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Java Interview: tips for the interviewer

This is a brief entry about how an interviewer should conduct a Java based interview. I have been on both side of the table and this is only based on my own observations.  I think most interviews that I attended in the past, and possibly some I have conducted myself, focus on the basic concept. I accept that developers should be aware of the language principles, but how can an interviewer test more advanced principles?

The interview time have to be split into: 

  1. Theoretical conceptsThis 1st phase is about asking the common questions about OOP concepts, differences between interfaces and abstract classes, differences between List and Set, multithreading and so on. If it is required to store answers, do provide a written paper and avoid multiple choice questions. In my experience, open-ended questions allow the developer to express his knowledge better. Multiple choice questions provide unnecessary hints to question answers. Even if I did forget a terminology or a definition by looking at the various answers provided, I can pick the right answer 9/10 times. Theories are central to practices but make sure can be related to the role you are recruiting for.An important point when interviewing a developer, if you have a developer present during the interview, avoid asking domain specific question unless it is something common. I had some interview with senior and lead developers asking questions about a programming problem they have recently encountered and were able to fix after spending months working on it, how am I supposed to know about that unless I have encountered the same issues in the past.
  2. Practical test
    In order to test a developer capability for the role, it is a must that he/she undertakes a practical test. You do not need to give the developer code with bugs for him/ her to fix, I believe this approach is not very useful. I would suggest that all interviewers prepare the developer to take a practical test using their favourite tools (provide two of the most common open source IDE) and provide them with a simple problem domain. In my experience, I had to write some simple factorial algorithm (a single recursive method) to a domain centric web service application (no DB, store data in memory instead) and to more advance concepts. If application multithreading is part of the main day to day job, then ask the developer to write a simple application that shows that.
    This practice exposes several features of the developer; from its reasoning by writing simple algorithm to coding practice (commenting and Java best practices) and problem solving.

After all, I believe that programming is more about logical reasoning and coding. The more senior we get in our profession, the harder it is to answer simple questions with straightforward answers; we get carried away and provide a complex answer to something so simple. We cannot talk baby talk anymore; our tongue is full of jargon. All developers should follow the KISS principle when answering theoretical questions but ultimately they should excel in the practical test. If they are good enough, they should use a text editor to write their codes and compile it through the shell (JVM command line).
Another thing that all interviewers should know; developers have very good memories and therefore can memorise more than 115 interview questions; I would recommend you to focus more on a practical test.

This was a brief entry for interviewers. The web is full of tips and questions for the interviewees and I do not see any point in duplicating them here.  As usual, this is based on my experience and belief, you are always welcome to comment. Also, support my blog by visiting my advertisers (by clicking on the link on the right) they might have something that you might need.

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10 Things all Java developers should know

Since Java (I know it’s not an acronym, but it stands out like that) was officially introduced in 1995, it has changed the way most of us look at the Operating System. Bill Gate (how ironic) once said that it was not about the hardware but the software which will be the future. A decade or more later, the fifth employee of SUN, John Gage said “The Network is the Computer”. Fast-forwarding to the 21st century and John seemed to be right. Anyway, Java was built not to depend on an Operating System and deployed through the network. Java through its applet technology gave birth to Rich Network Application aka Rich Internet Application (RIA). Java is not perfect; or we would not have various releases and more on the way, but Java has given birth to a wide range of programming language (just Google it to find out more).

Without further ado, I am going to get back to subject. This is a brief article on what I believe that every Java developers should know regardless of their experience. I do not personally believe that someone with 5 years experience is not as good as someone with 10 years experience. We all develop our own methods of working but as a developer you need to stay abreast of your technology. So, here are my top 10 not in order of importance (or?):

  1. Remember the basic of Java language and OOP paradigm.
    Most experience developers seem to forget the theory behind the language. I am not saying that they are not good at their job but can they explain to junior developers why they have used interfaces instead of abstract classes or why implement a pattern over another one? As a programmer, you become very arrogant as you believe that you write the best code but in the real world, people work in teams with different skill set and experiences. It is important that you can backup your actions/ codes. A very simple question such as; when should I use a String object instead of a StringBuilder/ StringBuffer? You might take this question lightly but can you actually tell someone else the difference?
  2. Know your technology stack
    All developers have to know their technology stack. What does it mean? Java is not like other languages; Java has subsets such J2ME and superset such as Java EE. We have our own area of expertise but it is important to know the differences between the various sets of Java. Some basic questions such as the differences between SWING, Applet, Servlets, EJBs and JavaFX will boost your confidence. Most developers do not know how to tweak the JVM and the differences between the JRE and the SDK environment. Do you know why you need the SDK to be installed to run Tomcat but you only need the JRE to run an application?
  3. Experiment with various Java EE framework
    I am not asking you to be an expert in every single Java EE framework but it will make the difference if you are familiar with Spring and EJB. That should actually be the de facto framework that should be on every developers CV. Developers should know the difference between Java EE 5 (soon 6) and Spring. Hibernate is also brilliant and it’s used for data access but all developers should have moved to JPA by now. Hibernate also comply with JPA therefore there is no more excuses.
  4. Know a scripting language
    Java can be heavyweight for some simple tasks which can be implemented using a simple dynamic language such as Python, Perl(?) and others. I would also recommend to developers to learn shell scripting on their target OS.
  5. Know how to develop web services
    The network is the computer, therefore it is important to know the different web services framework available. Data are integrated through web services and opening your services to the “cloud”. SWING developers will probably not develop web services but I am sure that they will be connecting to data through web services clients. Understanding the difference between the standardised SOAP and non-standardised ReST will help you choose which is best to implement your services.
  6. Know how and when to multithread your application
    I have to put that in there. Developers should know when and why to multithread an application, thread inter-communication and monitoring. All developers, junior or not, should know how to write a multi-threaded application.
  7. Database development using JDBC and JPA
    This should be a development law. All developers should know how to write SQL queries and how to create databases. All enterprise applications store data in some sort of relational database systems and it is therefore imperative that this knowledge should be of second nature. Java EE 5 introduced JPA (JDO was there before) but it is not applicable to all situation. Hence, knowing the difference and when to implement one instead of the other is important.
  8. Know a client side scripting language and what is AJAX
    The network is the computer and Internet is the deployment platform. Java EE and its various framework are server side executiong which can put extra “load” on the server. If you are looking to move a cloud based system where the providers charges you per resources used, it might be wise to move some of the execution to the client side. AJAX has been buzzing the scene for the last 3 years and more. This is not a technology but a new way of doing something that already existed. There are numerous Java AJAX framework such as GWT and DWR which makes it easy to develop AJAX based application which are compiled to JavaScript. Developers should also know what is the AJAX theories.
  9. Know your competitors and do not take part on “what is the best IDE” discussion
    Java is not the only language that can do what it does. I think that Java is more mature and complete as opposed to other languages. Knowing the difference between Java and .NET or Java and Ruby is a good asset to have. You also need to know when and why to use one instead of the other. Please please please, do not get into “my IDE is better than x because…” discussion as it is good for the Java community to have multiple IDEs and framework available to use. Every tools have their place as for example JDeveloper is better than x if you are going to solely develop on an Oracle stack and etc…
  10. Know ANT (MAVEN?), TOMCAT and any other mainstrean application server
    ANT is the de facto build script for Java and its IDE-based development. Maven is becoming popular and soon can be as popular as ANT (not sure of its popularity in the financial sector). TOMCAT  should be immortalised as the based servlet container that all developers should be familiar with.

There are alot more to add but this is just some of the basics that I think all developers should have in their repertoire. Feel free to add to this list in the comments box. If I could had another one to this, would be; all developers not just Java, should know how to search the web and Google is your best friends (now support my advertisers by clicking on the links on the right 😉 ). I hope you enjoyed the entry and feel free to comments good or bad!!! are welcome.

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ReST Web Services on Google App Engine using NetBeans 6.7

When Google announced early this year the availability of the Java language on their cloud system “App Engine”, this was turning point for Java on the web. The reason I am saying that is due to a simple questions; how many hosting providers support Java? And providing free hosting for that purpose… This was a good move in the direction of the JAVA community and the vast list of all the languages that run on the JVM.  But App Engine does not support the full range of the J2EE API. If you are looking to build any EJB, SOAP services or anything that access the file system, then the App Engine is not for you as it does not support it. To make matter worst, some URL connections are not supported by the Google cloud services. I am looking forward to the day when JBoss Seam will be supported entirely by their services without having to hack the code. Alright, it is not that bad; Google App engine supports a number of Java EE frameworks such as Spring.

Alright people, this was a long introduction but I believe it is worth it. You cannot create web services such as SOAP in the Google App Engine therefore, in this short article, I will show you how to develop a ReST based web services that works with the App Engine using NetBeans and Jersey API. Actually, NetBeans comes with Jersey support out the box. Now, let’s get started.
In order to follow the instructions, you will need the following:

NetBeans 6.7+

Google App Engine SDK

Google App Engine Plugin for NetBeans

I would expect you to know to be familiar with JAVA EE development and Google App Engine development. Once you have all the software and components installed, now we can start.

1.    Create a database structure to store your data. I used MySQL Workbench to design my DB structure (Google App Engine does not used MySQL and does not have plan to support it in the future). This schema is to help you understand the relationship between your entities. You can use any UML tools to design your objects’ relationship. There is a reason I chose to design DB in MySQL, the application generates SQL script which I will upload to MySQL DB. I will show you in the next step the main benefits.
 

2.    Based on your DB schema, create a database. You can use any database you want. I used MySQL to initially store my entities.

3.    Launch your NetBeans application and create new Web Application.
 

3.1    Choose Google App Engine as deployment server, click here to see how to register the App Engine in NetBeans.

4.    Now click on: File -> New File. In the popup window, choose Web Services in the Categories panel and RESTFul Web Services from Database and click next.
 

5.    Choose your the database that you want to generate your Entity classes from and click next. ( in the screenshot I am using the sample DB which came with the NetBeans and JAVA DB server. This is just for illustration purposes only as I have previously generated my Entity Classes from the DB schema I generated in step 1).

6.    Check your Class Names and how they relate to the database. Make any changes that you require in this screen, and then click next.
 

7.    In the next screen, just accept the default values and click finish.
 

Well we have done the hard parts. There is another step that missed out due to the fact that I already written the application. When generating Entities from Database, if you do not have a persistence unit available, it will ask to generate one. Here is more information on how to create a persistence unit with NetBeans. Make sure to make sure to choose “Create” as the table generation strategy.
 

By Now, you should be aware that we have create a back-end application store which we can call using normal http post, get, delete and create. NetBeans RestFull methods allows to use XML or JSON to send data to the services. The responses MIME can be anything you like as long as the application server supports it.
WARNING: JERSEY XML processing is not supported by Google App Engine as it uses JAXB. JAXB accesses API which is forbidden by the App Engine stack. If testing the application on the App engine, use the JSON MIME for your data.
Ok so we have generate the classes and methods require to expose our back-end to other application. As it is, this will not work on Google App Engine so we need to make a final change, this time we need to change the persistence.xml file manually. In the project window under the name of your project, click on Configuration files -> persistence.xml and open the file in the editor. Once the file is open in the editor, click on the XML tab and make the necessary changes to make it look like the screenshot.
 

Here is the content of persistence.xml; modify to reflect your entities and make sure the name of the provider is the same as mine and the properties are exactly the same.

    <?xml version=”1.0″ encoding=”UTF-8″?>
    <persistence version=”1.0″ xmlns=”http://java.sun.com/xml/ns/persistence” xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance” xsi:schemaLocation=”http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd”>
        <persistence-unit name=”ReSTWebApplicationPU” transaction-type=”RESOURCE_LOCAL”>
            <provider>org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider</provider>
            <class>com.test.api.Userlogs</class>
            <class>com.test.api.Customer</class>
            <class>com.test.api.User</class>
            <class>com.test.api.Business</class>
            <class>com.test.api.Reviews</class>
            <exclude-unlisted-classes>false</exclude-unlisted-classes>
            <properties>
                <property name=”datanucleus.NontransactionalRead” value=”true”/>
                <property name=”datanucleus.NontransactionalWrite” value=”true”/>
                <property name=”datanucleus.ConnectionURL” value=”appengine”/>
            </properties>
        </persistence-unit>
    </persistence>

Now we are ready to run the application and test it in our local environment. Right click your project name in the projects window and click Test RestFul web services, your favourite web browser with page that shows your resources. You can test your services by clicking on the nodes and or drilling through the nodes.
 

You can also use the Firefox RESTClient Plugin to test your app. Also, Google App Engine does not fully support JPA and might throw some exception about not supporting “integer type object for primary key”. If you do experience this issue, change the type of your key.
This is it for now, looking forward to your feedback, good or bad, they are all welcome. Also, if you need JAVA EE help, contact me directly. Also join me on facebook. Hope the guide or tutorial or whatever you call it, was good enough to help you with something.

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Android Mobile Application Development – Budget My Day

The last weeks or so, I have been contemplating on build a mobile application. I wanted to use a technology that I was familiar with and that is also currently available in the market. So Let me describe the factors that affected this weekend project:

  1. The user interface of the application have to be nice a la iphone.
  2. provide RAD tools, I do not have time coding in notepad.
  3. Good documentation and online support (through forums and etc..).
  4. Need to able to learn and develop a nice UI within hours.
  5. The ability to connect and display real-time maps such as Google Maps or Yahoo!Maps.

Ok, first of all I was not trying to develop a mobile webpage, the type of thing you can do with Yahoo! Blueprint. My aim is to later develop this weekend project into a full blown mobile application with other contents such as videos, telephone dialing and messaging features. Based on that, I realized that there are bunch of technologies there which can be separated into two categories:

  1. Vendor neutral: J2ME (JavaFX???) and Android
  2. Vendor (or Manufacturer): iPhone, Symbian and the list is very long.

I therefore decided to take a vendor neutral approach. I have some experience developing J2ME based applications and I can tell that the user interface is not as great as on the iPhone or Android based phones. So what about JavaFX, let me know the next time you see a JavaFX-based phone in a shop window or in public.

So I decided to take the Android route. I know the API were based on JAVA, making the learning curve an easy ride. One thing I don’t understand is; Android has been out for awhile and still do not provide a supported version of their development plugins for NetBeans or any other IDE but Eclipse. Nevertheless, I decided to use NetBeans to the develop the “weekend project”. Android emulator is nice to work but sometimes, i just had to run the application multiple times in order to see the app in the emulator.

I believe that in order to be a good Android developer, you need to familiarize yourself with building the UI through the XML and know your widget from your layouts. Anyway, this is just the start of the project but next time I blog about, I will discuss how to connect to web services to perform user authentication and persist data. For now here is a screenshot of the search tab taken from the emulator.

P.S. The application will be a recommendation engine that will recommend user how to go out and enjoy themselves on any budget. For example, a person with £100 budget can see what to do, where and when. For example, go on a date to cinema then to restaurant before heading out to night club. Users will be able to review and rate recommendations.

Please support my blog and its advertisers by clicking on the interesting products/ services on the right (Google ads).  Cheers.

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Google Wave – Wave 2 Skype Robot

Well it is time for the Google Wave 2 Skype robot. Awhile ago, I mentioned about writing a simple robot for Google Wave which will call a number through Skype, see here. I finally had some time to burn, therefore I decided to write the simple project.

This a very simple application that only checks the wave “blips” and provide users with an option of calling a number by prefixing with “call: “. The idea is very simple and can be applied in other context such as the following:

  • a travel agent can monitor for terms of place or cities and recommend tickets or provide city information retrieve from Wikipedia.
  • Or the robot can translate messages from one language to another (similar to the Google Wave initial demo).
  • you can connect to any system that you want to suffice your requirements.

The project was developed in JAVA and deployed to Google App as that is the only suppoirted domain. This is not a tutorial but you can take a look at the screenshot. Alternatively, if you a Google Wave account, why not add the robot to your wave and take it from a test drive. Feel free to leave any comme nts.

P.S. Google Sandbox seems to block the callto protocol, leave comments to let me know if that’s true on your side.

Please support my blog and its advertisers by clicking on the interesting products/ services on the right (Google ads).  Cheers.

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TwittDM – Automated Twitter Mass Direct Messenger (in JAVA)

Awhile ago, I wrote about the about an automated  mass direct messenger for Twitter to allow users to contact all their followers at once, and making sure that their tweets will not be lost in the wild. Well, the wait is now over. I wrote a proof concept that I will enhance with more features as users make request.

Here is a simple list of current features:

  • Direct Message – Users can write a single message and have sent directly to all their followers.
  • Mentions – Users can write a single message and have all their followers mentioned so that followers will read.

Future feature

  • Select message recipients – Users will be able to select which users will receive the direct messages or which users will be mentioned in their updates.
  • any feature requested by users.

The application was developed using JAVA, ReST API and Twitter4J API. This is a secure interface and I am not storing users’ passwords and username and authentication are handled by Twitter web services.

You can find the application @ http://twittdm.appspot.com/. Yup, the application is deployed on Google App engine.

Feel free to let me know what you think of the app, and please do not mentioned by graphic skills because I am not a designer.

All comments are welcome, and you request features by sending me a tweet.
          

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Building Portlet 1.0 (JSR168) with GWT 1.7 on NetBeans 6.7

In this tutorial, I will build a Portlet 1.0 (JSR168) which I will then deploy on Liferay and OpenPortlet Container. Alternatively, the portlet should be able to run on any other JSR168 compliant portlet container. I like the “Hello World” tutorial that we are accustomed to but I wanted to do something different this time. I decided to build the a GWT 1.7 based portlet which also make use of the Google Visualization API for GWT.
In order to follow this tutorial, you will need the following:

This is not a tutorial about GWT or JSR168 Portlet but a focus on how to make them both work together to provide a nice UI. Prior knowledge of building and deploying portlet applications and developing GWT applications is required.
Once the development environment is ready, launch NetBeans and create a new web application project with Portlet and GWT support. Follow these steps in order to create web application with Portlet and GWT support.

  1. Create a new web project
  2. Give a project name and click next
  3. Choose your deployment portlet container and click next

  1. Add Google Web Toolkit (GWT) framework to your project

  1. Add Portlet Support to your project, chise any version and tick the boxes to create portlet and jsps. Fill in any required fields and click finish


NetBeans then generates all the required files in order to build the application. Initially, the two frameworks; Portlet and GWT are unaware of each other. Depending on your folder structure the following will be different. Here is a screenshot of my project structure in NetBeans.


My project is called LiferayHomePortlet as my Portlet Container is Liferay 5.2. My root package is com.etapix. This package will be used by GWT as the default package and will create the client and server packages as follow:

  • Com.etapix.client: this is package will have all my client side code including my xxxxEntryPoint.java class (xxxx being the name that you have chosen for your GWT)
  • Com.etapix.server: this package will not be used for the purpose of this tutorial

xxxx.gwt.xml (xxxx should be replaced with the name you are chosen will setting up the GWT framework for the project) was created in my root package “com.etapix”

NetBeans portlet generation feature has created, among other files, three jsps file under the WEB-INF/jsp folder

  • xxxxPortlet_edit.jsp
  • xxxxPortlet_help.jsp
  • xxxxPortlet_view.jsp

and the java class which will be used to render the portlet are allocated in com.etapix.liferay.portlet folder as LiferayHomePortlet.java.

In order for the portlet to display the chart from the GWT Visualization API, I have changed the generated code from portletEntrtyPoint.java. Once the changed to the GWT file was done, change the following file:

  • xxxxPortlet.java to include the following line in the “doView” method. Here is how you doView method should look like

    public void doView(RenderRequest request, RenderResponse response) throws PortletException, IOException {

    response.setContentType(“text/html”);

    PortletRequestDispatcher dispatcher =

    getPortletContext().getRequestDispatcher(“/WEB-INF/jsp/LiferayHomePortlet_view.jsp”);

    PrintWriter writer = response.getWriter();

    writer.println(“<script language=’javascript’ src='” + request.getContextPath() + “/com.etapix.portlet/com.etapix.portlet.nocache.js’></script>”);

    dispatcher.include(request, response);

    }

  • xxxxPortlet_view.jsp. This is what your code should look like

    <%@page contentType=”text/html”%>

    <%@page pageEncoding=”UTF-8″%>

    <%– Uncomment below lines to add portlet taglibs to jsp

    <%@ page import=”javax.portlet.*”%>

    <%@ taglib uri=”http://java.sun.com/portlet_2_0″ prefix=”portlet”%>

    <portlet:defineObjects />

    <%PortletPreferences prefs = renderRequest.getPreferences();%>

    –%>

    <div id=”gwt”></div>

Once the changes are completed, build your application and deploy it to your portlet container of your choice.

This is what it looks like in Liferay Portlet container

this is what it looks in OpenPortal Portlet Container.


This was my first blog tutorial as I am looking to provide more tutorials in the future. I hope you found this helpful. I have included the NetBeans project folder for your to play with.
download NetBeans project

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