bought Rational.
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Class Diagram
Shows classes and the relationships between them
Static structure
Not time dependent
Most important and commonly used diagram in UML
By static structure we mean that this structure doesn’t depend on time.
Class diagrams can also show packages, objects, and interfaces. Sometimes a class diagram that shows packages is called a package diagram even though in UML it is just a kind of class diagram. Also, a class diagram that shows just objects is sometimes called an Object Diagram even though in UML it is just a kind of class diagram.
Georgia Institute of Technology

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Class Representation
Rectangles are used to represent classes
There are different sections for the class name, attributes and operations
Class Name
Dog
Attribute1
Attribute2
size
shape
Operation1()
Operation2()
wagTail()
bark()
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Visibility
Who can access the item
Types of Visibility
Public (+)
All can use
Private (-)
Only objects of the class
Attributes should be private
So the object has control of its’ data
Methods are public or private
Public if intended as a service. Private if for internal use. Ocassionally protected is used which subclasses can override
Note that the UML definition of these types of visibilities doesn’t always match with the visibilities defined in object-oriented languages. For examples in Java protected means that the item is accessible to objects of the class, objects of any subclasses, and objects of classes in the same package.
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17. Static Class Relationships
Association
has-a
A connector has shapes
Generalization
is-a-kind-of
A circle is a kind of shape
Aggregation
is-a-part-of
A display list is an aggregation (collection) of shapes
Composition is a stronger form of aggregation. It says that the whole must be destroyed if the part is removed and vice versa. Composition implies exclusive ownership.
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18. Dynamic Class Relationship
Dependency
Uses
A car uses a parking space
It doesn’t have a have-a relationship with it
Dynamic relationships are relationships that change over time
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19. Association Multiplicities
Associations have multiplicities (one for each end)
X can have how many objects of y associated with it?
Y can have how many objects of x associated with it?
Kinds of Multiplicities
m..n
Inclusive range from m to n n
There must be exactly n
* or 0..*
0 to many
An inclusive range includes the values that bound the range. So 0..1 means you can have 0 or 1.
The * means many. So 1..* means 1 to many. This can also be expressed as 1*.
You can specify multiple multiplicity ranges separated by commas.
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Roles
Each association end is a role
role A
role B
Roles can be explicitly named
Especially useful when there is more than one association between the classes
Or for use in generated code
A flight will have two airport objects associated with it. It will need to track the airport it is going to and the airport it left from.
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21. Class Diagram Perspectives
There are three perspectives that a class diagram can represent
Conceptual - Analysis Stage
Language independent, represents the domain
Specification - Design Stage
Represents a high level design of the solution
Implementation – Programming Stage
Represents the actual solution
Shows attributes, operations, types (if needed), and parameters to operations
The lines between these perspectives are not rigid.
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UML Challenge
Draw a class diagram for Solitaire
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23. Solitaire Class Diagram
Many classes in solitaire are kinds of card piles. You can add cards to card piles and remove cards.
The CardPile class is an abstract class (as shown by the italics).
The game Klondike has 1 stock, 1 waste, 7 tableaus, 4 foundations, and 1 deck.
The game Klondike has 3 option groups. One option group is kings only play for empty tableaus which has two option values, true and false. Another option group is the number of cards to draw from stock. The option values are 1 or 3. The third option group is auto-play which can be either on or off.
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Summary
In Analysis you need to understand the objects in the domain (“real world”)
Figure out what the objects are responsible for
What data do they need to have?
What things can they do?
UML class diagrams show lots of information in a picture
Can be helpful on exam questions
About inheritance and polymorphism
Determine the relationships between the classes
Has a (association)
Is a type of (inheritance)
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