Transcript Powerpoint of lecture 1 - Information Services and Technology

George Blank
University Lecturer
CS 602
Java and the Web
Object Oriented Software Development
Using Java
Chapter 1
Objectives for the Course
• Be able to program in Java
• Be able to use professional development tools
including the Eclipse IDE, Javadocs, JUnit, Use
Cases and Unified Modeling Language.
• Be able to share your code over a network using
Applets, Servlets, Java Server Pages, Java Network
Launch Protocol and Web Start, and by configuring a
server to allow others to run code.
Additional Emphasis
• This course will prepare students to work in a
corporate environment, and will therefore
require advance planning before creating
programs, use of an interactive development
environment, formal unit testing, and keeping
records of time spent on development. The
instructor was a software development
manager in Bell Labs.
Textbook is primary
• The lecture materials are supplemental to the
text. Every student is expected to read and
be thoroughly familiar with the materials in
the text.
• There will also be supplemental lectures,
often developed for other courses, and
sometimes by students, covering topics
referenced in the course.
Web Documentation
• A primary reference source for Java programming is
the Oracle web site at http://java.com . Students will
be expected to develop skill at using the materials on
this site to support their programming.
• Also critical for NJIT students are the materials at
http://ist.njit.edu The left side of that Web page
contains a menu with a guide to using many of the
technologies used in this course.
Technical support
• Technical support is primarily offered by student to student
help on Moodle. I monitor the technical support conference,
and often offer suggestions. I do believe in limiting help for the
following reason.
• A student wrote; “My project doesn't work yet. For a job
interview, I'd like to get it working and show it as an
application I created using java/Unix/Oracle.” What if this
student could only do the project with extensive help, then got
the job and could not perform the work?
Acceptable help
• Identifying to a student where the problem is or
what they are doing wrong.
• Pointing a student to an example that works, but
needs to be modified for the student to use it.
• Unacceptable: Showing the student exactly what
to do.
• Even worse: Doing it for the student.
Exceptions
• Most rules need exceptions. It is reasonable to
give a student precise help or even write the
code for them if the problem is very small (such
as a single line of defective code) or exact
precision is needed (such as the correct JDBC
string to connect to a database.)
Software Delivery Options
• The next few slides give a brief description of the
software delivery options that will be covered in this
course:
• Sharing applications on a server
• Applets
• Java Network Launch Protocol and Java Web Start
• Java Server Pages
• Java Servlets
Sharing Applications on a
Server.
• Students can give permissions to others, including
the instructor, to access Java code and run their
application on one of the University servers running
Solaris or Linux. To set up your file permissions to
do this, see the instructions at http://ist.njit.edu The
left side of that Web page contains a menu with the
top level topic AFS and sub-topic of Sharing Files.
Applets
• An applet is Java code that inherits from the
classes Applet or JApplet and runs on a Web
server such as the Apache Web servers on
web.njit.edu and harp.njit.edu.
• Typically, for this course you would put your
applet code in a sub-directory of your home
page and post a link to it at a specific
homework assignment in Moodle.
JNLP and Web Start
• The Java Network Launch Protocol, in
combination with Java Web Start, is a
browser independent way of sharing a Java
application (not applet) over a network and
running it on a client machine.
• There is a separate lecture in this course on
JNLP.
What if I cannot convert to an
Applet or JNLP?
• In the past, I have strongly encouraged students to
do all assignments as applets, even if the textbook
called for an application. I now believe that is a
serious mistake. You must use an applet or JNLP
to get an A, but only the top quarter of the class is
eligible for an A anyway. If you have trouble, you
are probably not in the top quarter, and would
might be better off just doing it as an application
and getting a B.
• Note: If you do an application that I cannot run from
your Web site, you must post screen shots to prove
that your program works!
Java Server Pages
• JSP allows you to embed Java Code along with
HTML in a Web page and display it in a client
browser. Just as you need a Web server like Apache
to service applets, you need a Java Web Container
like Tomcat to service JSP. This is a really simple
technology, but the amount of code on a single page
is usually quite limited, and JSP applications typically
have many pages.
Java Servlets
• Servlets are Java Programs that inherit from
HTTPServlet. They are similar to applets, except that
they are run from a Java container like Tomcat instead
of a Web Server like Apache.
• On the NJIT system, due to the large number of students
independently using Tomcat, servlets must be in a
directory called servlet or subdirectory of such a
directory. Tomcat identifies a servlet by detecting that
term in the URL that it is providing. That approach is
generally discouraged in commercial use.
Software Disasters
Why we need quality software
January 15, 1990
• I had just started work at AT&T when a software
problem brought down the entire national network of
the then-dominant (and no longer existing)
telecommunications company. It was a profoundly
disturbing episode that was very traumatic and
embarrassing for the company. The following pages
detail some other programming disasters.
False Attack Warning
• With large numbers of medical devices and
transportation systems controlled by software,
defects have been fatal.
• On June 3, 1980, the North American
Aerospace Defense Command (NORAD)
reported that the U.S. was under missile
attack. The report was traced to a faulty
computer circuit that generated incorrect
signals.
Civilian Aircraft Shot Down
• The 1988 shooting down of the Iranian Airbus
300 Flight 665. by the US Vincennes was
attributed to the cryptic and misleading output
displayed by the tracking software. It seems
that the Aegis system had passed only two
tests prior to being sent into combat in the
Middle East.
Iran Airbus (continued)
• In the first test, the $500 million Aegis radar and
weapons control system was set up near Exit 4 of
the New Jersey Turnpike where it merely watched
the local general aviation traffic. It's first "active"
test involved the shooting down of 10 out of 11
drones, all on courses and altitudes known in
advance to the system operators.
USS Rancocas,
The Cornfield Cruiser
Visible from I-285 in Moorestown NJ. This
is where the Navy did the development on
the Aegis Guided Missile Cruisers.
Iran Airbus (continued)
• Deployed in the Persian Gulf in 1988, The Aegis
radar on the U.S.S. Vincennes locked onto an
Airbus 300, but misidentified it as the much smaller
F-14. The Aegis also reported that the target was
descending even though the airbus was, in fact,
climbing, and finally, the Aegis erred on the altitude
by 4000 feet.
Iran Airbus (continued)
• The combination of all these errors presented by
the Aegis system convinced the Captain that his
ship was under attack, and the Airbus was shot
down.
• 290 People were killed.
Falkland War Incident
• The British destroyer H.M.S. Sheffield was
sunk in the Falkland Islands war. According to
one report, the ship's radar warning systems
were programmed to identify the Exocet
missile as "friendly" because the British
arsenal includes the Exocet's homing device
and allowed the missile to reach its target,
namely the Sheffield.
Medical Radiation Accident
A series of accidental radiation overdoses from
identical cancer therapy machines in Texas and
Georgia left one person dead and two others
with deep burns and partial paralysis, according
to federal investigators. Evidently caused by a
flaw in the computer program controlling the
highly automated devices, the overdoses unreported until now - are believed to be the
worst medical radiation accidents to date.
Radiation (continued)
The malfunctions occurred once in 1985 and
twice in March and April of 1986 in two of the
Canadian-built linear accelerators, sold under
the name Therac 25. Two patients were injured,
one who died three weeks later, at the East
Texas Cancer Center in Tyler, Texas, and
another at the Kennestone Regional Oncology
Center in Marietta, Ga.
Richard Saltos, The Boston Globe, June 20, 1986, p. 1
Radiation (continued)
The defect in the machines was a "bug" so
subtle, say those familiar with the cases, that
although the accident occurred in June 1985, the
problem remained a mystery until the third, most
serious accident occurred on April 11, 1986.
Estimates are that the patients received 17,000
to 25,000 rads to very small body areas. Doses
of 1,000 rads can be fatal if delivered to the
whole body.
Computer Instigated Murder
In 1982, a computer error in West Germany caused a
medical insurer to convince a 54-year old woman that she
suffered from a fatal form of syphilis, and that she had
transmitted the disease to her children; in panic, she
strangled her 15-year old daughter and tried to kill her 13year old son. The boy escaped, and succeeded in
preventing his mother's death from a drugs overdose. The
Duesseldorf court dismissed the accusation of murder, laid
all blame with the computer error, and declared the woman
unaccountable for her actions.
Responses to complexity
• Many errors in software systems are caused
by complexity that is difficult for humans to
manage. The object-oriented approach was
developed to manage complexity by dividing
a system into relatively small objects with well
defined interfaces.
Iterative Development
• Iterative development is another approach to
manage complexity. A large system is built in
several iterations, and each is tested rather
than developing the whole system and
attempting to test everything at once. The
Rational Unified Process is one of the most
widely used iterative processes.
Bibliography
• Jia, Xiaoping, Object Oriented Software
Development Using Java. Addison Wesley,
2003