Dunzon of Wahid Sadik

Content Repository API for Java a.k.a. JCR

2011-10-31T12:50:00.000-04:00

Acknowledgement and disclaimer
I used Wikipedia to do my research. And then, I added my own interpretation.

What is a Content Repository and why is it needed?
While Content Management Systems (CMS) stores users' content and allow people to access (read) it, there are few functions/features a CMS should provide for maintenance, query, version management, import, export, etc. Now that there are so many CMS around, people (involved in managing CMS) started asking whether a CMS provides these features. So, it has become more of a compliance issue.

These "Content Repository" features made into separate product (Example: Apache Jackrabbit). Some CMS(s) now delegate this "Content Repository" function to separate components (Example: Hippo CMS and Magnolia).

Java's implementation of Content Repository
"Content Repository API for Java", or JCR is Java's implementation of Content Repository. It has been developed via JSR-170 and JSR-283. The main Java packages are javax.jcr.

JCR has certain features:

Export and import via XML
Query by SQL and DOM
Associate types, attributes and values to each document

Implementation of JCR

Apache Jackrabbit is reference and open-source implementation of JCR.
Content Repository Extreme (CRX) is commercial JCR implementation.
Alfresco has CMS that offers JSR-170 API.
etc.

CMS using JCR

Hippo CMS and Magnolia use Apache Jackrabbit, and can switch to other JSR-170 implementation.
Oracle Beehive supports JSR-170.
etc.

Reference:

Content repository: http://en.wikipedia.org/wiki/Content_repository
Content Repository API for Java: http://en.wikipedia.org/wiki/JSR-170

Introduction to Databases by db-class.org

2011-10-24T21:47:00.000-04:00

Stanford University is offering a few free courses - Artificial Intelligence, Machine Language and Introduction to Databases. I signed up for the database course; link is here http://www.db-class.org/course/class/index.

I have taken this course before in college. However, it gives me an opportunity to refresh the ideas; so it feels great.

So far, I have finished Relational Algebra (RA), XML, DTD. I will have to cover XSD, SQL and few other topics.

For RA, the site has a simple workbench for the exercises. It is backed by a SQLLite installation. The expressions have to be written in a certain way and it does not support all aspects of RA, but that is not a problem. I am looking for a full-fledged open source tool.

There were two exercises on DTD and XSD. It forced me to write some DTD and it was helpful to shove the learning into the memory.

I will post the relevant links here later on.

References:

Android OS on VirtualBox

2011-10-24T21:32:00.001-04:00

Out of curiosity, today I goggled about installing Android OS on VirtualBox. And, I found something. There is a port of Android OS (v2.3?) called LiveAndroid. It is distributed in LiveUSB and LiveISO format. Anyway, I installed following a blog post (TBD: Put the link here); it was very easy.

Few notes about the installation:

I didn't need any username/password to install - simply because it is an OS targeted for phone, where I usually don't enter any credentials.
While running the Android OS, I did not see any mouse. It made sense - simply because it is an OS targeted for phone, where I usually don't have a mouse.

References:

Threads in Java

2011-04-30T09:07:00.001-04:00

Book: Java Concurrency in Practice
Author: Brian Goetz, et. al.

Chapter 3: Sharing Objects

"Sharing" here means sharing between threads. Before we dive deep, let me reiterate some basic behavior by the JVM.

Basic Behavior
--------------
1. The whole JVM memory is roughly divided between "heap" and "stack".
2. All methods are mere container of code, static, and lifeless.
3. Threads are like living persons that walk the instructions mentioned in methods. I will refer a thread that is executing a method as "walking thread".
4. When threads create method-local objects, they are created on the heap; the references to objects are created on the stack. All primitives are created on the stack.
5. When threads create method-local primitives, they are created on the stack.
6. References and primitives passed as parameter are copies from the source. While in a method, threads use their copies.

If the source is modified by some other thread, there is no guarantee that the changes will be visible immediately to the current thread. We should assume that things will go wrong.

7. When a primitive is written, it is done as an "atomic" operation. This means, the complete content is either fully written or not.

Two exceptions - long and double; both of these are 64-bit primitives. They are written as two 32-bit operations.

8. Class-level primitives, references (and objects, of course) are stored in the heap.

Problems
========
* Stale Data caused by Visibility

The problem depicted by #6 is this - the walking thread is seeing. "stale" data. The reason it is happening is because of lack of "visibility" management.

To solve,
Option 1: Use synchronized.
Option 2: Use volatiles.

* 64-bit primitives are non-atomic

Use volatile to solve.

* Unsafe publication
** "this" escapes the constructor
** Reference escapes through different methods
** Mutable objects

Techniques and their usage
==========================
1. synchronized

Solves visibility problem. It provides mutex locks reading/writing - instance primitives and instance references. Method-locals do not need that; thread-confinement guarantees single-thread access, UNLESS we allow a reference escape.

Allows to create atomic operation.

2. volatile

Solves visibility problem.
Must be used with 64-bit primitives to overcome partial writing problem.

Catch: Each read and write operation are guaranteed to reflect the central data. Operations like x++, or x = x + 4 may corrupt data (e.g. after reading x as 3, another thread may have modified it to 10; the current thread will not see that; and hence, it will set x to 7)

To overcome, use volatile only when one thread writes and more than one thread reads.

3. Immutable object

TBD

4.

Other issues to highlight
=========================
1. Statement reordering
2. Multiple processors executing the same method for the same thread.

Things a developer should make sure to eliminate thread-related problems
==================================================================
Method level
------------
1. Do not worry about objects and primitives created as method-local. Unless you explicitly design for it, do not escape any reference to any method-local.

Constructor level
-----------------
1. Do not allow "this" escape during construction. Common ways it can happen - (a) Allowing "this" to another object (b) Staring a thread.

If you have to do all of these, (a) Make your constructor private, (b) Provide factory method, so that you can wire necessary things are the object is created.

Instance variables
------------------
1. Make all 64-bit primitives volatile to fix partial writing problem, or access them only through synchronized getter/setter.

2. Use volatile only when you can make sure that only one thread can modify volatiles.

3. Atomicity of for 1+ instance variables can be also achieved by putting those variables in another object holder where the reference is volatile. Again, only one thread should assign objects to the reference. ** Check this concept.

Non-related topic
=================
1. How does hashtable works in Java

Some handy Linux links

2011-02-08T01:33:00.001-05:00

Some handy Linux links

http://distrowatch.com/ - A single place to know about all Linux distributions.
http://www.tightvnc.com/ - A free tool that can let you use remote GUI, including Unix.
http://polishlinux.org/ - Another good site.
http://polishlinux.org/choose/comparison/ - Compare different distros of Linux side by side.

Merlin Mann - Inbox Zero

2010-12-12T11:41:00.000-05:00

Loved it. I will write a summary of this presentation to remind myself about it.

Merlin Mann - Who moved my brain?

2010-12-12T08:56:00.001-05:00

I love this presentation.

Book Review: Practical Eclipse Rich Client Platform Projects

2010-12-12T00:35:00.000-05:00

About:
This blog entry is about a quick review of a book I recently read - Practical Eclipse Rich Client Platform Projects.

Eclipse Rich Client Platform (RCP) is new technology I am trying to become familiar with. The long term objective is to find any situation where I can use RCP to help my automation tasks.

I will capture my understanding of the technology as I learned from this book. This blogs contains only my view - be that right or wrong.

Review:
What is Eclipse? Here is how I know Eclipse to be. Eclipse is a Java development IDE that I use 10 hours a day, 5 days a week. I create amazing pieces of software with it. I use different plug-ins created by the wonderful people and these plug-ins make my life a lot easier.

This is how the Eclipse Foundation defines Eclipse to be - "Eclipse is an open source community, whose projects are focused on building an open development platform comprised of extensible frameworks, tools and run-times for building, deploying and managing software across the life-cycle." (Source: here).

As I think more about it, my experience is the reflection of the vision of Eclipse Foundation. This book on RCP describes different architectural components of Eclipse and how I can use them to enhance this platform (to make my life easier).

Eclipse Foundation wanted to see Eclipse (the IDE) as Rich Client Platform (RCP). This is a marketing attempt to invite and encourage developers create software that can run inside Eclipse. To back this vision up, Eclipse have be designed with ways to extend and integrate new software (in the mode of plug-ins). (I guess Eclipse Foundation envisioned it to grow it as big as Emacs.) .

Summary so far is, Eclipse Foundation encourages you to use Eclipse to create software on top of it, as it is a RCP. When you use write any software for Eclipse, you write a plug-in (which is one of Eclipse RCP components)

To use Eclipse as RCP, certain components work together:

Equinox (Eclipse's implementation of OSGi, a standard way of creating inter-connection between software)
Core platform (glues everything together; allows to write plug-in)
Standard Widget Toolkit (a.k.a. SWT)
JFace (Another component that works together with SWT)
Eclipse IDE workbench (that's the playground of your plug-ins)

(To be continued)

Reference:

Practical Eclipse Rich Client Platform Projects

Source of the book:

My local public library - Queens Library, Central Branch.

Vocabularies:

RCP = Rich Client Platform

JUnit Kung Fu: Getting More Out of Your Unit Tests

2010-12-07T13:00:00.000-05:00

JUnit Kung Fu: Getting More Out of Your Unit Tests

View more presentations from wakaleo.

Continuous Integration

2010-10-31T10:22:00.000-04:00

"It's (having a crack at Continuous Integration) not a question of failure because failures are going to happen. The more transparent failure is, the easier it is to diagnose what failed"

The above comment was made by Meciej Zawadzki, President and Founder of Urbancode. Source: Software Development Times, October 15, 2010.

Testing posts through Windows Live Writer

2009-06-30T23:38:00.001-04:00

I was using BlogSpot for my blogging for last two years. As time goes, my interests are being redefined more and more. Now, I feel I need specific blog for my different types of interest.

Column 1	Column 2	Column 3
Hi	There	:)
How	are	you?
How	is	life?
Everything	going	ok?

Googling with Bing - CollegeHumor video

2009-06-30T22:23:00.000-04:00

Googling with Bing - CollegeHumor video

InfoQ: Concurrency and Immutability

2009-06-30T16:57:00.000-04:00

InfoQ: Concurrency and Immutability

Lifehacker - Untiny Reveals Shortened URL Destinations - URL Hacks

2009-06-27T10:24:00.000-04:00

Lifehacker - Untiny Reveals Shortened URL Destinations - URL Hacks

Lifehacker - Nine Great Uses for Binder Clips - binder clips

2009-06-27T10:22:00.000-04:00

Lifehacker - Nine Great Uses for Binder Clips - binder clips

Cost of living: Compare prices in two cities - CNNMoney.com

2009-06-27T01:53:00.000-04:00

Cost of living: Compare prices in two cities - CNNMoney.com

Open Source Rule Engines in Java

2008-12-22T16:10:00.000-05:00

Open Source Rule Engines in Java
http://openrules.com/index.htm
http://www.jessrules.com/jess/

flamingo: Flamingo component suite

2008-12-22T15:01:00.000-05:00

flamingo: Flamingo component suite

MiG Layout Java Layout Manager for Swing and SWT

2008-12-22T14:58:00.000-05:00

MiG Layout Java Layout Manager for Swing and SWT

Anders Norås' Blog : What Makes a Good Programming Font?

2008-12-22T14:50:00.000-05:00

Anders Norås' Blog : What Makes a Good Programming Font?

HowStuffWorks "Why do they use salt to melt ice on the road in the winter?"

2008-12-17T13:31:00.000-05:00

HowStuffWorks "Why do they use salt to melt ice on the road in the winter?"

Finite state machine - Wikipedia, the free encyclopedia

2008-12-12T17:27:00.000-05:00

Finite state machine - Wikipedia, the free encyclopedia

Introduction to UniMod

2008-12-12T17:26:00.000-05:00

Introduction to UniMod

A very helpful plug-in to design software.

UML Tutorial - State Diagrams

2008-12-12T16:53:00.000-05:00

UML Tutorial - State Diagrams

An Introductory Example

2008-12-12T16:29:00.000-05:00

An Introductory Example of State Machine

define: duress - Google Search

2008-12-08T15:21:00.000-05:00

define: duress - Google Search: "When a person is forced to enter into an agreement or to perform some other act against his will."

Capital or Capitol?

2008-12-05T08:30:00.000-05:00

Capital or Capitol?

Health care insurance

2008-11-16T20:53:00.006-05:00

COBRA Insurance

COBRA Insurance (enforced through an act called COBRA) offers temporary insurance (usually 18-36 months max., you can discontinue any time) for people

Who had jobs and had employer-assisted insurance. Through employer's group (other employees where lost jobs) and COBRA provider, they can get insurance.
Who has a job, but employer doesn't pay insurance.
Family members (spouse, children, ...) can be covered.

Coverage:

You can take full coverage you were having before you lost job. For this, you have to 102% of all payments (your premium + premiums paid by your ex-employer + 2% administrative charge).
Or, you can take a lower coverage, resulting lower premium. (I've seen offers like $225/month for a family of four members)

Medicaid & Medicare

Medicare is for mostly for elderly persons. It's a health insurance program by federal government. Pays most of the claims, some copay may be required.

Medicaid is assist program. Can help to pay almost full health care costs. Eligible: pregnant woman or US children or disabled or blind, has low income. You could try even if you don't belong on of the mentioned group.

Proxool 0.9.1

2008-11-16T19:27:00.001-05:00

Proxool 0.9.1

Proxool is a JDBC connection-pool provider. Works near-seamlessly with standard way of JDBC. Here is how it works:

Change this
    Class.forName("org.hsqldb.jdbcDriver");
    connection = DriverManager.getConnection("jdbc:hsqldb:test");
to this
    Class.forName("org.logicalcobwebs.proxool.ProxoolDriver");
    connection = DriverManager.getConnection("proxool.example:org.hsqldb.jdbcDriver:jdbc:hsqldb:test");

Thats it.... or, it you want to configure stuff at startup (there are several options), you can do this:
    connection = DriverManager.getConnection("proxool.example");

Not bad... you might find a proper use this someday...

The providers say it's open-source, maintained. I am still not sure who uses it, though.

Blogged with the Flock Browser

Trying OpenJMS, Part 2

2008-11-16T05:29:00.024-05:00

In this part, I want to capture my initial knowledge about JMS, not OpenJMS in particular.

The problem JMS solves:

Enterprise applications grow at their own will. But, when the point of integration comes, nightmare begins.
MOM (see below) allows passing messages (containing information, transaction, etc.) between applications in asynchronous manner.

Characteristics of JMS:

Vendor-agnostic Java API for MOM (much like JDBC allows seamless connectivity to different databases)

Description:

Message indicates a piece of information, transaction etc.
In MOM, there are topics or queues where people share messages. (There is a different between topic and queue; explanation coming.)
There are applications called clients who work with specific topics or queues.Those to produce messages are called producers. Those to receives messages are called subscribers. A client can be both producer and consumer at the same time for a topic/queue.
For a specific topic/queue, there can be more that one producers, and consumers.
When a producer, subscribing to a particular topic/queue, sends a message to JMS,JMS pushes the message to consumer subscribing to that topic/queue. This way the producer and consumer are working asynchronously.
JMS Provider (JMS server) can make messages persistent, meaning it ensure that messages are not lost till they are consumed. (Store-and-Forward vs Fire-and-Forget)
Topic vs Queue: Topics can have more that one consumer, and each message is sent to all of the consumers. Queues can have more than one consumer, and the contract fulfills when exactly one consumer consumes the message.
Usually a subscriber doesn't receive a message if it is not present (i.e. connected) when a message is produced. A subscriber can request to be a durable subscriber (on a topic). If that consumer is not connected when a message is produced, JMS provider will make sure that i sends when that subscriber connects.
Durability modifies the behavior of subscriber.
From the producer side, it can request a particular message to be persistent. When the call from JMS provider returns, it guarantees that the message has be stored on a reliable media (file, or DB, or something else).

The buzz words:

MOM - Message Oriented Middleware (a.k.a. Enterprise Messaging System)

Links:

Book "Java Messaging Service" by Richard Monson-Haefel & David A. Chappell, from Oreilly - borrowed the book from my colleague Kevin

Trying OpenJMS

2008-11-15T22:40:00.016-05:00

I have become curious to know about processes running in same/different JVM. There are synchronization issues here.

For multi-JVM calls, one of the most common techniques is RMI (Java's implementation of RPC). In RMI, a call to remote machine is blocked. So, your threads are now at the mercy of a different JVM. Enterprise level applications faced this problem long ago. So, they solved the problem by making the call asynchronous. The technical term is Message Queuing (MQ). BTW, enterprise-designers solved on more problem with MQ - connecting legacy applications in a disjointed manner.

For Java, it is called JMS (Java Messaging System), which is a common interface of all major implementation of MQ. The committee for JMS comprised of representatives all major MQ vendors; so JMS essentially covers the common denominator.

OpenJMS is one such implementation of JMS. It came after JMS spec was created. It is open-source. I am using OpenJMS to do my initial R&D on JMS.

My initial comments about OpenJMS are:

It is very easy to install. Just unzip.
Very easy to run/stop. Run the startup.bat, shutdown.bat.
There is a even better way - run the admin.bat. It pops up a small swing-window. From there, you can start/stop OpenJMS instance.
Using Admin tool, you can see which topics (a JMS terminology, explanation coming) and queues (another one) are being maintained.
Very easy to try to hello-world type thing. Ready to run (you have to have Ant configured, which fortunately I had) sample application can give you scope to do immediate testing.

Q: How do I use JMS in my application?
A: I didn't try this yet. OpenJMS prefers that you get a handle to it (running on same or remote machine) using JNDI (I am also doing some JNDI study; refer to those concepts, I am not going to explain them again here).

I am planning to do some more R&D using OpenJMS with the following setup:

Try 2-machine testing using my personal laptop and office-laptop.
Try multi-machine testing using VMWare, where I will host 2/3 OS running.
Hand-code some JMS client stuff.

I will continue to update this entry.

Links:

http://openjms.sourceforge.net/

Why would you use JNDI?

2008-11-14T17:05:00.031-05:00

Basic Stuff

JNDI = Jave Naming and Directory Interface.
Example of similar services are: DNS, Sun NIS and NIS+, COS (for CORBA), LDAP (decedent from DAP, which ran over X.500) etc.
Taking example of DNS, we can locate a server's real location (IP) using its domain name.
JNDI enables large java application look up resources (e.g. database location, JMS server location etc.).

JNDI in a stand-alone Java application

Let's we have a 2000-class Java application.
Think about passing different resoucres to different classes. When you do that, you also have to take care of initializing, managing, scheduling, load balancing etc. issuse.
Resources we are talking about can be database connection, logging interface, configurations files, etc.
In the bootstrap of the application, we can launch a JNDI instance and plug these necessary resources against different names.
Codes, elsewhere in the application, can run a JNDI context to get a handle to JNDI, and then simply loopup objects using pre-agreed names.
Now, JNDI has different service providers, enabling access to FS,

JNDI in a stand-alone Java application

Now Consider a Java application that doesn't run the JNDI service.
No problem, just know where is the JNDI service is running, and then do how you were doing before.

JNDI Service Providers

JNDI wants to offers one-stop solution for different lookup services. So, it need service providers to do that. See one of the links for full list of SP (Service Provider).
The service providers act as JNDI service.

Examples of JNDI SP are:

RMI Registry
LDAP
NIS
File System
Windows Registry
COS Naming - for CORBA
Mirror JNDI - for Object to XML and vice-versa convertion

JNDI Rationale

I've copy/pasted stuff from the links given in the end.

As surprising as it may seem, the notion of a card catalog is quite handy in the world of computing, as well. In computing, we call it a naming service, which associates names with the locations of services and with information. It provides computer programs with a single location where they can find the resources they need. In the way, programs don't waste time by performing the electronic equivalent of walking up and down the aisles, and don't require that the locations be hard-coded into their logic, either.
Finding resources is of particular importance in large-scale enterprise environments, where the applications you build may depend on services provided by applications written by other groups in other departments. A well-designed naming infrastructure makes such projects possible -- and the lack of one makes them impossible. In fact, many business-process re-engineering efforts begin with the design and implementation of a robust, enterprise-wide naming and directory infrastructure.

Links:

So many dozens

2008-11-05T12:28:00.001-05:00

While taking an IQ test on Facebook, I bumped into a term called Baker's Dozen. Googling on that revealed some other dozens.

Baker's Dozen

During 16th century, bakers in England gave 13 (12+1) items when 12 were asked. There were severe punishment (losing hand) for not giving 12. So they gave 1 extra.
In the modern era, the 12+1 rule is followed for different reasons. Assuming 13 items are placed in 3 rows (4+5+4), they can form close-pack hexagon shapes. This makes processing, packing etc. more easy.
The concept is used beyond bakery industry.
A.k.a. Devil's dozen.

Banker's Dozen

It is a pun on the Baker's dozen.
Pointing to the ill intentions of the bankers, there are some loan scheme where lender is given the money after deducting the interest in advance.
So, the banker gives you less on what is agree upon.
Not related to the number 12.

Decimal Dozen

It is a dozen of 10 (12 - 2). And it is for a good reason.
Invented in Australia around in 1980s.
Stats showed that women bought 50%+ of wine.
The maximum recommended weight a lady should take was 15kg, which happen to be the minimum weight of 12-pack wine. The weight exceeded up to 20kg sometimes.
So, a company came up with the 10 pack solution.

It's all about dozens.. :)

Links:

Blogged with the Flock Browser

Smoke Testing

2008-10-22T23:00:00.004-04:00

My context: Software Development.

The term comes from plumbing, where smoke is used to check leaks before going into full and heavy duty testing with water.

In software development, "smoke" is used as a metaphor. When we smoke test a software/component, we do minimum testing before applying full-fledged testing.

I can recall where an anti-smoke test was applied. The famous Jamuna bridge of Bangladesh was a multi-purpose one. One of its goal was to carry natural gas across the river. When the engineers wanted to check the pipes, they checked them with water, instead of gas. Water, being many-times heavy, caused the pipes come out from below of the bridge and fell into the river. Irony, hah!

Links:

Smoke Testing

The Little Book of Semaphores

2008-10-22T12:42:00.004-04:00

Even after working with threads (in Java) for several years, I have feeling that I don't understand why Java allowed things in a certain way. In short, I don't feel ok not knowing the design considerations of threads in Java.

My way of address this:

Know threads from the basic. I am going back to good old Unix. This will be a one-month project. Outcomes to be blogged here.
Know JVM. This will be a three-month project. Outcomes to be blogged here.

There is a free book on semaphore, called "The Little Book of Semaphores". The author is teacher and knows well why students do/don't understand semaphore. This will be my starting point. I've read first two chapters, and I think it is a good one.

Links:

The Little Book of Semaphores, by Allen B. Downey

Regression Testing

2008-10-21T11:57:00.003-04:00

I had a blurred idea about Regression Testing for some time. Anyway, I had to handle an issue at work related to this, and this time I set the records straight.

Very quick and short understanding:

The verb regress: return to a previous state, usually worse state.
The noun regression: The act of getting back to a previous worse state.
Software Regression: The scenario where a previously solved bug reappear (i.e. regress) after some action taken on the software (e.g. a patch applied)
Software Performance Regression: The scenario where performance of a software goes back to a inferior state.
Regression Testing: A testing scheme aim to eliminate software regression. It involves testing the whole software for previously working features, even though they were not supposed to be affected.

Software Regression has 3 core types:

Local: a change introduces a new bug in the changed module or component.
Remote: a change in one part of the software breaks functionality in another module or component.
Unmasked: a change unmasks an already existing bug that had no effect before the change.

That's all for now. I will try to come back to this post.

Wireless sound system

2008-10-10T23:30:00.006-04:00

I was looking for GPS device for my car. While comparing different products, some features came to my notice - hands-free, text-to-speech, FM transmitter .... obviously, I didn't know many of them. So, I started digging and ended up how wireless sound system works. Eventually, it solved one of my problem at home.

The problem - when I watch movie on my laptop, I had to sit near the sound system. I have short cable.

The solution - USB FM Transmitter. Tune my spare FM player. Connect FM player to the sound system.

FM Transmitter

FM Transmitters work as FM broadcasting stations. They work in a smaller range, as they are for personal use. Within the range, any FM player can receive the signal and play. It will appear just another FM channel.

It costs around $20-40 to buy one.

How will it work

I connect FM transmitter to my laptop. I will use a USB one, so no extra power source is required.
I have a portable FM player. I will tune this player to the transmitting channel.
So, anything I play on the laptop, I can listen on the FM player. Anywhere in my home.
So can people nearby - I don't care.
I connect the input cable of my sound system to the FM player, just like I attach headphone.
Benefit: No cable is need to reach the sound system.

Issues to think about

Even with a highly capable sound card and sound system, having FM as the intermediary carrier, I will get FM quality sound at the end. Ok for me now.
Not secure. People in the range of 150ft can pick up the FM signal. Ok for me now.
FM player will need separate power, namely battery. Alternative: Connect player to a AC-to-USB power source.

Other products in the market

Conceptually, there are products that solve similar problem.
One problem to solve: so many cables from the central sound unit to the small boxes.
Some products use different frequency range (900 MHz, or 2.4 GHz) to distribute the signal to the smaller boxes. These products will have to operate in the ISM band (Industrial, Scientific and Medical)
Some (Bose) offer full 5.1 or 7.1 connectivity over proprietary wireless signal.
But you still need to connect your main audio source to the central unit.
Some products use WiFi or Bluetooth for the same connectivity.
My openion - Bluetooth can be too narrow carrier for good quality.
WiFi - I would love to have this. I already have a WiFi network for the laptop.
Some products allow different music on different wireless sound terminal. So, you can have different sound in different room, at the same time :). Neat!

So far ok.. I will add some more, if I find anything more.

About memory cards

2008-08-09T11:54:00.016-04:00

I am planning to buy a digital camera this week; soon, I ended up in analyzing different technologies around. Hence, I started understanding SD cards.

The wikipedia article says it all. I am capturing some of them.

SD stands for Secure Digital. Though, the original intention was Super Density Disc.
SD is now an industry standard, initiated by Toshiba, Panasonic and Sandisk.
The Secure part of SD was introduced by Toshiba, a legacy (good one) from it's MMC cards (MultiMediaCard). Toshiba included a encryption that prohibited music piracy - a movement mostly know as Digital Rights Management (DRM). This was done because of pressure from music industry.
SD cards larger than 2GB uses a different technology called SDHC (SD High Capacity).
(Read Access) Speed is an issue to consider of SD cards.
The form factor of SD cards can vary in all dimentions. Such variants are: miniSD, microSD (aka TransFlash). These require a simple passive adapater (a physical device to fit in SD slot). The electronic interface remains same.
SD cards can fit in other cards slots (e.g. CompactFlash, PC cards) via an active electronic adapter.
You would want to access SD cards from your other devices e.g. PC, printer etc. So, you will need a card reader. One card reader can support many differnet standards of cards (SD and others). Card readers can be built in, or can be externally connected (via UBB or other methods)

Links:

Interview of Kazi da

2008-07-17T21:06:00.002-04:00

Kazi da a.k.a. Kazi Anwar Hossain of Sheba Prokashoni - everybody knows him in Bangladesh. The Prothom Alo published an interview of him July 18, 2008. Some very interesting information and reality came up from it.

Link: http://www.prothom-alo.com/fcat.news.details.php?issuedate=2008-07-18&fid=MTY=&nid=Mjc0NDU=

XML.com: XML Namespaces by Example

2008-07-14T12:05:00.000-04:00

XML.com: XML Namespaces by Example

A nice article explaining XML Namespace and it's rationale.

URI vs. URL, Bernie Zimmermann

2008-07-08T15:05:00.000-04:00

URI vs. URL, Bernie Zimmermann

Explained in understandable language.

What is WiMAX? — WIMAX

2008-07-06T13:10:00.000-04:00

What is WiMAX? — WIMAX

I was discussing about wireless network with my wife and then ended up in understanding WiMAX vs WiFi. The attached link holds full details.

WiFi and WiMAX are implementation of WAN (Wireless Area Network).
Wifi and WiMAX are implementation by IEEE, numbered as 802.11 and 802.16 respectively.
Wifi has a range of 30-100m; WiMAX may have a range up to 30 mile.

Thread Pooling

2008-07-02T16:54:00.001-04:00

I am doing a thread pooling for my assignment.

I will write about the implementation of that.

Just note that, JDK 1.6 has an implementations of Thread Pool. Look inside package java.util.concurrent.Executor interface and its implementations.

Businee Casual Dressing

2008-07-02T16:52:00.000-04:00

Tie is running out
http://online.wsj.com/article/SB121253690573743197.html?mod=googlenews_wsj

Definition
http://en.wikipedia.org/wiki/Business_casual

Guide
http://www.career.vt.edu/JOBSEARC/BusCasual.htm
http://www.sartorish.com/modules.php?name=News&file=article&sid=13

Scrum

2008-05-30T11:47:00.006-04:00

I have been working for RealNetworks, Inc. since May 19, 2008. I work in a development wing. They follow scrum. This is my quick effort to clear my understanding about scrum.

What is scrum

Part of Agile
An iterative process
Management of SW Development Process

Why? The vocabularies

'Sequential approach' was predominant. It's like 'relay-race', handing over the baton to the next person.
It's better to have 'rugby', where team works as an unit, passes the ball back and forth, and achieves the result.
The term 'Scrum' came from a term in rugby.
Each iteration is called 'sprint'. Can be 15-30 days' cycle.
'potential shippable'
'product backlog'
'sprint planning meeting'

Roles

'Pig' roles - fully dedicated
--- There is a 'ScrumMaster' role who plays the PM role, and maintains the process.
--- There is a 'Product Owner' role who represents the stakeholders.
--- There is a 'Team' role who represents the developers.
'Chicken' roles - outside scrum team
--- Users
--- Managers
- Stakeholders

Reference

Java Externalizable

2008-05-29T12:36:00.005-04:00

Background

Interface: java.io.Externalizable
Super Interface: Serializable
Used to control how you want to do serialization (read/write)
Scenario: Some of the fields may not worthy of writing, or the format needs to be changed etc.
transient keyword simply instructs JVM not to read/write a variable, one at a time.
With Externalization, you can control all variables in one place.
During de-externalization, the default constructor will be called. Then readExternal(...) will be called.

Java Methods

readExternal(ObjectInput in)
writeExternal(ObjectOutput output)

Link

http://articles.techrepublic.com.com/5100-10878_11-6159276.html

Java Prefernece

2008-05-29T10:15:00.003-04:00

Java Preference

Introduced in JDK1.4
Acts like Windows Registry
Stores objects in a tree-like structure; items reside on nodes as key-value pair
Can be exported/imported to/from XML
A replacement option for JNDI/LDAP; but you don't need a server
A replacement for properties files also

Links

Forget Facebook. The web's platform is Mozilla's Firefox

2008-03-15T04:25:00.001-04:00

The most interesting topic discussed in our meeting was just how compelling Mozilla's Firefox will increasingly be as the platform for much that happens on the web. Forget Facebook, MySpace, the iPhone, and other so-called platforms. Firefox could well prove to be the most disruptive web platform on the market. Here's why.

read more | digg story

Happy Pi Day!

2008-03-15T04:15:00.001-04:00

It's the 3/14, or 3.14, so this obviously means just one thing - it's Pi day, a celebration of the mathematical ratio that man has been trying to unlock for millennia. But why are we driven to find the answers behind it?

read more | digg story

BBC NEWS | South Asia | NYC hails Muslim 'Good Samaritan'

2007-12-20T02:07:00.000-05:00

BBC NEWS South Asia NYC hails Muslim 'Good Samaritan'

How to listen better

2007-07-16T09:59:00.000-04:00

I am new to managing people ... suddenly I am leading a team 5/6 person. May be it's time to learn few skill of leadership. Here are some of the links:

http://www.ehow.com/how_12503_listen-better.html
http://www.rogerdarlington.co.uk/Listening.html

Listen with an open mind and an open heart - free of preconceptions and prejudices.

Always look the person in the eye when you are listening. This shows the person that you are paying attention.

Give the person your full attention. Be seated.

Give visual encouragement to the speaker - such as facing the speaker, offering eye contact, and indulging in mild head nodding.

Give oral encouragement to the speaker - such as, in conversation, periodically using words like "yes", "I see", "I understand" or even just sounds like "mmm" or "ah".

Don't interrupt. Let the speaker tell the story in his/her own words and at his/her own pace.

Don't rush to fill a silence. Often a speaker will be more forthcoming or revealing if he/she is given a chance to compose his/her thoughts.

When your partner is finished saying something, ask questions or discuss it further. Open ended questions are better. Don't jump into your own topic.

Let's blog

2007-03-24T01:32:00.000-04:00

It (blogging) starts
I have realized the importance of blog last few months. And, from now on, I want to use blog regular basis.

Now, all of these is a mind shift for me.

Let me explain my plans with blogging. Please read through.

Initial Target

I explicitly express my objective of blogging (to keep me focused)

Record different types of knowledge and interests. Things will be in summary. Sources of information will be maintained. This will help me to quickly review my old interests.
Writing the blog on different topics will help me to remember more efficiently.
My writing skill will improve in terms of richness, faster delivery, variety. I will come in contact of many books, sites, Google, other people's blog. These will be a rich source.
I minimize the chance of loosing my paper written logs. I will be able to access these anywhere anytime.

Resource Requirement

I look forward to commit my following resources for this:

Time - It takes time to write blogs. Sometimes, I may feel to skip the habit; let's not.
Money - Browsing web requires money. I will spend whatever required.
Myself - Well, as said before, I am committed.

Sofi's World

2007-03-08T22:22:00.000-05:00

I have started reading a book called "Sofi's World" - this book is changing my views about the whole. It's based on philosophy. Here, a philosopher teaches a young girl about philosophy from very early stage to modern world.

People having some time might try this one.

One relevant link to same topic is: http://www.friesian.com/greek.htm

RssReader - download

2006-10-12T11:21:00.000-04:00

Trying RSS Reader for the first time. I am trying to build habit of using RSS. Here is the link to download on such reader
RssReader - download

Here you can find tons of RSS links
RssReader - RSS feeds

Server monitoring that sends a text (SMS) message

2006-10-10T02:49:00.000-04:00

This is something I am assigned to do for the Solaris server I work on. This is a link relavent
digg - Server monitoring that sends a text (SMS) message for free!

Data Guard Overview

2006-10-10T02:14:00.000-04:00

Got the link from my boss. It's about Oracle Data Guard. I myself have to read this.
Data Guard Overview

InstallationTips - The CVSNT Wiki

2006-10-10T01:05:00.000-04:00

A very good tutorial on CVS. You cannot do without it
InstallationTips - The CVSNT Wiki

A Novices Tutorial on Subversion

2006-10-10T01:03:00.000-04:00

I want to have expand my existing knowledge of CVS to SVN (Subversion). This could be an very easy link to start with.
A Novices Tutorial on Subversion

1st entry in blog

2006-10-10T00:46:00.000-04:00

This is the first entry. I find it very attractive to use blog, especially, the feature of Google toolbar to automatically enter links into my blog page.

Dunzon of Wahid Sadik

Content Repository API for Java a.k.a. JCR

Introduction to Databases by db-class.org

Android OS on VirtualBox

Threads in Java

Some handy Linux links

Merlin Mann - Inbox Zero

Merlin Mann - Who moved my brain?

Book Review: Practical Eclipse Rich Client Platform Projects

JUnit Kung Fu: Getting More Out of Your Unit Tests

Continuous Integration

Testing posts through Windows Live Writer

Googling with Bing - CollegeHumor video

InfoQ: Concurrency and Immutability

Lifehacker - ﻿Untiny Reveals Shortened URL Destinations - URL Hacks

Lifehacker - Nine Great Uses for Binder Clips - binder clips

Cost of living: Compare prices in two cities - CNNMoney.com

Open Source Rule Engines in Java

flamingo: Flamingo component suite

MiG Layout Java Layout Manager for Swing and SWT

Anders Norås' Blog : What Makes a Good Programming Font?

HowStuffWorks "Why do they use salt to melt ice on the road in the winter?"

Finite state machine - Wikipedia, the free encyclopedia

Introduction to UniMod

UML Tutorial - State Diagrams

An Introductory Example

define: duress - Google Search

Capital or Capitol?

Health care insurance

Proxool 0.9.1

Trying OpenJMS, Part 2

Trying OpenJMS

Why would you use JNDI?

So many dozens

Smoke Testing

The Little Book of Semaphores

Regression Testing

Wireless sound system

About memory cards

Interview of Kazi da

XML.com: XML Namespaces by Example

URI vs. URL, Bernie Zimmermann

What is WiMAX? — WIMAX

Thread Pooling

Businee Casual Dressing

Scrum

Java Externalizable

Java Prefernece

Forget Facebook. The web's platform is Mozilla's Firefox

Happy Pi Day!

BBC NEWS | South Asia | NYC hails Muslim 'Good Samaritan'

How to listen better

Let's blog

Sofi's World

RssReader - download

Server monitoring that sends a text (SMS) message

Data Guard Overview

InstallationTips - The CVSNT Wiki

A Novices Tutorial on Subversion

1st entry in blog

Lifehacker - Untiny Reveals Shortened URL Destinations - URL Hacks