Introduction to Object-Oriented Design and the UML

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Introduction toObject-Oriented Designand the UML
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Object-Oriented Modeling

• UML Unified Modeling Language
• Emerging OO Modeling Standard
• What is depicted?
• System functionality
• Class details and static relationships
• Object interaction
• State transition within an object

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Modeling Techniques

• Use Cases/Use Case Diagrams
• Class Diagrams
• CRC Cards
• Interaction Diagrams
• State Diagrams

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ExampleUse Case Diagram
LIBRARY SYSTEM
Facilitate Borrow
Search for Book
Borrower
Librarian
Facilitate Return
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Class Diagramsand CRC Cards

• Class Diagrams similar to ER Diagrams but in
  addition, it incorporates
• methods, not just attributes for each entity
• inheritance
• Class-Responsibility-Collaboration Cards
• technique that depicts responsibilities of
  classes with respect to other classes (hints on
  both data and behavior details)

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ExampleInteraction Diagram
2 checkIfAvailable()
Borrow Screen
Book
1 checkIfDelinquent() 3 borrowBook()
4 setBorrower()
Borrower
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ExampleState Diagram (Book)
start
Reserved
Borrowed
New
Librarian activates book as available
Borrower returns book
Available
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Object-Oriented Design Models

• Static Model
• Class Diagrams
• Dynamic Model
• Use Cases, Interaction Diagrams, State Diagrams,
  others

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OO Static Model

• Class Diagrams
• Relationships
• Association
• Aggregation/Composition
• Inheritance
• Attribute and Method names

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Classes in a Class Diagram

• Class name only Example
• With Details Example

Bank Account
Class Name
Bank Acct double balance deposit() withdraw()
Class Name attributes methods
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Relationships

• Inheritance (arrow)
• example between Secretary and Employee
• Composition/Aggregation (diamond)
• example between Car and Wheel
• Association (line)
• example between Borrower and Book

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Inheritance
Employee
public class Secretary extends Employee
Secretary
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Composition
Car
Wheel
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w
public class Car Wheel w ...
public Car() w new Wheel4
...
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Association
Borrower
Book
0..3
0..1
currBorr
bk
public class Borrower Book bk
public Borrower() bk new Book3
public class Book Borrower currBorr
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OO Dynamic Model

• Goal Represent
• Object behavior
• Object interaction
• Traditional (relational) Dynamic Modeling
• Data Flow Diagrams (DFDs)
• Problem Processes separate from data
• Need modeling notation that highlight tight
  relationship between data processes

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DFD Example(Inventory Management)
Accept and Post Delivery
Delivery info
Transaction
Item Master
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OO CounterpartObject Interaction
new (delivery info)
Encoder
Transaction
post (item count)
Item Master
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Interaction Diagrams

• Rectangles Classes/Objects
• Arrows Messages/Method Calls
• Labels on Arrows
• sequence number
• method name
• more details, when necessary (conditions,
  parameters, types, return types)

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Interaction Diagram Borrow-Book Example
2 avail checkIfAvailable()boolean
Borrow Screen
bBook
1 delinq checkIfDelinquent()boolean 3!delinq
avail borrowBook(Book b)
4 setBorrower(r)
rBorrower
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Methods

• Interaction Diagrams suggest methods for classes
• consequence on detailed class diagram
• The label(s) of an arrow should be a method of
  the class the arrow points to
• Library System
• Borrower class should have at least two methods
  (checkIfDelinquent and borrowBook)