Object-Oriented Frameworks

Object-Oriented Frameworks

Supplementary reading:Java text (e.g. Budd Ch. 21, Ch. 22)

Object-Oriented Frameworks COMPSCI 230 Software Design & Construction 2

Frameworks

A framework is a set of classes that cooperate closely and collectively embody a reusable solution to a common problem

A framework is intended to be extended to meet the needs of a particular application Extension is carried out by

subclassing, overriding methods, and implementing interfaces

<< interface >>

Framework classes

Application classes


Reuse and specialisation

Window

setTitle( title : String ) : voidsetSize( width : int, height : int ) : voidmoveTo( x : int, y : int ) : voidaddMenu( menu : Menu ) : voidrepaint( ) : voidmouseDown( x : int, y : int ) : voidkeyPress( c: char ) : voidPaint( ) : void

SpecialWindow

}} Code reuse.

Methods called by class users and subclasses.

Concept reuse.Methods that are applicable to any kind of Window, but for which meaningful implementation is deferred to subclasses.

A windowing framework will expect any kind of Window object to understand, for example, a paint( ) message. However, the windowing framework won’t know the application-specific response. Such responses are implemented by subclassing and method overriding.

A windowing framework will expect any kind of Window object to understand, for example, a paint( ) message. However, the windowing framework won’t know the application-specific response. Such responses are implemented by subclassing and method overriding.


Inversion of control

Library code

Application code

Application calls an I/O library routine

Application calls a sort routine

The traditional case where the application code defines the flow of execution.

Control flow is dictated by the framework. The application programmer implements routines invoked by the framework, but doesn’t change the solution’s overall structure.

Time

Framework code

Application code

Framework generates a window resize event

Framework generates a button click event

Framework generates a window deiconification event

Time

We’ve already come across the idea of inverted control structures. Where?


Java applets: a simple framework

Applet framework (web browser)

Application code

init( )

start( )

paint( ) stop( )

destroy( )

Applet

init( )start( )paint( )stop( )destroy( )


Object

Component

getSize( ) : intsetSize( width : int, height : int ) : voidsetVisible( visible : boolean ) : voidrepaint( g : Graphics ) : voidpaint( g : Graphics ) : voidaddMouseListener( listener : MouseListener ) : voidaddKeyListener( listener : KeyListener ) : void

Container

setLayout( mgr : LayoutManager ) : voidadd( c : Component ) : void

Window

toFront( )toBack( )

Frame

setTitle( title : String ) : voidsetCursor( c : int ) : voidsetResizable( resizable : boolean ) : voidsetMenuBar( mb : MenuBar ) : void

Button Checkbox Choice Label List Scrollbar

TextComponent

TextArea TextField

Panel ScrollPanel

A Component is something that can be displayed on a GUI and with which a user can interact.

A Window is a special Container that can be stacked, and moved to the front/back.

A Frame is a special Window with a title, menubar, border and cursor.

repaint( ) schedules a Component instance for repainting. The AWT framework will subsequently call paint( ) on the Component object.

Interpret this diagram and write down at least 3 points of interest.

Java’s AWT framework

A Container is a special component that can nest other components, be they simple components (e.g. Buttons, Labels) or themselves Containers (e.g. Panels).

paint( ) is a hook method.

add( ) is a polymorphic method; it can take as actual argument any kind of Component.

Generalisation

Specialisation


FramePanel

LabelTextField

Label

Panel

Button

Button

Panel

Component

Container

add( c : Component ) : void

class Container extends Component { private List<Component> children; … public void add( Component c ) { children.add( c ); }}

Frame instance

TextField instance

Panel instance

Buttoninstance

Buttoninstance

Labelinstance

Panel instance

Panel instance

Labelinstance


Traversing the nested structure

Frame instance

TextField instance

Panel instance

Buttoninstance

Buttoninstance

Labelinstance

Panel instance

Panel instance

Labelinstance

class Container extends Component { private List<Component> children; … public void add( Component c ) { children.add( c ); }

public void paint( Graphics g ) { for( Component c : children ) c.paint( ); }}

1: paint( )

2: paint( )

3: paint( ) 4: paint( )

5

6

7

8

9


Layout management

Container

setLayout( mgr : LayoutManager ) : voiddoLayout( )add( c : Component ) : void

Component

<< interface >>LayoutManager

layoutContainer( c : Container )minimumLayoutSize( c : Container ) : DimensionpreferredLayoutSize( c : Container ) : Dimension

BorderLayout BoxLayout FlowLayout GridLayout

Why is this design for layout management so effective?


Layout management

Container

Panel

PanelWithBorderLayout PanelWithBoxLayout…

Alternative design: for each special kind of container, implement further subclasses, one for each kind of layout strategy.

Composition and interfaces Inheritance

This solution requires only one class for each special type of container, and one class for each layout strategy. Any kind of container instance can be configured with any kind of strategy object.

Subclass explosion! To support all container (c) and layout strategy (s) combinations, c * s classes would be required.

Composition offers run-time flexibility. A Frame can change how it lays out its children simply by swapping its current layout strategy (e.g. BorderLayout) for another (e.g. GridLayout).

Overly rigid structure. Once a PanelWithBorderLayout object, for example, has been created, the panel will always be laid out according to the border strategy.

Frame

…

FrameWithBorderLayout FrameWithBoxLayout…


Layout management

COMPSCI 230 Software Design & Construction 11

public class Container extends Component { … private List< Component > children; private LayoutManager layoutManager;

public void setLayout( LayoutManager lm ) { layoutManager = lm; }

public void doLayout( ) { layoutManager.layout( this ); }}

Frame instance

TextField instance

Panel instance

Buttoninstance

Buttoninstance

Labelinstance

Panel instance

Panel instance

Labelinstance

1: doLayout( )

2: layoutContainer( this )

LayoutManager instance


Event handling

Components generate events in response to user interaction

To hook in application-specific responses to events, listeners are used A listener is an object

that is registered with a component; in handling user interaction the component informs any registered listeners of the event

Framework code

Application code

Framework generates button click event

Framework waits for next user interaction

Framework generates next event

Registered listener executes


Event handling

<< interface >>ActionListener

actionPerformed( e : ActionEvent ) : void

<< interface >>KeyListener

keyPressed( e : KeyEvent ) : voidkeyReleased( e : KeyEvent ) : voidkeyTyped( e : KeyEvent ) : void

<< interface >>MouseListener

mouseReleased( e : MouseEvent ) : voidmouseClicked( e : MouseEvent ) : voidmouseEntered( e : MouseEvent ) : voidmouseExited( e : MouseEvent ) : void

AWT frameworkButton

addActionListener( listener : ActionListener )

ApplicationListener

Application

Buttoninstance

ActionListener Instance

listener

(an instance of a class that implements the ActionListener interface)


public class PalindromeGUI extends Frame implements ActionListener {

private TextField text; private Button isPalindrome, quit; private Label output;

public PalindromeGUI() { super( "Palindrome detector" ); … isPalindrome.addActionListener( this ); quit.addActionListener( this ); }

public void actionPerformed( ActionEvent e ) { if( e.getSource( ) == isPalindrome ) { // isPalindrome pressed. String enteredText = text.getText( ); if( enteredText.length( ) > 0 ) { if( isPalindromic( enteredText ) ) { output.setText( enteredText + " is palindromic" ); } else { output.setText( enteredText + " is not palidromic" ); } } } else { // quit pressed. System.exit( 0 ); } }}

PalindromeGUI / ActionListener instance

Button instance

isPalindrome

quit

listenerlistener

addActionListener( this )

actionPerformed( )

Button instance


public class PalindromeGUI extends Frame { private TextField text; private Button isPalindrome, quit; private Label output;

public PalindromeGUI( ) { … isPalindrome.addActionListener( new ActionListener( ) { public void actionPerformed( ActionEvent e ) { String enteredText = text.getText( );

if( enteredText.length( ) > 0 ) { if( isPalindromic( enteredText ) ) { output.setText( enteredText + " is palindromic" ); } } else { output.setText( enteredText + " is not palindromic" ); } } } );

quit.addActionListener( new ActionListener( ) { public void actionPerformed( ActionEvent e ) { System.exit( 0 ); } } ); …}

PalindromeGUI instance

Button instance

isPalindrome

quit

listenerlistener

actionPerformed( )

Button instance

ActionListener instance

ActionListener instance


MouseListenerpublic class MouseMain extends Frame {

public MouseMain() { super( “MouseListener" );

Panel mousePanel = new MousePositionPanel( ); add( mousePanel );

setBounds( 100, 100, 200, 200 ); setVisible( true ); }

public static void main( String[ ] args ) { MouseMain mouseMain = new MouseMain( ); }}

class MousePositionPanel extends Panel implements MouseListener { private int mouseX, mouseY;

public MousePositionPanel( ) { mouseX = 100; mouseY = 100;

addMouseListener( this ); }

public void paint( Graphics g ) { g.drawString( "(" + mouseX + ", " + mouseY + ")", mouseX, mouseY ); }

public void mousePressed( MouseEvent e ) { mouseX = e.getX( ); mouseY = e.getY( ); repaint( ); }

public void mouseReleased( MouseEvent e ) { } public void mouseClicked( MouseEvent e ) { } public void mouseEntered( MouseEvent e ) { } public void mouseExited( MouseEvent e ) { }}


Custom painting in AWT

The MouseListener application is an example where custom painting is required The MousePositionPanel

component is painted by displaying the position where the mouse was clicked

Each time the mouse is clicked, the application updates its state and requests that its MousePositionPanel component be repainted

To carry out custom painting in a subclass of Component, you should override method paint( ).

Component subclasses should not override method repaint( ).

To carry out custom painting in a subclass of Component, you should override method paint( ).

Component subclasses should not override method repaint( ).

Container

Component

paint( g : Graphics ) : voidrepaint( ) : void

Panel

MousePositionPanel


Overrides paint( )


Swing

Swing is a more complex and powerful replacement for the AWT

Swing includes: A richer set of GUI components, many of which are located in package

javax.swing By convention, Swing component names are prefixed by J (e.g. JButton,

JLabel etc.) and are subclasses of JComponent, which is a subclass of the AWT’s Component class

Components that have separate models; the Swing framework originates from the Model-View-Control (MVC) paradigm

Components that have a pluggable look-and-feel Cosmetic improvements – e.g. buttons and labels can show images

rather than just text, and components can be decorated with a variety of borders

Swing’s painting model improves the AWT’s but is slightly more complex

Swing uses the AWT’s layout management and event handling infrastructure



Pluggable look and feel


With a Swing application, it is possible to change the look-and-feel at run-time.

What technique do you think has been used in implementing this feature?

JButton

setUI( delegate : ButtonUI ) : void

<< interface >>ButtonUI

paint( g : Graphics ) : void

Implemented by one class for each different look-and-feel, e.g. Windows, Metal, Motif.


Custom painting in Swing


For custom painting in Swing, JComponent subclasses should override paintComponent( ) (and, in general, make a super.paintComponent( ) call).

JComponent subclasses should not override paint( ) or repaint( ).

For custom painting in Swing, JComponent subclasses should override paintComponent( ) (and, in general, make a super.paintComponent( ) call).

JComponent subclasses should not override paint( ) or repaint( ).

JComponent

paintComponent( g : Graphics )

Component

paint( g : Graphics ) : voidrepaint( ) : void

JPanel

MousePositionPanel


public void paint ( Graphics g ) { paintComponent( g ); // Code to paint border. // Code to paint children. …}

public void paintComponent( Graphics g ) { // Code to paint the background.}

public void paintComponent( Graphics g ) { // Make sure the background is painted. super.paintComponent( g );

// Now do custom painting. g.drawString ( "(" + mouseX + ", " + mouseY + ")", mouseX, mouseY );}


Custom painting in Swing


import java.awt.*;import java.awt.event.*;import javax.swing.*;

public class SwingMouseMain extends JFrame {

public SwingMouseMain( ) { super( "Mouse Listener" );

JPanel mousePanel = new MousePositionPanel( ); add( mousePanel );

setBounds( 100, 100, 200, 200 ); setVisible( true ); }

public static void main( String[ ] args ) { SwingMouseMain mouseMain = new SwingMouseMain( ); }}

class MousePositionPanel extends JPanel { private int mouseX, mouseY;

public MousePositionPanel( ) { mouseX = 100; mouseY = 100;

addMouseListener( new MouseAdapter( ) { public void mousePressed( MouseEvent e ) { mouseX = e.getX( ); mouseY = e.getY( ); repaint( ); } } ); }

public void paintComponent( Graphics g ) { super.paintComponent( g ); g.drawString( "(" + mouseX + ", " + mouseY + ")", mouseX, mouseY ); }}

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Object-Oriented Frameworks