Java applets

SSBN Degree College, ATP M Vishnuvardhan
Java Applets
-M Vishnuvardhan,
Dept. of Computer Science,
SSBN Degree College, ATP

» Java programs are divided into two main
categories, applets and applications
» An application is an ordinary Java program
» An applet is a kind of Java program that can
be run across the Internet
Applets: Introduction

» Applets are mainly used convert a static web
page to dynamic page
» Web is created with the help of Hypertext
markup language (HTML).
» Web site is collection of webpages of a
particular organization.
» A browser is a software which is used to browse
the internet ie., used to view web pages
Applets: Introduction

» Applets do not use main() method
» Applets needs html code to run
» Applets are run by Java enabled
web browser.
» Applets are by default GUI Apps.
Applets vs. Applications

» To deal with applets in java a special class is
defined in java.applet package called as
Applet.
» Applet class contains five special methods
init() :- used for initialization of applet
start() :- used to start an applet
paint() :- used to paint the contents of the
applet on the window
stop() :- used to stop an applet
destroy() :- used to destroy an applet
»Applet methods are automatically called one
after another once they are loaded into web
browser
Applet Class

In order to create an applet the following steps
are to be followed
»Create a class by extending applet class
»Override any one of the applet class method
»Compile the program to obtain the class file
»Create a html document and embed the applet
»Run the applet along with the html page in
java enabled web browser
Creation of Applets

// Sample Applet program
import java.awt.*;
import java.applet.*;
public class DemoApp extends Applet
{
public void paint(Graphics g)
{
g.drawString(“Java applets”, 50,50);
}
}
Note:- After compiling the program embed the applet in a
html file and open in java enabled web browser.
Creation of Applets

Html is a language used to design a web page
Basic structure of html file is
<html>
<! ------Comment Section ---- >
<head> <title> title of the page </title>
</head>
<body>
Body of the web page
</body>
</html>
HTML

Commonly used html tags
<b> … </b>
<i> … </i>
<u> … </u>
<h1> .. </h1> to <h7> … </h7>
<applet> …. </applet>
HTML

An Applet is embedded in a html file using
<applet> tag. Applet tag contains three main
attributes
Code :- specifies the class name of applet
Height :- specifies the height of the applet
Width :- specifies the width of the applet
Alignment :- specifies the alignment of applet
Hspace :- specifies the horizontal and
Vspace :- vertical space around the applet
EG:-
<applet code=“Demo” width=“300” height=“300”>
</applet>
Embedding an applet in html file

Applet life cycle contains four necessary states
1. Born or Initialization state
2. Running State
3. Idle state
4. Dead state
In this four states applet class five methods are
executed on after another.
Applet Life Cycle

Applet Life Cycle
Born
Running Idle
Dead
start()
stop()
destroy()
start()
paint()
Loading of
applet
Exit of
browser

It is possible to pass data from a html page to
applet program. This can be done with the
help of <PARAM> tag in html
<APPLET .. . .. . .>
<PARAM name=“ ..” value=”…”/>
</APPLET>
Here the name corresponds the name of the
parameter and value associates the value of
the parameter
Passing parameters to Applet

The parameters from the <PARAM> tag can be
read in the applet program with the help of
following method
String getParameter(String name):
returns the value associated with the
specified parameter.
Passing parameters to Applet

Questions

Java applets

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