===== Οι κλάσεις ButtonGroup και JRadioButton =====
Τα //radio buttons// οργανώνονται σε //button groups//. Τα //radio buttons// είναι ανάλογα με τα //check boxes// με την ιδιαιτερότητα ότι μόνο ένα //radio button// μπορεί να είναι επιλεγμένο κάθε φορά στο ίδιο //button group//. Επιπλέον, από τα κουμπιά ενός //button group// μόνο ένα είναι επιλέξιμο.
Κάθε φορά που ο χρήστης επιλέγει ένα radio button τότε δημιουργείται ένα αντικείμενο τύπου [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ActionEvent.html|java.awt.events.ActionEvent]] το οποίο λαμβάνεται από ένα αντικείμενο τύπου [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ActionListener.html|ActionListener]] που συνδέεται με το //radio button//.
Παράλληλα, δημιουργούνται και δύο αντικείμενα τύπου [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ItemEvent.html|java.awt.events.ItemEvent]] ένα αντικείμενο για το button που επιλέχθηκε και ένα αντικείμενο για το button που απο-επιλέχθηκε (εάν υπήρξε τέτοιο), τα οποία λαμβάνονται από ένα αντικείμενο του τύπου [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ItemListener.html|ItemListener]].
Παρακάτω δίνονται δύο παραλλαγές του ιδίου προγράμματος **α)** με χρήση [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ActionListener.html|ActionListener]] και **β)** με χρήση [[http://docs.oracle.com/javase/7/docs/api/java/awt/event/ItemListener.html|ItemListener]]. Για τα δύο παραδείγματα που ακολουθούν θα χρειαστείτε τις εικόνες {{:swing:animals.zip|}}.
==== Παράδειγμα χρήσης ActionListener ====
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*
* RadioButtonDemo.java requires these files:
* images/Bird.gif
* images/Cat.gif
* images/Dog.gif
* images/Rabbit.gif
* images/Pig.gif
*/
public class RadioButtonDemo extends JPanel {
static String birdString = "Bird";
static String catString = "Cat";
static String dogString = "Dog";
static String rabbitString = "Rabbit";
static String pigString = "Pig";
JLabel picture;
public RadioButtonDemo() {
super(new BorderLayout());
//Create the radio buttons.
JRadioButton birdButton = new JRadioButton(birdString);
birdButton.setMnemonic(KeyEvent.VK_B);
birdButton.setActionCommand(birdString);
birdButton.setSelected(true);
JRadioButton catButton = new JRadioButton(catString);
catButton.setMnemonic(KeyEvent.VK_C);
catButton.setActionCommand(catString);
JRadioButton dogButton = new JRadioButton(dogString);
dogButton.setMnemonic(KeyEvent.VK_D);
dogButton.setActionCommand(dogString);
JRadioButton rabbitButton = new JRadioButton(rabbitString);
rabbitButton.setMnemonic(KeyEvent.VK_R);
rabbitButton.setActionCommand(rabbitString);
JRadioButton pigButton = new JRadioButton(pigString);
pigButton.setMnemonic(KeyEvent.VK_P);
pigButton.setActionCommand(pigString);
//Group the radio buttons.
ButtonGroup group = new ButtonGroup();
group.add(birdButton);
group.add(catButton);
group.add(dogButton);
group.add(rabbitButton);
group.add(pigButton);
//Register a listener for the radio buttons.
birdButton.addActionListener(listener);
catButton.addActionListener(listener);
dogButton.addActionListener(listener);
rabbitButton.addActionListener(listener);
pigButton.addActionListener(listener);
//Set up the picture label.
picture = new JLabel(new ImageIcon(
birdString
+ ".gif"));
//The preferred size is hard-coded to be the width of the
//widest image and the height of the tallest image.
//A real program would compute this.
picture.setPreferredSize(new Dimension(177, 122));
//Put the radio buttons in a column in a panel.
JPanel radioPanel = new JPanel(new GridLayout(0, 1));
radioPanel.add(birdButton);
radioPanel.add(catButton);
radioPanel.add(dogButton);
radioPanel.add(rabbitButton);
radioPanel.add(pigButton);
add(radioPanel, BorderLayout.WEST);
add(picture, BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
}
ActionListener listener = new ActionListener() {
/* Listens to the radio buttons. */
public void actionPerformed(ActionEvent e) {
picture.setIcon(new ImageIcon(e.getActionCommand() + ".gif"));
}
};
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("RadioButtonDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new RadioButtonDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
==== Παράδειγμα χρήσης ItemListener ====
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/*
* RadioButtonDemo.java requires these files:
* images/Bird.gif
* images/Cat.gif
* images/Dog.gif
* images/Rabbit.gif
* images/Pig.gif
*/
public class RadioButtonDemo2 extends JPanel {
static String birdString = "Bird";
static String catString = "Cat";
static String dogString = "Dog";
static String rabbitString = "Rabbit";
static String pigString = "Pig";
JLabel picture;
public RadioButtonDemo2() {
super(new BorderLayout());
//Create the radio buttons.
JRadioButton birdButton = new JRadioButton(birdString);
birdButton.setMnemonic(KeyEvent.VK_B);
birdButton.setSelected(true);
JRadioButton catButton = new JRadioButton(catString);
catButton.setMnemonic(KeyEvent.VK_C);
JRadioButton dogButton = new JRadioButton(dogString);
dogButton.setMnemonic(KeyEvent.VK_D);
JRadioButton rabbitButton = new JRadioButton(rabbitString);
rabbitButton.setMnemonic(KeyEvent.VK_R);
JRadioButton pigButton = new JRadioButton(pigString);
pigButton.setMnemonic(KeyEvent.VK_P);
//Group the radio buttons.
ButtonGroup group = new ButtonGroup();
group.add(birdButton);
group.add(catButton);
group.add(dogButton);
group.add(rabbitButton);
group.add(pigButton);
//Register a listener for the radio buttons.
birdButton.addItemListener(itemListener);
catButton.addItemListener(itemListener);
dogButton.addItemListener(itemListener);
rabbitButton.addItemListener(itemListener);
pigButton.addItemListener(itemListener);
//Set up the picture label.
picture = new JLabel(new ImageIcon(birdString + ".gif"));
//The preferred size is hard-coded to be the width of the
//widest image and the height of the tallest image.
//A real program would compute this.
picture.setPreferredSize(new Dimension(177, 122));
//Put the radio buttons in a column in a panel.
JPanel radioPanel = new JPanel(new GridLayout(0, 1));
radioPanel.add(birdButton);
radioPanel.add(catButton);
radioPanel.add(dogButton);
radioPanel.add(rabbitButton);
radioPanel.add(pigButton);
add(radioPanel, BorderLayout.WEST);
add(picture, BorderLayout.CENTER);
setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
}
ItemListener itemListener = new ItemListener() {
public void itemStateChanged(ItemEvent e) {
if(e.getStateChange() == ItemEvent.SELECTED) {
JRadioButton btn = (JRadioButton)e.getItemSelectable();
picture.setIcon(new ImageIcon(btn.getText() + ".gif"));
}
}
};
/**
* Create the GUI and show it. For thread safety,
* this method should be invoked from the
* event-dispatching thread.
*/
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("RadioButtonDemo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Create and set up the content pane.
JComponent newContentPane = new RadioButtonDemo();
newContentPane.setOpaque(true); //content panes must be opaque
frame.setContentPane(newContentPane);
//Display the window.
frame.pack();
frame.setVisible(true);
}
public static void main(String[] args) {
//Schedule a job for the event-dispatching thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}