Fondamenti di Java

Introduzione alla costruzione di GUI (graphic user interface)

component - container - layout

Un Container contiene [0 o +] ComponentsIl Layout specifica come i Components sono disposti nel

ContainerUn Container è un Component (quindi il contenimento è

ricorsivo)Un Component ha una Graphics associata

Component

Container

posiziona Layout

Graphics

awt component hierarchy

Component

Button Canvas Checkbox Choice TextComponent

ScrollbarList Label

TextArea TextField

awt container hierarchy Container

Frame

Window

Dialog

FileDialog

ScrollPanelPanel

Applet

javax.swing

java.awt

Swing component hierarchy

Container

JComponent

Swing “containers”

JPanel

Swing “components”

JButton

Component

Top Level Containers

TUTORIAL:http://java.sun.com/docs/books/tutorial/uiswing/

General Purpose Containers

Special Purpose Containers

Basic Controls

Uneditable Information

More complex structures

Prima applicazione

App YellowWindow

JFrame

JFrame

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); }}

class Apppackage it.unitn.science.prog2.guiApp;import javax.swing.*;import java.awt.*;

public class App {

JFrame finestra=null; public static void main(String[ ] a){

new App(); } public App() { // aggiungere qui: set look&feel (vedi oltre)

this.setupGraphicEnvironment(); }

class Appprivate 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 > screenSize.height) frameSize.height = screenSize.height; if (frameSize.width > screenSize.width)

frameSize.width = screenSize.width;

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.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE );

// rendi la finestra visibile finestra.setVisible(true); }}

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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.

Seconda applicazione

ButtonPanel PainterJFrame

ActionListenerJPanel

ButtonaddActionListener

3

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Esempiopackage actionlistener;

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

public 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 f=new 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.contenitore=contenitore; } public void actionPerformed(ActionEvent actionEvent) { contenitore.setBackground(colore); } }

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Esempio 2public class ButtonPanel extends JPanel { public ButtonPanel() { super(); Painter p=new Painter(this); String c[]={"Giallo","Verde","Rosso"}; for (int i=0;i<c.length;i++) { JButton b=new JButton(c[i]); this.add(b); b.addActionListener(p); // b.setActionCommand(c[i]); }}

public static void main(String a[]) { JFrame f=new 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.contenitore=contenitore; } public void actionPerformed(ActionEvent actionEvent) { String s=((JButton)actionEvent.getSource()).getText(); //String s=actionEvent.getActionCommand(); if (s.equals("Giallo")) colore=Color.YELLOW; else if (s.equals("Rosso")) colore=Color.RED; else if (s.equals("Verde")) colore=Color.GREEN; contenitore.setBackground(colore); } }

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Esempio 3public class ButtonPanel extends JPanel { public ButtonPanel() { super(); Painter p=new Painter(this); this.setLayout(null); String c[]={"Giallo","Verde","Rosso"}; for (int i=0;i<c.length;i++) { JButton b=new JButton(c[i]); b.setSize(100,50); b.setLocation(i*100,i*50); this.add(b); b.addActionListener(p); b.setActionCommand(c[i]); } }

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, l’altro 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 un’applicazione 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.

Pluggable Look&Feel

Scelta del Look&Feelpublic 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.

Scelta del Look&Feelpublic 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”.

Available Look&Feel"com.sun.java.swing.plaf.gtk.GTKLookAndFeel"

Specifies the GTK+ look and feel. Introduced in release 1.4.2.

"javax.swing.plaf.metal.MetalLookAndFeel" Specifies the Java look and feel.

"com.sun.java.swing.plaf.windows.WindowsLookAndFeel" Specifies the Windows look and feel. Currently, you can use this look and feel only on Microsoft Windows systems.

"com.sun.java.swing.plaf.motif.MotifLookAndFeel" Specifies the CDE/Motif look and feel. This look and feel can be used on any platform.