Java Programming

1
Java Programming
Introduction to Swing Class 7
2
Swing

• Graphical User Interface
• Provides
• Windows
• Menus
• Buttons
• Labels
• Textboxes
• In the beginning, there was AWT .
• Abstract Windowing Toolkit
• Relied on peers
• Heavyweight Native Code interfaces
• Written for each target
• Enabled original AWT to be written in 6 weeks!
• Portability problems

3
A Swing Program

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

4
A Swing Program

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

5
A Swing Program

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

6
Constants

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

7
Arrays

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• JWindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

8
Construct a window

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• JWindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

9
Where can I draw things?

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• JWindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

10
Panes?

• There are 3 of them
• contentPane
• JPanel
• Resides in layeredPane
• Contains components
• glassPane
• JPanel
• Floats above others
• Traps mouse events first
• layeredPane
• JLayeredPane
• Contains contentPane and menuBar
• menuBar
• JMenuBar

11
Visibility and Layout

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• JWindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

12
Adding things to a window

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

13
Some Java features

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

14
Almost there ...

• import java.awt.
• import javax.swing.
• public class JWTest
• static final int n_label 10
• public static void main( String args )
• JLabel lab1
• Jwindow w new JWindow()
• Container content_pane w.getContentPane()
• w.setVisible( true )
• content_pane.setLayout( new BorderLayout( ) )
• lab1 new JLabeln_label
• for(int k0kltn_labelk)
• lab1k new JLabel("Label " k)
• content_pane.add( lab1k )
• w.pack()
• w.show()
• System.exit(0)

15
Those labels are boring ...

• Changing them
• Swing API
• Documentation cached at ..
• http//www.javasoft.com
• Observe the hierarchy

Object
Component
Container
JComponent
JLabel
16
Those labels are boring ...

• Changing them
• Note the specification

public class JLabel extends
JComponent implements
SwingConstants, Accessible
17
Those labels are boring ...

• Look for methods that operate on JLabel
• Note that most of them dont have arguments
• They operate on a JLabel

Icon getIcon() int getHorizontalAlignment() int
getHorizontalTextPosition() String
getText() void setText( String text ) etc
JLabel label new JLabel(Test label) Icon img
label.getIcon()
18
But I want to change the text font!

• Look for methods on the superclasses
• On JComponent
• Since a JLabel is also a Jcomponent ..
• works fine!

void setFont( Font font )
Jlabel label new Jlabel(Test
label) label.setFont( newfont )
19
and I want to change the location ..

• Look for methods on the superclasses
• On JComponent
• ?? Nothing likely
• Try the next ancestor ..
• On Container
• ?? Nothing likely
• On Component
• looks promising ...
• But theres two???
• works fine!

setLocation
20
Polymorphism in practice ...

• But theres two .. !!
• Choose the most convenient
• the compiler determines which one to use by
  matching the signature ..

void setLocation( int x, int y )void
setLocation( Point p )
label.setLocation( X_POS, Y_POS )
void setLocation( int, int )
21
Polymorphism in practice ...

• Multiple Constructors
• Common situation
• Again choose the most convenient
• Other attribute values will assume default
  values, eg
• No icon, centre alignment

JLabel() JLabel( Icon image ) JLabel( Icon
image, int horAlign )JLabel( String text
)JLabel( String text, Icon image,
int horAlogin JLabel( String text, int horAlign )
22
Other common components

• Buttons
• JButton
• Standard way for initiating some action from a
  screen
• Used with an ActionListener (next lecture!)
• JToggleButton
• Two states selected / de-selected
• Query with
• boolean isSelected()
• ButtonGroup
• Found in the parent AbstractButton!!
• Allows groups of buttons
• Select one
• Automatic de-select of remainder

23
Other common components

• Buttons
• JCheckBox
• Checked box ..
• Selected / Not selected
• Its a specialization of JToggleButton!
• JRadioButton
• Similar to JCheckBox

24
Frames Applets

• JFrame
• Specialization of Frame
• Adds
• Border
• Menubar
• Close box
• JApplet
• Similar to JFrame
• Both have
• ContentPane
• GlassPane

25
Panels

• JPanel
• Useful as a container for other elements

26
Panels

• JPanel
• Useful as a container for other elements

JWindow w new JWindow()JPanel panel1 new
JPanel() JPanel panel2 new JPanel() JButton
b1 new JButton() panel1.add( b1 ) w.add(
panel1 ) panel2.add( b2 ) w.add( panel2 )
27
Panels

• JPanel
• Make the panels classes!

28
Text - Edit for user input

• JTextField
• Single line of editable text
• public class TextExample extends JPanel
  JTextField tf
• public TextExample( String s )
• tf new JTextField( s ) add( tf )
• public String getText() return
  tf.getText()

29
Text - Edit for user input

• JTextArea
• Multiple lines of editable text
• public class TextExample extends JPanel
  JTextArea ta
• static final int rows 10
• static final int cols 20
• public TextExample( String s )
• ta new JTextArea( s, rows, cols ) add(
  ta )
• public String getText( int row )
• int offset ta.getLineStartOffset( row )
  return tf.getText( offset, cols )
  

30
Menus

• Menus are attached to a JMenuBar
• A Menu(JMenu)contains items (JMenuItem)
• Recipe
• Create a frame
• Create a menubar
• Create a menu
• Create some menu items
• Add an ActionListener (next lecture!)
• Add them to the menu
• Add the menu to the menubar
• Set the menubar

Repeat as needed
31
Menus

• Example
• Create a frame
• Create a menubar
• Create a menu
• Create some menu items
• Trap events
• Add them to the menu
• Add the menuto the menubar
• Set the menubar

32
Swing Example

• Jwindow
• Simple usage example
• import javax.swing.public class windowexample
  public static void main(String args)
  JWindow w JLabel label int n w
  new JWindow() label new JLabel(Example
  label) w.add( label ) n
  w.getComponentCount() System.out.println(Wi
  ndow has n
  components) w.show()
  

33
Java ProgrammingSwing (continued)
10 mins break (not more)
34
Menus

• Menus are attached to a JMenuBar
• A Menu(JMenu)contains items (JMenuItem)
• Recipe
• Create a frame
• Create a menubar
• Create a menu
• Create some menu items
• Add an ActionListener (next lecture!)
• Add them to the menu
• Add the menu to the menubar
• Set the menubar

Repeat as needed
35
Menus

• Example
• Create a frame
• Create a menubar
• Create a menu
• Create some menu items
• Trap events
• Add them to the menu
• Add the menuto the menubar
• Set the menubar

36
Thats all very pretty but ...

• Our GUI needs some action!
• Add Listeners to Components
• Component fire events,
• Listeners trap them
• Various types of listeners ..
• ActionListener
• MouseListener
• MenuListener
• and some more ...
• Listeners are interfaces
• No code!
• Remember just a specification for methods you
  must supply

37
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
38
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
39
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
40
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
41
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
42
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
43
Making a Listener - Method 1

• Define a class implementing ActionListener

// Event Handler import java.awt. import
java.awt.event. import javax.swing. public
class EventHandler implements ActionListener
JPanel parent JComponent src public
EventHandler( JPanel m ) // Establish a link
to my parent parent m //
ActionListener interface public void
actionPerformed( ActionEvent e )
System.out.println("aP event " e ) src
(JComponent)(e.getSource())
44
wed better attach the listener to something!

• An Action button
• import javax.swing.public class windowexample
  public static void main(String args)
  JWindow w new JWindow() JButton b new
  JButton(Action!) EventHandler h new
  EventHandler( this ) Container cp
  getContentPane() cp.add( b )
  b.addActionListener( h ) w.pack()
  w.show()

45
How does the listener talk to us??

• Various possibilities
• Call a method on the parent

46
How does the listener talk to us??

• Various possibilities
• Call a method in another class

47
A case for an interface!!

• Define a class of objects which can be
  incremented
• Must provide a void incX( int ) method

48
A case for an interface!!

• Define a class of objects which can be
  incremented
• Must provide a void incX( int ) method
• The interface provides the signature for a method
• (or methods - it can require many)
• The class implements the method(s) in the
  interface
• and any others that it needs!

49
A case for an interface!!

• A class may implement several interface

50
Comparable ..

• To make many common structures ..
• Look up tables, search trees
• and perform common operations
• Sort, Match
• We need to compare items ..
• A Comparable interface is part of java.lang
• It has one method
• Class implementor decides how objects of a class
  are ordered
• May depend on some very complex rules!!
• So compareTo can only be implemented in specific
  classes
• but there are many places where ordering is
  needed!!

51
Talking to the handler ...

• The handler class can update one of its
  attributes and provide a method to access it

52
Making a Listener - Method 2

• Define a separate class is a pain!
• Too many files, overhead
• No problem - make it an inner class

public class windowexample int x class
EventHandler implements ActionListener
// ActionListener interface public void
actionPerformed( ActionEvent e ) x
public static void main(String args)
JWindow w new JWindow() JButton b new
JButton(Action!) EventHandler h new
EventHandler( this ) Container cp
getContentPane() cp.add( b )
b.addActionListener( h )
53
Making a Listener - Method 2

• Define a separate class is a pain!
• Too many files, too much overhead
• No problem - make it an inner class

public class windowexample int x class
EventHandler implements ActionListener
// ActionListener interface public void
actionPerformed( ActionEvent e ) x
public static void main(String args)
JWindow w new JWindow() JButton b new
JButton(Action!) EventHandler h new
EventHandler( this ) Container cp
getContentPane() cp.add( b )
b.addActionListener( h )
54
Making a Listener - Method 3

• But thats a whole class with only one method!
• Im lazy!
• No problem - make it an anonymous class

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x ) Container cp
getContentPane() cp.add( b )
55
Making a Listener - Method 3

• But thats a whole class with only one method!
• Im lazy!
• No problem - make it an anonymous class

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x ) Container cp
getContentPane() cp.add( b )
56
Making a Listener - Method 3

• But thats a whole class with only one method!
• Im lazy!
• No problem - make it an anonymous class

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x )
Container cp getContentPane() cp.add( b
)
57
Anonymous classes

• The syntax can be confusing!

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x )
Container cp getContentPane() cp.add( b
)
58
Anonymous classes

• The syntax can be confusing!

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x )
Container cp getContentPane() cp.add( b
)
59
Anonymous classes

• The syntax can be confusing!

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x )
Container cp getContentPane() cp.add( b
)
60
Anonymous classes

• The syntax can be confusing!

public class windowexample int x public
static void main(String args) JWindow w
new JWindow() JButton b new
JButton(Action!) b.addActionListener(
new ActionListener() public
void actionPerformed( ActionEvent e )
x )
Container cp getContentPane() cp.add( b
)
61
MouseListener interface

• Fine control of your GUI, but
• 5 methods!
• An interface must implement each one
• Fine if you want special effects,but painful if
  you only want a click!

JButton b new JButton(Action!)b.addMouseList
ener( new MouseListener() public
void mouseClicked(MouseEvent e)
public void mouseEntered(MouseEvent e)
public void mouseExited(MouseEvent e)
public void mousePressed(MouseEvent e)
public void mouseReleased(MouseEvent e)
)
62
MouseListener interface

• 5 methods!
• A classic case for an adapter!
• MouseAdapter is a class implementing
  MouseListener
• Provides dummy implementations for all 5 required
  methods
• You override only the one you want to use
• Fine if you want special events,but painful if
  you only want a click!

JButton b new JButton(Action!)b.addMouseList
ener( new MouseAdapter() // Only
interested in clicks .. public void
mouseClicked(MouseEvent e) x x 1
)
63
What about the event parameter?

• Look in the ..Event classes
• Properties of events
• eg Location
• For those fancy drag-and-drop applications!
• Now you can set the location of some other object
  ..And repaint making the object follow the
  mouse, ...

JPanel p new JPanel()p.addMouseListener(
new MouseAdapter() // Want to know where
the mouse was pressed public void
mousePressed(MouseEvent e) x
e.getX() y e.getY() // Code to
move something here repaint()
)