Michael Brockway

Advanced Applications Development in Java

Model-View-Controller Architecture

MVC ArchitectureDelegate-Model ArchitectureObserver Design PatternMVC and the Observer Design Pattern

Observable class, Observer interfaceMVC Example in JavaExamples in Java of Delegate-Model architecture.

MVT Architecture 2

MVC Architecture A typical application includes software to

maintain application data, document text in a word processor state of a chess game -- positions of pieces

present output outline view or print preview in a word

processor graphical view of chess game

process user input key presses mouse click on controls

Model-View-Controller Architecture is an object-oriented program structure which separates these functions into 3 separate classes The Model contains and maintains the

application data The View provides a visible presentation of the

data (or output) There may be multiple views There may be multiple types of view (View

classes)

Ref: Deitel, Deitel & Santry Chapter 3

MVT Architecture 3

MVC Architecture The Controller is a class which implements

logic for handling user input. There application may have several controllers

On user input, a controller modifies the model it controls, which in turn notifies all its views so each view can update its presentation to reflect the state of the model.

Model

Controller

View

modifies

notifies

MVT Architecture 4

Delegate-Model Architecture

A variation of MVC architecture A single class (application component) has functionality

for both accepting user input and processing it, and presenting output

Java example: javax.swing contains

a JButton class a ButtonModel interface

A Jbutton is delegate for an associated ButtonModel The ButtonModel maintains information on the state

of the button (pressed? Enabled? etc) The JButton presents a graphical view of the button

(pressed/unpressed/enabled/disabled) as well as receiving clicks, doubleclicks.

Model

Delegate

modifies notifies

MVT Architecture 5

Example: Observer Pattern

Defines a 1 to many dependency between objects so that when one changes state, all dependents are notified and updated.

Subject class maintains list list of Observer objects; has methods for adding and removing Observers and notifying them of changes of state in the Concrete Subject.

ConcreteSubject – particular class of interest Observer interface specifies the interface by which

ConcreteObservers are notified ConcreteObserver implements Observer interface and provides

particular behaviours for responding to changes in ConcreteSubject’s state.

<<interface>>

Observer

update(Event)

<<abstract>>Subject

add(Observer)remove(Observer)

notifyAll( )

ConcreteSubject

ConcreteObserver

update(Event)

*

For each observer oo.update( )….

MVT Architecture 6

MVC and the Observer Design Pattern,

The observer design pattern corresponds to the model/view part of MVC.

The subject in the observer design pattern corresponds to the model in an MVC architecture

The observer in the design pattern corresponds to an MVC view.

<<interface>>

java.util. Observer

update(Observable o, Object arg)

<<abstract>>java.util.Observable

add Observer(….)deleteObserver(...)notifyObservers( )

…..

Model

View

update(….)

*

For each observer oo.update( )….

MVT Architecture 7

MVC Example in Java

Refer to DDS section 3.3: figs 3.4 -- 3.10

Account (the

model)

AccountController (the controller)

AccountTextView

modifies

notifies

AccountBarGraphView

AssetPiechartView

MVT Architecture 8

MVC Example in Java

<<interface>>

java.util. Observer

update(Observable o, Object arg)

<<abstract>>java.util.Observable

add Observer(….)deleteObserver(...)notifyObservers( )

…..

Account<<abstract>> AbstractAccountView

update(….)

*

Balance: doublename: string

ConstructorGet & Set methodswithdraw(amount)deposit(amount)

JPanel

account

AccountTextView

AccountBarGraphView

AssetPieChartView

JPanel

AccountController

MVT Architecture 9

MVC Example in Java (ctd)

AccountManager uses these MVC components as follows For test purposes, it makes two Accounts For each account it makes an “account panel”

consisting of an AccountController (JPanel) above an AccountTextView and an

AccountBarGraphView (Jpanels) side by side The two account panels are laid out in the

frame along with an AssetPieChartView giving a composite view of the accounts.

The source files are on this module’s intranet site and on the DD&S CD; printed listings accompany these slides

Account.java, AbstractAccountView.java, AccountTextView.java, AccountBarGraphView.java, AssetPieChartView.java, AccountController.java, AccountManager.java

Try the application. Exercise: modify it so that it manages three

accounts.

MVT Architecture 10

Examples in Java of Delegate-Model architectureJList

A javax.swing.ListModel is an object which maintains a list of objects: it knows how big the list is, which object is where in the list, etc, and can insert/remove objects

A javax.swing.JList is a graphical component giving a view of the list and able to receive user input to modify the list

See DD&S section 3.4 and listing of PhilosophersJList.java

DefaultListModel

Javax.swing.JList (delegate)

modifies notifies

DefaultListModel

<<abstract>>

AbstractListModel

<<interface>>Javax.swing.ListModel

isEmpty(): booleangetSize(): intaddElement(Object)removeElement(Object)elementAt(): ObjectremoveElementAt(int)insertElementAt(int)indexOf(Object): intetc

JList

Javax.swing.JComponent

MVT Architecture 11

Examples in Java of Delegate-Model architectureJTable

A javax.swing.table.TableModel is an object which maintains a table (rows, columns) of objects

A javax.swing.JTable is a graphical component giving a view of the table (and can receive user input to modify it)

See DD&S section 3.5 and listing of PhilosophersJTable.java

DefaultTableModel

Javax.swing.JTable (delegate)

modifies notifies

DefaultTableModel

<<abstract>>

AbstractTableModel

<<interface>>Javax.swing.table.TableModel

addColumn(Object)addRow(Object[])insertRow(int, Object[])removeRow(int)setValueAt(Object, int, int)getValueAt(, int, int): Objectetc

JTable

Javax.swing.JComponent

MVT Architecture 12

Examples in Java of Delegate-Model architectureJTree

A

CB D

E FG

H

I

JK

A

B

E

F

C

G

H

I

D

J

K

A tree is a data structure often represented drawn in one of these ways, with a piece of data at each node.

Examples are

• Family trees

•The structure of an organisation

•The directory structure of a file system in Windows or Unix.

Thinking of “family trees” we get the following terminology:Node C has parent node A and children G, H, I. A is an ancestor of G and G a descendent of A. G, H, I are siblings of each other.The node A (with no parent) is the root. Nodes E, F, G, H, I, J, K (with no children) are leaves.

MVT Architecture 13

Examples in Java of Delegate-Model architectureJTree

DefaultTreeModel

<<interface>>Javax.swing.tree.TreeModel

getPathToRoot(TreeNode) : TreeNode[]removeNodeFromParent( MutableTreeNode node) void insertNodeInto( MutableTreeNode newChild, MutableTreeNode parent, int index)

JTree

Javax.swing.JComponent

getChild(Obj parent, int index): ObjectgetIndexOfChild(Object): intgetRoot(): ObjectisLeaf(Object node): booleangetRoot(TreeNode): Object

getLastSelectedPathComponent : Object

<<interface>>Javax.swing.tree.TreeNode

getChildAt(int index): ObjectgetChildCount(): intgetParent(): TreenodeisLeaf(): booleanetc

<<interface>>MutableTreeNode

Insert(MutableTreeNode chld, int idx)remove(int idx)etc

DefaultMutableTreeNode

Constructor(Object o)add(MutableTreeNode chld)Insert(MutableTreeNode chld, int idx)remove(int idx)getDepth(): intbreadthFirstEnumeration() :EnumerationdepthFirstEnumeration() :Enumerationetc

MVT Architecture 14

Examples in Java of Delegate-Model architectureJTree

A TreeNode is constructed from a given Object Encapsulates the extra functionality for the object to

be stored as a node of a tree DDS section 3.6.1 illustrates a tree with the DefaultTreeModel The object stored at each node are Strings This application allows string object to to added as

nodes and removed from the tree See listing of PhilosophersJTree.java

DDS section 3.6.2 illustrates a custom (non-default) implementation of the TreeModel interface

public class FileSystemModel implements TreeModel ... Displays a disk file system (from some root

directory) as a tree A FileSystemModel object is constructed from a File object as “root directory”.

It implements the TreeModel methods using File class methods of get information about a directory and its children (subdirectories & files)

See listing of FileSystemModel.java. FileFreeFrame.java is a simple application

making use of a FileSystemModel.

MVT Architecture 15

Exercises

Try each of the example programs out and make sure you understand them.

Do DDS exercises 3.6: Make LiabilityPieChartView as a subclass of AssetPieChartView that includes only Accounts with negative balances. Modify class AccountManager to include a LiabilityPieChartView in addition to an AssetPieChartView

3.7: Make a new version of AccountBarGraphView which shows multiple Accounts in a single bar graph [Hint -- imitate AssetPieChartView]

3.8: Enhance 3.7 to allow transfers between accounts. Modify the AccountController to include a JComboBox to select the destination account, and a JButton to perform the transfer.