GUI BASICS - Introduction to Java Programming - page 473

To group radio buttons, you need to create an instance of java.swing.ButtonGroup
and use the add method to add them to it, as follows:

ButtonGroup group = new ButtonGroup();
group.add(jrb1);
group.add(jrb2);

This code creates a radio-button group for the radio buttons jrb1 and jrb2 so that they are
selected mutually exclusively. Without grouping, jrb1 and jrb2 would be independent.

Note
ButtonGroup is not a subclass of java.awt.Component , so a ButtonGroup
object cannot be added to a container.
To see if a radio button is selected, use the isSelected() method.

GUI helper class

12.32

How do you create a radio button? How do you create a radio button with the button
selected initially? How do you group radio buttons together? How do you determine
whether a radio button is selected?

✓ ✓

Check

Point

12.14 Labels
To create a label, use the JLabel class.

Key
Point

A label is a display area for a short text, an image, or both. It is often used to label other
components (usually text fields). Figure 12.24 lists the constructors and methods in the
JLabel class.

javax.swing.JComponent

The get and set methods for these data fields are provided
in the class, but omitted in the UML diagram for brevity.

javax.swing.JLabel
-text: String
-icon: javax.swing.Icon
-horizontalAlignment: int
-horizontalTextPosition: int
-verticalAlignment: int
-verticalTextPosition: int
-iconTextGap: int
+JLabel()
+JLabel(icon: javax.swing.Icon)
+JLabel(icon: Icon, hAlignment: int)
+JLabel(text: String)
+JLabel(text: String, icon: Icon,
hAlignment: int)
+JLabel(text: String, hAlignment: int)

The label's text.
The label's image icon.
The horizontal alignment of the text and icon on the label.
The horizontal text position relative to the icon on the label.
The vertical alignment of the text and icon on the label.
The vertical text position relative to the icon on the label.
The gap between the text and the icon on the label.
Creates a default label without any text or icons.
Creates a label with an icon.
Creates a label with an icon and the specified horizontal alignment.
Creates a label with text.
Creates a label with text, an icon, and the specified horizontal alignment.

Creates a label with text and the specified horizontal alignment.

F IGURE 12.24

JLabel displays text or an icon, or both.

JLabel inherits all the properties from JComponent and has many properties similar to the
ones in JButton , such as text , icon , horizontalAlignment , verticalAlignment ,
horizontalTextPosition , verticalTextPosition , and iconTextGap . For example,
the following code displays a label with text and an icon: