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• What motivates people to learn a new programming language?

  - by szabgab

  There are plenty of question asking Which Programming Language Should I Learn? but I have not found an answer yet to the question what really motivates people to learn a specific new language?. There are the people who think they should learn a new language every year for educational purpose. How do they decide on the languages to be learned? Then I guess there are people who learn a new language because people around them told it is a fun language and they can build nice things with it. Of course if the current job requires it people would learn a new language but I think if the language seems to have a potential to earn money (e.g. There are plenty of jobs in Java or ObjectiveC can be used to write apps for the iPhone and make money). So why are you learning a new language or why have you learned the languages you know?

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• Formal name of Magento’s Class Override Design Pattern?

  - by Alan Storm

  Magento is a newish (past 5 years) PHP based Ecommerce system with an architecture that's similar to the Java Spring framework (or so I've been told) One of the features of the Framework is certain classes are not directly instantiated. Rather than do something like $model = new Mage_Foo_Model_Name(); you pass an identifier into a static method on a global application object $model = Mage::getModel('foo/name'); and this instantiates the class for you. One of the wins with this approach is getModel checks a global configuration system for the foo/name identifier, and instantiates the class name it finds in the configuration system. This allows you to change the behavior of a Model system wide with a single configuration change. Is there a formal, Gang of Four or otherwise, name that describes this system/design pattern? The instantiation itself looks like a classic Factory pattern, but I'm specifically interested in the whole "override a class in the system via configuration" aspect. Is there a name/concept that covers this, or is it contained within the worldview of a Factory?

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• What the best way to convert from String to HashMap?

  - by eugenn

  I would like to serialize a Java HashMap to string representation. The HashMap will contains only primitive values like string and integer. After that this string will be stored to db. How to restore back the HashMap? Is it make sense to use BeanUtils and interface Converter or use JSON? For example: List list = new ArrayList(); list.add(new Long(1)); list.add(new Long(2)); list.add(new Long(4)); Map map = new HashMap(); map.put("cityId", new Integer(1)); map.put("name", "test"); map.put("float", new Float(-3.2)); map.put("ids", list); map.toString() -> {float=-3.2,ids=[1, 2, 4],name=test,cityId=1} map.toJSON -> {"float":-3.2,"ids":[1,2,4],"name":"test","cityId":1}

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• Understanding flow of object creation

  - by Boris Mandovskes

  I'm new to java and I wonder if there is simple way to know flow like the following of object creation, I'm using eclipse and when I write new ObjectInputStream and press CTRL+SPACE. I don't see any option that I can enter new BufferedInputStream (I have copied the code from example) and than to create new object for FileInputStream etc. in = new ObjectInputStream(new BufferedInputStream(new FileInputStream("emp.dat"))); List temp = (List)in.readObject(); I give that example since this is the first time that I saw this kind of creation new object flow and I want to use some best practice for the next times.

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• When and why does an EventHandler require objects to be final?

  - by Michiel Borkent

  I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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• Writing my first blackberry app

  - by skyeagle

  I am contemplating writing my first blackberry app. I am fundamentally, a C/C++ programmer (not Java), can anyone provide some guidelines on the quickest route (i.e. shallowest learning curve) to writing a blackberry app? Any resources/links would be useful. As an aside: In an ideal world, I would like to write once and deploy for both Blackberry and the iPhone, but since I am targetting largely business people, I guess blackberry should be my target - right? Is it possible to write once and deploy on BOTH iphone and BB?

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• reading unicode

  - by user121196

  I'm using java io to retrieve text from a server that might output character such as é. then output it using System.err, they turn out to be '?'. I am using UTF8 encoding. what's wrong? int len=0; char[]buffer=new char[1024]; OutputStream os = sock.getOutputStream(); InputStream is = sock.getInputStream(); os.write(query.getBytes("UTF8"));//iso8859_1")); Reader reader = new InputStreamReader(is, Charset.forName("UTF-8")); do{ len = reader.read(buffer); if (len0) { if(outstring==null)outstring=new StringBuffer(); outstring.append(buffer,0,len); } }while(len0); System.err.println(outstring);

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• errorPage directive works, but error-page in web.xml doesn't?

  - by danb

  I get jsp exceptions causing a forward to my error page when I put this at the top of my JSPs... <%@ page errorPage="/error.page" %> but when I try to do it globally with web.xml like so: <error-page> <exception-type>java.lang.Throwable</exception-type> <location>/error.page</location> </error-page> I just get a blank page... I've also tried putting /error.jsp in the location element.. but no love with that either.. I am triggering an exception with a jsp that just contains this: <%if(true)throw new RuntimeException("test exception");%> I do see the exception in the console from tomcat but I just can't get that error page to show without a directive on every jsp... am I missing something simple here?

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• In Eclipse, how do I change the default modifiers in the class/type template?

  - by gustafc

  Eclipse's default template for new types (Window Preferences Code Style Code Templates New Java Files) looks like this: ${filecomment} ${package_declaration} ${typecomment} ${type_declaration} Creating a new class, it'll look something like this: package pkg; import blah.blah; public class FileName { // Class is accessible to everyone, and can be inherited } Now, I'm fervent in my belief that access should be as restricted as possible, and inheritance should be forbidden unless explicitly permitted, so I'd like to change the ${type_declaration} to declare all classes as final rather than public: package pkg; import blah.blah; final class FileName { // Class is only accessible in package, and can't be inherited } That seems easier said than done. The only thing I've found googling is a 2004 question on Eclipse's mailing list which was unanswered. So, the question in short: How can I change the default class/type modifiers in Eclipse? I'm using Eclipse Galileo (3.5) if that matters.

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• Need help on how to setup package structure and project

  - by jax

  I am new to Java and am making a license generator. This is my current setup. com.example.licensegenerator.client (used by the client application) :LicenseLoader (no Main method) :LicenseDownloader (no Main method) com.example.licensegenerator.server.keys (used by the server) :ProductKeyGenerator(Main method) com.example.licensegenerator.server.license (used on the server also) :LicenseGenerator(Main method) com.example.licensegenerator.lib (Shared classes between client and server) :Contants (no main) Now I have a few questions. Is it OK to have multiple Main() methods in a single project? Will I be able to compile them to different .jar files? (In this case I need two different jars for the server) Is there a better way to setup the packages? And a totally unrelated question, with exceptions, is it better to handle them right then and there or throw them and let the main method catch them all (the program cannot recover if an error occurs)

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• Override the methods of classes from a .war file.

  - by Sweety

  I have a base application war file say homeApp.war. This contains default operations which user can carry out on the web browser. Now I need to extend the operations available on the same application using that .war file. Like I need to add the extra menus, some shortcuts like icon for log out etc. Please let me know how can I use this .war file to extend the operations and also fix the already existing issues on the application. This web application uses java server faces.

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• FTP - way to programatically determine time remaining or bytes transfered?

  - by ciaranarcher

  Hi all I want to make an FTP connection (ideally using Coldfusion 8, but Java is fine too) that will copy a file to a remote server. Crucially however, I want to know how many bytes have been transferred so I can give some feedback to the user. Is this possible, and if so what FTP API would you recommend as I understand the Sun implementation may be a bit lacking. Thanks in advance! PS: I could have another process/thread poll the file size on the destination machine via a web service call while the file is being transferred but it's not ideal. Getting it through FTP API would be the neatest solution.

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• JFileChooser returns incorrect path in OS X (folders only mode)

  - by Virat Kadaru

  I have a problem in java swing where the user has to select a folder, so I am using the code below. JFileChooser fc = new JFileChooser(); fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY); if(fc.showDialog(singleton, SELECT) == JFileChooser.APPROVE_OPTION) { File folder = fc.getSelectedFile(); String path = folder.getPath() + File.separatorChar + MYAPPFOLDER; } Now there are 2 ways a user may select the folder Navigate to the folder and select the folder Navigate to the folder, go into the folder, and click select Both ways work fine on windows but on OS X, I get If I do 1 : path = Users/<username>/Desktop/MYAPPFOLDER If I do 2 : path = Users/<username>/Desktop/Desktop/MYAPPFOLDER How do I avoid this 2nd case? Thanks in advance.

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• Interactive Charts for web application

  - by user227290

  We are working on a web based application (implemented in JAVA) on commodity prices and one part of it is interactive charting. I provide a simplified example here. We have a table in Mysql database where we have information on commodity prices in US states and counties. One aspect of the application is to create interactive plots based on user choice. For example, if the user needs to see the price density in Oregon and Linn county then she chooses it from the menu in a webpage and it is rendered on fly with accompanying quantile information in a table. As the user changes state and county these plots and table change on fly.For our computational need we are using R (and use rjava to integrate it to our web application) and I know that if interactivity is not an issue this is a piece of cake in ggplot2, but I am not aware of any interactive version of R graphics framework (like lattice, ggplot2). We are exploring google visualization API but I am not sure we can have the statistical power we need in some of the plots.Please help.

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• How to continue copying on error with copyDirectory from FileUtils (Apache Commons IO 2.4)

  - by Exocom

  I am trying to copy files from one folder to another using the FileUtils method "static void copyDirectory(File srcDir, File destDir)" from apache commons io (2.4) with the following code: String srcDir = "/sourceDirectory/examples/"; String destDir = "/tmp/examples/"; try{ FileUtils.copyDirectory(new File(srcDir), new File(destDir)); } catch (IOException e){ e.printStackTrace(); } The file structure looks like the following: examples/ (read access) examples/.subdirectory (NO access) examples/file1.txt (read access) examples/file2.txt (read access) examples/subdirectory2/file1.txt (read access) examples/subdirectory2/file2.txt (NO access) The problem is, that in srcDir there are a few files and one subdirectory I don't have access to. FileUtils.copyDirectory throws an "java.io.FileNotFoundException: .subdirectory (Permission denied)" and aborts. Is it possible to ignore those files I don't have permission to and just copy all the other files I can read?

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• How to instantiate a Singleton multiple times?

  - by Sebi

  I need a singleton in my code. I implemented it in Java and it works well. The reason I did it, is to ensure that in a mulitple environment, there is only one instance of this class. But now I want to test my Singleton object locally with a Unit test. For this reason I need to simulate another instance of this Singleton (the object that would be from another device). So is there a possiblity to instantiate a Singleton a second time for testing purpose or do I have to mock it? I'm not sure, but I think it could be possible by using a different class loader?

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• Store date object in sqlite database

  - by bnabilos

  Hello, I'm using a database in my Java project and I want to store date in it, the 5th and the 6th parameter are Date Object. I used the solution below but I have errors in these 2 lines : creerFilm.setDate(5, new Date (getDateDebut().getDate())); creerFilm.setDate(6, new Date (getDateFin().getDate())); PreparedStatement creerFilm = connecteur.getConnexion().prepareStatement("INSERT INTO FILM (ID, REF, NOM, DISTRIBUTEUR, DATEDEBUT, DATEFIN) VALUES (?, ?, ?, ?, ?, ?)"); creerFilm.setInt(1, getId()); creerFilm.setString(2, getReference()); creerFilm.setString(3, getNomFilm()); creerFilm.setString(4, getDistributeur()); creerFilm.setDate(5, new Date (getDateDebut().getDate())); creerFilm.setDate(6, new Date (getDateFin().getDate())); creerFilm.executeUpdate(); creerFilm.close(); Can you help me to fix that please ? Thank you

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• how do i close a frame yet open a new frame?(revisited)

  - by altvali

  I'm new at Java and I'm trying to do what the title says, my application has page A, a jpanel with some controls and a specific button, and when the user clicks the button i want page A to disappear and page B to appear (page B has controls that depend on the choices that are made by the user on page A). This has been asked before but there was no satisfactory answer. In the ActionListener implementation, namely public void ActionPerformed(ActionEvent e) from my jpanelForPageA class i can comfortably write this.setVisible(false), but how can i set page B to a visible state?

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• Language neutral plugin architectures

  - by Mmarquee

  I am looking at extending an existing application through the use of a plugin architecture. The application id written in Delphi, but I want to be able to implement various plugins in whatever language is best of the job. Currently we have skills in Delphi, C# and Java, and would like to be able to implement a plugin in whatever language is required. Does anyone know of an example system that can be used to implement this ? I am assuming that I could standardise on a particular COM interface and anything that implements that interface could be a plugin. Does anyone have any pointers ? Thanks

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• What is the absolute fastest way to implement a concurrent queue with ONLY one consumer and one producer?

  - by JohnPristine

  java.util.concurrent.ConcurrentLinkedQueue comes to mind, but is it really optimum for this two-thread scenario? I am looking for the minimum latency possible on both sides (producer and consumer). If the queue is empty you can immediately return null AND if the queue is full you can immediately discard the entry you are offering. Does ConcurrentLinkedQueue use super fast and light locks (AtomicBoolean) ? Has anyone benchmarked ConcurrentLinkedQueue or knows about the ultimate fastest way of doing that? Additional Details: I imagine the queue should be a fair one, meaning the consumer should not make the consumer wait any longer than it needs (by front-running it) and vice-versa.

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• the use of private keyword

  - by LAT

  Hi everyone I am new to programming. I am learning Java now, there is something I am not really sure, that the use of private. Why programmer set the variable as private then write , getter and setter to access it. Why not put everything in public since we use it anyway. public class BadOO { public int size; public int weight; ... } public class ExploitBadOO { public static void main (String [] args) { BadOO b = new BadOO(); b.size = -5; // Legal but bad!! } } I found some code like this, and i saw the comment legal but bad. I don't understand why, please explain me.

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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• Applet in client-server infrastructure

  - by Andrey

  Hello! I have a general question concerning client-server design. We have a Java server with Spring, a GWT client program and some HTTP-servlets for our site. At the moment we also want to develop an applet which would communicate with that server in such a way GWT-client and site requests do. Is it a good idea to communicate with the server from applet by RMI? I.e. to create some Remote services, register them with Spring and call them from applet? Thanks in advance!

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• Groovy: Dynamically addings methods with a specific signature.

  - by Reverend Gonzo

  So, I need to dynamically create (or inject) methods into an object that have a specific return type and method signature, because a Java tool we're using will be finding this methods via Reflection and checks for void type. Method names will be determined at runtime. Using metaClass. = { ... } however adds a closure which doesn't show up as a regular method (even if it can be used as one) and also has a return type. I can't modify the method finding code, and it it not Groovy-aware. I can't use methodMissing() or invokeMethod() because the method needs to actually exist. If I could overload class.getMethods() I think it would be possible, but I can't figure out how. Is there any way to do this in Groovy?

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• How to store matrix information in MySQL?

  - by dedalo

  Hi, I'm working on an application that analizes music similarity. In order to do that I proccess audio data and store the results in txt files. For each audio file I create 2 files, 1 containing and 16 values (each value can be like this:2.7000023942731723) and the other file contains 16 rows, each row containing 16 values like the one previously shown. I'd like to store the contents of these 2 file in a table of my MySQL database. My table looks like: Name varchar(100) Author varchar (100) in order to add the content of those 2 file I think I need to use the BLOB data type: file1 blob file2 blob My question is how should I store this info in the data base? I'm working with Java where I have a double array containing the 16 values (for the file1) and a matrix containing the file2 info. Should I process the values as strings and add them to the columns in my database? Thanks

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