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• Low latency technologies for c++, c# and java?

  - by James

  I've been reading job descriptions and many mention 'low latency'. However, I wondered if someone could clarify what type of technologies this would refer to? One of the adverts mentioned 'ACE' which I googled to find out was some CISCO telephony technology. If you were hiring someone for a low latency role, what would you use as a checklist for ensuring they knew about low latency programming? I'm using this to learn more about low latency programming myself.

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• Java, two JPanel on JFrame - Settings JPanel, StartMenu JPanel [on hold]

  - by Andy Tyurin

  There is my first question and I welcome community! I'm making a simple game and have some problems with Start menu. I have three buttons on my JPanel StartMenu and when I click "Settings" button, new JPanel will be open, but I don't know why buttons from StartMenu JPanel appeared in my Settings JPanel. My "Settings" JPanel has one ugly button "Back" in center and ugly grey background. I made some screens to see a problem. Start Menu JPanel when game launched Settings JPanel when button clicked Settings JPanel when mouse was over settings window There is code of StartMenu class: public class StartMenu extends JPanel { private GameButton startGameButton = new GameButton("Start game"); private GameButton settingsGameButton = new GameButton("Settings"); private GameButton exitGameButton = new GameButton("Exit game"); private Image bgImage = new ImageIcon(getClass().getClassLoader().getResource("ru/andydevs/astraLaserForce/bg.png")).getImage(); private int posX; private int posY; final private int WIDTH=(int)Game.SCREEN_DIMENSION.getWidth()/3; final private int HEIGHT=(int)Game.SCREEN_DIMENSION.getHeight()/2; public StartMenu() { setLayout(new GridBagLayout()); GridBagConstraints c = new GridBagConstraints(); setSize(new Dimension(WIDTH, HEIGHT)); posX=(int)Game.SCREEN_DIMENSION.getWidth()/2-WIDTH/2; posY=(int)Game.SCREEN_DIMENSION.getHeight()/2-HEIGHT/2; setBounds(posX, posY,WIDTH,HEIGHT); c.ipadx=95; c.ipady=15; c.fill = GridBagConstraints.HORIZONTAL; c.insets = new Insets(20,0,0,0); c.gridy=0; add(startGameButton, c); c.gridy=1; c.insets = new Insets(20,0,0,0); System.out.println(settingsGameButton.getWidth()); add(settingsGameButton, c); c.gridy=2; c.insets = new Insets(20,0,0,0); add(exitGameButton, c); settingsGameButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { GameOptionsPanel gop = new GameOptionsPanel(); Game.container.add(gop); Game.container.setComponentZOrder(gop, 0); Game.container.revalidate(); Game.container.repaint(); } }); exitGameButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { Main.currentGame.stop(); } }); } public void paintComponent(Graphics g) { g.drawImage(bgImage,0,0,WIDTH,HEIGHT,null); } } There is code of Settings JPanel public class GameOptionsPanel extends GamePanel { private GameButton backButton = new GameButton("Back"); private GameOptionsPanel that; public GameOptionsPanel() { super((int) (Game.SCREEN_DIMENSION.getWidth()/3), (int) (Game.SCREEN_DIMENSION.getHeight()/2), new Color(50,50,50)); that=this; setLayout(new GridBagLayout()); GridBagConstraints gbc = new GridBagConstraints(); gbc.fill=gbc.HORIZONTAL; add(backButton); backButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { Game.container.remove(that); Game.container.revalidate(); Game.container.repaint(); } }); } } I glad to see some suggestions. Thanks.

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• HTML Parsing for multiple input files using java code [closed]

  - by mkp

  FileReader f0 = new FileReader("123.html"); StringBuilder sb = new StringBuilder(); BufferedReader br = new BufferedReader(f0); while((temp1=br.readLine())!=null) { sb.append(temp1); } String para = sb.toString().replaceAll("<br>","\n"); String textonly = Jsoup.parse(para).text(); System.out.println(textonly); FileWriter f1=new FileWriter("123.txt"); char buf1[] = new char[textonly.length()]; textonly.getChars(0,textonly.length(),buf1,0); for(i=0;i<buf1.length;i++) { if(buf1[i]=='\n') f1.write("\r\n"); f1.write(buf1[i]); } I've this code but it is taking only one file at a time. I want to select multiple files. I've 2000 files and I've given them numbering name from 1 to 2000 as "1.html". So I want to give for loop like for(i=1;i<=2000;i++) and after executing separate txt file should be generated.

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• Drawing graphics in Java game

  - by wolf

  I am quite new to game development, so here is a question (maybe a stupid one): In my sidescroller i have a bunch of different graphics objects that i need to draw (player, background tiles, creatures, projectiles etc). Most tutorials i've read so far show that each object has its own draw method, which is then called from some other method. What if I had one method that does all the drawing? Lets say i keep all my objects in an array or queue (or multiple arrays) and then go through each of them, get an image and draw it. So basically would it be better (and why) to have each object have its own draw method or one method that does all the drawing? Or does it matter at all? I feel like the second option is more comfortable, because then all the stuff to do with drawing would be in one place...

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• Tech Article: Build a Java Application with Eclipse, Spring, and Oracle WebLogic Server

  - by OracleTechnologyNetwork

  Oracle Enterprise Pack for Eclipse makes developing applications for the Spring Framework and/or for Oracle WebLogic Server easier. Here's how.

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• Limiting game loop to exactly 60 tics per second (Android / Java)

  - by user22241

  So I'm having terrible problems with stuttering sprites. My rendering and logic takes less than a game tic (16.6667ms) However, although my game loop runs most of the time at 60 ticks per second, it sometimes goes up to 61 - when this happens, the sprites stutter. Currently, my variables used are: //Game updates per second final int ticksPerSecond = 60; //Amount of time each update should take final int skipTicks = (1000 / ticksPerSecond); This is my current game loop @Override public void onDrawFrame(GL10 gl) { // TODO Auto-generated method stub //This method will run continuously //You should call both 'render' and 'update' methods from here //Set curTime initial value if '0' //Set/Re-set loop back to 0 to start counting again loops=0; while(System.currentTimeMillis() > nextGameTick && loops < maxFrameskip){ SceneManager.getInstance().getCurrentScene().updateLogic(); //Time correction to compensate for the missing .6667ms when using int values nextGameTick+=skipTicks; timeCorrection += (1000d/ticksPerSecond) % 1; nextGameTick+=timeCorrection; timeCorrection %=1; //Increase loops loops++; } render(); } I realise that my skipTicks is an int and therefore will come out as 16 rather that 16.6667 However, I tried changing it (and ticksPerSecond) to Longs but got the same problem). I also tried to change the timer used to Nanotime and skiptics to 1000000000/ticksPerSecond, but everything just ran at about 300 ticks per seconds. All I'm attempting to do is to limit my game loop to 60 - what is the best way to guarantee that my game updates never happen at more than 60 times a second? Please note, I do realise that very very old devices might not be able to handle 60 although I really don't expect this to happen - I've tested it on the lowest device I have and it easily achieves 60 tics. So I'm not worried about a device not being able to handle the 60 ticks per second, but rather need to limit it - any help would be appreciated.

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• Best Practices in Setting up a Build and Deployment environment for the Java Platform

  - by Genadinik

  I have a project for which "quick and dirty" isn't the best solution. What is the most stable and currently accepted set of procedures/tools that I should look into when setting up my build/deploy dev (and later production) environment? What I mean is: Should I use ANT? Or has there been something better that has evolved? In what instances should I use Maven? What are some best practices to create a continuous integration/deployment environment? What are best practices for doing test-driven development? Anything else?

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• Java - 2d Array Tile Map Collision

  - by Corey

  How would I go about making certain tiles in my array collide with my player? Like say I want every number 2 in the array to collide. I am reading my array from a txt file if that matters and I am using the slick2d library. Here is my code if needed. public class Tiles { Image[] tiles = new Image[3]; int[][] map = new int[500][500]; Image grass, dirt, mound; SpriteSheet tileSheet; int tileWidth = 32; int tileHeight = 32; public void init() throws IOException, SlickException { tileSheet = new SpriteSheet("assets/tiles.png", tileWidth, tileHeight); grass = tileSheet.getSprite(0, 0); dirt = tileSheet.getSprite(7, 7); mound = tileSheet.getSprite(2, 6); tiles[0] = grass; tiles[1] = dirt; tiles[2] = mound; int x=0, y=0; BufferedReader in = new BufferedReader(new FileReader("assets/map.txt")); String line; while ((line = in.readLine()) != null) { String[] values = line.split(","); for (String str : values) { int str_int = Integer.parseInt(str); map[x][y]=str_int; //System.out.print(map[x][y] + " "); y=y+1; } //System.out.println(""); x=x+1; y = 0; } in.close(); } public void update() { } public void render(GameContainer gc) { for(int x = 0; x < 50; x++) { for(int y = 0; y < 50; y ++) { int textureIndex = map[y][x]; Image texture = tiles[textureIndex]; texture.draw(x*tileWidth,y*tileHeight); } } } } I tried something like this, but I it doesn't ever "collide". X and y are my player position. if (tiles.map[(int)x/32][(int)y/32] == 2) { System.out.println("Collided"); }

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• how do you read from system.out in Java [closed]

  - by Dan

  I'm trying to create a word scramble game and so far I have taken a vector of randomly assorted strings that contains both words and hints and split them into two vectors. I have randomly scrambled the word and set this all up in text boxes. Right now I'm stuck because I have a text box that takes input but I'm not sure how to read that in? I want the user to type the unscrambled word into the text box and have it calculate as correct and move on to the next word immediately. I also don't know how to get the keys working. I want the "?" character to be the hint button that shows the hint. At the moment the hint box works if I type the question mark in using the System.in but it doesn't work if I type it directly in to the text box. The characters are showing up in the text box but nothing is working after that.

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• Struggling to get set up with JOGL2.0

  - by thecoshman

  I guess that Game Dev' is a more sensible place for my problem then SO. I did have JOGL1.1 set up and working, but I soon discovered that it did not support the latest OpenGL, so I started work on upgrading to JOGL2.0 it's not gone too well. Firstly, is it worth me trying to get JOGL to work, or should I just move over to LWJGL? I am fairly comfortable with OpenGL (via C++) and from what I did get working with JOGL1.1, I seem to be OK adapting to it. Assuming that I stick with JOGL, am I foolish for trying to use JOGL2.0? From what I can gather, JOGL2.0 is still in beta, but I am willing to go with it as I want to make use of the latest OpenGL I can. I have been using the Eclipse IDE and have set up a user library for JOGL, here is a screen shot of the configuration and I have added this user library to my own Eclipse project. the system variable %JOGL_HOME% points to "C:\Users\edacosh\Downloads\JOGL2.0" so that should work fine. Now, the problem I actually having, when I try to run my code, on the line GLProfile glp = GLProfile.getDefault(); The code stops with the following message... Exception in thread "main" java.lang.NoClassDefFoundError: com/jogamp/common/jvm/JVMUtil at javax.media.opengl.GLProfile.<clinit>(GLProfile.java:1145) at DiCE.DiCE.<init>(DiCE.java:33) at App.<init>(App.java:17) at App.main(App.java:12) Caused by: java.lang.ClassNotFoundException: com.jogamp.common.jvm.JVMUtil at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 4 more I have also set my project to ensure that it is using jre6 along with jdk6, as I was having some issues. I hope I have given you enough information to be able to help me. It probably doesn't help that I am rather new to Java, been developing in C++ for ages. Thanks

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• Help to organize game cycle in Java

  - by ASIO22

  I'm pretty new here (as though to a game development). So here's my question. I'm trying to organize a really simple game cycle in my public static main() as follows: Scanner sc = new Scanner(System.in); //Running the game cycle boolean flag=true; while (flag) { int action; System.out.println("Type your action please:"); System.out.println("0: Exit app"); try { action = sc.nextInt(); switch (action) { case 0: flag=false; break; case 1: break; } } catch (InputMismatchException ex) { System.out.println(ex.getClass() + "\n" + "Please type a correct input\n"); //action = sc.nextInt(); continue; } What's wrong with this cycle: I want to catch an exception when user types text instead of number, show a message, warning user, and the continue game cycle, read user input etc. But instead of that, when users types wrong data, it goes into a eternal cycle without even prompting user. What I did wrong?

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• Java game object pool management

  - by Kenneth Bray

  Currently I am using arrays to handle all of my game objects in the game I am making, and I know how terrible this is for performance. My question is what is the best way to handle game objects and not hurt performance? Here is how I am creating an array and then looping through it to update the objects in the array: public static ArrayList<VboCube> game_objects = new ArrayList<VboCube>(); /* add objects to the game */ while (!Display.isCloseRequested() && !Keyboard.isKeyDown(Keyboard.KEY_ESCAPE)) { for (int i = 0; i < game_objects.size(); i++){ // draw the object game_objects.get(i).Draw(); game_objects.get(i).Update(); //world.updatePhysics(); } } I am not looking for someone to write me code for asset or object management, just point me into a better direction to get better performance. I appreciate the help you guys have provided me in the past, and I dont think I would be as far along with my project without the support on stack exchange!

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• Mobile apps suck time with the help of Java ME tech

  - by hinkmond

  Here's a new Flurry Mobile report on how Mobile Apps are sucking up more of our precious minutes in a day, even more than the Mobile Web. See: Mobile Apps suck more than Web Here's a quote: Flurry tracked 85,000 apps on [blah-blah-blah], BlackBerry, [yadda-yadda-yadda] and J2ME mobile devices, and their report includes a breakdown on how users spend their time. Greeeaaaaat... People are spending more time on mobile games and doing more Facebook and Twitter from their cell phones. Just what the world needed. Well, you know what they say: "Time == Money". So, the more time you spend, the more money someone, somewhere is getting... Hinkmond

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• help installing some java and flash

  - by william

  ok so i have git now and some other stuff but ive looked around and all and i dont get very help full info Instructions 1 Download the latest version of Flash Player from the Adobe Website. Click on "Download the Latest Player," and choose ".deb for Ubuntu" from the drop down list. 2 Choose "Save File" from the pop up window. Sponsored Links Google Cloud Hosting Build And Run Your App Using Google App Engine cloud.google.com/appengine 3 Open a terminal window. The terminal window will be found under Applications - Utilities. 4 Change to the directory where your downloaded file was saved. cd Download 5 Install the libcurl3 library. sudo apt-get install libcurl3 6 Install the Flash Player. sudo dpkg --install install_flash_player__linux.deb Replace with the latest version number. 7 Restart Firefox. 8 Check that Flash Player was installed. Type about:plugins in a browser window, and look for the flash player MIME type. Read more: http://www.ehow.com/how_5068467_install-flash-player-ubuntu.html#ixzz2ixPj47qS what i dont is how the heck i change the directory and all that crap witch they say every one know

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• Data Aggregation of CSV files java

  - by royB

  I have k csv files (5 csv files for example), each file has m fields which produce a key and n values. I need to produce a single csv file with aggregated data. I'm looking for the most efficient solution for this problem, speed mainly. I don't think by the way that we will have memory issues. Also I would like to know if hashing is really a good solution because we will have to use 64 bit hashing solution to reduce the chance for a collision to less than 1% (we are having around 30000000 rows per aggregation). For example file 1: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,50,60,70,80 a3,b2,c4,60,60,80,90 file 2: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,30,50,90,40 a3,b2,c4,30,70,50,90 result: f1,f2,f3,v1,v2,v3,v4 a1,b1,c1,80,110,160,120 a3,b2,c4,90,130,130,180 algorithm that we thought until now: hashing (using concurentHashTable) merge sorting the files DB: using mysql or hadoop or redis. The solution needs to be able to handle Huge amount of data (each file more than two million rows) a better example: file 1 country,city,peopleNum england,london,1000000 england,coventry,500000 file 2: country,city,peopleNum england,london,500000 england,coventry,500000 england,manchester,500000 merged file: country,city,peopleNum england,london,1500000 england,coventry,1000000 england,manchester,500000 The key is: country,city. This is just an example, my real key is of size 6 and the data columns are of size 8 - total of 14 columns. We would like that the solution will be the fastest in regard of data processing.

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• Java 2D Rectangle Collision? [on hold]

  - by Andreas Elia

  I am just wanting to know of another (longer OR shorter) way of getting 100% effective collisions on a 2D plat-former. The current collision system that is in place works from coords on the level and does not always work reliably. Thank you in advance for any help/support. The current system draws a rectangle and is checking to see if any two points collide. From testing, the system can sometimes "glitch" and allow the player to collide into walls etc. Player Class http://pastebin.com/2zE8vz8R Main Class http://pastebin.com/A6Utb3ti

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• Java - Tile engine changing number in array not changing texture

  - by Corey

  I draw my map from a txt file. Would I have to write to the text file to notice the changes I made? Right now it changes the number in the array but the tile texture doesn't change. Do I have to do more than just change the number in the array? public class Tiles { public Image[] tiles = new Image[5]; public int[][] map = new int[64][64]; private Image grass, dirt, fence, mound; private SpriteSheet tileSheet; public int tileWidth = 32; public int tileHeight = 32; Player player = new Player(); public void init() throws IOException, SlickException { tileSheet = new SpriteSheet("assets/tiles.png", tileWidth, tileHeight); grass = tileSheet.getSprite(0, 0); dirt = tileSheet.getSprite(7, 7); fence = tileSheet.getSprite(2, 0); mound = tileSheet.getSprite(2, 6); tiles[0] = grass; tiles[1] = dirt; tiles[2] = fence; tiles[3] = mound; int x=0, y=0; BufferedReader in = new BufferedReader(new FileReader("assets/map.dat")); String line; while ((line = in.readLine()) != null) { String[] values = line.split(","); for (String str : values) { int str_int = Integer.parseInt(str); map[x][y]=str_int; //System.out.print(map[x][y] + " "); y=y+1; } //System.out.println(""); x=x+1; y = 0; } in.close(); } public void update(GameContainer gc) { } public void render(GameContainer gc) { for(int x = 0; x < map.length; x++) { for(int y = 0; y < map.length; y ++) { int textureIndex = map[y][x]; Image texture = tiles[textureIndex]; texture.draw(x*tileWidth,y*tileHeight); } } } Mouse picking public void checkDistance(GameContainer gc) { Input input = gc.getInput(); float mouseX = input.getMouseX(); float mouseY = input.getMouseY(); double mousetileX = Math.floor((double)mouseX/tiles.tileWidth); double mousetileY = Math.floor((double)mouseY/tiles.tileHeight); double playertileX = Math.floor(playerX/tiles.tileWidth); double playertileY = Math.floor(playerY/tiles.tileHeight); double lengthX = Math.abs((float)playertileX - mousetileX); double lengthY = Math.abs((float)playertileY - mousetileY); double distance = Math.sqrt((lengthX*lengthX)+(lengthY*lengthY)); if(input.isMousePressed(Input.MOUSE_LEFT_BUTTON) && distance < 4) { System.out.println("Clicked"); if(tiles.map[(int)mousetileX][(int)mousetileY] == 1) { tiles.map[(int)mousetileX][(int)mousetileY] = 0; } } System.out.println(tiles.map[(int)mousetileX][(int)mousetileY]); }

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• Write this java source in Clojure

  - by tikky

  Need to write this code in clojure.... package com.example.testvaadin; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import clojure.lang.RT; import com.vaadin.Application; import com.vaadin.terminal.gwt.server.AbstractApplicationServlet; public class Clojure4Vaadin extends AbstractApplicationServlet { @Override protected Class getApplicationClass()throws ClassNotFoundException { return Application.class; } @Override protected Application getNewApplication(HttpServletRequest request) throws ServletException { try { RT.load(getServletConfig().getInitParameter("script-name"), true); return (Application)RT.var(getServletConfig().getInitParameter("package-name"),getServletConfig().getInitParameter("function-name")).invoke(new String[0]); } catch (Exception e) { throw new ServletException(e); } } }

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• Why do we (really) program to interfaces?

  - by Kyle Burns

  One of the earliest lessons I was taught in Enterprise development was "always program against an interface".  This was back in the VB6 days and I quickly learned that no code would be allowed to move to the QA server unless my business objects and data access objects each are defined as an interface and have a matching implementation class.  Why?  "It's more reusable" was one answer.  "It doesn't tie you to a specific implementation" a slightly more knowing answer.  And let's not forget the discussion ending "it's a standard".  The problem with these responses was that senior people didn't really understand the reason we were doing the things we were doing and because of that, we were entirely unable to realize the intent behind the practice - we simply used interfaces and had a bunch of extra code to maintain to show for it. It wasn't until a few years later that I finally heard the term "Inversion of Control".  Simply put, "Inversion of Control" takes the creation of objects that used to be within the control (and therefore a responsibility of) of your component and moves it to some outside force.  For example, consider the following code which follows the old "always program against an interface" rule in the manner of many corporate development shops: 1: ICatalog catalog = new Catalog(); 2: Category[] categories = catalog.GetCategories(); In this example, I met the requirement of the rule by declaring the variable as ICatalog, but I didn't hit "it doesn't tie you to a specific implementation" because I explicitly created an instance of the concrete Catalog object.  If I want to test the functionality of the code I just wrote I have to have an environment in which Catalog can be created along with any of the resources upon which it depends (e.g. configuration files, database connections, etc) in order to test my functionality.  That's a lot of setup work and one of the things that I think ultimately discourages real buy-in of unit testing in many development shops. So how do I test my code without needing Catalog to work?  A very primitive approach I've seen is to change the line the instantiates catalog to read: 1: ICatalog catalog = new FakeCatalog();   once the test is run and passes, the code is switched back to the real thing.  This obviously poses a huge risk for introducing test code into production and in my opinion is worse than just keeping the dependency and its associated setup work.  Another popular approach is to make use of Factory methods which use an object whose "job" is to know how to obtain a valid instance of the object.  Using this approach, the code may look something like this: 1: ICatalog catalog = CatalogFactory.GetCatalog();   The code inside the factory is responsible for deciding "what kind" of catalog is needed.  This is a far better approach than the previous one, but it does make projects grow considerably because now in addition to the interface, the real implementation, and the fake implementation(s) for testing you have added a minimum of one factory (or at least a factory method) for each of your interfaces.  Once again, developers say "that's too complicated and has me writing a bunch of useless code" and quietly slip back into just creating a new Catalog and chalking any test failures up to "it will probably work on the server". This is where software intended specifically to facilitate Inversion of Control comes into play.  There are many libraries that take on the Inversion of Control responsibilities in .Net and most of them have many pros and cons.  From this point forward I'll discuss concepts from the standpoint of the Unity framework produced by Microsoft's Patterns and Practices team.  I'm primarily focusing on this library because it questions about it inspired this posting. At Unity's core and that of most any IoC framework is a catalog or registry of components.  This registry can be configured either through code or using the application's configuration file and in the most simple terms says "interface X maps to concrete implementation Y".  It can get much more complicated, but I want to keep things at the "what does it do" level instead of "how does it do it".  The object that exposes most of the Unity functionality is the UnityContainer.  This object exposes methods to configure the catalog as well as the Resolve<T> method which is used to obtain an instance of the type represented by T.  When using the Resolve<T> method, Unity does not necessarily have to just "new up" the requested object, but also can track dependencies of that object and ensure that the entire dependency chain is satisfied. There are three basic ways that I have seen Unity used within projects.  Those are through classes directly using the Unity container, classes requiring injection of dependencies, and classes making use of the Service Locator pattern. The first usage of Unity is when classes are aware of the Unity container and directly call its Resolve method whenever they need the services advertised by an interface.  The up side of this approach is that IoC is utilized, but the down side is that every class has to be aware that Unity is being used and tied directly to that implementation. Many developers don't like the idea of as close a tie to specific IoC implementation as is represented by using Unity within all of your classes and for the most part I agree that this isn't a good idea.  As an alternative, classes can be designed for Dependency Injection.  Dependency Injection is where a force outside the class itself manipulates the object to provide implementations of the interfaces that the class needs to interact with the outside world.  This is typically done either through constructor injection where the object has a constructor that accepts an instance of each interface it requires or through property setters accepting the service providers.  When using dependency, I lean toward the use of constructor injection because I view the constructor as being a much better way to "discover" what is required for the instance to be ready for use.  During resolution, Unity looks for an injection constructor and will attempt to resolve instances of each interface required by the constructor, throwing an exception of unable to meet the advertised needs of the class.  The up side of this approach is that the needs of the class are very clearly advertised and the class is unaware of which IoC container (if any) is being used.  The down side of this approach is that you're required to maintain the objects passed to the constructor as instance variables throughout the life of your object and that objects which coordinate with many external services require a lot of additional constructor arguments (this gets ugly and may indicate a need for refactoring). The final way that I've seen and used Unity is to make use of the ServiceLocator pattern, of which the Patterns and Practices team has also provided a Unity-compatible implementation.  When using the ServiceLocator, your class calls ServiceLocator.Retrieve in places where it would have called Resolve on the Unity container.  Like using Unity directly, it does tie you directly to the ServiceLocator implementation and makes your code aware that dependency injection is taking place, but it does have the up side of giving you the freedom to swap out the underlying IoC container if necessary.  I'm not hugely concerned with hiding IoC entirely from the class (I view this as a "nice to have"), so the single biggest problem that I see with the ServiceLocator approach is that it provides no way to proactively advertise needs in the way that constructor injection does, allowing more opportunity for difficult to track runtime errors. This blog entry has not been intended in any way to be a definitive work on IoC, but rather as something to spur thought about why we program to interfaces and some ways to reach the intended value of the practice instead of having it just complicate your code.  I hope that it helps somebody begin or continue a journey away from being a "Cargo Cult Programmer".

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• How to install an older version of Java

  - by Alex Spurling

  I updated my installation of the sun-java6-jdk package today to version 6.24-1build0.10.10.1 after being prompted by the update manager. However this now causes some compilation failures so I'd like to revert back to the previous version that I had installed. I've tried using Synaptic but the 'Force Version' menu command is disabled. I've tried the following command to install the previous version sudo apt-get install sun-java6-jdk=6.22-0ubuntu1~10.10 But I'm not sure that I have the correct version: Reading package lists... Done Building dependency tree Reading state information... Done E: Version ‘6.22-0ubuntu1~10.10’ for ‘sun-java6-jdk’ was not found I've taken this version number from this changelog: https://launchpad.net/ubuntu/+source/sun-java6/+changelog Is this the correct way to install a previous version of a package? Have I got the correct version from the sun-java6 change log?

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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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• SOA, Java EE and data organization

  - by jolasveinn

  At the company I work for, we're currently splitting up our monolith solution into a number of small services (SOA). Many of the services are small, so we'd like to deploy a number of these services on the same application server, JBoss 7.1 in this case. As per the SOA philosophy, the independence of each service and the teams working on them is very important. What would be the best way to organize the data? Use one schema per service Would you use one datasource per schema in the application server? Or use one datasource, prefixing all DB object names with the schema name in some transparent manner? Use a shared schema, but evading any naming collisions by requiring each service to use a distinct prefix for all DB objects Other options? Am I maybe thinking this completely wrong here? :)

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• Most efficient way to handle coordinate maps in Java

  - by glowcoder

  I have a rectangular tile-based layout. It's your typical Cartesian system. I would like to have a single class that handles two lookup styles Get me the set of players at position X,Y Get me the position of player with key K My current implementation is this: class CoordinateMap<V> { Map<Long,Set<V>> coords2value; Map<V,Long> value2coords; // convert (int x, int y) to long key - this is tested, works for all values -1bil to +1bil // My map will NOT require more than 1 bil tiles from the origin :) private Long keyFor(int x, int y) { int kx = x + 1000000000; int ky = y + 1000000000; return (long)kx | (long)ky << 32; } // extract the x and y from the keys private int[] coordsFor(long k) { int x = (int)(k & 0xFFFFFFFF) - 1000000000; int y = (int)((k >>> 32) & 0xFFFFFFFF) - 1000000000; return new int[] { x,y }; } } From there, I proceed to have other methods that manipulate or access the two maps accordingly. My question is... is there a better way to do this? Sure, I've tested my class and it works fine. And sure, something inside tells me if I want to reference the data by two different keys, I need two different maps. But I can also bet I'm not the first to run into this scenario. Thanks!

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• NetBeans Hangs on New Project Creation

  - by Jason

  When creating a New Project in NetBeans, it hangs on the creation screen; Screenshot I'm running Netbeans 7.0.1 on Xubuntu 13.04. Java -version prints: java version "1.7.0_25" OpenJDK Runtime Environment (IcedTea 2.3.10) (7u25-2.3.10-1ubuntu0.13.04.2) OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode) /usr/lib/jvm/ contains the following folders; java-1.5.0-gcj-4.7-amd64 java-6-openjdk-amd64 java-7-openjdk-common java-1.6.0-openjdk-amd64 java-6-openjdk-common java-1.7.0-openjdk-amd64 java-7-openjdk-amd64 I tried editing /usr/share/netbeans/7.0.1/etc/netbeans.conf with the following (as was suggested in another post); netbeans_jdkhome="/usr/lib/jvm/java-7-openjdk-amd64/jre/" But that didn't work. Instead, NetBeans then presented an error on the loading splash when it reached "Turning on Modules..." claiming the JDK was missing. Both NetBeans and the OpenJDK Java 7/6 Runtimes were installed through the Ubuntu Software Centre. I've also tried uninstalling and reinstalling both Java and NetBeans. Any help would be greatly appreciated, thanks!

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• Android/Java AI agent framework/middleware

  - by corneliu

  I am looking for an AI agent framework to use as a starting point in an Android game I have to create for a university research project. It has been suggested to me to use JADE, but, as far as I can tell, it's not a suitable framework for games (at least for my game idea) because it runs in a split-execution mode, and it needs an always-active network connection to a main host. What I want is just a little something to give me a headstart. I am willing to adjust the game's features to the framework because it's more of a mockup game, and the purpose is to compare the performance of a couple of agents in the game world. The game will be very simplistic, with a minimal UI that displays various stats about the characters in the game (so no graphics, no pathfinding). Thank you.

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