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• Good learning resources for JNDI implementation (JBoss 5)

  - by iandisme

  I have been working with JavaEE/EJB3 web apps for about half a year now. Until recently, I haven't had to touch a lot of the behind-the-scenes stuff, just the meat of the code. I have been wrestling with JNDI problems, and though I've solved a couple of them, I'm pretty much just doing the whole cargo cult copy-paste routine. It would really help me to better understand JNDI; my understanding of it right now can be summarized as "it's that thing these classes sometimes do to find other classes." My question is, has anyone had success learning JNDI/EJB3/related topics from a book or online content? I've googled for it but the stuff that comes up is old or specific to a certain framework I'm not using. I'm looking for something that's either JBoss-specific or generic enough to be useful anyway.

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• How Java Runtime Maps to Targets

  - by zharvey

  According to the Javadocs for Runtime here: Every Java application has a single instance of class Runtime that allows the application to interface with the environment in which the application is running. The current runtime can be obtained from the getRuntime method. An application cannot create its own instance of this class. My question is: what's their definition of an application? Is each JAR/WAR/EAR considered a standalone application? What about a plain ole' Driver.class class with a main() method? What about JEE containers that house EARs and EJBs? I guess I'm trying to understand how many Runtime instances could be up and running inside a complex (JEE) system. And understanding that requires me to understand what specific "things" constitute an "application" in Java terminology. Thanks in advance!

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• What exactly is a Monad?

  - by WeNeedAnswers

  Can someone please explain to me what a Monad is. I think I grasp Monoids and I grasp that they basically control the input of state into a system. I just look at the text in Haskell and glaze over. A simple example in python would be great. My current understanding is that a Monoid is a procedural piece of code that needs to be read from top to bottom in sequence with the output being the input for the function. I think that I may even got that wrong, but hey I am here to learn.

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• ORM framework that extends base class with database-implementation.

  - by aioobe

  I have a game consisting of a client / server + a webpage. A central notion in both client and game-/webserver is an Account. Accounts are stored in a database thus I'm in need of some ORM and recently had a look at Hibernate and Cayenne. My understanding however, is that both frameworks provide an "DatabaseBackedAccount"-class which I extend with my other Account methods. My problem is that the Account class is reused heavily on the client side, and I would obviously not want to include database-related code on the client implementation. My current solution is to have an Account class (shared by server and client) and extend this with a DatabaseBackedAccount (overriding setter-methods and providing a commit method) on the server side. I find this quite natural and nice, however I've had to implement all gory sql-details and ORM myself. Is there any way to "turn the table" in any existing ORM framework, so that the generated classes extend my existing class?

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• strategies for learning complex software packages

  - by Tom

  I am a fairly novice Java programmer and I am currently working on a project to extend a piece of software that has been developed over a few years. So it has pretty big code base and the previous developers knew it well, so extending it is not going to be easy without a thorough understanding of the structure and function. 1) I had begun by trying to tackle small parts of the system and document them with mindmap. (particularly I am trying to document the interactions with external systems) 2) I have the book "code complete", which I am working through. 3) I have pointed some tools like "tattletale" at the code to get some diagrams of dependency relationships. What other strategies should I employ, should I focus on one particular aspect?

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• Are Scala "continuations" just a funky syntax for defining and using Callback Functions?

  - by Alex R

  And I mean that in the same sense that a C/Java for is just a funky syntax for a while loop. I still remember when first learning about the for loop in C, the mental effort that had to go into understanding the execution sequence of the three control expressions relative to the loop statement. Seems to me the same sort of effort has to be applied to understand Continuations (in Scala and I guess probably other languages). And then there's the obvious follow-up question... if so, then what's the point? It seems like a lot of pain (language complexity, programmer errors, unreadable programs, etc) for no gain.

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• Preserving original StackTrace/LineNumbers in .NET Exceptions

  - by Sam

  Understanding the difference between throw ex and throw, why is the original StackTrace preserved in this example: static void Main(string[] args) { try { LongFaultyMethod(); } catch (System.Exception ex) { Console.WriteLine(ex.StackTrace); } } static void LongFaultyMethod() { try { int x = 20; SomethingThatThrowsException(x); } catch (Exception) { throw; } } static void SomethingThatThrowsException(int x) { int y = x / (x - x); } But not in this one: static void Main(string[] args) { try { LongFaultyMethod(); } catch (System.Exception ex) { Console.WriteLine(ex.StackTrace); } } static void LongFaultyMethod() { try { int x = 20; int y = x / (x - 20); } catch (Exception) { throw; } } The second scenario is producing the same output as throw ex would? In both cases, one expects to see the line number where y is initialized.

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• What is the "task" in twitter Storm parallelism

  - by John Wang

  I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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• Do comments slow down an interpreted language?

  - by mvid

  I am asking this because I use Python, but it could apply to other interpreted languages as well (ruby, php). Whenever I leave a comment in my code, is it slowing down the interpreter? My limited understanding of an interpreter is that it reads program expressions in as strings and converts those strings into code. It seems that every time it parses a comment, that is wasted time. Is this the case? Is there some convention for comments in interpreted languages, or is the effect negligible?

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• Arrays in database tables and normalization

  - by Ivan Petrov

  Hi! Is it smart to keep arrays in table columns? More precisely I am thinking of the following schema which to my understanding violates normalization: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), Permissions varchar(max) not null default(''), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); and this: create table Permissions( GroupID int not null default(-1), CategoryID int not null default(-1), PermissionID int not null default(-1), constraint PK_GroupCategory primary key clustered(GroupID,CategoryID) ); UPD: Forgot to mention, in the scope of this concrete question we will consider that the "fetch rows that have permission X" won't be performed, instead all the lookups will be made by GroupID and CategoryID only Thoughts? Thanks in advance!

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• Authentication from url in Restlet

  - by DutrowLLC

  I've been using Restlets "ChallengeResponse" mechanism to authenticate users so far. ChallengeResponse challengeResponse = getRequest().getChallengeResponse(); if( challengeResponse == null ){ throw new RuntimeException("not authenticated"); } String login = challengeResponse.getIdentifier(); String password = new String(challengeResponse.getSecret()); From my understanding, "ChallengeResponse" requires that the username and password are put into headers. However a client needs to put the credentials into the url like so: https://username:[email protected]/my_secure_document When I looked at what was actually sent, it looks like the password is being hashed. What is the proper way to authenticate in this fashion using Restlet?

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• How to write a Compiler in C for C

  - by Kerb_z

  I want to write a Compiler for C. This is a Project for my College i am doing as per my University. I am an intermediate programmer in C, with understanding of Data Structures. Now i know a Compiler has the following parts: 1. Lexer 2. Parser 3. Intermediate Code Generator 4. Optimizer 5. Code Generator I want to begin with the Lexer part and move on to Parser. I am consulting the following book: Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman. The thing is that this book is highly theoretical and perplexing to me. I really appreciate the authors. But the point is i am not able to begin my project, as if i am blinded where to go. Need guidance please help.

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• Handling ID's with db4o and ASP.NET MVC2

  - by Craig McGuff

  So, i'm looking at the TekPub sample for ASP.NET MVC2 (http://mvcstarter.codeplex.com/) using DB4o and there are a bunch of templates to create controllers etc, the generated code looks like: public ActionResult Details(int id) { var item = _session.Single<Account>(x=>x.ID == id); return View(item); } Now, my understanding is that using DB4o or a simliar object database that ID's are not required, so how/what exactly do I pass to enable this kind of templated code to function? UPDATE: Both answers were useful, I have modifed the templates to use GUID as the ID. I will add any relevant code/notes here once I see how it works out.

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• is there a downside to putting N in front of strings in scripts? Is it considered a "best practice"?

  - by jcollum

  Let's say I have a table that has a varchar field. If I do an insert like this: INSERT MyTable SELECT N'the string goes here' Is there any fundamental difference between that and: INSERT MyTable SELECT 'the string goes here' My understanding was that you'd only have a problem if the string contained a Unicode character and the target column wasn't unicode. Other than that, SQL deals with it just fine and converts the string with the N'' into a varchar field (basically ignores the N). I was under the impression that N in front of strings was a good practice, but I'm unable to find any discussion of it that I'd consider definitive. Title may need improvement, feel free.

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• What's the ROI of using a build tool like ant or nant?

  - by leeand00

  To me this sounds like a really stupid question. Why would you not use a build tool? However, I need to explain my co-worker why he should be using a build tool of some sort. He's getting really into the idea of working as a team with more programmers, but he isn't understanding the bigger picture of what needs to change in the build process in order to work with a larger team; (i.e. defensive programming/unit testing your code, having a bug database, programming modular libraries, and using sub-repositories to store modules in version control. This is a rather large stack of technologies that I need to prove the ROI of...so I figured I'd start with the ROI of using a build tool rather than just...say...clicking compile.

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• Assigning a MVC Controller property from Asp.Net page

  - by JasonMHirst

  I don't know if I've understanding MVC correctly if my question makes no sense, but I'm trying to understand the following: I have some code on a controller that returns JSON data. The JSON data is populated based on a choice from a dropdown box on an Asp.Net page. I thought (incorrectly) that Session variables would be shared between the Asp.Net project and the MVC Project. What I'd like to do therefore (if this is possible), is to call a Sub on the MVC that sets a variable before the JSON query is run. I have the following: Sub SetCountryID(ByVal CountryID As Integer) Me.pCountrySelectedID = CountryID End Sub Which I can call by the following: Response.Write("http://localhost:7970/Home/SetCountryID/?CountryID=44") But this then results in a blank page - again obviouslly totally incorrect! Am I going about MVC the wrong way or do I still have a hell of a lot more learning to do? Is this even possible to do?

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• How do negated patterns work in .gitignore?

  - by chrisperkins

  I am attempting to use a .gitignore file with negated patterns (lines starting with !), but it's not working the way I expect. As a minimal example, I have the folllowing directory structure: C:/gittest -- .gitignore -- aaa/ -- bbb/ -- file.txt -- ccc/ -- otherfile.txt and in my gitignore file, I have this: aaa/ !aaa/ccc/ My understanding (based on this: http://ftp.sunet.se/pub//Linux/kernel.org/software/scm/git/docs/gitignore.html) is that the file aaa/ccc/otherfile.txt should not be ignored, but in fact git is ignoring everything under aaa. Am I misunderstanding this sentence: "An optional prefix ! which negates the pattern; any matching file excluded by a previous pattern will become included again."? BTW, this is on Windows with msysgit 1.7.0.2.

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• What software analogies have helped you?

  - by Galwegian

  I have often enjoyed the use of analogies in understanding a software scenario or problem. For example, to understand the concept of public key encryption, the 'locked mailbox' analogy or similar is often used as an aid: An analogy for public-key encryption is that of a locked mailbox with a mail slot. The mail slot is exposed and accessible to the public; its location (the street address) is in essence the public key. Anyone knowing the street address can go to the door and drop a written message through the slot; however, only the person who possesses the key can open the mailbox and read the message. My question is: What analogies have you used or heard of in your career that have given you that "Eureka" moment with a complex concept? EDIT: If you have a good one, don't just state the name, please share with the group!

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• How does struts 1.X ActionForm handle pure html checkbox list?

  - by BlueDolphin

  I am dealing with an old application which uses struts 1.2. And for some reason, we are using pure html form to submit to struts action. For example: for the content output of testAction.do, I try to submit to itself. item 1 item 2 Then I associate an form bean TestForm with testAction. I am not sure how to specify the properties in the form so that it take the value from myitem1 after user click "submit" I tried to add getMyitem1(), setMyitem1(String[] items), getSelectedMyitem1(), setSelectedMyitem1(String[] items) Those set methods are only called when page are loaded. I guess my understanding of ActionForm in struts 1.x must be wrong. Please advise, thanks.

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• LAMP Stack with APC installed - WordPress Site - Is WP opcode being cached with APC?

  - by Christopher Altman

  I have a LAMP stack with APC installed. I have a WordPress site on this server. Is WP taking advantage of the opcode caching? I have done no WP configurations. My understanding is that simply having APC installed means that all PHP code is being cached. If that is untrue, please point me to the direction where I can configure WP to take advantage of APC. Note: I thought about this as a ServerFault question, but since the solution to is code related I posted on Stackoverflow.

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• EXC_BAD_ACCESS when not using self.

  - by chris

  I got nabbed by the following bug again and would like some clarification to exactly why it is a bug. I have a simple UITableView that loads some data: // myclass.h @property (nonatomic, retain) NSArray *myData // myclass.m @synthesize myData; - (void) viewDidLoad { ... myData = someDataSource // note the lack of self } - (UITableViewCell *) cellForRowAtIndexPath ... { ... cell.textLabel.text = [self.myData objectAtIndex:indexPath.row]; // EXC_BAD_ACCESS } The table first loads fine, but when scrolling up enough that one of the cells is totally out of the view I then get the EXC_BAD_ACCESS error. Am I missing something in regards to @property retain. My understanding is that it releases anything that the pointer was previously pointing to before the reassignment. If I am correct then why would not using self. cause any problems? Thanks for the help.

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• How do I use SDl_Threads properly?

  - by Anoymonous

  I am new to threads,SDL and how graphic work in general. I've been looking through all of LazyFoo's SDL tutorials, and had helped me greatly. But in his tutorials about multi threading, he commented that you should never use video functions in separate threads, or might cause problem. I am curious how it should be done, as I still have a vague understanding of graphics and threads. As one of my projects is a shoot'em up, I was wondering if I should create one thread that displays all the graphics, one threads receives all the player input for his ship, and another thread for the enemy AI. If this is NOT how it should be done, (I think it's wrong) does anyone have any advice of how graphics should be implemented with user input and enemy AI with threads? For the Lazyfoo's tutorials, this is the link: http://lazyfoo.net/SDL_tutorials/

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• Magento layout override!

  - by Farid

  Hi, I'm kind of new to the Magento, so forgive me for my stupid question! As I understand the whole concept of Magento is base on overriding the basic components that's are available with in the Magento. So based on my understanding I've decided to update the layout of onepage checkout in Magento. I've created my own layout and in the config file set that my layout updates the checkout module layout. But the problem is it's actually does not update the base layout, it replaces it self with base layout! Should it be act like this or am I wrong?!

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• Why should I reuse XmlHttpRequest objects?

  - by Xavi

  From what I understand, it's a best practice to reuse XmlHttpRequest objects whenever possible. Unfortunately, I'm having a hard time understanding why. It seems like trying to reuse XHR objects can increase code complexity, introduce possible browser incompatibilities, and lead to other subtle bugs. After researching this question for a while, I did come up with a list of possible explanations: Fewer objects created means less garbage collecting Reusing XHR objects reduces the chance of memory leaks The overhead of creating a new XHR object is high The browser is able to perform some sort of network optimization under hood But I'm not sure if any of these reasons are actually valid. Any light you can shed on this question would be much appreciated.

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• MPI4Py Scatter sendbuf Argument Type?

  - by Noel

  I'm having trouble with the Scatter function in the MPI4Py Python module. My assumption is that I should be able to pass it a single list for the sendbuffer. However, I'm getting a consistent error message when I do that, or indeed add the other two arguments, recvbuf and root: File "code/step3.py", line 682, in subbox_grid i = mpi_communicator.Scatter(station_range, station_data) File "Comm.pyx", line 427, in mpi4py.MPI.Comm.Scatter (src/ mpi4py_MPI.c:44993) File "message.pxi", line 321, in mpi4py.MPI._p_msg_cco.for_scatter (src/mpi4py_MPI.c:14497) File "message.pxi", line 232, in mpi4py.MPI._p_msg_cco.for_cco_send (src/mpi4py_MPI.c:13630) File "message.pxi", line 36, in mpi4py.MPI.message_simple (src/ mpi4py_MPI.c:11904) ValueError: message: expecting 2 or 3 items Here is the relevant code snipped, starting a few lines above 682 mentioned above. for station in stations #snip--do some stuff with station station_data = [] station_range = range(1,len(station)) mpi_communicator = MPI.COMM_WORLD i = mpi_communicator.Scatter(station_range, nsm) #snip--do some stuff with station[i] nsm = combine(avg, wt, dnew, nf1, nl1, wti[i], wtm, station[i].id) station_data = mpi_communicator.Gather(station_range, nsm) I've tried a number of combinations initializing station_range, but I must not be understanding the Scatter argument types properly. Does a Python/MPI guru have a clarification this?

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