The document discusses the basics of Java applets. It defines applets as small Java programs used in internet computing that are transported over the internet, automatically installed on client machines, and run as part of a web document using a tool called appletviewer. Applets interact with users through AWT instead of console I/O and can be classified as local or remote. Key differences between applets and applications are that applets cannot access local files or run local programs and require an internet connection for remote applets, while applications can do these things and generally do not need an internet connection.

1. 1
Basics of Applet

2. 2
Objective
On completion of this period, you will be able
to learn
• Basics of applet

3. 3
Recap
In the previous classes, we have studied about
• The various I/O streams and classes
• How to write console based Java programs or
applications

4. 4
Basics of Applets
• Applets are small Java programs that are used
in Internet computing
• Applets
• Transported over the Internet
• Automatically installed in client machine
• Run as part of a web document
• Applets can be run using a tool ‘appletviewer’

5. 5
Basics of Applets contd..
• Applets interact with the user through the AWT,
not through the console-based I/O classes
• Clients download applets via Web browser
• Browser runs applet in a Java Virtual Machine
(JVM)

6. 6
Basics of Applets contd..
• Applets can be classified into two types
• Local applets
• Remote applets
• Local applet
• Developed and stored in local system
• No need for internet connection for the local system
• Local directories were searched to locate the
specified applet

7. 7
Basics of Applets contd..
• Remote applet
• Developed by someone else
• Stored on a remote computer connected to the
internet
• Our system needs an internet connection
• The applet is downloaded into our local system via
internet
• Run it on our system

8. 8
Loading of Remote Applet
Internet
Local Computer
(Client)
Remote Computer
(Server)
Remote Applet
Fig. 53.1 Loading of remote applet
Applet

9. 9
Web Browsers Requests Applet
Client
Computer
Fig. 53.2 Request for applet
1. Browser shows web
document
2. Web document contains
an applet tag
3. Web browser identifies
the tag
4. Client computer makes
a request to web
browser via internet
1, 2
Browser showing
web document
Web Server
3
4 4

10. Web Server Transmits Applet along with HTML
7 6 5
10
5. Web server locates the
applet
6. Sends the applet code to
the web browser
7. Through internet it is
downloaded to client
8. Applet is executed
4 4
Fig. 53.3 Applet downloading
3
1, 2
Browser showing
web document
Client
Computer
5
8
HTML, applets etc

11. 11
Some Points About Applets
• Applets do not use main() method
• They run in a browser
• They cannot read or write the files from the
local system
• Applets cannot run any other program from the
local computer

12. Some Points About Applets contd..
• Applets are restricted from using libraries from
other languages such as C or C++
• They cannot communicate with other servers
on the local network
12

13. 13
Discussion
• What are the differences between applications and applets ?
main() method
Run stand-alone Possible Not possible
Access local files
Applications Applets
Needed Not needed
Can access
Cannot access
Run local programs Can run Cannot run
Internet connection Needed for Remote
applet
GUI based
Generally not
needed
GUI May or may not

14. 14
Summary
• Java programs are two types
• application
• applet
• Java applications are the console based
programs
• Applets are web enabled internet applications
• Two types of applets
• Local applets
• Remote applets

15. 15
Quiz
1. Applets are console based applications
1. true
2. false

16. 16
Quiz contd..
2. Internet browser runs Java applets
1. true
2. false

17. 17
3. Java applications are web enabled internet
applications
1. true
2. false
Quiz contd..

18. 18
Frequently Asked Questions
• Explain about Java applets
• List the differences between applets
and applications