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Java
E-Commerce
Prof. Sheizaf Rafaeli
1
What is Java?
A fundamentally new way of computing,
based on the power of networks
Write once -- run anywhere
– 450 million vs. 120 million?
With Java technology, you can use the same application on
any kind of machine -- a PC, a Macintosh computer, a
network computer, a Ford car or a Krups coffee pot, or
even new technologies like Internet screen phones.
E-Commerce: Java intro: Prof. Rafaeli
2
Java Hype
Java could surpass Windows as the
software platform with the world's
largest base by the turn of the
century.
"All of you who have anything to do
with software development ignore JAVA
at your own peril"
" JAVA - TODAY THE WEB,
TOMMOROW THE WORLD!!"
E-Commerce: Java intro: Prof. Rafaeli
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“Thin clients”
Computers designed to be centrally-managed
Configured with only essential equipment
No CD-ROM, disk drives or expansion slots
Therefore lower in cost, esp.
Cost-Of-Ownership.
Net PC (Intel and Windows)
NC (Oracle and Sun)
Web TV
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Client systems range from dumb terminals to mostly autonomous PCs.
Thin clients fall in between.
(Source: Byte Magazine)
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Why is Java important?
With Java technology, the Internet and
private networks become your computing
environment.
Remote computing, thin clients, distributed
control and access
Java animates the Web, makes it interactive,
distributes content and power, and
transforms the internet and information
systems.
6
E-Commerce: Java intro: Prof. Rafaeli
How it works
(in a web browser)
References to java software
(applets) are embedded in HTML
The Java virtual machine first does stringent
security checks, and then runs the applet, which
appears and interoperates inside the browser.
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7
Java’s Secret:
the Virtual Machine (VM)
Virtual Machine: a layer of software just above the CPU that
emulates a theoretical ("virtual") chip's behavior.
It hides--or Abstracts--the machine-level stuff into a single layer of
software.
The Java Virtual Machine, when properly implemented, allows a
Java application to run on the CPU for which the VM is written,
regardless of the type of system on which the Java programmers
worked.
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How it works (2)
(in a web browser)
The computer's operating system
provides machine-specific support for
many of the actual operations and
interactions.
Result: The user gets an interactive Java
applet running in a browser. The Java virtual
machine serves as consistent platform on
different kinds of computers and operating
systems, so that the same Java applet runs in
browsers on PCs, Macs, UNIX, PDAs,
workstations, Network Computers, and
elsewhere.
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How it works (3)
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Java’s Promises
Simple
– like and unlike C, C++
– no implementationdependent aspects
Object Oriented
Distributed
Robust
– no pointers
Dynamic
– adaptable
High Performance
– could be better
– still hybrid
compile/interpret
– careful at handling
data types
Secure
Portable, small
Multithreaded
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Java’s Perils
A native OS might offer features that Java can't use
without sacrificing cross-platform compatibility.
Interpreted Java byte-code doesn't run as fast as
complied native code.
If a program must interact with legacy code or data, a
more established tool or language might work better.
A developer may have superior tools for another
language or may be more productive using a familiar
tool or language.
A developer may not want to change, even if it costs
money and customers.
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12
Java is not JavaScript
Java is a full-fledged objectoriented programming
language. Hybrid JIT
compilation to byte code.
can be used to create standalone
applications
Both client and server side, and
used much in stand-alone
embedded environments.
Interpreted, does not create
applets or standalone
applications
Mostly client side, but some
server software, (Netscape's
SuiteSpot), lets developers
write CGI programs in a serverside version of JavaScript.
Owned by Netscape
Owned by Sun
A Java-enabled browser is not automatically a JavaScript-enabled browser:
they require entirely separate interpreters (licensed from separate companies)
Rather than competing with each other, Java and JavaScript are a
powerful combination. E-Commerce: Java intro: Prof. Rafaeli
13
Applets
Applets vs. applications
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Anatomy of an Applet
Reference
<applet code=Filename.class
height=number
width=number
codebase=Directory_containing_applet
align=setting hspace=number vspace=number
name=string>
<param name=name1 value=value1>
<param name=name2 value=value2>
<!-- Define alternate content, for non-Java browsers -->
<H2>Imagine an impressive Java applet
here</H2>
</applet>
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Example
<applet code=ScrollingNeonMessage.class
height=200 width=400 codebase=applets>
<param name=MessageText
value="Bookmark this page!">
<param name=ScrollSpeed value=10>
<H2>Bookmark This Page!</H2>
</applet>
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Java applet restrictions
Not too fast!
Byte code, not
compiled
No (or limited) access
to files
Applets have no
memory-- they are
stateless (however
secure servers allow
bypass)
Limitations on number
of sockets open
(connections)
How much of a
closely held property
of and by Sun
Microsystems?
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Microsoft vs. Sun?
Scott McNealy vs. Bill Gates?
Sun thinks (hopes?)
that Java will be an
alternative to Windows
Microsoft thinks otherwise…
Others now in the game
http://www.javasoft.com/lawsuit/index.html
Source: Fortune Magazine
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Microsoft vs. Sun (2)
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How, where, by whom is Java
used?
Check
out Sun’s report, at
http://www.javasoft.com/nav/used/
See
JARS and GAMELAN
C & L experiment with office
Wordperfect office suite?
Net-It
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How, where, by whom is Java
used? (2)
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Embedding an applet on your
page
You can find the applet.class files in your
browser's on-disk cache and copy them
To be used locally
Or on your own server
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Embedding a remote applet on
your page
<APPLET CODE=“Clock2.class”
Width=170 Height=150
CODEBASE=“http://mis.huji.ac.il/ttt/”>
</APPLET>
Try the applet on
– http://mis.huji.ac.il/ttt/java.lecture.html
– and on
http://wwwpersonal.umich.edu/~sheizaf/tryjava.html
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How to enable/disable Java
Netscape 3.0
Go to "Options | Network Preferences..."
from the main menu
Change to the "Languages" tab To enable:
make sure "Enable Java" check box is
checked
To disable: make sure "Enable Java" check
box is unchecked
Restart the browser
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How to enable/disable Java
Netscape 4.x (Communicator)
Go to "Edit | Preferences..." from the main
menu
Select "Advanced" panel To enable: make
sure "Enable Java" check box is checked.
To disable: make sure "Enable Java" check
box is unchecked. Restart the browser
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How to enable/disable Java
Explorer
Go to "View | Options..." from the main menu
Change to the "Security" tab
To enable: make sure "Enable
Java
programs" check box is checked
To disable: make sure "Enable
Java
programs" check box is unchecked
Restart the browser
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How to enable/disable Java
Explorer 4.x and 5.x
Go to "View | Internet Options..." Change to
the "Security" tab
Select "Custom" and click on the
"Settings..." button
To enable: make sure "Disable
Java" is
selected under "Java."
To disable: make sure a setting other than
"Disable Java" is selected under "Java." If
you're not sure which setting to choose, select
"High
safety"
E-Commerce: Java intro: Prof. Rafaeli
Restart the browser
27
Sample IDE for Java online
Try
the online Java Web IDE at:
* http://www.chami.com/webide/
IBM’s
“Visual Age for java”
Check out Symantec’s “Café”, Visual Café
Pro.
Borland, Microsoft’s Visual J, Lotus
Sybase PowerJ • Metrowerks
CodeWarrior • Inprise Jbuilder •
Supercede for Java
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Java & Security?
Java’s “sandbox” security model
Active-X “trust” model
In any case,
safe network computing is an oxymoron
Orange Juice works better
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The 10 Java Buzzwords
Java Virtual Machine
HotJava,
Appletviewer, javac,.
“Servlets”
JDK, Java
Development kit
JAR, zip, & Java
Beans
“Sandbox” vs. “Trust”
security models
AWT, Abstract
Window Toolkit
ByteCode
JIT Compiling
.class, .java (source
and bytecode)
JDBC, Java Database
Connectivity ODBC in
Java
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Java Glossary
and cheatsheets
http://www.mindprod.com/gloss.html
http://www.freewarejava.com/
http://metalab.unc.edu/javafaq/javatutorial.h
tml
http://www.javacoffeebreak.com/
http://java.sun.com/docs/books/tutorial/
http://www.mercury.com/javatutor/session01/session01.html
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The “Java backlash”
“It
still does nothing” (?)
Does the world really need programmable toasters?
How
long does it take to develop, load, run?
Will Microsoft succeed in busting the
“platform agnostic” monopoly buster?
Animation, interaction and dynamic content
easier to achieve with DHTML
Is it truly slow, secure, portable?
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Is Java taking root?
In
the browser
On the server (servlets)
As commercial applications
In the arena of enterprise applications
In teaching institutions
For some bubble bursting and iconoclasm, see:
http://www.disordered.org
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A few more, and URLs
Gamelan, JARS, Developer
http://java.sun.com
Best Java tutorial at:
http://www.phrantic.com/scoop/onjava.html
IBM’s introduction to java, at:
http://www.javaworld.com
http://www.ibm.com/java/education/intro/courseoptions.htm/
“Java in five minutes”
http://www.zdnet.com/products/garage/java/applet/
Java in the future:
Windows, or OS/2 and hypercard?
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