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• What's a good Java-based Master-Slave communication mechanism?

  - by plecong

  I'm creating a Java application that requires master-slave communication between JVMs, possibly residing on the same physical machine. There will be a "master" server running inside a JEE application server (i.e. JBoss) that will have "slave" clients connect to it and dynamically register itself for communication (that is the master will not know the IP addresses/ports of the slaves so cannot be configured in advance). The master server acts as a controller that will dole work out to the slaves and the slaves will periodically respond with notifications, so there would be bi-directional communication. I was originally thinking of RPC-based systems where each side would be a server, but it could get complicated, so I'd prefer a mechanism where there's an open socket and they talk back and forth. I'm looking for a communication mechanism that would be low-latency where the messages would be mostly primitive types, so no serious serialization is necessary. Here's what I've looked at: RMI JMS: Built-in to Java, the "slave" clients would connect to the existing ConnectionFactory in the application server. JAX-WS/RS: Both master and slave would be servers exposing an RPC interface for bi-directional communication. JGroups/Hazelcast: Use shared distributed data structures to facilitate communication. Memcached/MongoDB: Use these as "queues" to facilitate communication, though the clients would have to poll so there would be some latency. Thrift: This does seem to keep a persistent connection, but not sure how to integrate/embed a Thrift server into JBoss WebSocket/Raw Socket: This would work, but require a lot more custom code than I'd like. Is there any technology I'm missing? Edit: Also looked at: JMX: Have the client connect to JBoss' JMX server and receive JMX notifications for bidirectional comms.

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• problem with evolutionary algorithms degrading into simulated annealing: mutation too small?

  - by Schnalle

  i have a problem understanding evolutionary algorithms. i tried using this technique several times, but i always ran into the same problem: degeneration into simulated annealing. lets say my initial population, with fitness in brackets, is: A (7), B (9), C (14), D (19) after mating and mutation i have following children: AB (8.3), AC (12.2), AD (14.1), BC(11), BD (14.7), CD (17) after elimination of the weakest, we get A, AB, B, AC next turn, AB will mate again with a result around 8, pushing AC out. next turn, AB again, pushing B out (assuming mutation changes fitness mostly in the 1 range). now, after only a few turns the pool is populated with the originally fittest candidates (A, B) and mutations of those two (AB). this happens regardless of the size of the initial pool, it just takes a bit longer. say, with an initial population of 50 it takes 50 turns, then all others are eliminated, turning the whole setup in a more complicated simulated annealing. in the beginning i also mated canditates with themselves, worsening the problem. so, what do i miss? are my mutation rates simply too small and will it go away if i increase them? here's the project i'm using it for: http://stefan.schallerl.com/simuan-grid-grad/ yeah, the code is buggy and the interface sucks, but i'm too lazy to fix it right now - and be careful, it may lock up your browser. better use chrome, even thought firefox is not slower than chrome for once (probably the tracing for the image comparison pays off, yay!). if anyone is interested, the code can be found here. here i just dropped the ev-alg idea and went for simulated annealing. ps: i'm not even sure about simulated annealing - it is like evolutionary algorithms, just with a population size of one, right?

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• Namespace constants and use as

  - by GordonM

  I'm having some problems with using constants from a namespace. If I define the constant and try to use as it, PHP seems unable to find it. For example, in my file with the constants I have code along the lines of the following: namespace \my\namespace\for\constants; const DS = DIRECTORY_SEPARATOR; Then in the consuming file I have: namespace \some\other\namespace; use \my\namespace\for\constants\DS as DS; echo (realpath (DS . 'usr' . DS 'local')); However, instead of echoing '/usr/local' as expected I get the following notice and an empty string. Notice: Use of undefined constant DS - assumed 'DS' If I change the code as follows: use \my\namespace\for\constants as cns; echo (realpath (cns\DS . 'usr' . cns\DS 'local')); I get the expected result, but it's obviously quite a bit less convenient than just being able to pull the constants in directly. You can alias a class/interface/trait in a namespace, are you not able to alias a constant too? If you can do it, then how?

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• Which software for intranet CMS - Django or Joomla?

  - by zalun

  In my company we are thinking of moving from wiki style intranet to a more bespoke CMS solution. Natural choice would be Joomla, but we have a specific architecture. There is a few hundred people who will use the system. System should be self explainable (easier than wiki). We use a lot of tools web, applications and integrated within 3rd party software. The superior element which is a glue for all of them is API. In example for the intranet tools we do use Django, but it's used without ORM, kind of limited to templates and url - every application has an adequate methods within our API. We do not use the Django admin interface, because it is hardly dependent on ORM. Because of that Joomla may be hard to integrate. Every employee should be able to edit most of the pages, authentication and privileges have to be managed by our API. How hard is it to plug Joomla to use a different authentication process? (extension only - no hacks) If one knows Django better than Joomla, should Django be used?

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• Transitioning from desktop app written in C++ to a web-based app

  - by Karim

  We have a mature Windows desktop application written in C++. The application's GUI sits on top of a windows DLL that does most of the work for the GUI (it's kind of the engine). It, too, is written in C++. We are considering transitioning the Windows app to be a web-based app for various reasons. What I would like to avoid is having to writing the CGI for this web-based app in C++. That is, I would rather have the power of a 4G language like Python or a .NET language for creating the web-based version of this app. So, the question is: given that I need to use a C++ DLL on the backend to do the work of the app what technology stack would you recommend for sitting between the user's browser and are C++ dll? We can assume that the web server will be Windows. Some options: Write a COM layer on top of the windows DLL which can then be access via .NET and use ASP.NET for the UI Access the export DLL interface directly from .NET and use ASP.NET for the UI. Write a custom Python library that wraps the windows DLL so that the rest of the code can be written. Write the CGI using C++ and a C++-based MVC framework like Wt Concerns: I would rather not use C++ for the web framework if it can be avoided - I think languages like Python and C# are simply more powerful and efficient in terms of development time. I'm concerned that my mixing managed and unmanaged code with one of the .NET solutions I'm asking for lots of little problems that are hard to debug (purely anecdotal evidence for that) Same is true for using a Python layer. Anything that's slightly off the beaten path like that worries me in that I don't have much evidence one way or the other if this is a viable long term solution.

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• SIGABRT on iPhone when changing xib

  - by Boz

  I've just finished off an app for the iPhone which, until today, ran fine on the iPhone simulator and actual devices. I tried changing the xib which is loaded in the applicationDidFinishLaunching method in my application delegate class - all I did was change the string in initWithNibName. When I launch the app on the simulator, the Default.png image is shown, then the app crashes with an uncaught exception. When running on a device, the Default.png image is shown for about 10 seconds, the UI is never loaded and I get 'GDB: Program received signal: "SIGABRT".' on the Xcode status bar. Debugging shows that applicationDidFinishLaunching is never actually reached before the app crashes. Setting the starting xib back to the original solves the issue, but now I've made a change and saved it in the Interface Builder and the app shows the same issues as above - I've made no code changes at all. Is this a memory issue, or a known issue of a common mistake? NOTE: I've made no code changes whatsoever, and the only changes I've made to the xib are cosmetic, the IBOutlets are all intact.

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• UIImagePickerControllerDelegate Returns Blank "editingInfo" Dictionary Object

  - by Leachy Peachy

  Hi there, I have an iPhone app that calls upon the UIImagePickerController to offer folks a choice between selecting images via the camera or via their photo library on the phone. The problem is that sometimes, (Can't always get it to replicate.), the editingInfo dictionary object that is supposed to be returned by didFinishPickingImage delegate message, comes back blank or (null). Has anyone else seen this before? I am implementing the UIImagePickerControllerDelegate in my .h file and I am correctly implementing the two delegate methods: didFinishPickingImage and imagePickerControllerDidCancel. Any help would be greatly appreciated. Thank you in advance! Here is my code... my .h file: @interface AddPhotoController : UIViewController <UIImagePickerControllerDelegate, UINavigationControllerDelegate> { IBOutlet UIImageView *imageView; IBOutlet UIButton *snapNewPictureButton; IBOutlet UIButton *selectFromPhotoLibraryButton; } @property (nonatomic, retain) UIImageView *imageView; @property (nonatomic, retain) UIButton *snapNewPictureButton; @property (nonatomic, retain) UIButton * selectFromPhotoLibraryButton; my .m file: @implementation AddPhotoController @synthesize imageView, snapNewPictureButton, selectFromPhotoLibraryButton; - (IBAction)getCameraPicture:(id)sender { UIImagePickerController *picker = [[UIImagePickerController alloc] init]; picker.delegate = self; picker.sourceType = UIImagePickerControllerSourceTypeCamera; picker.allowsImageEditing = YES; [self presentModalViewController:picker animated:YES]; [picker release]; } - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo { NSLog(@"Image Meta Info.: %@",editingInfo); UIImage *selectedImage = image; imageView.image = selectedImage; self._havePictureData = YES; [self.useThisPhotoButton setEnabled:YES]; [picker dismissModalViewControllerAnimated:YES]; } - (void)imagePickerControllerDidCancel:(UIImagePickerController *)picker { [picker dismissModalViewControllerAnimated:YES]; }

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• Is there a way to use Linq projections with extension methods

  - by Acoustic

  I'm trying to use AutoMapper and a repository pattern along with a fluent interface, and running into difficulty with the Linq projection. For what it's worth, this code works fine when simply using in-memory objects. When using a database provider, however, it breaks when constructing the query graph. I've tried both SubSonic and Linq to SQL with the same result. Thanks for your ideas. Here's an extension method used in all scenarios - It's the source of the problem since everything works fine without using extension methods public static IQueryable<MyUser> ByName(this IQueryable<MyUser> users, string firstName) { return from u in users where u.FirstName == firstName select u; } Here's the in-memory code that works fine var userlist = new List<User> {new User{FirstName = "Test", LastName = "User"}}; Mapper.CreateMap<User, MyUser>(); var result = (from u in userlist select Mapper.Map<User, MyUser>(u)) .AsQueryable() .ByName("Test"); foreach (var x in result) { Console.WriteLine(x.FirstName); } Here's the same thing using a SubSonic (or Linq to SQL or whatever) that fails. This is what I'd like to make work somehow with extension methods... Mapper.CreateMap<User, MyUser>(); var result = from u in new DataClasses1DataContext().Users select Mapper.Map<User, MyUser>(u); var final = result.ByName("Test"); foreach(var x in final) // Fails here when the query graph built. { Console.WriteLine(x.FirstName); } The goal here is to avoid having to manually map the generated "User" object to the "MyUser" domain object- in other words, I'm trying to find a way to use AutoMapper so I don't have this kind of mapping code everywhere a database read operation is needed: var result = from u in new DataClasses1DataContext().Users select new MyUser // Can this be avoided with AutoMapper AND extension methods? { FirstName = v.FirstName, LastName = v.LastName };

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• Windows Azure - access webrole local storage from separate workerrole

  - by Brett Smith

  I'm running an application on windows azure, the MVC views need to be dynamic, I started by storing them as records in the database, but am quite keen to move them to a physical location. My concept was to create the physical file via code... which worked great and speeds up the page load dramatically. This was of course before I realised that the files were only available for the duration of the role Next I looked at a start up task to create the files when the role was started - however I then realised that any separate instances weren't going to sync up unless I monitored the database for changes. So I moved from a start up task to a function in the run method of the role that checks the database every 10 minutes to see if changes have occurred. The problem is that this seems to choke up the application (at least in the warm up stage). Ideally I would like to move the run function to it's own worker role that can sit there and push files out to web role instances, but I'm unsure on how I would go about accessing the web roles local storage from the worker role. Can anybody tell me whether this is actually possible? and hopefully point me in the right direction to achieve this? Just to clarify what I'm trying to achieve -View is created in user interface running on web role and stored in database -Separate web role (front end) has clientside application with virtualpath provider pointing Views requests to local storage (localresource) -separate worker role to create View structure and load this into clientside web role local storage

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• With a browser, how do I know which decimal separator does the client use?

  - by Quassnoi

  I'm developing a web application. I need to display some decimal data correctly so that it can be copied and pasted into a certain GUI application that is not under my control. The GUI application is locale sensitive and it accepts only the correct decimal separator which is set in the system. I can guess the decimal separator from Accept-Language and the guess will be correct in 95% cases, but sometimes it fails. Is there any way to do it on server side (preferably, so that I can collect statistics), or on client side? Update: The whole point of the task is doing it automatically. In fact, this webapp is a kind of online interface to a legacy GUI which helps to fill the forms correctly. The kind of users that use it mostly have no idea on what a decimal separator is. The Accept-Language solution is implemented and works, but I'd like to improve it. Update2: I need to retrive a very specific setting: decimal separator set in Control Panel / Regional and Language Options / Regional Options / Customize. I deal with four kinds of operating systems: Russian Windows with a comma as a DS (80%). English Windows with a period as a DS (15%). Russian Windows with a period as a DS to make poorly written English applications work (4%). English Windows with a comma as a DS to make poorly written Russian applications work (1%). All 100% of clients are in Russia and the legacy application deals with Russian goverment-issued forms, so asking for a country will yield 100% of Russian Federation, and GeoIP will yield 80% of Russian Federation and 20% of other, incorrect answers.

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• java annotations - problem with calling a locator class from a Vaadin Project

  - by George

  Hello, I'm not sure how to explain this without writing several pages so I hope the actual code is more expressive. I've made a jar containing multiple annotation declaration similar to the following: @Target(ElementType.PACKAGE) @Retention(RetentionPolicy.RUNTIME) public @interface MarkedPackage { } then I have made a test jar containing several classes in several packages and marked just one package with the above annotation (with package-info.java) like below: @myPackage.MarkedPackage package package.test.jar; this jar had in its build path the jar containing the annotations. then I made a static class that has a method (LoadPlugins) that retrieves a list with all the jars of a directory. Then it searches through the jars for the 'package-info' class and checks if that classes package contains the MarkedPackage annotation. by calling this: if (checkPackageAnnotation(thisClass.getPackage())) where thisClass is the package-info class retrieved via a classloader. and: public static boolean checkPackageAnnotation(AnnotatedElement elem) { System.out.println(elem.getAnnotations().length); if (elem == null || !elem.isAnnotationPresent(MarkedPackage.class)) return false; return true; } the elem.getAnnotatios().length is there for debug purposes. And the problem appears when I call the method from the static class: if I call it from a main function: public class MyMain { public static void main(String[] args){ PluginUtils.LoadPlugins(); } } everything works perfectly it displays '1' from that System.out.println(elem.getAnnotations().length); But if I call it from a button from my Vaadin project: header.addComponent(new Button("CallThat", new Button.ClickListener() { public void buttonClick(ClickEvent event) { PluginUtils.LoadPlugins(); } })); It displays '0' from that System.out.println(elem.getAnnotations().length); Also I should mention that I created the main inside my Vaadin project so it would have the exact same build path and resources. Is there a problem with web applications and that "@Retention(RetentionPolicy.RUNTIME)" ? hope I was clear enough... Hope someone has a solution for me... If you need more information - let me know. Thank you.

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• Losing URI segments when paginating with CodeIgniter

  - by Danny Herran

  I have a /payments interface where the user should be able to filter via price range, bank, and other stuff. Those filters are standard select boxes. When I submit the filter form, all the post data goes to another method called payments/search. That method performs the validation, saves the post values into a session flashdata and redirects the user back to /payments passing the flashdata name via URL. So my standard pagination links with no filters are exactly like this: payments/index/20/ payments/index/40/ payments/index/60/ And if you submit the filter form, the returning URL is: payments/index/0/b48c7cbd5489129a337b0a24f830fd93 This works just great. If I change the zero for something else, it paginates just fine. The only issue however is that the << 1 2 3 4 page links wont keep the hash after the pagination offset. CodeIgniter is generating the page links ignoring that additional uri segment. My uri_segment config is already set to 3: $config['uri_segment'] = 3; I cannot set the page offset to 4 because that hash may or may not exists. Any ideas of how can I solve this? Is it mandatory for CI to have the offset as the last segment in the uri? Maybe I am trying an incorrect approach, so I am all ears. Thank you folks.

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• Singleton EXC_BAD_ACCESS

  - by lclaud

  Hi, so I have a class that I decleare as a singleton and in that class I have a NSMutableArray that contains some NSDictionaries with some key/value pairs in them. The trouble is it doesn't work and I dont't know why... I mean it crashes with EXC_BAD_ACCESS but i don't know where. I followed the code and it did create a new array on first add, made it to the end of the funtion ..and crashed ... @interface dataBase : NSObject { NSMutableArray *inregistrari; } @property (nonatomic,retain) NSMutableArray *inregistrari; -(void)adaugaInregistrareCuData:(NSDate *)data siValoare:(NSNumber *)suma caVenit:(BOOL)venit cuDetaliu:(NSString *)detaliu; -(NSDictionary *)raportIntreData:(NSDate *)dataInitiala siData:(NSDate *)dataFinala; -(NSArray *)luniDisponibileIntreData:(NSDate *)dataInitiala siData:(NSDate *)dataFinala; -(NSArray *)aniDisponibiliIntreData:(NSDate *)dataInitiala siData:(NSDate *)dataFinala; -(NSArray *)vectorDateIntreData:(NSDate *)dataI siData:(NSDate *)dataF; -(void)salveazaInFisier; -(void)incarcaDinFisier; + (dataBase *)shareddataBase; @end And here is the .m file #import "dataBase.h" #import "SynthesizeSingleton.h" @implementation dataBase @synthesize inregistrari; SYNTHESIZE_SINGLETON_FOR_CLASS(dataBase); -(void)adaugaInregistrareCuData:(NSDate *)data siValoare:(NSNumber *)suma caVenit:(BOOL)venit cuDetaliu:(NSString *)detaliu{ NSNumber *v=[NSNumber numberWithBool:venit]; NSArray *input=[NSArray arrayWithObjects:data,suma,v,detaliu,nil]; NSArray *keys=[NSArray arrayWithObjects:@"data",@"suma",@"venit",@"detaliu",nil]; NSDictionary *inreg=[NSDictionary dictionaryWithObjects:input forKeys:keys]; if(inregistrari == nil) { inregistrari=[[NSMutableArray alloc ] initWithObjects:inreg,nil]; }else { [inregistrari addObject:inreg]; } [inreg release]; [input release]; [keys release]; } It made it to the end of that adaugaInregistrareCuData ... ok . said the array had one object ... and then crashed

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• Adding web reference on client when using Net.TCP

  - by Marko

  Hi everyone... I am trying to using Net.TCP in my WCF Service, which is self hosted, when i try to add this service reference through web reference to my client, i am not able access the classes and methods of that service, can any have any idea to achieve this... How I can add web references in this case. My Service has one method (GetNumber) that returns int. WebService: public class WebService : IWebService { public int GetNumber(int num) { return num + 1; } } Service Contract code: [ServiceContract] public interface IWebService { [OperationContract] int GetNumber(int num); } WCF Service code: ServiceHost host = new ServiceHost(typeof(WebService)); host.AddServiceEndpoint(typeof(IWebService), new NetTcpBinding(), new Uri("net.tcp://" + Dns.GetHostName() + ":1255/WebService")); NetTcpBinding binding = new NetTcpBinding(); binding.TransferMode = TransferMode.Streamed; binding.ReceiveTimeout = TimeSpan.MaxValue; binding.MaxReceivedMessageSize = long.MaxValue; Console.WriteLine("{0}", Dns.GetHostName().ToString()); Console.WriteLine("Opening Web Service..."); host.Open(); Console.WriteLine("Web Service is running on port {0}",1255); Console.WriteLine("Press <ENTER> to EXIT"); Console.ReadLine(); This works fine. Only problem is how to add references of this service in my client application. I just want to send number and to receive an answer. Can anyone help me?

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• Errors with redefinitions after upgrade to XCode 3.2.3

  - by CA Bearsfan

  I recently upgraded to Snow Leopard and Xcode 3.2.5 so I could test on my iPod Touch and iPhone and ran into some problems with the project I was working on. First it couldn't find a Base SDK, then my old frameworks weren't hooking up correctly. Finally after setting the Project Format to Xcode 3.1 compatible (3.2 also worked) and the Base SDK for all configurations to iOS 4.2, then setting my iOS deployment target to iOS 3.0 I was able to get the system to find a Base SDK and attempt a build. That's when the frameworks didn't want to cooperate. 4/6 I'm using displayed in red, so I re routed the path to the iPhone simulator 4.2 platform which worked perfectly. I was able to build my project, no errors or warnings and my app worked fine. I went to work last night thinking I had fixed the problem. This morning I fired up the laptop and went to build my code base and now have 1142 errors all of which have to do with code I haven't written deemed as being redefined. Suggestions? The following is just a small sample of the error list (obviously don't need to see all 1142) //Frameworks/Foundation.framework/Headers/NSZone.h:48: error: redefinition of 'NSMakeCollectable' /Frameworks/Foundation.framework/Headers/NSObject.h:65: error: duplicate interface declaration for class 'NSObject' /Frameworks/Foundation.framework/Headers/NSObject.h:67: error: redefinition of 'struct NSObject'

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• asyncore callbacks launching threads... ok to do?

  - by sbartell

  I'm unfamiliar with asyncore, and have very limited knowledge of asynchronous programming except for a few intro to twisted tutorials. I am most familiar with threads and use them in all my apps. One particular app uses a couchdb database as its interface. This involves longpolling the db looking for changes and updates. The module I use for couchdb is couchdbkit. It uses an asyncore loop to watch for these changes and send them to a callback. So, I figure from this callback is where I launch my worker threads. It seems a bit crude to mix asynchronous and threaded programming. I really like couchdbkit, but would rather not introduce issues into my program. So, my question is, is it safe to fire threads from an async callback? Here's some code... {{{ def dispatch(change): global jobs, db_url # jobs is my queue db = Database(db_url) work_order = db.get(change['id']) # change is an id to the document that changed. # i need to get the actual document (workorder) worker = Worker(work_order, db) # fire the thread jobs.append[worker] worker.start() return main() . . . consumer.wait(cb=dispatch, since=update_seq, timeout=10000) #wait constains the asyncloop. }}}

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• JBoss Clustered Service that sends emails from txt file

  - by michael lucas

  I need a little push in the right direction. Here's my problem: I have to create an ultra-reliable service that sends email messages to clients whose addresses are stored in txt file on FTP server. Single txt file may contain unlimited number of entries. Most often the file contains about 300,000 entries. Service exposes interface with just two simple methods: TaskHandle sendEmails(String ftpFilePath); ProcessStatus checkProcessStatus(TaskHandle taskHandle); Method sendEmails() returns TaskHandle by which we can ask for ProcessStatus. For such a service to be reliable clustering is necessary. Processing single txt file might take a long time. Restarting one node in a cluster should have no impact on sending emails. We use JBoss AS 4.2.0 which comes with a nice HASingletonController that ensure one instance of service is running at given time. But once a fail-over happens, the second service should continue work from where the first one stopped. How can I share state between nodes in a cluster in such a way that leaves no possibility of sending some emails twice?

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• How can I provide users with the functionality of the DBUnit DatabaseOperation methods from a web in

  - by reckoner

  I am currently updating a java-based web application which allows database developers to create stored procedure regression test suites for database testing. Currently, for test setup, execution and clean-up stages, the user is provided with text boxes where they are able to enter SQL code which is executed by the isql command. I would like to extend the application to use DB Unit’s DatabaseOperation methods to provide more ways to setup the state of the database than just SQL statements. The main reason for using Db Unit rather than just SQL statements is to be able to create and store xml and xls DataSets on a server where they can be associated with their test cases and used for data setup. My question is: How can I provide users with the functionality of the DBUnit DatabaseOperation methods from a web interface? I have considered: Creating a simple programming language and a parser to read some simple syntax involving the DB Unit method names which accept a parameter being the file location to an xml or xls DataSet. I was thinking of allowing the user to register the files they need with the web app which would catalogue them and provide each file with an identifier which could passed as a parameter to the methods in this simple programming language. Creating an XML DTD which provides the user with the ability to specify operations and parameters. If I went this approach, how can I execute the methods and their parameters that I parse from the XML document? Creating a table in the database which stores the method and a FK relation to a catalogued DataSet file, however I don’t think this would be good solution due to the fact that data entry would be tedious. Thanks for your help.

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• Compiling Objective-C project on Linux (Ubuntu)

  - by Alex

  How to make an Objective-C project work on Ubuntu? My files are: Fraction.h #import <Foundation/NSObject.h> @interface Fraction: NSObject { int numerator; int denominator; } -(void) print; -(void) setNumerator: (int) n; -(void) setDenominator: (int) d; -(int) numerator; -(int) denominator; @end Fraction.m #import "Fraction.h" #import <stdio.h> @implementation Fraction -(void) print { printf( "%i/%i", numerator, denominator ); } -(void) setNumerator: (int) n { numerator = n; } -(void) setDenominator: (int) d { denominator = d; } -(int) denominator { return denominator; } -(int) numerator { return numerator; } @end main.m #import <stdio.h> #import "Fraction.h" int main( int argc, const char *argv[] ) { // create a new instance Fraction *frac = [[Fraction alloc] init]; // set the values [frac setNumerator: 1]; [frac setDenominator: 3]; // print it printf( "The fraction is: " ); [frac print]; printf( "\n" ); // free memory [frac release]; return 0; } I've tried two approaches to compile it: Pure gcc: $ sudo apt-get install gobjc gnustep gnustep-devel $ gcc `gnustep-config --objc-flags` -o main main.m -lobjc -lgnustep-base /tmp/ccIQKhfH.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' I created a GNUmakefile Makefile: include ${GNUSTEP_MAKEFILES}/common.make TOOL_NAME = main main_OBJC_FILES = main.m include ${GNUSTEP_MAKEFILES}/tool.make ... and ran: $ source /usr/share/GNUstep/Makefiles/GNUstep.sh $ make Making all for tool main... Linking tool main ... ./obj/main.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction' So in both cases compiler gets stuck at undefined reference to `__objc_class_name_Fraction' Do you have and idea how to resolve this issue?

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• Singleton Pattern combine with a Decorator

  - by Mike

  Attached is a classic Decorator pattern. My question is how would you modify the below code so that you can wrap zero or one of each topping on to the Pizza Right now I can have a Pepporini - Sausage -- Pepporini -- Pizza class driving the total cost up to $10, charging twice for Pepporini. I don't think I want to use the Chain of Responsibility pattern as order does not matter and not all toppings are used? Thank you namespace PizzaDecorator { public interface IPizza { double CalculateCost(); } public class Pizza: IPizza { public Pizza() { } public double CalculateCost() { return 8.00; } } public abstract class Topping : IPizza { protected IPizza _pizzaItem; public Topping(IPizza pizzaItem) { this._pizzaItem = pizzaItem; } public abstract double CalculateCost(); } public class Pepporini : Topping { public Pepporini(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 0.50; } } public class Sausage : Topping { public Sausage(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 1.00; } } public class Onions : Topping { public Onions(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + .25; } } }

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• Suggested (simple) approach for drawing large numbers of visual elements in WPF?

  - by Ender

  I'm writing an interface that features a large (~50000px width) "canvas"-type area that is used to display a lot of data in a fairly novel way. This involves lots of lines, rectangles, and text. The user can scroll around to explore the entire canvas. At the moment I'm just using a standard Canvas panel with various Shapes placed on it. This is nice and easy to do: construct a shape, assign some coordinates, and attach it to the Canvas. Unfortunately, it's pretty slow (to construct the children, not to do the actual rendering). I've looked into some alternatives, it's a bit intimidating. I don't need anything fancy - just the ability to efficiently construct and place objects in a coordinate plane. If all I get are lines, colored rectangles, and text, I'll be happy. Do I need Geometry instances inside of Geometry Groups inside of GeometryDrawings inside of some Panel container? Note: I'd like to include text and graphics (i.e. colored rectangles) in the same space, if possible.

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• garbage collector Issue

  - by Eslam

  this question is like my previous one Given: 3. interface Animal { void makeNoise(); } 4. class Horse implements Animal { 5. Long weight = 1200L; 6. public void makeNoise() { System.out.println("whinny"); } 7. } 8. public class Icelandic extends Horse { 9. public void makeNoise() { System.out.println("vinny"); } 10. public static void main(String[] args) { 11. Icelandic i1 = new Icelandic(); 12. Icelandic i2 = new Icelandic(); 13. Icelandic i3 = new Icelandic(); 14. i3 = i1; i1 = i2; i2 = null; i3 = i1; 15. } 16. } When line 14 is reached, how many objects are eligible for the garbage collector? A. 0 B. 1 C. 2 D. 3 E. 4 F. 6 i choosed A but the right answer is E, but i don't know Why?

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• Class initialization and synchronized class method

  - by nybon

  Hi there, In my application, there is a class like below: public class Client { public synchronized static print() { System.out.println("hello"); } static { doSomething(); // which will take some time to complete } } This class will be used in a multi thread environment, many threads may call the Client.print() method simultaneously. I wonder if there is any chance that thread-1 triggers the class initialization, and before the class initialization complete, thread-2 enters into print method and print out the "hello" string? I see this behavior in a production system (64 bit JVM + Windows 2008R2), however, I cannot reproduce this behavior with a simple program in any environments. In Java language spec, section 12.4.1 (http://java.sun.com/docs/books/jls/second_edition/html/execution.doc.html), it says: A class or interface type T will be initialized immediately before the first occurrence of any one of the following: T is a class and an instance of T is created. T is a class and a static method declared by T is invoked. A static field declared by T is assigned. A static field declared by T is used and the reference to the field is not a compile-time constant (§15.28). References to compile-time constants must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field never cause initialization. According to this paragraph, the class initialization will take place before the invocation of the static method, however, it is not clear if the class initialization need to be completed before the invocation of the static method. JVM should mandate the completion of class initialization before entering its static method according to my intuition, and some of my experiment supports my guess. However, I did see the opposite behavior in another environment. Can someone shed me some light on this? Any help is appreciated, thanks.

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• Giving another object a NSManagedObject

  - by Wayfarer

  Alright, so I'm running into an issue with my code. What I have done is subclassed UIButton so I can give it some more infomormation that pertain to my code. I have been able to create the buttons and they work great. Capiche. However, one of the things I want my subclass to hold is a reference to a NSMangedObject. I have this code in my header file: @interface ButtonSubclass : UIButton { NSManagedObjectContext *context; NSManagedObject *player; } @property (nonatomic, retain) NSManagedObject *player; @property (nonatomic, retain) NSManagedObjectContext *context; - (id)initWithFrame:(CGRect)frame andTitle:(NSString*)title; //- (void)setPlayer:(NSManagedObject *)aPlayer; @end As you can see, it has a instance variable to the NSMangedobject I want it to hold (as well as the Context). But for the life of me, I can't get it to hold that NSManagedObject. I run both the @synthesize methods in the Implementation file. @synthesize context; @synthesize player; So I'm not sure what I'm doing wrong. This is how I create my button: ButtonSubclass *playerButton = [[ButtonSubclass alloc] initWithFrame:frame andTitle:@"20"]; //works playerButton.context = self.context; //works playerButton.player = [players objectAtIndex:i]; //FAILS And I have initilaized the players array earlier, where I get the objects. Another weird thing is that when it gets to this spot in the code, the app crashes (woot) and the the console output stops. It doesn't give me any error, and notification at all that the app has crashed. It just... stops. So I don't even know what the error is that is crashing the code, besides it has to do with that line up there setting the "player" variable. Thoughts and ideas? I'd love your wisdom!

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• handle large Parcelable ArrayList in Android

  - by Gal Ben-Haim

  I'm developing an Android app that is a client to a JSON webservice API. I have classes of resource objects (some are nested) and I pass results from an IntentService that access the webserive using the Parcelable interface for all the resource classes. the webservice returns arrays or results that can be potentially large (because of the nesting, for example, a post object also contains comments array, each comment also contains a user object). currently I'm either inserting the results into a SQlite database or displaying them in a ListView. (my relevant methods are accepting ArrayList<resourceClass> as arguments). (some data need to be persistent stored and some should not). since I don't know what size of lists I can handle this way without reaching the memory limits, is this a good practice ? is it a better idea to save the parsed JSON to a local file immediately and pass the file path to the ResultReceiver, then either insert to database from that file or display the data ? is there a better way to handle this ? btw - I'm parsing the JSON as a stream with Gson's Reader so there shouldn't be memory issues at that stage.

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