2 fast 2 furious

Top 10 Errors Java Programmers Make

2008-09-11T20:57:00.000-07:00

Here' s the top 10 list of errors that most of the java programmers make,

Accessing non-static member variables from static methods (such as main method)
Mistyping the name of a method when overriding
Comparison assignment ( = rather than == )
Comparing tow objects ( == instead of .equals )
Confusion over passing by value, and passing by reference
Writing blank exception handlers
Forgetting that Java is zero-indexed
Preventing concurrent access to shared variables by threads
Capitalization errors
Null pointers

2008-09-08T01:30:00.000-07:00

Configuring Ring Topology by using industrial automation switches
Most of the automation industries uses switches which intern connected to PLC/IO control etc to automate their work. The switches can be connected in bus/ring/star topologies. Out of these existing topologies ring topology overcome the issues in other topologies.
When devices are connected in ring topology, at anytime if the connection fails the switch has the built-up mechanism to detect the failure link/unreachable switch and it finds the different path to communicate to the switch. This mechanism is called 'Redundancy'.
In general industrial switches comes with Normal, Stand-by, Redundancy manager modes. Network redundancy is important to have if a failure in the communication links can result in disastrous consequences. Different automation vendors optimized the network redundancy through their 'ring redundancy algorithms' by faster recovery time. The recovery time should be as low as possible (not more than a second). Following is the procedure to configure ring topology,

Minimum number of switches required to create ring topology is 2.
Assume there are 3 switches sw-1, sw-2, sw-3 each with 4 port (p-1 to p-4). Most of the switches supports web-based, telnet based, CLI based ring configuration. Atleast 1 switch should be enabled with 'Redundancy Manager' mode.
Enable the RM mode on sw-1 (over the switches pins are available to enable/disable the switch modes).
Before configuring the switches make a connection like, Connect p-1(sw-1) to p-2(sw-2), p-1(sw-2) to p-2(sw-3). Do not connect p-1(sw-3) to p-2(sw-1).
Access the web page of sw-1 and configure the ring ports as 1 and 2. Then disable the STP (spanning tree protocol)/RSTP (rapid spanning tree protocol) for these ports. Because STP and Ring algorithms should not work at a time.
Access the web page of sw-2 and configure the ring port as 1 and 2. Then disable the STP/RSTP for these ports.
Access the web page of sw-3 and configure the ring ports as 1 and 2. Then disable the STP/RSTP for these ports.
Now connect the p-1(sw-3) to p-2(sw-1). This link is called 'back up link'
Connect only one port of one switch to the network. The reachability to other switches in the ring should be through this switch.

Working flow:
Even though the communication b/w switches support full-duplex operation, always the packets will use clock-wise direction to reach other nodes in the ring. This time the backup link path physically exist but it will not do any communication with other switches. In case of any connection failure, the other switches inform the switch with RM mode(sw-1) that some connection failure occurred. The sw-1 immediately enables the backup link path to communicate with rest of the switches in the ring. This redundancy mechanism does not work correctly if ring ports of the switches do support STP/RSTP. The network recovery time should always be minimal.

Further:
Up to now I described the configuration of a single ring. Even we can do couple the different rings (communication between different rings).

Note: The above explained ring redundancy working functionality is a general one. It may differ a little bit from vendor-to-vendor.

SCJP Study Material

2008-08-11T03:46:00.001-07:00

Following links gives information on SCJP exam study material, way of preparation and simulation downloads.

http://www.javabeat.net/

http://www.anilbachi.8m.com/docs/certification/jcpquestions/index.htm
http://www.jchq.net/mockexams/exam3.htm
http://liang.armstrong.edu/selftest/selftest5e?chapter=2
http://www.lanw.com/java/javacert/HardestTest2.htm
http://www.javaolympus.com/J2SE/JavaCertification/JavaCertification.jsp
http://home-1.worldonline.nl/~bmc88/java/javacert/index.html
http://enterprisedeveloper.com/jcertify/
http://www.aniyog.com/java/certification/java_mock_test.htm
http://www.geocities.com/technofundo/tech/scjp/scjp1_4.html
http://www.jchq.net/mockexams/exam2.htm
http://www.danchisholm.net/july21/topic/index.html
http://www.jdiscuss.com/index.html
http://www.java-tips.org/
http://www.javaprepare.com/quests/question.html
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=forum&f=24
http://saloon.javaranch.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic&f=84&t=000189
http://faq.javaranch.com/view?ScjpFaq#sectionWiseMocks
http://faq.javaranch.com/view?ScjpMockTests
http://www.vivek.4mg.com/javacertification/jsexam.htm
http://www.javaranch.com/maha/_Mock_Exams/_mock_exams.html
http://www.javaranch.com/gramps/SCJPLinks.jsp
http://www.mihaiu.name/2004/sun_java_scjp_310_035_test1/
http://www.examsguide.com/scjp/freequestions.html
http://www.witscale.com/scjp_studynotes/chapter9.html
http://www.witscale.com/my_witscale.html
http://java.about.com/od/certification/tp/topscjpexams.htm
http://www.acmerocket.com/skinny/index.html
http://www21.brinkster.com/infoway02/asp/AllQnAns4.asp?start=100&end=200
http://www.geocities.com/SiliconValley/Screen/5046/
http://www.javabeat.net/javabeat/scjp2/mocks/index.php?page=mock13
http://www.javabeat.net/javabeat/scjp2/downloads/index.php
http://www.geocities.com/skmajji/Main.html

Schneider-Electric

2008-08-11T03:42:00.000-07:00

Visit the top MNC in industrial automation sector…

http://schneider-electric.com/sites/corporate/en/home.page

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2008-08-11T00:04:00.000-07:00

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