This document discusses the basics of Java applets. It explains that applets are small Java programs used in web pages that are automatically downloaded and run in a web browser. Applets interact with the user through AWT instead of console I/O. Applets can be local or remote, with remote applets requiring an internet connection to download from a server. The document contrasts applets and applications, noting that applets do not use main() and cannot access local files or programs.

1. Basics of Applet
1

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

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
3

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’
4

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)
5

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
6

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
7

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

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

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

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
11

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

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
14

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

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

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

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