21Jan2003

1
Demeter Take 2-n-E/B/C

• 21-Jan-2003
• Lecture 8

2
Outline

• Previous Business
• HW1 due NOW
• Electronic submission to be worked out. Will
  accept email (heineman_at_cs.wpi.edu) until 800 PM
  tonight
• Reading Questions
• Lecture Contents
• Determined Demeter
• Entity/Boundary/Controller evolution from MVC

3
Determined Demeter

• Cast Demeter issue into MVC example

a ExampleApplet1
mTemperature
vTemperatureView
sScrollbar
vTextView
scrollbar_AdjustmentValueChanged
setTemperature (t)
modelChanged()
getTemperature()
getScale()
modelChanged()
getTemperature()
time
getScale()

• Observe that each class obeys Demeter

4
Demeter violations

• Controller asks model for views and then contacts
  them
• Original Applet
• BogusApplet

/ Set the value within the temperature model
/public void updateModel (int val) //
set model. model.setTemperature ((float)
val) Enumeration listEn
model.getListeners() while
(listEn.hasMoreElements()) IListener
view (IListener) listEn.nextElement()

5
Demeter violations

• Convert Gets into Do
• Instead of obj.getObject().doSomething() you now
  have obj.doSomething() which is then delegated to
  proper object
• Reduce micro-management into delegation

6
Missing concerns with MVC

• Who constructs these objects?
• Who associates the relationships?
• is this static or dynamic?
• How does the user interact with the system to
  cause changes in the model?
• does the view play a dual role?

7
Entity/Boundary/Controller

• All objects are not created equal
• Entity ? Represent persistent information
  required to implement desired system
• Boundary ? Represent interactions between actors
  and system
• Control ? Represent tasks that are performed by
  user and supported by system

8
Use case analysis

• Use case name ApplyStyle
• Entry Condition Text selected
• Flow of Events 1. Selection range identified
• 2. TextRegion contacted with s,e) and style
• 3. Updated HTML extracted from TextRegion
• 4. HTMLview refreshed with HTML String
• Exit Condition none

9
How do Use Cases fit in?
b Boundary
cControl
b2 Boundary
e Entity
initiate
doSomething
doSomething

• Control Object maps to use case
• Pay attention to creation of objects

10
Thursday Assignments

• Reading
• read Chapter 5 handout
• TAOO Chapter 4

11
References

• Law of Demeter