Java Reference
In-Depth Information
Our next example introduces a framework for building GUI applications. Several concepts
in this framework will appear in many of our GUI applications. This is our first example
in which the application appears in its own window. Most windows you'll create that can
contain Swing GUI components are instances of class
JFrame
or a subclass of
JFrame
.
JFrame
is an
indirect
subclass of class
java.awt.Window
that provides the basic attributes
and behaviors of a window—a
title bar
at the top, and
buttons
to
minimize
,
maximize
and
close
the window. Since an application's GUI is typically specific to the application, most
of our examples will consist of
two
classes—a subclass of
JFrame
that helps us demonstrate
new GUI concepts and an application class in which
main
creates and displays the appli-
cation's primary window.
Labeling GUI Components
A typical GUI consists of many components. GUI designers often provide text stating the
purpose of each. Such text is known as a
label
and is created with a
JLabel
—a subclass of
JComponent
. A
JLabel
displays read-only text, an image, or both text and an image. Ap-
plications rarely change a label's contents after creating it.
Look-and-Feel Observation 12.6
Text in a
JLabel
normally uses sentence-style capitalization.
The application of Figs. 12.6-12.7 demonstrates several
JLabel
features and presents
the framework we use in most of our GUI examples. We did
not
highlight the code in this
example, since most of it is new. [
Note:
There are many more features for each GUI com-
ponent than we can cover in our examples. To learn the complete details of each GUI
component, visit its page in the online documentation. For class
JLabel
, visit
docs.oracle.com/javase/7/docs/api/javax/swing/JLabel.html
.]
1
// Fig. 12.6: LabelFrame.java
2
// JLabels with text and icons.
3
import
java.awt.FlowLayout;
// specifies how components are arranged
4
import
javax.swing.JFrame;
// provides basic window features
5
import
javax.swing.JLabel;
// displays text and images
6
import
javax.swing.SwingConstants;
// common constants used with Swing
7
import
javax.swing.Icon;
// interface used to manipulate images
8
import
javax.swing.ImageIcon;
// loads images
9
10
public
class
LabelFrame
extends
JFrame
11
{
12
private final
JLabel label1;
// JLabel with just text
13
private final
JLabel label2;
// JLabel constructed with text and icon
14
private final
JLabel label3;
// JLabel with added text and icon
15
16
// LabelFrame constructor adds JLabels to JFrame
17
public
LabelFrame()
18
{
Fig. 12.6
|
JLabels
with text and icons. (Part 1 of 2.)
