Java Reference
In-Depth Information
window.setVisible(true);
}
private static SketchFrame window; // The application window
private static Sketcher theApp; // The application object
}
To run Sketcher as an applet, you should add an
.html
file to the
Sketcher
directory with the contents:
<APPLET CODE="Sketcher.class" WIDTH=300 HEIGHT=200>
</APPLET>
If you recompile the revised version of the
Sketcher
class, you can run it as before, or using
AppletViewer
.
How It Works
The class now extends the class
JApplet
, and an
import
statement has been added for the
javax.swing
package.
The
init()
method now does most of what the method
main()
did before. The method
main()
now
creates an instance of the
Sketcher
class and stores it in the
static
data member
theApp
. The
method
main()
then calls the
init()
method for the new
Sketcher
object. The
window
variable no
longer needs to be declared as
static
since it is always created in the
init()
method.
The class member,
theApp
, must be declared as
static
for the case when the program is run as an
application. When an application starts execution, no
Sketcher
object exists, so the data member,
theApp
, does not exist either. If
theApp
is not declared as
static
, you can only create the
Sketcher
object as a local variable in
main()
.
Even if Sketcher is running as an applet, the application window appears as a detached window from
the
AppletViewer
window, and it is still positioned relative to the screen.
Of course, when we come to implement the
File
menu, it will no longer be legal to derive the
Sketcher
class from the
JApplet
class since it will contravene the rule that an applet must not access
the files on the local machine. It is also not recommended to create frame windows from within an
untrusted applet, so you will get a warning from the
appletviewer
about this.
All you need to do to revert back to just being an application is to remove the
import
statement for
javax.swing
and remove
extends
JApplet
from the
Sketcher
class header line. Everything else
can stay as it is.
