toggle button

Video Note

Use check boxes

17.3 Check Boxes

A toggle button is a two-state button like a light switch. JToggleButton inherits AbstractButton and implements a toggle button. Often JToggleButton's subclasses JCheckBox and JRadioButton are used to enable the user to toggle a choice on or off. This section introduces JCheckBox. JRadioButton will be introduced in the next section.

JCheckBox inherits all the properties from AbstractButton, such as text, icon, mnemonic, verticalAlignment, horizontalAlignment, horizontalTextPosition, verticalTextPosition, and selected, and provides several constructors to create check boxes, as shown in Figure 17.11.

Adds an ActionListener for this object.

Adds an ItemListener for this object.

FIGURE 17.12 Three check boxes are added to specify how the message is displayed.

There are at least two approaches to writing this program. The first is to revise the preceding ButtonDemo class to insert the code for adding the check boxes and processing their events. The second is to create a subclass that extends ButtonDemo. Please implement the first approach as an exercise. Listing 17.3 gives the code to implement the second approach.

LISTING 17.3 CheckBoxDemo.java

1 import java.awt.*;

2 import java.awt.event.*;

3 import javax.swing.*;

4

5 public class CheckBoxDemo extends ButtonDemo {

6 // Create three check boxes to control the display of message 7 private JCheckBox jchkCentered = new JCheckBox("Centered");

8private JCheckBox jchkBold = new JCheckBox("Bold");

9 private JCheckBox jchkItalic = new JCheckBox("Italic");

10

11public static void main(String[] args) {

12CheckBoxDemo frame = new CheckBoxDemo();

13frame.setTitle("CheckBoxDemo");

14frame.setSize(500, 200);

15frame.setLocationRelativeTo(null); // Center the frame

16frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

17frame.setVisible(true);

18}

19

20public CheckBoxDemo() {

21// Set mnemonic keys

22jchkCentered.setMnemonic('C');

23jchkBold.setMnemonic('B');

24jchkItalic.setMnemonic('I');

26// Create a new panel to hold check boxes

27JPanel jpCheckBoxes = new JPanel();

28jpCheckBoxes.setLayout(new GridLayout(3, 1));

29jpCheckBoxes.add(jchkCentered);

30jpCheckBoxes.add(jchkBold);

31jpCheckBoxes.add(jchkItalic);

32add(jpCheckBoxes, BorderLayout.EAST);

34// Register listeners with the check boxes

35jchkCentered.addActionListener(new ActionListener() {

36public void actionPerformed(ActionEvent e) {

37messagePanel.setCentered(jchkCentered.isSelected());

38}

39});

40jchkBold.addActionListener(new ActionListener() {

JFrame

ButtonDemo

CheckBoxDemo

create frame

create UI

register listener

register listener

17.4 Radio Buttons

Radio buttons, also known as option buttons, enable you to choose a single item from a group of choices. In appearance radio buttons resemble check boxes, but check boxes display a square that is either checked or blank, whereas radio buttons display a circle that is either filled (if selected) or blank (if not selected).

JRadioButton inherits AbstractButton and provides several constructors to create radio buttons, as shown in Figure 17.13. These constructors are similar to the constructors for

JCheckBox.

Video Note

Use radio buttons