Java Reference
In-Depth Information
Example 10•20: ComponentTree.java (continued)
" height: " + c.getHeight());
}
else {
msgline.setText("component is not showing");
}
}
});
// Now that we've set up the tree, add it to the scrollpane
scrollpane.setViewportView(tree);
// Finally, set the size of the main window, and pop it up.
frame.setSize(600, 400);
frame.setVisible(true);
}
}
A Simple Web Browser
The two previous examples have shown us the powerful
JTable
and
JTree
com-
ponents. A third powerful Swing component is
javax.swing.text.JTextComponent
and its various subclasses, which include
JTextField
,
JTextArea
, and
JEditor-
Pane
.
JEditorPane
is a particularly interesting component that makes it easy to dis-
play (or edit) HTML text.
As an aside, it is worth noting here that you do not have to create a
JEditorPane
to display static HTML text. In Java 1.2.2 and later, the
JLabel
,
JButton
, and other
similar components can all display multiline, multifont formatted HTML labels. The
trick is to begin the label with the string “<html>”. This tells the component to
treat the rest of the label string as formatted HTML text and display it (using an
internal
JTextComponent
) in that way. You can experiment with the feature using
the
ShowComponent
program; use it to create a
JButton
component and set the
text
property to a value that begins with “<html>”.
Example 10-21 is a listing of
WebBr owser.java
,a
JFrame
subclass that implements
the simple web browser shown in Figure 10-17. The
WebBrowser
class uses the
power of the
java.net.URL
class to download HTML documents from the Web
and the
JEditorPane
component to display the contents of those documents.
Although defined as a reusable component, the
WebBrowser
class includes a
main()
method so that it can be run as a standalone application.
Example 10-21 is intended as a demonstration of the power of the
JEditorPane
component. The truth is, however, that using
JEditorPane
is quite trivial: simply
pass a URL to the
setPage()
method or a string of HTML text to the
setText()
method. So, when you study the code for this example, don't focus too much on
the
JEditorPane
. You should instead look at
WebBrowser
as an example of pulling
together many Swing components and programming techniques to create a fairly
substantial GUI. Points of interest include the enabling and disabling of
Action
objects and the use of the
JFileChooser
component. The example also uses a
JLabel
as an application message line, with a
javax.swing.Timer
that performs a
simple text-based animation in that message line.
