Java Reference
In-Depth Information
In the preceding applet, the statement in Line 1 invokes the
paint
method of the
class
JApplet
. Notice that the method
paint
uses a
Graphics
object
g
as the argument.
Recall that the
class
Graphics
is an
abstract
class, and for this reason, you cannot
create an instance of the
class
Graphics
. The system will create a
Graphics
object for
you; you need not be concerned about it. The statement in Line 2 draws the string
"Welcome to Java Programming"
at the coordinate position
(30, 30)
.
Until now, when we created a GUI application program, we used methods such as
setTitle
and
setSize
. As you can see in the preceding applet, such methods are not
used in an applet. Note the following about applets:
The method
setTitle
is not used in applets because applets do not have
titles. An applet is embedded in an HTML document, and the applet
itself does not have a title. The HTML document may have a title, which
is set by the document.
The method
setSize
is not used in applets because the applet's size is
determined in the HTML document, not by the applet. You do not need
to set the size of the applet.
You do not need to invoke the method
setVisible
.
You do not need to close the applet. When the HTML document
containing the applet is closed, the applet is destroyed.
There is no method
main
.
As with an application, you compile an applet and produce a
.class
file. Once the
.class
file is created, you need to place it in a Web page to run the applet. For
example, you can create a file with the
.html
extension, say,
WelcomeApplet.html
,
with the following lines in the same folder where the
WelcomeApplet.class
file
resides:
<HTML>
<HEAD>
<TITLE>WELCOME APPLET</TITLE>
</HEAD>
<BODY>
<OBJECT code = "WelcomeApplet.class" width = "250"
height = "60">
</OBJECT>
</BODY>
</HTML>
Once the HTML file is created, you can run your applet either by opening
WelcomeApplet.html
with a Web browser, or you can enter:
appletviewer WelcomeApplet.html
at a command-line prompt, if you are using the JDK (Java Development Kit).
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