Example

In the original Java AWT, radio buttons were handled differently from the Swing approach.

which allows you to find out which of the checkboxes in the CheckboxGroup is selected.

Unfortunately, there is no equivalent mechanism for JRadioButtons and


  ButtonGroup

s in Swing. When they moved to a Model-View-Controller separation of state versus presentation approach, they sacrificed some of the simplicity of the original approach.

It is much harder to figure out how to do the same thing in Swing. You have to resort to Actions to do it, and it's more awkward that it ought to be.

package swingExamples;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

class ColorRadioButtonsPanel extends JPanel
{
  public ColorRadioButtonsPanel()
  {
    setLayout(new BorderLayout());
    add(m_colorPanel, BorderLayout.CENTER);
    add(new InputPanel(), BorderLayout.SOUTH);
  }
  
  private void setPanelColor()
  {
    Color back = null;
    if (m_colorCommand.equals(YELLOW))
    {
      back = Color.YELLOW;
    }
    else if (m_colorCommand.equals(BLUE))
    {
      back = Color.BLUE;
    }
    else if (m_colorCommand.equals(RED))
    {
      back = Color.RED;
    }
    m_colorPanel.setBackground(back);
  }
  
  /////// Private data ///////
  
  // Action commands
  private static final String YELLOW = "Yellow";
  private static final String BLUE = "Blue";
  private static final String RED = "Red";
  private String m_colorCommand = YELLOW; 
                                  // Current color "command"
  
  private ColorPanel m_colorPanel = new ColorPanel();
  
  /////// Inner classes /////
  
  class ColorPanel extends JPanel
  {
  }
  
  class InputPanel extends JPanel 
      implements ActionListener
  {
    public InputPanel()
    {
      addRadioButton(m_yellow, YELLOW);
      m_yellow.setSelected(true); // Make yellow the default
      addRadioButton(m_blue, BLUE);
      addRadioButton(m_red, RED);
      setPanelColor();
    }
    
    // ActionListener required methods
    public void actionPerformed(ActionEvent evt)
    {
      m_colorCommand = 
          m_group.getSelection().getActionCommand();
      setPanelColor();
    }
    
    private JRadioButton addRadioButton(
                            JRadioButton button, 
                            String command)
    {
      add(button);
      m_group.add(button);
      button.setActionCommand(command);
      button.addActionListener(this);
      return button;
    }
    
    ///// Private data /////
    private ButtonGroup m_group = new ButtonGroup();
    private JRadioButton m_yellow = new JRadioButton("Yellow");
    private JRadioButton m_blue = new JRadioButton("Blue");
    private JRadioButton m_red = new JRadioButton("Red");
  }
}

class ColorRadioButtonsFrame extends JFrame
{
  public ColorRadioButtonsFrame()
  {
    setTitle("ColorRadioButtons");
    setSize(300, 200);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    Container contentPane = getContentPane();
    contentPane.add( new ColorRadioButtonsPanel() );
  }
}

public class ColorRadioButtons
{
  public static void main(String[] args)
  {
    ColorRadioButtonsFrame frame = 
                new ColorRadioButtonsFrame();
    frame.setVisible(true);
  }
}

Determining which Radio Button is Set within a Group