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• Programming language features that help to catch bugs early

  - by Christian Neumanns

  Do you know any programming language features that help to detect bugs early in the software development process - ideally at compile-time or else as early as possible at run-time? Examples of well-known and effective bug-reducing features are: Static typing and generic types: type incompatibility errors are detected by the compiler Design by Contract (TM), also called Contract Programming: invalid values are quickly detected at runtime (through preconditions, postconditions and class invariants) Unit testing I ask this question in the context of improving an object-oriented programming language (called Obix) which has been designed from the ground up to 'make it easy to quickly write reliable code'. Besides the features mentioned above this language also incorporates other Fail-fast features such as: Objects are immutable by default Void (null) values are not allowed by default The aim is to add more Fail-fast concepts to the language. If you know other features which help to write less error-prone code then please let us know. Thank you.

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• Lending epub files for limited time to users

  - by JP Hellemons

  I am looking for components to build a digital library who lends people epub (ebooks) for about a week. It's like a digital version of the offline old public library. Now I have found several flash (pdf) file streaming solutions. But that would require an active internet link. And like the public library, you are able to take your books to the beach or pool on holiday abroad where you have no connection. So streaming is no option. The other file restriction method I have found was DRM, but that would require a really expensive license of Adobe Content Server 4 which is not suitable for my little hobby project. But it seems that adobe content server and Adobe Digital Editions is the only option at the moment. Or are there open source alternatives?

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• Oracle WebLogic Server - Technologietage

  - by franziska.schneider(at)oracle.com

  Dieser Technologietag richtet sich insbesondere an Interessierte, die den Oracle WebLogic Server bereits im Einsatz haben und sich einen umfassenden technischen Überblick verschaffen wollen bzw. sich für die Neuerungen des aktuellen Releases interessieren. Folgende Themen werden im Rahmen des WLS Technologietages betrachtet: Design und Architektur - Entwicklung - Diagnose und Optimierung - Administration und Betrieb - Virtualisierung und Cloud Stuttgart am 29. März 2011München am 30. März 2011Frankfurt am 31.März 2011Düsseldorf am 6. April 2011Hamburg am 12. April 2011Potsdam am 13.April 2011 Der Teilnehmerkreis ist auf 25 Personen begrenzt. Bitte melden Sie sich bei uns und wir senden Ihnen das Anmeldeformular umgehend zu.

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• OOD: All classes at bottom of hierarchy contain the same field

  - by My Head Hurts

  I am creating a class diagram for what I thought was a fairly simple problem. However, when I get to the bottom of the hierarchy, all of the classes only contain one field and it is the same one. This to me looks very wrong, but this field does not belong in any of the parent classes. I was wondering if there are any suggested design patterns in a situation like this? A simplified version of the class diagram can be found below. Note, fields named differently cannot belong to any other class +------------------+ | ObjectA | |------------------| | String one | | String two | | | +---------+--------+ | +---------------+----------------+ | | +--------|--------+ +--------|--------+ | ObjectAA | | ObjectAB | |-----------------| |-----------------| | String three | | String four | | | | | +--------+--------+ +--------+--------+ | | | | +--------|--------+ +--------|--------+ | ObjectAAA | | ObjectABA | |-----------------| |-----------------| | String five | | String five | | | | | +-----------------+ +-----------------+ ASCII tables drawn using http://www.asciiflow.com/

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• Is Java's ElementCollection Considered a Bad Practice?

  - by SoulBeaver

  From my understanding, an ElementCollection has no primary key, is embedded with the class, and cannot be queried. This sounds pretty hefty, but it allows me the comfort of writing an enum class which also helps with internationalization (using the enum key for lookup in my ResourceBundle). Example: We have a user on a media site and he can choose in which format he downloads the files @Entity @Table(name = "user") public class User { /* snip other fields */ @Enumerated @ElementCollection( targetClass = DownloadFilePreference.class, fetch = FetchType.EAGER ) @CollectionTable(name = "download_file_preference", joinColumns = @JoinColumn(name = "user_id") ) @Column(name = "name") private Set<DownloadFilePreference> downloadFilePreferences = new HashSet<>(); } public enum DownloadFilePreference { MP3, WAV, AIF, OGG; } This seems pretty great to me, and I suppose it comes down to "it depends on your use case", but I also know that I'm quite frankly only an initiate when it comes to Database design. Some best practices suggest to never have a class without a primary key- even in this case? It also doesn't seem very extensible- should I use this and gamble on the chance I will never need to query on the FilePreferences?

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• Where to store global enterprise properties?

  - by shylynx

  I'm faced with a crowd of java applications, which need different global enterprise wide properties for operation, for example: hostname of the central RDBMS, hostname and location of the central self-service portal, host location of central LDAP, host location of central mail server etc. Formally we build each application with a properties file, where all this properties are definied. But that's a very bad solution, because if the hostname of the mail server changes, we need to change the properties files for each application and deploy all applications again. Our idea is to centralize this properties, so that each application can ask for each property at runtime, for example: Idea: Put the properties file to an easy accessible file share. So if we need to change a property, each application uses the new properties. Idea: Put the properties to database. Main disadvantage: we need a dependency to database client libraries for each application. Idea: Put all applications into one big application server, that provides system properties for each application. Main disadvantage: needs deployment of each application to one application server. But that isn't a realistic scenario. Idea: Webservice that provides global enterprise wide properties. Main disadvantage: not very secure, because some properties are passwords or user credentials. What other alternatives are recommended? What is state of the art?

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• Is event sourcing ready for prime time?

  - by Dakotah North

  Event Sourcing was popularized by LMAX as a means to provide speed, performance scalability, transparent persistence and transparent live mirroring. Before being rebranded as Event Sourcing, this type of architectural pattern was known as System Prevalence but yet I was never familiar with this pattern before the LMAX team went public. Has this pattern proved itself in numerous production systems and therefore even conservative individuals should feel empowered to embrace this pattern or is event sourcing / system prevalence an exotic pattern that is best left for the fearless?

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• Authentication for users on a Single Page App?

  - by John H

  I have developed a single page app prototype that is using Backbone on the front end and going to consume from a thin RESTful API on the server for it's data. Coming from heavy server side application development (php and python), I have really enjoyed the new different design approach with a thick client side MVC but am confused on how best to restrict the app to authenticated users who log in. I prefer to have the app itself behind a login and would also like to implement other types of logins eventually (openid, fb connect, etc) in addition to the site's native login. I am unclear how this is done and have been searching - but unsuccessful in finding information that made it clear to me. In the big picture, what is the current best practice for registering users and requiring them to login to use your single page app? Once a user is logged in, how are the api requests authenticated? Can I store a session but how do I detect for this session in the API calls? Any answers to this would be much appreciated!

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• What tools, libraries, or framework is needed to create a completely offline Javascript application?

  - by makerofthings7

  I am interested in creating a HTML application that can run as disconnected from the server as possible. Two examples of this include OWA in Exchange 2013 and to a lesser extent and the client available at www.ripple.com With the focus on OWA in Exchange 2013, what is needed to replicate the offline functionality available in a different application? A list technologies, frameworks, etc would be immensely helpful

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• How to manage security of these self hosted web apis, to ensure that the request coming for accessing data is authenticated?

  - by Husrat Mehmood

  Let's pretend I am going to work on an enterprise application. Say I have 11 modules in the application and I would have to develop Dashboards for every role in the organization for whom I are going to develop application. We Decided to use Asp.Net Web Api and return json data from our apis. We are going to include 11 Self hosted web apis projects in our application (one self hosted web api) for every module. All 11 modules are connected to one Sql server 2012 Database. Then once api is ready we would have to create Business Dashboards (Based upon roles in Organization). So Now my web api client is Asp.Net Mvc application.Asp.Net mvc will consume those web apis. Here is the part for whom all explanation is done. How should I manage Security of all 11 self hosted web apis? How should I only authenticated request is coming? If I authenticate user by login and password and then redirect user to appropriate Dashboard designed for the role that user have and load data by consuming web apis. How should I ensure that the request coming for accessing data is authenticated?

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• Transmitting Form Data from the Client to the Web Server

  The steps involved in transmitting form data from the client to the web server User loads web form User enters data in to web form fields User clicks submit On submit page validates fields using JavaScript. If validation errors are found then the validation script stops the browser from canceling posting the data to the web server and displays error messages as needed If the form passes the data validation process then the browser will URL encode the values of every field and post it to the server.  The server reads the posted data from the query string and then again validates the data just to ensure data consistency and to prevent any non-validated data because JavaScript was turned off on the clients browser from being inserted in to a database or passed on to other process If the data passes the second validation check then the server side code will continue with the requested processes

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• Where to store shaders

  - by Mark Ingram

  I have an OpenGL renderer which has a Scene member variable. The Scene object can contain N SceneObjects. I use these SceneObjects for storing the vertex position and any transforms. My question is, where should shaders be stored in this arrangement? I guess they need to be in a central location because multiple objects can use the same shader. But then each object needs access to the shader because it needs to set attributes into the shader. Does anyone have any advice?

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• SceneManagers as systems in entity system or as a core class used by a system?

  - by Hatoru Hansou

  It seems entity systems are really popular here. Links posted by other users convinced me of the power of such system and I decided to try it. (Well, that and my original code getting messy) In my project, I originally had a SceneManager class that maintained needed logic and structures to organize the scene (QuadTree, 2D game). Before rendering I call selectRect() and pass the x,y of the camera and the width and height of the screen and then obtain a minimized list containing only visible entities ordered from back to front. Now with Systems, originally in my first attempt my Render system required to get added all entities it should handle. This may sound like the correct approach but I realized this was not efficient. Trying to optimize It I reused the SceneManager class internally in the Renderer system, but then I realized I needed methods such as selectRect() in others systems too (AI principally) and make the SceneManager accessible globally again. Currently I converted SceneManager to a system, and ended up with the following interface (only relevant methods): /// Base system interface class System { public: virtual void tick (double delta_time) = 0; // (methods to add and remove entities) }; typedef std::vector<Entity*> EntitiesVector; /// Specialized system interface to allow query the scene class SceneManager: public System { public: virtual EntitiesVector& cull () = 0; /// Sets the entity to be used as the camera and replaces previous ones. virtual void setCamera (Entity* entity) = 0; }; class SceneRenderer // Not a system { vitual void render (EntitiesVector& entities) = 0; }; Also I could not guess how to convert renderers to systems. My game separates logic updates from screen updates, my main class have a tick() method and a render() method that may not be called the same times. In my first attempt renderers were systems but they was saved in a separated manager, updated only in render() and not in tick() like all other systems. I realized that was silly and simply created a SceneRenderer interface and give up about converting them to systems, but that may be for another question. Then... something does not feel right, isn't it? If I understood correctly a system should not depend on another or even count with another system exposing an specific interface. Each system should care only about its entities, or nodes (as optimization, so they have direct references to relevant components without having to constantly call the component() or getComponent() method of the entity).

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• Does semi-normalization exist as a concept? Is it "normalized"?

  - by Gracchus

  If you don't mind, a tldr on my experience: My experience tldr I have an application that's heavily dependent upon uncertainty, a bane to database design. I tried to normalize it as best as I could according to the capabilities of my database of choice, but a "simple" query took 50ms to read. Nosql appeals to me, but I can't trust myself with it, and besides, normalization has cut down my debugging time immensely over and over. Instead of 100% normalization, I made semi-redundant 1:1 tables with very wide primary keys and equivalent foreign keys. Read times dropped to a few ms, and write times barely degraded. The semi-normalized point Given this reality, that anyone who's tried to rely upon views of fully normalized data is aware of, is this concept codified? Is it as simple as having wide unique and foreign keys, or are there any hidden secrets to this technique? Or is uncertainty merely a special case that has extremely limited application and can be left on the ash heap?

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• Multiple sites with the same codebase in Python

  - by Jimmy

  I am trying to run a large amount of sites which share about 90% of their code. They are simply designed to query an API and return the results. They will have a common userbase / database but will be configured slightly different and will have different CSS (perhaps even different templating). My initial idea was to run them as separate applications with a common library but I have read about the sites framework which would allow them to run from a single instance of Django which may help to reduce memory usage. https://docs.djangoproject.com/en/dev/ref/contrib/sites/ Is the site framework the right approach to a problem like this, and does it have real benefits over running separate applications? Initially I thought it was, but now I think otherwise. I have heard the following: Your SITE_ID is set in settings.py, so in order to have multiple sites, you need multiple settings.py configurations, which means multiple distinct processes/instances. You can of course share the code base between them, but each site will need a dedicated worker / WSGIDaemon to serve the site. This effectively removes any benefit of running multiple sites under one hood, if each site needs a UWSGI instance running. Alternative ideas of systems: https://github.com/iivvoo/django_layers https://github.com/shestera/django-multisite I don't know what route to be taking with this.

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• Mac mini 2012 graphic upgrade for UE4 Unity3D Blender

  - by DaCrAn

  I have a mac mini (late 2012) i7, 16gb ram Vengeance graphic card intel HD4000. I buy recently a thunderbolt expansion PCIE whit support a graphic card PCIE 2.0 16x whit space for Full leght card. I have dubts about what graphic card gona give me the best results for using the Unreal Engine 4 UE4 or Unity3D, and Blender. My badget cover a Nvidia Quadro K4000 3gb or ATI Firepro W7000 4gb. Any recomendation? What professional graphic card can be better for design games in 3D? Thanks. DaCrAn

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• Using an actor model versus a producer-consumer model?

  - by hewhocutsdown

  I'm doing some early-stage research towards architecting a new software application. Concurrency and multithreading will likely play a significant part, so I've been reading up on the various topics. The producer-consumer model, at least how it is expressed in Java, has some surface similarities but appears to be deeply dissimilar to the actor model in use with languages such as Erlang and Scala. I'm having trouble finding any good comparative data, or specific reasons to use or avoid the one or the other. Is the actor model even possible with Java or C#, or do you have do use one of the languages built for the purpose? Is there a third way?

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• Materialized View vs POJO View based on Objects representing Oracle tables

  - by Zack Macomber

  I have about 12 Oracle tables that represent data that's being integrated from an external system into my web application. This data is going to be used in an informational and comparative manner for the clients using my web application. On one particular page of my web application, I need to combine data from 3 - 5 Oracle tables for display as an HTML table on the page. We are NOT currently using a framework (Apache Struts for instance) and we're not in a position to move this Java web application into one at this moment (I'm trying to get us there...). I am certainly not an architect, but I see one of two ways that I can effectively build this page (I know there are other ways, but these seem like they would be good ones...): 1. Create an Oracle Materialized View that represents what the HTML table should look like and then create a POJO based on the View that I can then integrate into my JSP. 2. Create POJOs that represent the Oracle tables themselves and then create another POJO that is the View used for the HTML table and then integrate that POJO into my JSP. To me, it seems the Materialized View would possibly offer quicker results which is always what we strive for in web applications. But, if I just create 12 POJOs that represent the Oracle tables and then build POJO Views off of those, I have the advantage of keeping all the code in one place for this and possibility for creating any number of different views and reusable components in my web application. Any thoughts on which one might be the better route? Or, maybe you know of an even better one?

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• Adding sub-entities to existing entities. Should it be done in the Entity and Component classes?

  - by Coyote

  I'm in a situation where a player can be given the control of small parts of an entity (i.e. Left missile battery). Therefore I started implementing sub entities as follow. Entities are Objects with 3 arrays: pointers to components pointers to sub entities communication subscribers (temporary implementation) Now when an entity is built it has a few components as you might expect and also I can attach sub entities which are handled with some dedicated code in the Entity and Component classes. I noticed sub entities are sharing data in 3 parts: position: the sub entities are using the parent's position and their own as an offset. scrips: sub entities are draining ammo and energy from the parent. physics: sub entities add weight to the parent I made this to quickly go forward, but as I'm slowly fixing current implementations I wonder if this wasn't a mistake. Is my current implementation something commonly done? Will this implementation put me in a corner? I thought it might be a better thing to create some sort of SubEntityComponent where sub entities are attached and handled. But before changing anything I wanted to seek the community's wisdom.

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• How to make players be creative in a game, if the game cannot evaluate it?

  - by Mensonge

  I am working on a prototype game with several funny/visual effects that the player can trigger. The player can be quite creative in the way to use or combine these effects but it seems impossible to make detect/evaluate this creativity by the computer. So, from a game design perspective, I wonder what could be the features to drive the players to be creative (experiment various combinations). For the moment i think about "Draw something" where the result is evaluated by other players. I think about levels designed by "Little Big Planet" players but this aspect is out of the core game. I think also about "Minecraft" but I do not understand really how this game encourages the people to be creative (except of the open world). Please tell me if you have any ideas, articles or references that could help me coping with this problem.

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• How to play many sounds at once in OpenAL

  - by Krom

  Hello, I'm developing an RTS game and I would like to add sounds to it. My choice has landed on OpenAL. I have plenty of units which from time to time make sounds: fSound.Play(sfx_shoot, location). Sounds often repeat, e.g. when squad of archers shoots arrows, but they are not synced with each other. My questions are: What is the common design pattern to play multiple sounds in OpenAL, when some of them are duplicate? What are the hardware limitations on sounds count and tricks to overcome them?

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• Distributing an Android game with plugins via the market

  - by Peter Serwylo

  I'm new to Android development, and was wondering how the following could be achieved within the confines of the Android market as a distribution channel: One main application, which handles the main menu, networking, high scores, etc. Several games which can be launched from the main menu, which all work within the same eco system. The main application is not just a pseudo launcher for other games, these different games will share high scores and other achievements/preferences. In a traditional package management system such as apt, pacman or yum, this could be handled quite happily through dependencies. This does not appear to be possible via the Android market. The closest I've seen is when apps scan to check if the required app is installed, and if not, launches the market and asks the user to download the app. This sounds like a very messy solution. It also begs the question, would they download the game (plugin) first, which then downloads the main shell application? Or would they download the main shell application, and when they navigate to a menu item which says "Play game", then it scans for any installed games, and if none exist, redirects to the market? Also, I'm not even sure if it is possible to dig up the package from another application on the device, and start invoking classes from within (e.g. when you want to launch the game (plugin)) A final option is just to have a 3rd component which is a .jar that each game includes, which effectively contains the entire shell application. Then each game would appear to have the same menu, but it would become a nightmare as soon as you want to update the menu component and have to re-release each game. It would be especially worse if other people released games (plugins) based on the same framework and didn't update them. Is there any other options which I haven't thought of? Has anyone else solved this or seen a solution in any apps they've installed (doesn't have to be games)? cheers.

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• REST - Tradeoffs between content negotiation via Accept header versus extensions

  - by Brandon Linton

  I'm working through designing a RESTful API. We know we want to return JSON and XML for any given resource. I had been thinking we would do something like this: GET /api/something?param1=value1 Accept: application/xml (or application/json) However, someone tossed out using extensions for this, like so: GET /api/something.xml?parm1=value1 (or /api/something.json?param1=value1) What are the tradeoffs with these approaches? Is it best to rely on the accept header when an extension isn't specified, but honor extensions when specified? Is there a drawback to that approach?

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• How can I save state from script in a multithreaded engine?

  - by Peter Ren

  We are building a multithreaded game engine and we've encountered some problems as described below. The engine have 3 threads in total: script, render, and audio. Each frame, we update these 3 threads simultaneously. As these threads updating themselves, they produce some tasks and put them into a public storage area. As all the threads finish their update, each thread go and copy the tasks for themselves one by one. After all the threads finish their task copying, we make the threads process those tasks and update these threads simultaneously as described before. So this is the general idea of the task schedule part of our engine. Ok, well, all the task schedule part work well, but here's the problem: For the simplest, I'll take Camera as an example: local oldPos = camera:getPosition() -- ( 0, 0, 0 ) camera:setPosition( 1, 1, 1 ) -- Won't work now, cuz the render thread will process the task at the beginning of the next frame local newPos = camera:getPosition() -- Still ( 0, 0, 0 ) So that's the problem: If you intend to change a property of an object in another thread, you have to wait until that thread process this property-changing message. As a result, what you get from the object is still the information in the last frame. So, is there a way to solve this problem? Or are we build the task schedule part in a wrong way? Thanks for your answers :)

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• Entity Component System for HUD and GUI

  - by Jason L.

  This is a very rough sketch of how I currently have things designed. It should, at least, give an idea of how my ECS is currently designed. If you notice in that diagram, I have basically split the HUD out of the ECS. They have their own set of things (HudLayer, HudComponent, etc) and are handled differently. This is where I'm struggling, though. There are many different instances in which the HUD will need to know about entities. Not just data changing (I have an event dispatcher for that), but the actual entity and all it encompasses. There are also situations where entities will need to be able to query the HUD for data. Let's take a couple examples: First, my equipment screen. On here I can change the equipment on a character (Entity). In order for this to happen, I need to know about the entity. At least I think I do? How can I handle this? The second scenario involves my Systems needing to query a HudComponent for data. A specific example would be my battle system. Each "team" is given a 3x3 grid they can move around in. See here: Skills target these cells, and not the player, so I would need a way for my systems to determine which cells are occupied and which are not. Basically I need a way for two way communication between Systems and my HUD. I know it's recommended (by some people, anyways) to take your HUD out of the ECS. Is that appropriate in my case?

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