1. CS 501: Software Engineering Fall 1999
Lecture 17
Object-Oriented Design II

2. Administration  Recitation session: Rational Rose
 Submission of Assignment 4

3. The "Hello, World" Example
import java.awt.Graphics;
class HelloWorld extends java.applet.Applet {
public void paint (Graphics g) {
g.drawString ("Hello, World!", 0, 10); }
Example from: BJR

4. Abstraction for HelloWorld
class
HelloWorld
paint()
name
annotation
g.drawString ("HelloWorld", 0, 10)"
operations

5. Class Diagram
Applet
Note that the Applet and Graphics classes are shown elided.
generalization
HelloWorld
paint()
dependency
Graphics

6. Class Inheritance Diagram
Object
Panel
interface
Component
ImageObserver
Applet
Container
HelloWorld

7. Packaging Classes
java
applet
HelloWorld
package
awt
Graphics
lang

8. Notation for Classes and Objects
AnyClass
attribute1
attribute2
operation1()
operation2()
anObject:AnyClass or
:AnyClass or
anObject or
AnyClass
The names of objects are underlined.

9. Sequence Diagram:Painting Mechanism
:Thread
:Toolkit
:ComponentPeer
target:HelloWorld
run
run
callbackLoop
handleExpose
paint

10. Component Diagram executable component hello.java hello.hml
HelloWorld.class
hello.jpg

11. Modeling Classes
Given a real-life system, how do you decide what classes to use?
 What terms do the users and implementers use to describe the system? They are candidates for classes.
 Is each candidate class crisply defined?
 For each class, what is its set of responsibilities? Are the responsibilities evenly balanced among the classes?
 What attributes and operations does each class need to carry out its responsibilities?

12. Noun Identification: A Library Example
The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals.
The system must keep track of when books and journals are borrowed and returned and enforce the rules.

13. Candidate Classes Library the name of the system Book Journal Copy
ShortTermLoan event
LibraryMember
Week measure
MemberOfLibrary repeat
Item book or journal
Time abstract term
MemberOfStaff
System general term
Rule general term

14. Relations between Classes
Book is an Item
Journal is an Item
Copy is a copy of a Book
LibraryMember
Item
MemberOfStaff is a LibraryMember
Is Item needed?

15. Operations LibraryMember borrows Copy LibraryMember returns Copy
MemberOfStaff borrows Journal
MemberOfStaff returns Journal
Item appears not to be needed.

16. Class Diagram MemberOfStaff LibraryMember 1 1 on loan on loan 0..*
0..12
Journal
Copy
is a copy of
1..*
Book

17. Rough Sketch: Wholesale System
A wholesale merchant supplies retail stores from stocks of goods in a warehouse.
What classes would you use to model this business?

18. Rough Sketch: Wholesale System
RetailStore
Order
Merchant
Product
Warehouse
Shipment
Invoice

19. Rough Sketch: Wholesale System
Merchant
RetailStore
name
address
contactInfo
financialInfo
Shipment
Responsibilities
-track status of shipped products
Warehouse
Order
Product
responsibility (text field)
Reversals
damaged()
return()
wrongItem()
Invoice

20. Expanding a Class: Modeling Financial Information
RetailStore
association *
Transaction
Which class is responsible for the financial records for a store?
Payment
Invoice

21. Modeling Invoice Shipment ??? RetailStore invoiceRecord goodsShipped
invoiceNumber
+goodsShipped()
-sendInvoice()
PartsList
adornments
+ public
- private

22. Lessons Learned
Design is empirical. There is no single correct design. During the design process:
 Eliding: Elements are hidden to simplify the diagram
 Incomplete: Elements may be missing.
 Inconsistency: The model may not be consistent
The diagram is not the whole design. Diagrams must be backed up with specifications.

23. Levels of Abstraction
The complexity of a model depends on its level of abstraction:
 High-levels of abstraction show the overall system.
 Low-levels of abstraction are needed for implementation.
Two approaches:
 Model entire system at same level of abstraction, but present diagrams with different levels of detail.
 Model parts of system at different levels of abstraction.