Java Reference
In-Depth Information
}
}
Note that there are four methods in the
MyApplet
class. All four methods override
methods from the
JApplet
class. The
init
method is the first method that is called. Its
job is to initialize the local variables, get data from the user, and display different GUI
components.
The same applet can be started and stopped multiple times. Every time the applet
starts, the
start
method is called. The
start
method is initially called immediately after
the
init
method. The
start
method will also be called if the web browser decides to restart
the applet. For example, consider a resource-intensive applet that displays 3D animation.
If the user navigates away from the applet's web page, then the web browser will stop the
applet. At this point, the
stop
method will be called. If the user navigates back to the web
page, then the
start
method will be called. In this case, the job of the
start
method will
be to resume the animation, while the job of the
stop
method will be to stop the animation.
Note that the
stop
method is also called just before the applet is terminated (e.g., the user
closes the web browser). The
destroy
method is called just before the applet is terminated
by the web browser.
Consider the above program. It creates a panel and adds it to the applet. The
paintComponent
method of the panel displays the current value of
i
and the last method
that is called. Note that the value of
i
starts at 0 and is incremented by 1 every time one
of the four methods is called. As expected, our applet application does not have a
main
method, methods that make the applet window visible, or methods that set the title or
size of the applet. All these parameters are specified from the HTML file. In NetBeans, one
can just select the applet file, right-click on it, and run it. NetBeans will emulate a web
browser and start the applet. NetBeans also automatically creates a
.html
file in the
build
subdirectory of the project. We can launch this file from a web browser to see the look and
feel of our applet in different web browsers.
15.3 Creating Popup Windows
One may get the impression that a Java Applet is stuck inside a web browser. That
is, we cannot create our own windows, set their size, and so on. This is not the case. The
following code demonstrates how we can incorporate our Calculator program inside a web
browser. The applet launches the Calculator program in a new window.
import
java .awt. event .
∗
;
import
javax . swing .
∗
;
public class
MyApplet
extends
JApplet
{
public void
init()
{
JButton calcButton =
new
JButton(
"Calculator"
);
final
JFrame frame =
new
JFrame () ;
frame. setTitle(
"Calculator"
);
frame. setSize (200,200) ;
frame .add(
new
CalculatorPanel ()) ;
calcButton . addActionListener(
new
ActionListener ()
{
public void
actionPerformed(ActionEvent e)
{
frame. setVisible (!frame. isVisible());
}}
);