Αντικειμενοστραφής Προγραμματισμός

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 java.awt.events.ActionEvent το οποίο λαμβάνεται από ένα αντικείμενο τύπου ActionListener που συνδέεται με το radio button.

Παράλληλα, δημιουργούνται και δύο αντικείμενα τύπου 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 ItemListener.

Παρακάτω δίνονται δύο παραλλαγές του ιδίου προγράμματος α) με χρήση ActionListener και β) με χρήση ItemListener. Για τα δύο παραδείγματα που ακολουθούν θα χρειαστείτε τις εικόνες animals.zip.

RadioButtonDemo.java

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();
      }
    });
  }
}

RadioButtonDemo2.java

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();
      }
    });
  }
}