Conditionals and Loops - Java Software Solutions: Foundations of Program Design - page 257

The QuoteOptionsPanel class, shown in Listing 5.17, sets up and displays
the GUI components. A radio button is represented by the JRadioButton class.
Because the radio buttons in a set work together, the ButtonGroup class is used to
define a set of related radio buttons.
Note that each button is added to the button group, and also that each button
is added individually to the panel. A ButtonGroup object is not a container to
organize and display components; it is simply a way to define the group of radio
buttons that work together to form a set of dependent options. The ButtonGroup
object ensures that the currently selected radio button is turned off when another
in the group is selected.
A radio button produces an action event when it is selected. The actionPer-
formed method of the listener first retrieves the source of the event using the
getSource method and then compares it to each of the three radio buttons in
turn. Depending on which button was selected, the text of the label is set to the
appropriate quote.
LISTING 5.17
//********************************************************************
// QuoteOptionsPanel.java Author: Lewis/Loftus
//
// Demonstrates the use of radio buttons.
//********************************************************************
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class QuoteOptionsPanel extends JPanel
{
private JLabel quote;
private JRadioButton comedy, philosophy, carpentry;
private String comedyQuote, philosophyQuote, carpentryQuote;
//-----------------------------------------------------------------
// Sets up a panel with a label and a set of radio buttons
// that control its text.
//-----------------------------------------------------------------
public QuoteOptionsPanel()
{
comedyQuote = "Take my wife, please.";
philosophyQuote = "I think, therefore I am.";
carpentryQuote = "Measure twice. Cut once.";