An applet is a small Java program that can run in a web browser. It is embedded in an HTML page and downloaded from a server to run on a client computer. Applets have a lifecycle of initialization, startup, running, idle, and destruction. They allow for interactive graphics and animations to be added to webpages but have security restrictions around accessing files and making network connections.

1. APPLET
By
M. Sri Nandhini

2. Introduction
 Applet is small java program that can be
easily transported over the network from
one computer to other.
 Used in internet applications.
 Embedded in an html page, can be
downloaded from the server and run on the
client, so as to do a specific kind of job.
 An applet is a program that runs in the
context of a browser session.

3. Applets, Webpage,
Client, Server
 Applets are programs stored on a web
server, similar to web pages.
 When an applet is referred to in a web page
that has been fetched and processed by a
browser, the browser generates a request
to fetch the applet program, the executes
the program in the browser’s execution
context on the client host.

4. Types of java programs
 Stand Alone Program
 Run on a single machine
 Compiler-javac
 Interpreter-java
 Web Based Program
 Compiler-javac
 Interpreter-applet viewer or web browser
 Must Subclass of Applet
 Import java.awt

5. Application vs Applet
Java Applications
• Stand-alone program
• Runs independently
• Has a main() method
• No HTML file
• Run using JDK’s
java interpreter
Java Applet
• Embedded program
• Runs in a Web
browser
• No main() method
• Requires an HTML
file
• Run using JDK’s
applet viewer.

6. Applet Class

7. Applet Example
import java.applet.*;
import java.awt.*;
public class FirstApplet extends applet{
public void paint(Graphics g)
{
g.drawString(“Hello World”,10,50);
}
}

8. Output

9. Applet Life Cycle
 An applet may move from one state to
another dependent upon a set of default
behaviours inherited in the form of methods
from ‘Applet’ class.
 These states are
 Born
 Running
 Idle
 Dead

10. Applet state diagram

11. Life Cycle of Applet
 Init()-
 Creates the objects needed by the applet
 Sets up initial values, load font and images or
set up colors.
 Called only once during the lifetime of an
applet.
 Start()-
 Moves to this phase automatically after the
initialization state.
 If the applet is stopped or it goes to idle state
start() method must be called in order to force
the applet again to the running state.

12. Life Cycle of Applet
Paint()-
 This method is called each time to draw
and redraw the output of an applet.
Stop()-
 Idle state, once it is stopped from
running.
 Destroy()-
 An applet goes to dead state when it is
destroyed by invoking the destroy() of
applet class.
 It results in complete removal of applet
from the memory.

13. Common Methods
 drawString()-
 Member of graphics class used to output a
string to an applet.
 It is typically called from within the paint() or
update() method.
 Void drawString(String msg,int a, int b).
 setBackground() & getBackground()-
 Belongs to component class used to set
and get the background color.
 Void setBackground(Color anyColor)

14. Common Methods
 Predefined constants for each color such as
Color.red can be used.
 setForeground()& getForeground()-
 Set and gets the color of the text to be
displayed on the foreground of the applet
window.
 Void setForeground(Color anyColor)
 showStatus()-
 Display any string In the status window of
the browser.
 Void showString(Stringtext).

15. Applet Execution
 An applet program is a written as a
subclass of the java. Applet class or the
javax.swing.Japplet class. There is no main
method: you must override the start
method. Applet objects uses AWT for
graphics. Japplet uses SWING.
 It is a graphics object that runs in a thread
object, so every applet can perform
graphics, and runs in parallel to the browser
process.

16. Applet Execution
When the applet is loaded,these methods are
automatically invoked in order:
 The init() method is invoked by the Java
Virtual Machine.
 The start() method.
 The paint()method.
 The applet is now running and rendered on
the web page.

17. Applet Security
For security reasons, applets that are loaded
over the network have several restrictions.
 An applet cannot ordinarily read or write
files on the computer that its executing on.
 An applet cannot make network
 connections except to the host that it came
from.

18. Summary
 An applet is a java class.
 Its code is downloaded from a web server.
 It is run in the browser’s environment on the
client host.
 It is invoked by a browser when it scans a
web page and encounters a class specified
with the APPLET tag. For security reason ,
the execution of an applet is normally
subject to restrictions:

19.  Applet cannot access files in the file system
on the client host.
 Applet cannot make network connection
exception to the server host from which it
originated.