1. Architectural Patterns for Interactive Software
Yonglei Tao
School of Computing and Info Systems

2. Interactive Software Design
Application data and logic
Relatively stable
Look and feel
Support multiple views
Evolve in response to changes in requirements, user profiles, display and interaction mechanisms, and …
Desirable properties for software design
Domain objects – reusable
User interfaces – extensible, pluggable

3. Model-View-Controller
A common structure for interactive applications
Originally intended for applications with multiple views for the same data
Benefits
De-couple domain objects from user interfaces
Reduce complexity
Support reuse
Allow separate development

4. Model, View, and Controller
Encapsulate fundamental abstractions for interactive applications
the model maintains application data
the view is responsible for its visual presentation
the controller handles events for views

5. An Example Model – class Counter View Controller int Value
setValue(), getValue(), inc(), and dec()
View
Shows the current value of a Counter
Controller
Handles user requests
Controller is listener in Java.

6. Design Issues - Dependencies
1..*
View
Screen
update()
display 1
getValue()
Model 1
1..*
inc()
Controller
Mouse
click a button

7. The Observer Pattern Problem How to handle such a relationship?
A subject is observed by several observers
When its state changes, all observers are notified and updated to reflect the change automatically
How to handle such a relationship?
One to many
Two-way dependency

9. A MVC Example

10. // CounterModel.java - an Observable class for a counter
import java.util.Observable;
public class CounterModel extends Observable {
private int value;
public CounterModel () {
setValue( 0 ); }
public int getValue () {
return value;
public void setValue (int newValue) {
value = newValue;
setChanged();
notifyObservers();
public void inc () {
setValue( getValue() + 1 );
public void dec () {
setValue ( getValue() - 1 );
public void reset () {
setValue ( 0 );

11. /** CounterView.java - an Observer class for a counter */
import java.util.*;
import java.lang.*;
public class CounterView extends JFrame implements Observer {
private CounterModel theModel;
public CounterView(CounterModel model) throws NullPointerException {
initComponents();
theModel = model;
theModel.addObserver(this); }
private void initComponents() { … } // automatically generated
private void incButtonActionPerformed(ActionEvent evt) {
theModel.inc();
private void decButtonActionPerformed(ActionEvent evt) {
theModel.dec();

12. private void resetButtonActionPerformed(ActionEvent evt) {
theModel.reset(); }
private void exitButtonActionPerformed(ActionEvent evt) {
System.exit(0);
/** update the display with the current value of the counter */
public void update (Observable observable, Object obj) {
valueLabel.setText(theModel.getValue() + "");
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
CounterModel model = new CounterModel();
public void run() {
new CounterView(model).setVisible(true);
});
private JButton decButton, exitButton, incButton, resetButton;
private JLabel labelForValue, titleLabel, valueLabel;