17-Jan-2003

1
Binary Association Classes and their
Implementation

• 17-Jan-2003
• Lecture 6

2
Outline

• Previous Business
• HW1 assigned
• posted instructions to run examples
• Reading Questions
• Lecture Contents
• Binary association classes and their
  implementation

3
Reading Questions

• TBA

4
Extend our MVC

• What if wanted views to have priorities?
• the model should propagate change events
  according to the priority of the views
• higher priority views receive events ahead of
  lower priority views
• This complicates model

5
Model/View could look like

• Overly complicated implementation
• we should move relationship into association
  class
• separate model from process view updates

notifies
1

Model
IListener
Sort by priority whenregistering Issue
modelChangedas before
6
Model/View should look like

• Outsource the complexity into its own class
• ModelManager contains update algorithm
• subclasses overriding can replace algorithm
• IListener objects register with ModelManager

Model
IListener

1
notifies
ModelManager
ModelManager
1
1
listeners IListener priorities int
IListener
ModelManager (Model m) register (IListener
listener, int priority) notifyAll ()
modelChanged (Model m)
7
Model/View

• Continuing this logic may ultimately lead to
• complete separation of Model with Views
• putting view update logic into controller
• All design evolves
• Split class into two
• Elevate attribute into class
• Make association link into association class

8
Association and Links

• A link between two objects can possess its own
  properties
• this is a powerful statement!
• these link properties do not exclusively belong
  to either class involved in the association
• simplify host classes

9
Binary Association Classes

• Complexity reduction even more impressive when
  bidirectional relationships
• both affected classes are made simpler

C1
C2
Items C2
Items C1


prop1 intprop2 String
prop1 int Prop2 String
10
Specific Java Mechanisms

• Inner Classes
• When a class is used by only one class
• When you want to restrict access
• Note that inner class can access any method/data
  of its outer class.
• Anonymous Classes
• Look inside main() method.
• Bridges between existing classes
• Typically used for anonymous listeners

11
Monday Assignments

• Get started on the homework which is due by the
  start of class.
• design books will be accepted ONLY at the
  beginning of class
• electronic submission of assignment must be
  received by 400 PM
• any late assignments will be ungraded

12
References

• None