Model/View Applications in Swing

Supplementary readingJava tutorial (http://www.cs.auckland.ac.nz/JavaCache/tutorial)

Trail: “Learning the Java Language”Lesson: “Swing features and concepts”

The JFC Swing Tutorial, Walrath & CampioneCopy available in University library, call no. 005.133 Java W22

Model / View with Swing COMPSCI 230 Software Design & Construction 2

A typical model/view application

JTable component instance

Model

JCombobox component instance

Stats view

Graphical viewChange request

Update notification

Many desktop applications provide multiple views of some data model.

Invariant : all views should offer a mutually consistent representation of the model.

Model / View with Swing COMPSCI 230 Software Design & Construction 3

Model/view GUIs with Swing

Contemporary GUI frameworks, like Swing, are based on a separable model architecture

Unlike the AWT, in Swing all components (JComponents) have separate models

COMPSCI 230 Software Design & Construction 3

JTable << interface >>TableModel

JComboBox << interface >>ComboBoxModel

JTree << interface >>TreeModel

JList << interface >>ListModel

JTable component instance

TableModelinstance

setValueAt( row, col )

tableChanged( event )

Model / View with Swing COMPSCI 230 Software Design & Construction 4

A multiview text editor

COMPSCI 230 Software Design & Construction 4

JFrame

TextEditor

JTextArea<< interface >>Document

JMenuBar JMenu JMenuItem

<< interface >>ActionListener

PlainDocument

TextEditor instance

JTextArea instance

JMenuItem is a special kind of button.

PlainDocument is an implementation of the Document (model) interface.

JTextArea instance

view 1

view 2 PlainDocument instance

1 2

Model / View with Swing COMPSCI 230 Software Design & Construction 5

The basis for a model

COMPSCI 230 Software Design & Construction 5

Course

addStudentResult( r : StudentResult ) : voidgetResultAt( index : int ) : StudentResultiterator( ) : Iterator< StudentResult > size( ) : intsetAssessmentPolicy( p : AssesmentPolicy ) : void

<< interface >>AssessmentPolicy

calculate( r : StudentResult ) : Percentage

StudentResult

studentIDsurnameforenameexamMarktestMarkassignmentMarkoverallMark

calculateOverallMark( p : AssessmentPolicy ) : void

Courseinstance

StudentResultinstance

SeventyTenTwentyPolicyinstance

StudentResultinstance

resultspolicy

Implemented by several classes, each implementing a different policy.E.g. class SeventyTenTwentyPolicy calculates a students overall mark as

exam * 0.7 + test * 0.1 + assignment * 0.2

1: setAssessmentPolicy( … )

2: calculateOverallMark( policy )

3: calculate( this )

4: calculateOverallMark( policy )

5: calculate( this )

Model / View with Swing COMPSCI 230 Software Design & Construction 6COMPSCI 230 Software Design & Construction 6

<< interface >>TableModel

addTableModelListener( l : TableModelListener ) : voidgetColumnCount( ) : intgetRowCount( ) : intgetValueAt( row : int, col : int ) : ObjectisCellEditable( row : int, col : int ) : booleanremoveTableModelListener( l : TableModelListener ) : voidsetValueAt( value : Object, row : int, col : int ) : void

JTable

Course

addStudentResult( r : StudentResult ) : voidgetResultAt( index : int ) : StudentResultiterator( ) : Iterator< StudentResult > size( ) : intsetAssessmentPolicy( p : AssesmentPolicy ) : void

<< interface >>AssessmentPolicy

calculate( r : StudentResult ) : Percentage

StudentResult

studentIDsurnameforenameexamMarktestMarkassignmentMarkoverallMark

calculateOverallMark( p : AssessmentPolicy ) : void

So, we can plug in any kind of TableModel object into a JTable and the JTable will provide a visual representation of the TableModel instance.

But unfortunately class Course isn’t a TableModel implementation. What can we do?

Model / View with Swing COMPSCI 230 Software Design & Construction 7COMPSCI 230 Software Design & Construction 7

<< interface >>TableModel

addTableModelListener( l : TableModelListener ) : voidgetColumnCount( ) : intgetRowCount( ) : intgetValueAt( row : int, col : int ) : ObjectisCellEditable( row : int, col : int ) : booleanremoveTableModelListener( l : TableModelListener ) : voidsetValueAt( value : Object, row : int, col : int ) : void

JTable

Course

addStudentResult( r : StudentResult ) : voidgetResultAt( index : int ) : StudentResultiterator( ) : Iterator< StudentResult > size( ) : intsetAssessmentPolicy( p : AssesmentPolicy ) : void

<< interface >>AssessmentPolicy

calculate( r : StudentResult ) : Percentage

CourseAdapterCourse instance

CourseAdapter instance

JTable instance

TableModel query message

Course query message

StudentResult

studentIDsurnameforenameexamMarktestMarkassignmentMarkoverallMark

calculateOverallMark( p : AssessmentPolicy ) : void

Model / View with Swing COMPSCI 230 Software Design & Construction 8

<< interface >>TableModel

addTableModelListener( l : TableModelListener ) : voidgetColumnCount( ) : intgetRowCount( ) : intgetValueAt( row : int, col : int ) : ObjectisCellEditable( row : int, col : int ) : booleanremoveTableModelListener( l : TableModelListener ) : voidsetValueAt( value : Object, row : int, col : int ) : void

AbstractTableModel

fireTableCellUpdated( row : int, col : int ) : voidfireTableDataChanged( ) : voidfireTableRowsDeleted( startRow : int, endRow : int ) : voidfireTableRowsInserted( startRow : int, endRow : int ) : voidfireTableRowsUpdated( startRow : int, endRow : int ) : void

Default TableModel implementation

AbstractTableModel provides a partial implementation of the TableModel interface.

Code reuse methods (add/removeTableModelListener( )) are implemented.

Code reuse methods (fireXX( )) are implemented and provide a convenient facility for subclasses to fire events to listeners of a TableModel.

Concept reuse methods that must be implemented in order for a JTable to extract sufficient information to build the visual representation.

Concept reuse methods that should be implemented in order for the model to be edited by a JTable component.

Model / View with Swing COMPSCI 230 Software Design & Construction 9

public class CourseAdapter extends AbstractTableModel { private Course adaptee; // Implement composition relationship.

public CourseAdapter( Course course ) { adaptee = course; }

public int getColumnCount() { return 7; // Columns are: Student ID, surname, forename, exam, // test, assignment, overall. }

public int getRowCount() { return adaptee.size(); // Number of rows to display equates to the // number of students in the Course object. }

public Object getValueAt( int row, int col ) { // row identifies a particular student held within the Course instance. // col identifies a student attribute, e.g. surname, exam mark etc. StudentResult result = ( StudentResult )adaptee.getResultAt( row ); Object value = null;

// Get the StudentResult attribute at the specified column. switch( col ) { case 0: // Student ID. value = result.studentID; break; case 1: // Surname. value = result.studentSurname; break; … case 6: // Overall. … } return value; }}

Course instance

CourseAdapter instance

1: getValueAt( 4, 3 )

2: getResultAt( 4 )

JTable instance

3: getExamMark( )

Dave Bell

StudentResultinstance

67

Model / View with Swing COMPSCI 230 Software Design & Construction 10

TableModelListener<< interface >>TableModel

addTableModelListener( l : TableModelListener ) : voidgetColumnCount( ) : intgetRowCount( ) : intgetValueAt( row : int, col : int ) : ObjectisCellEditable( row : int, col : int ) : booleanremoveTableModelListener( l : TableModelListener ) : voidsetValueAt( value : Object, row : int, col : int ) : void

AbstractTableModel

fireTableCellUpdated( row : int, col : int ) : voidfireTableDataChanged( ) : voidfireTableRowsDeleted( startRow : int, endRow : int ) : voidfireTableRowsInserted( startRow : int, endRow : int ) : voidfireTableRowsUpdated( startRow : int, endRow : int ) : void

JTable

<< interface >>TableModelListener

tableChanged( event : TableModelEvent ) : void

Any party that is interested in changes to a TableModel implements the TableModelListener interface.

When a TableModel changes its state, it creates a TableModelEvent, which describes how the TableModel has changed, and sends a tableChanged message to each registered listener.

JTable offers a visual representation of a TableModel and thus implements the TableModelListener interface.

Model / View with Swing COMPSCI 230 Software Design & Construction 11

public class CourseAdapter extends AbstractTableModel {

// As before plus …

public boolean isCellEditable( int row, int col ) { boolean editable = false;

if( col > 2 && col < 6 ) // Allow editing of exam, test and assignment columns. editable = true; return editable; }

public void setValueAt( Object value, int row, int col ) { StudentResult result = adaptee.getResultAt(row);

switch( col ) { case 3: // Exam. adaptee.updateStudentResult(result, … ); break; case 4: // Test. … break; case 5: // Assignment. … break; } fireTableRowsUpdated( row, row ); }

public void setAssessmentPolicy(AssessmentPolicy policy) { adaptee.setAssessmentPolicy(policy); fireTableDataChanged(); }}

1: setAssessmentPolicy( … )

2: setAssessmentPolicy( … )

Course instance

CourseAdapter instance

JTable instance

3: fireTableDataChanged( )

4: create

TableModelEvent instance (evt)

5: tableChanged( evt )

For each student, recalculate overall mark (see slide 5)

All rows changed

Model / View with Swing COMPSCI 230 Software Design & Construction 12

JTable

<< interface >>TableModelListener

<< interface >>TableModel

AbstractTableModel

CourseAdapter

CourseDistributionPanel

JPanel

StatisticsPanel

DistributionPanelAdapter StatisticsPanelAdapter

StudentResult

Application classes

Adapter classes

Framework classes

Model / View with Swing COMPSCI 230 Software Design & Construction 13

Key instances & messages

JTable instanceCourseAdapter instance

Course instance

DistributionPanelAdapter instance

StatisticsPanelAdapter instance

DistributionPanel instance

StatisticsPanel instance

model listenersadaptee

adapteeadaptee

1: setValueAt 2: getResultAt

TableModelEvent instance (evt)

3: create

4: tableChanged( evt )

5: tableChanged( evt )

6: repaint 8: repaint

7: tableChanged( evt )

Model / View with Swing COMPSCI 230 Software Design & Construction 14

Integrity / enforcing design intent All registered listeners (views) of a model are guaranteed to be

notified when the model changes its state => Invariant of model/view applications is satisfied

Reuse A model/view framework promotes reuse

GUI component classes implement application independent behaviour for viewing / editing an application model

Model interfaces are intended to be implemented by adapter classes that allow application classes to be reused without modification

Maintainability It’s very easy to add new views

All that’s required is to write a new implementation of the listener interface Existing model and view classes need not be changed

Flexibility Views can easily be added to (and removed from) a model at run-time

What can we say to sum up the benefits of the model/view approach?