How to Figure out what checkboxes are selected upon a button click...

Question

If I have a panel with some JCheckBoxes and a JButton, how can I figure out what checkboxes are selected upon the button click? If I add an actionlistener to the button, inside actionPerformed, how would I know what checkboxes are selected? One caveat is that the name and number of these checkboxes are dymanically chaing based on a configuration file so I do not know what the names of these check boxes are.
Any help/code sample would be appreciated.

Answer 1

Here's one of several different ways to do it. It attaches an ItemListener to each checkBox. When the checkBox is clicked, it is either added or removed from a List of selected items. Clicking the button will show you the selected items.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;
public class CheckBoxTest extends JFrame
  JCheckBox chkChoice1 = new JCheckBox("English");
  JCheckBox chkChoice2 = new JCheckBox("French");
  JCheckBox chkChoice3 = new JCheckBox("German");
  JCheckBox chkChoice4 = new JCheckBox("Italian");
  JTextArea txaDisplay = new JTextArea(5, 20);
  JButton btnShow = new JButton("Show Selected Items");
  ArrayList <JCheckBox>choices = new ArrayList<JCheckBox>();
  public CheckBoxTest()
    super("");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    chkChoice1.addItemListener(new CheckBoxListener(chkChoice1));
    chkChoice2.addItemListener(new CheckBoxListener(chkChoice2));
    chkChoice3.addItemListener(new CheckBoxListener(chkChoice3));
    chkChoice4.addItemListener(new CheckBoxListener(chkChoice4));
    btnShow.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent event)
        txaDisplay.setText("");
        for (JCheckBox jcb : choices)
          txaDisplay.append(jcb.getText() + "\n");
    JPanel buttonPanel = new JPanel(new FlowLayout());
    buttonPanel.add(chkChoice1);
    buttonPanel.add(chkChoice2);
    buttonPanel.add(chkChoice3);
    buttonPanel.add(chkChoice4);
    JScrollPane scroll = new JScrollPane(txaDisplay);
    scroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    JPanel dataPanel = new JPanel();
    dataPanel.add(btnShow);
    dataPanel.add(scroll);
    Container c = getContentPane();
    c.setLayout(new BorderLayout());
    c.add(buttonPanel, BorderLayout.NORTH);
    c.add(dataPanel, BorderLayout.CENTER);
    pack();
  public static void main( String[] args )
    CheckBoxTest frame = new CheckBoxTest();
    frame.setVisible(true);
  class CheckBoxListener implements ItemListener
    JCheckBox checkBox;
    public CheckBoxListener(JCheckBox checkBox)
      this.checkBox = checkBox;
    public void itemStateChanged(ItemEvent event)
      if (checkBox.isSelected())
        choices.add(checkBox);
      else
        choices.remove(checkBox);
}Or, you could just maintain all the checkboxes in a Collection ahead of time. When the Show button is selected, simple query isSelected() on each item.
Again, there are several different ways.