Download Lecture 2

CS 7: Introduction to
Computer Programming
Java and the Internet
Sections 1.4-1.6,2.1
Review
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What are the 3 control structures?
Project 1 handed out
Overview
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Internet
Java and the Internet
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Applets
Java and GUIs
The Internet
Collections of Computers
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Network
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internet
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Connection of ≥ 2 networks
Internet
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System for connecting ≥ 2 computers so can
share resources
The world-wide connection of computers that are
accessible to the public
IntraNet
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An network set up confined to a particular
organization
Computer Roles
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Client
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Server
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computer / software that gets information from
another computer
Web Browser - client software to get Internet
Resources
computer / software that provides a service to a
client
Protocol
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set of rules defining how two systems
communicate
Application Layer Protocols
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FTP
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HTTP
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File Transfer Protocol
Moving files between computers
HyperText Transfer Protocol
Moving hypertext between computers
HyperText - text documents with links to other
text documents
FTPS, HTTPS, SSH
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Secure communication
What’s the address?
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IP address
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32-bit address to identify computer
Each computer connected has unique IP
Ex: 130.49.222.47
URLs
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Uniform Resource Locator
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address to resource (files or request some
processing be done) from the Internet
http://www.cs.pitt.edu/~hoffmanp/cs7.html
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http
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protocol
www.cs.pitt.edu
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Fully qualified domain name (FQDN) of server machine
Domain name servers (DNS)
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convert FQDN to IP address (130.49.220.23)
~hoffmanp/cs7.html
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Path to resource on the server
Internet vs. WWW
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World Wide Web (WWW) - 2 definitions
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set of resources that can be gotten using
the HTTP protocol
set of HTTP servers ("web servers")
The WWW Works on top of the Internet
Java and the Internet
Java
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Why use Java?
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Portable
Internationalization (Unicode)
Network features
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Many features and libraries promoting networking
Applets can be distributed over Internet
Designed with security in mind
Swing classes make creating GUIs easier, portable
Applets
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Java programs that can be embedded in
HTML to run on your browser
Examples:
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http://www.cse.ucsc.edu/~pohl/JBD/chap8/MiniCa
lcApplet.html
Games
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http://java.sun.com/applets/other/Hangman/index.html
http://www.npac.syr.edu/projects/java/magic/Magic.html
Education
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http://www.dhpc.adelaide.edu.au/projects/vishuman2/
http://www.stat.sc.edu/~west/javahtml/CLT.html
Difference Between Applets
and Applications
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Applets – little applications
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Run under a browser
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No main() method
Security restrictions
Applet Loader
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Applets loaded over the Internet are
loaded by an applet class loader
Uses verifier to check there are no
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Stack overflows / underflows
Invalid register accesses and store
Illegal data conversion
Uses the applet security manager
Untrusted Applets
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Put in a “Sandbox”. Restrictions on
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Files, directories
Programs on your machine
System properties
Connecting to other computers
Windows the applet creates
Trusted Applets
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Trusted applets don’t have these
restrictions
Trusted applets are applets that either:
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Are installed on your machine
Are a signed applet with an identity you
mark as trusted
Graphical User Interface (GUI)
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User-Interface (UI)
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Text-based (DOS)
GUI (Windows XP)
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Windows
Icons
Java has the Swing classes
Working from home
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PuTTY
F-Secure SSH Client
Windows, Mac, UNIX and new lines
Getting Comfortable with
UNIX