Fondamenti di Java

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Fondamenti di Java

• Introduzione alla
• costruzione di GUI
• (graphic user interface)

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component - container - layout
Un Container contiene 0 o Components Il
Layout specifica come i Components sono disposti
nel Container Un Container è un Component (quindi
il contenimento è ricorsivo) Un Component ha una
Graphics associata
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awt component hierarchy

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awt container hierarchy

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Swing component hierarchy
java.awt

Component
Container
javax.swing
JComponent
Swing containers
Swing components
JPanel
JButton
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Top Level Containers

TUTORIAL http//java.sun.com/docs/books/tutorial/
uiswing/
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General Purpose Containers

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Special Purpose Containers

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Basic Controls

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Uneditable Information

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More complex structures

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Prima applicazione

JFrame
App
YellowWindow
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JFrame

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class YellowWindow
package it.unitn.science.prog2.guiApp import
java.awt. import javax.swing. public class
YellowWindow extends JFrame private JPanel
contentPane public YellowWindow() try
jbInit() catch(Exception e)
e.printStackTrace() private void
jbInit() throws Exception
contentPane(JPanel)this.getContentPane()
this.setSize(new Dimension(400, 300))
contentPane.setBackground(Color.YELLOW)

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class App
package it.unitn.science.prog2.guiApp import
javax.swing. import java.awt. public class
App JFrame finestranull public static
void main(String a) new App() public
App() // aggiungere qui set lookfeel
(vedi oltre) this.setupGraphicEnvironment()

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class App
private void setupGraphicEnvironment()
finestra new YellowWindow() //new
CalculatorWindow // trova le dimensioni
dello schermo e della finestra Dimension
screenSize
Toolkit.getDefaultToolkit().getScreenSize()
Dimension frameSize finestra.getSize() //
assicurati che la finestra non sia più grande
dello schermo if (frameSize.height gt
screenSize.height) frameSize.height
screenSize.height if (frameSize.width gt
screenSize.width) frameSize.width
screenSize.width

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class App
// centra la finestra nello schermo
finestra.setLocation((screenSize.width -
frameSize.width) / 2, (screenSize.height -
frameSize.height) / 2) // fai in modo che
la chiusura della finestra // termini
l'applicazione finestra.setDefaultCloseOperati
on(JFrame.EXIT_ON_CLOSE ) // rendi la
finestra visibile finestra.setVisible(true)

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Event Listeners
Some Events and Their Associated Event Listeners Some Events and Their Associated Event Listeners
Act that Results in the Event Listener Type
User clicks a button, presses Enter while typing in a text field, or chooses a menu item ActionListener
User closes a frame (main window) WindowListener
User presses a mouse button while the cursor is over a component MouseListener
User moves the mouse over a component MouseMotionListener
Component becomes visible ComponentListener
Component gets the keyboard focus FocusListener
Table or list selection changes ListSelectionListener
Any property in a component changes such as the text on a label PropertyChangeListener
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ActionListener

• public interface ActionListener extends
  EventListener
• The listener interface for receiving action
  events. The class that is interested in
  processing an action event implements this
  interface, and the object created with that class
  is registered with a component, using the
  component's addActionListener method.
• void actionPerformed(ActionEvent e)          
•  Invoked when an action occurs

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ActionEvent

• ActionEvent extends AWTEvent
• A semantic event which indicates that a
  component-defined action occured. This high-level
  event is generated by a component (such as a
  Button) when the component-specific action occurs
  (such as being pressed). The event is passed to
  every every ActionListener object that registered
  to receive such events using the component's
  addActionListener method.

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ActionEvent

• Method Summary 
• String getActionCommand()      Returns the
  command string associated with this action. 
• int getModifiers()      Returns the modifier
  keys held down during this action event. 
• long getWhen()      Returns the timestamp of
  when this event occurred. 
• String paramString()      Returns a parameter
  string identifying this action event. 
• Methods Inherited 
• public Object getSource()
• Returns The object on which the Event initially
  occurred.

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Seconda applicazione
ActionListener
JPanel
Painter
ButtonPanel
JFrame
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addActionListener
Button
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Esempio

• package actionlistenerimport
  java.awt.import java.awt.event.import
  javax.swing.import javax.swing.JFramepublic
  class ButtonPanel extends JPanel public
  ButtonPanel()    super()        JButton
  button1 new JButton("Giallo")    JButton
  button2 new JButton("Verde")     JButton
  button3 new JButton("Rosso")   
  this.add(button1)    this.add(button2)   
  this.add(button3)     Painter azioneGiallo
  new Painter(Color.YELLOW,this)
• Painter azioneVerde new Painter(
  Color.GREEN,this)
• Painter azioneRosso new
  Painter(Color.RED,this)
•     button1.addActionListener(azioneGiallo)
      button2.addActionListener(azioneVerde)   
  button3.addActionListener(azioneRosso)   

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Esempio - continua

•   public static void main(String a)
• JFrame fnew JFrame()
• f.setContentPane(new ButtonPanel())
• f.setSize(300,300)
• f.setVisible(true)
•       
• class Painter implements ActionListener
• private Color colore
• private JPanel contenitore
• public Painter(Color colore, JPanel
  contenitore)
• this.colore colore
• this.contenitorecontenitore
• public void actionPerformed(ActionEvent
  actionEvent)
• contenitore.setBackground(colore)

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Esempio 2

• public class ButtonPanel extends JPanel
• public ButtonPanel()
• super()
• Painter pnew Painter(this)
• String c"Giallo","Verde","Rosso"
• for (int i0iltc.lengthi)
• JButton bnew JButton(ci)
• this.add(b)
• b.addActionListener(p)
• // b.setActionCommand(ci)
• public static void main(String a)
• JFrame fnew JFrame()
• f.setContentPane(new ButtonPanel())
• f.setSize(300,300)
• f.setVisible(true)

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Esempio 2 - continua

• class Painter implements ActionListener
• private JPanel contenitore
• private Color colore
• public Painter(JPanel contenitore)
• this.contenitorecontenitore
• public void actionPerformed(ActionEvent
  actionEvent)
• String s((JButton)actionEvent.getSource())
  .getText()
• //String sactionEvent.getActionCommand()
• if (s.equals("Giallo")) coloreColor.YELLOW
  
• else if (s.equals("Rosso"))
  coloreColor.RED
• else if (s.equals("Verde"))
  coloreColor.GREEN
• contenitore.setBackground(colore)

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Esempio 3

• public class ButtonPanel extends JPanel
• public ButtonPanel()
• super()
• Painter pnew Painter(this)
• this.setLayout(null)
• String c"Giallo","Verde","Rosso"
• for (int i0iltc.lengthi)
• JButton bnew JButton(ci)
• b.setSize(100,50)
• b.setLocation(i100,i50)
• this.add(b)
• b.addActionListener(p)
• b.setActionCommand(ci)

NON CONSIGLIATO LAYOUT NON LIQUIDO!
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Compito

• Scrivere un applicazione contenente un bottone
  che quando viene premuto si sposta altrove nella
  finestra.
• Scrivere una applicazione contenente due bottoni
  uno ingrandisce la dimensione della finestra,
  laltro la rimpicciolisce

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Mouse events

• This low-level event is generated by a component
  object for
• Mouse Events
• a mouse button is pressed
• a mouse button is released
• a mouse button is clicked (pressed and released)
• the mouse cursor enters the unobscured part of
  component's geometry
• the mouse cursor exits the unobscured part of
  component's geometry
• Mouse Motion Events
• the mouse is moved
• the mouse is dragged

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Compito

• Scrivere un applicazione contenente un TextField
  il cui valore inizialmente è zero, e che viene
  incrementato di uno ogni volta che il bottone del
  mouse viene cliccato.
• Scrivere unapplicazione contenente un bottone
  che si posiziona dove viene cliccato il bottone
  del mouse. Se invece viene cliccato il bottone
  grafico, questo si riposiziona nella sua sede
  iniziale.

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Pluggable LookFeel

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Scelta del LookFeel
public static void main(String args) try
UIManager.setLookAndFeel(
UIManager.getCrossPlatformLookAndFeelClassName())
catch (Exception e) new
SwingApplication() //Create and show the GUI.
UIManager.getCrossPlatformLookAndFeelClassName()
Returns the Java look and feel.
UIManager.getSystemLookAndFeelClassName()
Specifies the look and feel for the current
platform.

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Scelta del LookFeel
public static void main(String args) try
UIManager.setLookAndFeel(
"com.sun.java.swing.plaf.gtk.GTKLookAndFeel")
catch (Exception e) new
SwingApplication() //Create and show the GUI.
UIManager.getSystemLookAndFeelClassName(String
s) Specifies the look and feel for the platform
described by s.

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Available LookFeel
"com.sun.java.swing.plaf.gtk.GTKLookAndFeel"
Specifies the GTK look and feel. Introduced in
release 1.4.2. "javax.swing.plaf.metal.MetalLookA
ndFeel" Specifies the Java look and feel.
"com.sun.java.swing.plaf.windows.WindowsLookAndF
eel" Specifies the Windows look and feel.
Currently, you can use this look and feel only on
Microsoft Windows systems. "com.sun.java.swing.pla
f.motif.MotifLookAndFeel" Specifies the
CDE/Motif look and feel. This look and feel can
be used on any platform.