Appletjava

RENUGADEVI.S, MSC.,CS
NADAR SARASWATHI COLLEGE
OF ARTS AND SCINCE. THENI.
applet

What is applet?
 An applet is a java program that can be
embedded into a webpage. It runs inside the
web browser and works at client side.
 An applet is embedded in an HTML page
using the applet or object tag and hosted on a
web server.
 Applet are used to make the website more
dynamic and entertaining.

Important points about
Applet
1. All applets are sub-classes(either directly or
indirectly) of java.applet.Applet class.
2. Applet are not stand-alone programs.
Instead, they run within either a web
browser or an applet viewer. JDK provides a
standard applet viewer tool called applet
viewer.
3. In general, execution of an applet does not
begin at main() method.

4. Output of an applet window is not
performed by System.out.println().
5. Rather with various AWT methods, such as
drawString().

 It is important to understand the order in
which the various methods shown in the
above image are called. When an applet
begins, the following methods are called, in
this sequence:
1.init()
2.start()
3.paint()

 When an applet is terminated, the following
sequence of method calls takes place:
1.stop()
2.destory()
 init()
The init() method is the first method to be
called. Where you should initialize variables.
This method is called only once during the
runtime of applet.

Start(): The start() method is called after
init(). It is also called to restart an applet after
it has been stopped. Note that init() is called
once. i.e.,When the first time an applet is
loaded whereas start() is called each time an
applet’s HTML document is displayed
onscreen. So, if a user leaves a web page and
comes back, the applet resumes execution at
start().

Paint():
The paint() method is called each time an
AWT-based applet’s output must be redrawn.
This situation can occur for several reasons.
For example, the window in which the applet
is running may be overwritten by another
window and then uncovered. ORThe applet
window may be minimized and then
restored.

 Paint() is also called when the applet
begins execution. Whatever the cause,
whenever the applet must redraw its output,
paint() is called.
 paint() method has one parameter of
type Graphics. This parameter will contain
the graphics context, which describes the
graphics environment in which the applet is
running.

Stop():
The stop() method is called when a web
browser leaves the HTML document
containing the applet-when it goes to
another page, example: When stop() is
called, the applet is probably running. Use
stop() to suspend threads that don’t need to
run when the applet is not visible. Restart
them when start() is called if the user returns
to the page.

destroy():
The destroy() method is called when
the environment determines that applet
needs to be removed completely from
memory. At this point , should free up any
resources the applet may be using. The
stop() method is always called before
destroy().

CREATING AN EXECUTABLE
APPLET
 Executable applet is nothing but the .class file
of the applet, which is obtained by compiling
the source code of the applet. Compiling an
applet is exactly the same as compiling an
application. Therefore, we can use the

The Applet class
 Every applet is an extension of the
java.applet.Applet class. The base Applet
class provides methods that a derived Applet
class may call to obtain information and
services from the browser context.
 These include methods that do the following-
 Get applet parameters
 Get the network location of the HTML file
that contains the applet.

 Get the network location of the applet class
directory.
 Print a status message in the browser
 Fetch an image
 Fetch an audio clip
 Play an audio clip
 Resize the applet

 Additionally, the Applet class provides an
interface by which the viewer or browser
obtains information about the applet and
controls the applet’s execution. The viewer
may-
 Request information about the author,
version, and copyright of the applet.
 Request a description of the parameters the
applet recognizes.

 Initialize the applet
 Destroy the applet
 Start the applet’s execution
 Stop the applet’s execution
The Applet class provides default
implementations of each of these methods.
Those implementations may be overridden as
necessary.

Invoking an Applet
 An applet may be invoked by embedding
directives in an HTML file and viewing the file
through an applet viewer or java enabled
browser.
 The <applet> tag is the basis for embedding
an applet in an HTML file.

Example program
 Draw smiley in applet window using java applet class
method.
Import java.applet.Applet;
Import java.awt.*;
Public class smileyexe extendsApplet{
Public void paint(Graphics g){
g.Set color(color,yellow);
g.filloval(20,20,150,150);
g.Set color(color,black);
g.filloval(50,60,15,25);
g.Set color(color,black);
g.filloval(120,60,15,25);
Int x[ ]={95,85,106,95};
Int y[ ]={85,104,104,85};
g.drawpolygon(x,y,4);
g.DrawArc(55,95,78,50,0,-180);

g.drawLine(50,126,60,116);
g.drawLine(128,115,139,126);
}
}
/* <appletcode=“smiley class” width=“200” height=“200”>
</applet>
*/

Appletjava

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