selected Checkbox

Question

Hi, I am new to swing, I would like to ask how can I make this code , so when the submit button is pressed to get the selected checkboxes and display their names.

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.GridLayout;

import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.Border;

public class ACheckBox {
  public static void main(String args[]) {
    String title = (args.length == 0 ? "CheckBox Sample" : args[0]);
    JFrame frame = new JFrame(title);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel(new GridLayout(0, 1));
    Border border = BorderFactory.createTitledBorder("Pizza Toppings");
    panel.setBorder(border);
    JCheckBox check = new JCheckBox("Anchovies");
    panel.add(check);
    check = new JCheckBox("Garlic");
    panel.add(check);
    check = new JCheckBox("Onions");
    panel.add(check);
    check = new JCheckBox("Pepperoni");
    panel.add(check);
    check = new JCheckBox("Spinach");
    panel.add(check);
    JButton button = new JButton("Submit");
    Container contentPane = frame.getContentPane();
    contentPane.add(panel, BorderLayout.CENTER);
    contentPane.add(button, BorderLayout.SOUTH);
    frame.setSize(300, 200);
    frame.setVisible(true);
  }
}

Answer 1

You need to define a bespoke ActionListener implementation whose job is to analyse each JCheckBox's selected state when an action is fired; i.e. when the "Submit" button is clicked.

// ActionListener implementation that maintains a reference to each JCheckBox.
// We will register this listener with the Submit button.
public class MyActionListener implements ActionListener {
  private final List<JCheckBox> checkBoxes = new LinkedList<JCheckBox>();

  /**
   * Adds the specified JCheckBox to the list of JCheckBoxes.
   */
  public void addCheckBox(JCheckBox checkBox) {
    this.checkBoxes.add(checkBox);
  }

  /**
   * Called when the Submit button is pressed.
   */
  public void actionPerformed(ActionEvent evt) {
    StringBuilder sb = new StringBuilder();
    sb.append("Selected Check Boxes: ");

    // Iterate over each JCheckBox and build message ready for display.
    // Could do something more sophisticated here if required.
    for (JCheckBox checkBox : checkBoxes) {
      if (checkBox.isSelected()) {
        sb.append(checkBox.getText()).append(' ');
      }
    }

    JOptionPane.showMessageDialog(null, sb);
  }
}

// 1. Create ActionListener implementation.
MyActionListener al = new MyActionListener();

// 2. Register JCheckBoxes with ActionListener.
al.addCheckBox(checkBox);
// etc.

// 3. Finally register ActionListener with Submit button.
submitButton.addActionListener(al);

Answer 2

You need to add an ActionListner to your button and then query the state of the check boxes.

I suggest you read How to Use Buttons, Check Boxes and Radio Buttons from the Swing Tutorial.

Answer 3

If you don't want to create a new Action for every checkbox (e.g. if the checkboxes are added dynamically) you can do something like this:

    for (Component child: panel.getComponents()) {
        if (child instanceof JCheckBox) {
            JCheckBox checkBox = (JCheckBox) child;
            if (checkBox.isSelected()) {
                System.out.println(checkBox.getAction().getValue(Action.NAME));
            }
        }
    }