Wednesday, April 27, 2011

Java Synchronization Tutorial : What, How and Why?

Multit-hreading and synchronization is a very important topic for any Java programmer. Good knowledge of multithreading, synchronization, and thread-safety can put you in front of other developers, at same time it's not easy to master these concept. In fact writing correct concurrent code is one of the hardest thing, even in Java, which has several inbuilt synchronization utilities. In this Java synchronization tutorial we will learn what is meaning of Synchronization in Java, Why do we need Synchronization in Java, What is java synchronized keyword, examples of using Java synchronized method and blocks, What can happen in multithreading code in absence of synchronized constructs, tips to avoid mistakes, while locking critical section in Java and some of important points about synchronization in Java. Since Java provides different constructs to provide synchronization and locking e.g. volatile keyword, atomic variable, explicitly locking using java.util.concurrent.lock.Lock interface and there popular implementations e.g. ReentrantLock and ReentrantReadWriteLock, It becomes even more important to understand difference between synchronized and other constructs. Remember, clear understanding of synchronization is must to write correct concurrent code in Java, which is free of multithreading issues like deadlock, race conditions and thread-safety. I am sure, things learned in this Java synchronization tutorial will help. Once you gone through this article, You can further read Java Concurrency in Practice to develop your concept.  That's the one of those book which every Java developer must read.

Sunday, April 24, 2011

Difference between ConcurrentHashMap, Hashtable and Synchronized Map in Java

ConcurrentHashMap vs Hashtable vs Synchronized Map
Though all three collection classes are thread-safe and can be used in multi-threaded, concurrent Java application, there is significant difference between them, which arise from the fact that how they achieve their thread-safety. Hashtable is a legacy class from JDK 1.1 itself, which uses synchronized methods to achieve thread-safety. All methods of Hashtable are synchronized which makes them quite slow due to contention if number of thread increases. Synchronized Map is also not very different than Hashtable and provides similar performance in concurrent Java programs. Only difference between Hashtable and Synchronized Map is that later is not a legacy and you can wrap any Map to create it's synchronized version by using Collections.synchronizedMap() method. On the other hand, ConcurrentHashMap is especially designed for concurrent use i.e. more than one thread. By default it simultaneously allows 16 threads to read and write from Map without any external synchronization. It is also very scalable because of stripped locking technique used in internal implementation of ConcurrentHashMap class. Unlike Hashtable and Synchronized Map, it never locks whole Map, instead it divides the map in segments and locking is done on those. Though it perform better if number of reader threads is greater than number of writer threads.

Thursday, April 21, 2011

How to Create, Update and Remove Soft link in UNIX

Symbolic links , Symlink or Soft link in Unix are very important concept to understand and use in various UNIX operating systems e.g. Linux , Solaris or IBM AIX. Symlinks gives you so much power and flexibility that you can maintain things quite easily.I personally feel that along with find, grep and other UNIX commands, command to create soft link and update soft link i.e. ln -s  is also must for any one working in UNIX machine. Whenever I do scripting or write any UNIX script I always write for symlinks rather than pointing to absolute path of directories in UNIX. It gives you flexibility of changing the symlink or soft link without making any change on your tried and tested scripts. I have worked on many different core Java projects which run on Linux and UNIX machine and make extensive use of UNIX symbolic links or symlinks. All my project which are on finance domain and on electronic trading systems have there server running on Linux,  Since speed is major concern in online stock or futures trading where orders has to hit the market within micro seconds Linux server is ideal choice for electronic and fix trading systems and since your server is on UNIX you have to be expert of Unix command to work efficiently and these articles are my result of those effort to learn and share new UNIX commands. In this UNIX fundamental tutorial we will see How to create soft link in UNIX, How to update soft link and Difference between Soft link and Hard link in Unix and Linux. By the way this UNIX command tutorial is  in continuation of my earlier article top networking commands in Unix  and CVS command examples ,  if you haven’t read already you may find some useful information based on my experience in Unix and Linux commands.

FIX Protocol Tutorial for beginners


FIX Protocol Tutorial for beginnersI have been writing FIX Protocol Tutorial from last few months and today I thought about doing a revision on all those tutorials. It’s very easy to read and forget about anything you have learn so periodic revision is very important and I see its important here as well. In this article I will put summary of each of my previous FIX Protocol Tutorials and give a link back to original article for further reading. This will allow any beginner or new comer to get an idea of what topics from FIX has been already covered in these tutorials and helps them to quickly navigate between those. With growing use of  online trading and electronic trading for various Asset classes such as futures ,options, equities , Fixed Income and Commodities and growing number of online stock trading companies and broker in world market demand of FIX Protocol developers  are increasing day by day and now I can see more jobs for FIX developer than few years back. This  is a niche area and these online stock trading companies or brokers pay very good for any one who is very good knowledge of  FIX simply because it’s very difficult to find a good FIX Protocol developer

Saturday, April 16, 2011

Top 10 Java Serialization Interview Questions and Answers

What is Serialization in Java
Java Serialization is one of important concept but it’s been rarely used as persistence solution and developer mostly overlooked Java serialization API. As per my experience Java Serialization is quite an important topic in any core Java interview, In almost all the interview I have faced there is one or two Java serialization questions and I have seen interview where after few question on serialization candidate start feeling uncomfortable because of lack of experience in this area. They don’t know How to serialize object in Java or they are not familiar with any Java Serialization example to explain, forget about questions like Difference between transient and volatile variable or Difference between Externalizable and Serializable in Java. In this article we will question from both beginner and advanced level, which can be equally beneficial to freshers, new comers and senior Java developers with some years of Java development experience.

Friday, April 15, 2011

UNIX Command Tutorial, Tips and Examples for Beginners.

UNIX and Linux commands tutorial and tips for beginners.
Hi, this is a kind of revision post where I would like share some of my earlier posted UNIX commands tutorial. Purpose of this post is to put together all UNIX commands tutorial in one place for easy access to anyone. These are collection of my favorite UNIX commands which you guys may find it interesting. I have been working in UNIX from almost 4 years and I have learned many UNIX commands during these year which has helped me a lot during by day 2 day working on Unix shell. These UNIX command s tutorials are based on my experience; I have shared UNIX command which I used so these are quite practical tips and tricks. It may not be in proper tutorial format like any other UNIX commands tutorial but I am sure this will be useful. This list is by no means complete so please share your UNIX commands experience so that we both can benefit from each others experience.

Monday, April 11, 2011

How Garbage Collection works in Java

I have read many articles on Garbage Collection in Java, some of them are too complex to understand and some of them don’t contain enough information required to understand garbage collection in Java. Then I decided to write my own experience as an article. You can call it a tutorial about garbage collection in simple word, which would be easy to understand and have sufficient information to understand how garbage collection works in Java. Garbage collection works by employing several GC algorithm e.g. Mark and Sweep. There are different kinds of garbage collector available in Java to collect different area of heap memory e.g. you have serial, parallel and concurrent garbage collector in Java. A new collector called G1 (Garbage first) are also introduced in JDK 1.7.  First step to learn about GC is to understand when an object becomes eligible to garbage collection? Since JVM provides memory management, Java developers only care about creating object, they don't care about cleaning up, that is done by garbage collector, but it can only collect objects which has no live strong reference or it's not reachable from any thread. If an object, which is suppose to be collected but still live in memory due to unintentional strong reference then it's known as memory leak in Java. ThreadLocal variables in Java web application can easily cause memory leak. 

Friday, April 8, 2011

Replaying messages in FIX protocol


Replaying messages in FIX protocol

In FIX Protocol two FIX engines communicate with each other using FIX messages and every FIX messages is assign with unique sequence number denoted by tag 34. Apparently every FIX engine has two sequence numbers Incoming Sequence Number (which FIX engine is expecting from counter party) and Outgoing Sequence Number (which FIX engine is sending to counter party). This sequence numbers along with rules specified in FIX protocol technical specification ensures that no FIX engine should lose any FIX messages in the event of any disconnect.
In this FIX Protocol Tutorial we will discuss some scenarios where disconnect between two FIX Engine occurs and how they recover from that situation. Normally disconnect and reconnect can cause replay of messages which would be require from either party e.g. either client or broker based upon who has higher sequence number.


This FIX Protocol Tutorial is in continuation of my earlier tutorial FIX Protocol Session or Admin messages tutorial and Difference between FIX 4.2 vs FIX 4.4 in FIX connectivity.

Thursday, April 7, 2011

Top 20 Core Java Interview Questions and Answers asked on Investment Banks

Core Java Interview Question Answer
This is a new series of sharing core Java interview question and answer on Finance domain and mostly on big Investment bank.Many of these Java interview questions are asked on JP Morgan, Morgan Stanley, Barclays or Goldman Sachs. Banks mostly asked core Java interview questions from multi-threading, collection, serialization, coding and OOPS design principles. Anybody who is preparing for any Java developer Interview on any Investment bank can be benefited from these set of core Java Interview questions and answers. I have collected these Java questions from my friends and I thought to share with you all. I hope this will be helpful for both of us. It's also beneficial to practice some programming interview questions because in almost all Java interview, there is at-least 1 or 2 coding questions appear. Please share answers for unanswered Java interview questions and let us know how good these Java interview questions are?

Friday, April 1, 2011

Understanding DATALOSS Advisory in Tibco Rendezvous or Tibco RV

Understanding DATALOSS Advisory in Tibco Rendezvous
tibco rendezvous tutorial, tibco tutorials
While working with TIBCO rendezvous you guys must have been faced problem of DATALOSS and might be aware of its severe consequences and in worst case how it can cause TIBCO Storm (A situation where TIBCO publisher bombards network with publishing so many messages and exhaust all network bandwidth of WAN links resulting in complete breakdown of network lines and communication). 

This Tibco Tutorial is in continuation of my Tibco Tutorial series and in this short TIBCO tutorial I will explain what is DATALOSS in Tibco and How we can minimize or prevent DATALOSS in Tibco RV.