Friday, November 25, 2011

Database Transaction Tutorial in SQL with Example for Beginners

Database transaction is an important concept to understand while working in database and SQL. Transaction in database is required to protect data and keep it consistent when multiple users access the database at same time.  In this database transaction tutorial we will learn what is transaction in database, why do you need transaction in database, ACID properties of database transaction and an example of database transaction along with commit and rollback.   Almost all vendors like Oracle, MySQL, SQL Server or Sybase provide transaction facility though MySQL only provide it for certain storage engine like InnoDB and BDB and not for MyISAM.

Thursday, November 24, 2011

Great Example of Open Closed Design Principle in Java

Great Example of Open Closed Design Principle
I am big fan of design pattern article and love to read articles on design patterns and recently wrote about decorator design pattern in JavaObserver patternstatic factory pattern and about Singleton pattern. Today I come across this good article on open closed design pattern, what I like most is there example and clear way of explanation, first example is true value and it will help you understand open closed principle very quickly and second example is also not bad. I have also shared many questions on design patterns and Object oriented design principles like 10 Java singleton interview questions , which discusses some of the most common questions on Singleton pattern like how to write Thread-Safe Singleton class , should we use Enum as Singleton or not etc and 20 design pattern interview questions, if you are preparing for senior level Java interview, where questions from design is expected, its worth looking for quick review.

open closed design principle exampleOne word about Open Closed principle is a design principle which says that a class should be open for extension but closed for modification. Open Closed Principles is one of the principle from SOLID design principle where it represent "O". Read more about OOPS and SOLID design pattern in my post 10 OOPS and SOLID design principles Java programmer should know.  


In Simple language Open closed design principles says that new functionality should be added by introducing new classes, methods or fields instead of modifying already tried and tested code. One of the way to achieve this is Inheritance where class is extended to introduce new functionality on top of inherited basic features.

Benefit or Open Closed Design Principle:
1) Application will be more robust because we are not changing already tested class.
2) Flexible because we can easily accommodate new requirements.
3) Easy to test and less error prone.

Wednesday, November 23, 2011

Top 10 Struts Interview Question And Answer - J2EE

This time its Struts interview questions, After writing Spring interview questions few weeks back I was thinking what to pick for my interview series and than I thought about any web framework, and on that struts is my favorite. Struts are open source framework used for web application. These Struts interview questions are based on my experience as well as collected by friends and colleague and they are not only good for interview practice but also shows a new direction of learning for any one who is not very familiar with struts. Best way to use these interview questions is do revise before going for any Struts interview or any Java or J2EE interview. I have also provided answers of these struts interview questions but you can also research more on Google but these answers of struts are sufficient on interview perspective.

Sunday, November 20, 2011

XPath Tutorials Examples for Beginners and Java Developers

XPath Tutorials for Beginners and Java Developers
This XPath Tutorial is collection of my Xpath Notes which I prepared recently when I was working on XML and XPATH. Though I was familiar with XML but not with Xpath and thought to note down bullet points about Xpath to get myself up and running. It’s not quite detailed but gives a nice overview on what is Xpath and how can you use Xpath in Java. I have not edited order of notes and presented it as it is in this XPath Tutorial. It also contains some example of xpath expression to give you an idea of how they look like but its analogous to SQL which is used to retrieve data from tables.

Saturday, November 19, 2011

Top 25 Java Collection Framework Interview Questions Answers for Freshers and Experienced Programmers

Interview questions from Collection package or framework is most common in any Core Java Interview yet a tricky one. Together Collection and multithreading makes any Java interview tough to crack and having a good understanding of Collection and threads will help you to excel in Java interview. I thought about writing interview questions on collection when I wrote 10 multi-threading Interview questions and Top 20 Core Java Interview questions answers but somehow it got delayed. In this article we will see mix of some beginners and advanced Java Collection interviews and there answers which has been asked in various Core Java interviews. These Collection interview questions have been collected from various friends and colleagues and Answers of these interview questions can also be found by Google.

Friday, November 18, 2011

Decorator design Pattern in Java with Example Java Tutorial

I was thinking to write on decorator design pattern in Java when I first wrote 10 interview questions on Singleton Pattern in Java. Since design pattern is quite important while building software and it’s equally important on any Core Java Interview, It’s always good to have clear understanding of various design patterns in Java. In this article we will explore and learn Decorator Design pattern in Java which is a prominent core Java design pattern and you can see lot of its example in JDK itself. JDK use decorator pattern in IO package where it has decorated Reader and Writer Classes for various scenario, for example BufferedReader and BufferedWriter are example of decorator design pattern in Java. From design perspective its also good idea to learn how existing things work inside JDK itself for example How HashMap works in Java or How SubString method work in Java, that will give you some idea of things you need to keep in mind while designing your Class or interface in Java. Now let’s Move on to Decorator pattern in Java.

Thursday, November 17, 2011

File permissions in UNIX Linux with Example >> Unix Tutorial

Whenever we execute ls command in UNIX you might have observed that it list file name with lot of details e.g.
stock_options:~/test ls -lrt
total 8.0K
-rw-r--r-- 1 stock_options Domain Users 1.1K Jul 15 11:05 sample

If you focus on first column you will see the file permissions as "-rw-r--r--" this is made of three parts user, group and others. User part is permission relate to user logged in, group is for all the members of group and others is for all others. also each part is made of three permissions read, write and execute so "rw-" means only "read and write" permission and "r--" means read only permission. So if you look permission of example file it has read and writes access for user, read only access for groups and others. Now by using chmod command in UNIX we can change the permissions or any file or directory in UNIX or Linux. Another important point to remember is that we need execute permission in a directory to go inside a directory; you can not go into directory which has just read and write permission.

Tuesday, November 15, 2011

LDAP Active Directory Authentication in Java Spring Security Example Tutorial

LDAP authentication is one of the most popular authentication mechanism around the world for enterprise application and Active directory (an LDAP implementation by Microsoft for Windows) is another widely used ldap server. In many project we need to authenticate against active directory using ldap by credentials provided in login screen. Some time this simple task gets tricky because of various issues faced during implementation and integration and no standard way of doing ldap authentication. Java provides ldap support but in this article I will mostly talk about spring security because its my preferred Java framework for authentication, authorization and security related stuff. you can do same thing in Java by writing your own program for doing LDAP search and than LDAP bind but as I said its much easier and cleaner when you use spring security for LDAP authentication.

Thursday, November 10, 2011

Helloworld Example Java : How to run Java Program from command prompt

This article contains HelloWorld Example in Java and step by step guide to run Java program from command prompt. Beginners who just started to learn Java or using Java often struggled and doesn't know how to run a Java program from command prompt. Running a Java program is simple but setting up Java environment is rather cumbersome specially if you are new in Programming world and not
very familiar with words like PATH, CLASSPATH or even command prompt. I don't blame you because we all start at some point of time and even When I started to wrote my first Java program, What I was doing was simply typing HelloWorld from a text book in a notepad editor, to my surprise my Java program ran without any issue because I was running that on school PC where PATH and CLASSPATH was already setup but when I tried the same thing in my home Windows PC I had tough time to run my Java program including HelloWorld Example in Java.

Tuesday, November 8, 2011

Result of Recent Google PageRank Update in November 2011

Just come to know about recent Google PR update which is due today 8th November 2011 and thought about this post to share result of recent Google Page Rank update based on my experience.
Everybody in web is talking about this Google PR update which is coming after recent Google Panda or Caffeine update, which has affected many sites ranking. I think Google PR update has been done or under work because I can see PR updates from zero to two on some of my articles. I can also see that this time Google is more restrict on awarding page rank and the one which got PR 3 on last Google PR update on Augst 2011 is getting PR 2 this time. Google has also adjusted PR of existing articles along with new articles.

10 Examples of HotSpot JVM Options in Java

There are hundreds of JVM parameters or JVM Options exists inside sun JDK and its virtually impossible to keep track of every single JVM option and based on my experience we don't even use most of JVM flags except couple of important JVM option related to java heap size, java options for printing garbage collection details and most likely JVM switches for setting up remote debugging in Java. but there are many other useful category of JVM parameters which you at least like to be familiar even if not intending to use it more frequently. In this article we will see examples of 10 different categories of JVM parameter which I found useful and use more frequently than other. I would recommend to get a full knowledge of what does a particular JVM options does by referring official list of JVM options.

Monday, November 7, 2011

What is Static Variable Class method and keyword in Java - Example Tutorial

What is Static in Java
Static in Java is an important keyword and used to create static method, static class and static variable in Java. Correct understanding of static keyword is required to understand and write sophisticated Java programs. Java 5 also introduced static imports along with Autoboxing, Generics, Enum and varargs method, which allows to import static members of one class or package into another using import keyword and then using them like they are member of that class. In this Java tutorial we will learn about What is is static in Java, What does it mean to be a static field, static class or method in Java and various points and issues involved around How to use static members in Java. This Java tutorial is also about how to use static keyword in Java and where not to use static keyword. Common rule is anything which you want to share between all object can be made static e.g. singleton instance of a  Singleton Class in Java.

Saturday, November 5, 2011

10 Examples of tar command in UNIX and Linux

tar command in UNIX or Linux is one of the important command which provides archiving functionality in unix. we can use UNIX tar command to create compressed or uncompressed archive files by using either gzip or bzip2. In this unix tar command tutorial we will see examples of unix tar command related to basic archiving task e.g. How to create tar archive in Unix and Linux, How to extract files from tar archive in unix, How to view contents of tar file in Unix and Linux or how to update and existing tar file in Unix. Examples of tar command in unix are kept simple and easy to understand and master each of basic task using unix tar command.

Thursday, November 3, 2011

How to override compareTo method in Java - Example Tutorial

compareTo in Java is in the same league of equals() and hashcode() and used to implement natural order of object, compareTo is slightly different to compare() method of Comparator interface which is used to implement custom sorting order. I have seen during java interviews that many Java programmers not able to correctly write or implement equals(), hashCode() and compareTo() method for common business objects like Order or Employee. Simple reason behind this is that they either not understand the concept well enough or doesn't write this stuff at all. I will try to fill that gap in this Java tutorial and will see What is compareTo() method in java, how to write compareTo in Java and things to remember while implementing compareTo in Java.