Helo Hari anna.

hari's kumakona info web,

http://kumbakonam.info

and his home,

http://hariprakash.tripod.com

java notes

results from the worked out examples,

Facts about interface:
======================
1.all methods of interface are abstract.
2.all the members of interface are static & final.
3.interface cant have mehod with definition.
4. A class can extend one class but can implement many interfaces..
5. A class can extend more than one interface.
6. An interface only can extend another interface.
7. An interface can not be private/protected.
8. An interface can extend another interface and not a class.
9. Assume an interface i, class c have a method sum(). If a class implements
i, extends c means, it needs not to define the method sum() of i. (if class c
omits the body, then it shd. Also, the remaining methods of i, shd be defined
the body.)
10. An interface can be defined in side a class. (Nothing wrong, a nested
class can implement that interface)


Facts about abstract
===================
1.If an abstract class defines body of a method, the extending class needs not
to implement it again
2. If an abstract class doesnt define body of a method, then extending class
should implement it.
3. If there is a class having no method definitions, the extending class
should implement the body...(similiar to Abstract class)
4. 'abstract' key word insists that 'you cant create object for the class'
5. abstract class can have reference variable but not objects(initialization/
using new keyword)

Interface Vs Abstract class:
=============================
1.An interface has adv over abstract, since it helps in achieving multiple
inheritance.
2.Interfaces are slow as it requires extra indirection to to find
corresponding method in in the actual class. Abstract classes are fast.
3. for interface its possible to create reference. But for abstract classes it
is not.

Why Ejb?, Jdk6.0 features

I often think of the situtation to use Ejb. Still I never had a chance to assist ejb code in anywhere. Java people recommend Ejb, when the project scope is really complex and in Enterprise level. Unwanted usage of EJb results in performance, effort & money lost. Surprisingly they say, some alternatives are tried to replace the Ejbs. One more problem with j2ee is integration of different language & s/w. This makes me lazy in learning Ejb. I just touch Ejb, when I have free time & no interest in touching it alone.


theserversid.com lists the new features in Mustang (jdk6).
*embedded Rhino (Javascript) interpreter,
* extending java.io.File to discover free disk space,
* an embedded light weight HTTP server,
* XML Digital Signatures API,
* JAX-WS 2.0, JAXB 2,
* JDBC 4, JMX 1.3,
and a user-requested improvements and big fixes.

But, I see Java is losing its standards...by the name 'flexibility' :-)

Jpcap - Java Packet Capture Library

I tried packet capture library for java (jpcap). I installed the lib, as per the installation procedures given in the readme file. The first problem is Jdk version mismatch. Next wpcap.dll file missing, then downloaded wpcap.dll from www. & again said: packet.dll missing. Then, again downloaded packet.dll. Then, "procedure Entry signature missing...in packet.dll"? Oops! I cant rewrite the dll source again. What a hell is it?
Google suggested to reinstall the complete winpcap pack. Did the same. Atlast I see tcpdump.java working fine. But, I didnt go thro the complete Api!. But I am so happy to see classes ICMP, TCPPacket,..and the likes.
Yes, I am ready for sniffing.

Internet traffic. Realize the worth of....

I often think of our net traffic. I surprise to see the bandwidth & speed of my campus !!:-) . I have never seen these servers speed crossing the limit of158KBps. But, they promised many times the bandwidth 1250Kbytes/sec. (1.2 MBps). And 1:4 shared bandwidth!
The peak performance I saw by wget-log is: 158KBps (rarely). How is the bandwidth swallowed? I never believed all the ridiculous reasons that they answered me. Also, this pity with an additional wireless tower sharing bandwidth!
They have to think of it. Link down for an hour wastes money in thousands!

Google defines a computer guy's Skill!

Prp gets over today. I was net reading about Internet traffic (added the link in my home). Thanks to google, to get me this much explanation. Also, got a chance to explore google opportunities (We are hiring!). I have seen this already. I saw the skill sets they requested. Really, these are the skill sets I often think of :)

I just copy & paste the list:

* People with broad knowledge and expertise in many different areas of
* computer science and mathematics, including distributed systems,
* operating systems, data mining, information retrieval, machine
* learning, performance optimization, algorithms, user interface design,
* statistical inference and information theory, and related areas.
* People with world-class programming skills.
* People with excellent communication and organizational skills.
* People who are passionate about their work and are great colleagues.
* People who enjoy working in a high-energy, unstructured environment on
* very small project teams to build amazing products used by millions of
* people every day.
* People with diverse interests and skills.

Oops! This is what the engineering skill! .Each & every computer engineer should have to go through this list! But, they mention long experience (with atleast a PhD!). Also, I am inspired by the comment given by a google guy:
"It's fantastic to come straight out of school and build something that's used
by millions of people." - Lauren, Software Engineer

Yes, Really! challenges make the life meaningful.

PRP test planned on 17th june

Thanks to those, who infomed me about Scja. I saw the exame objectives. It seems like the test is for experienced people. However, I am not that much prepared. And also this PRP test pressure tights my neck. They confirmed the final test date on June 17th.
7 days given for preparation. Have to use the days for preparing for test alone. Now, I feel some what relaxed after getting decided to spend forthcomming days.

Then? Scjp progress bar: 4.2 chapters.

Thus the last week went.

I just highlight the last week's happenings.

* Worked out all the doubts in sql. (constraints, joins, functions, normal forms & etc)
* Just now completed 3 chapters of Azim Khlid mughal.
* Had lot of dicussion on very fundo things in unix,rdbms... & etc.
* Enjoyed with Google maps, Internet Backpone map.
* Meet many of my friends online.

Thinking to refresh on JMS, JAXP. But, not having enough time.

Some 2 days back we had a meet with Subramanian Swaminathan .He gave an once-over on the structure of Corporate & various process going inside.

Also, we were informed that we'd have our test by june 15/16th. However no clear idea about joining date or any thing.

Then, I am so glad about my juniors. I always notice that the "growth rate of junior generation is faster than its precursors!". Yes, they bring out lot of ideas & work out them, with passion. Best of luck guys!!

new Thread("SQL");

Talk of today is Sql. Anitha mam kick started the new thread. I remember she took the same subject for us some 2 years ago. I practiced almost all the basic queries.
Then got a doubt about on escape character with like keyword.
This query solved my doubt,

select * from emp where name like 'like!%' escape "!" ;

(Sql is smart in using escape char!).

Then, I got the book "A Programmer's Guide to Java Certification" by Khalid Mughal. Have to start preparation. I heard about Sun's 20% discount on scjp. But I saw it was applicable only for Singapore people! (Still, not sure ). Any way I am not going to do it now. I need deep understanding, then good score. So, will try after some months.