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• decouple software components via nameconvention

  - by csteinmueller

  I'm currently evaluating alternatives to refactor a drivermanagement. In my multitier architecture I have Baseclass DAL.Device //my entity Interfaces BL.IDriver //handles the dataprocessing between application and device BL.IDriverCreator //creates an IDriver from a Device BL.IDriverFactory //handles the driver creation requests Every specialization of Device has a corresponding IDriver implementation and a corresponding IDriverCreator implementation. At the moment the mapping is fix via a type check within the business layer / DriverFactory. That means every new driver needs a) changing code within the DriverFactory and b) referencing the new IDriver implementation / assembly. On a customers point of view that means, every new driver, used or not, needs a complex revalidation of their hardware environment, because it's a critical process. My first inspiration was to use a caliburn micro like nameconvention see Caliburn.Micro: Xaml Made Easy BL.RestDriver BL.RestDriverCreator DAL.RestDevice After receiving the RestDevicewithin the IDriverFactory I can load all driver dlls via reflection and do a namesplitting/comparing (extracting the xx from xxDriverCreator and xxDevice) Another idea would be a custom attribute (which also leads to comparing strings). My question: is that a good approach above layer borders? If not, what would be a good approach?

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• Why is the remove function not working for hashmaps? [migrated]

  - by John Marston

  I am working on a simple project that obtains data from an input file, gets what it needs and prints it to a file. I am basically getting word frequency so each key is a string and the value is its frequency in the document. The problem however, is that I need to print out these values to a file in descending order of frequency. After making my hashmap, this is the part of my program that sorts it and writes it to a file. //Hashmap I create Map<String, Integer> map = new ConcurrentHashMap<String, Integer>(); //function to sort hashmap while (map.isEmpty() == false){ for (Entry<String, Integer> entry: map.entrySet()){ if (entry.getValue() > valueMax){ max = entry.getKey(); System.out.println("max: " + max); valueMax = entry.getValue(); System.out.println("value: " + valueMax); } } map.remove(max); out.write(max + "\t" + valueMax + "\n"); System.out.println(max + "\t" + valueMax); } When I run this i get: t 9 t 9 t 9 t 9 t 9 .... so it appears the remove function is not working as it keeps getting the same value. I'm thinking i have an issue with a scope rule or I just don't understand hashmaps very well. If anyone knows of a better way to sort a hashmap and print it, I would welcome a suggestion. thanks

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• Bitmap & Object Collision Help

  - by MarkEz

  Is it possible to detect when an object and a bitmap collide. I have an arraylist of sprites that I am shooting with an image. I tried using this method here but as soon as the bitmap appears the sprite disappears, this is in the Sprite class: public boolean isCollision(Bitmap other) { if(other.getWidth() > x && other.getWidth() < x + width && >other.getHeight() > y && other.getHeight() < y + height); return true; }

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• Finding which tiles are intersected by a line, without looping through all of them or skipping any

  - by JustSuds

  I've been staring at this problem for a few days now. I rigged up this graphic to help me visualise the issue: http://i.stack.imgur.com/HxyP9.png (from the graph, we know that the line intersects [1, 1], [1, 2], [2, 2], [2, 3], ending in [3,3]) I want to step along the line to each grid space and check to see if the material of the grid space is solid. I feel like I already know the math involved, but I haven't been able to string it together yet. I'm using this to test line of sight and eliminate nodes after a path is found via my pathfinding algorithms - my agents cant see through a solid block, therefore they cant move through one, therefore the node is not eliminated from the path because it is required to navigate a corner. So, I need an algorithm that will step along the line to each grid space that it intersects. Any ideas? I've taken a look at a lot of common algorithms, like Bresenham's, and one that steps at predefined intervals along the line (unfortunately, this method skips tiles if they're intersecting with a smaller wedge than the step size). I'm populating my whiteboard now with a mass of floor() and ceil() functions - but its getting overly complicated and I'm afraid it might cause a slowdown.

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• Z axis trouble with glTranslatef(...) - LWJGL

  - by Zarkopafilis

  Here is the code: private static boolean up = true , down = false , left = false , right = false, reset = false, in = false , out = false; public void start() { try { Display.setDisplayMode(new DisplayMode(800,600)); Display.create(); } catch (LWJGLException e) { e.printStackTrace(); System.exit(0); } GL11.glMatrixMode(GL11.GL_PROJECTION); GL11.glLoadIdentity(); GL11.glOrtho(0, 800, 0, 600, 0.00001f, 1000); GL11.glMatrixMode(GL11.GL_MODELVIEW); Keyboard.enableRepeatEvents(true); while (!Display.isCloseRequested()) { GL11.glClear(GL11.GL_COLOR_BUFFER_BIT); input(); if(up){ GL11.glTranslatef(0,0.1f,0); } if(down){ GL11.glTranslatef(0,-0.1f,0); } if(left){ GL11.glTranslatef(-0.1f,0,0); } if(right){ GL11.glTranslatef(0.1f,0,0); } if(in){ GL11.glTranslatef(0, 0, 1f); } if(out){ GL11.glTranslatef(0, 0, -1f); } if(reset){ GL11.glLoadIdentity(); } GL11.glBegin(GL11.GL_QUADS); GL11.glColor3f(255, 255, 255); GL11.glVertex3f(800/2, 600/2, 0); GL11.glVertex3f(800/2 + 200, 600/2, 0); GL11.glVertex3f(800/2 + 200, 600/2 + 200, 0); GL11.glVertex3f(800/2, 600/2 + 200, 0); GL11.glColor3f(0, 255, 0); GL11.glVertex3f(800/2, 600/2, 1); GL11.glVertex3f(800/2 + 200, 600/2, 1); GL11.glVertex3f(800/2 + 200, 600/2 + 200, 1); GL11.glVertex3f(800/2, 600/2 + 200, 1); GL11.glEnd(); Display.update(); } Display.destroy(); } public static void main(String[] argv){ new main().start(); } public void input(){ up = false; down = false; left = false; right = false; reset = false; in = false; out = false; if(Keyboard.isKeyDown(Keyboard.KEY_SPACE)){ reset = true; } if(Keyboard.isKeyDown(Keyboard.KEY_W)){ up = true; } if(Keyboard.isKeyDown(Keyboard.KEY_S)){ down = true; } if(Keyboard.isKeyDown(Keyboard.KEY_A)){ left = true; } if(Keyboard.isKeyDown(Keyboard.KEY_D)){ right = true; } if(Keyboard.isKeyDown(Keyboard.KEY_Q)){ in = true; } if(Keyboard.isKeyDown(Keyboard.KEY_E)){ out = true; } } As you can see I am creating 2 quads , a white one at z 0 and a green one at z 1. WASD keys function correctly. Also when I hit SPACEBAR the white quad is being shown. If I then press E , I can see the green quad. But if I press Q afterwards , I dont see the white one again!(Space Works everytime). Also if I render the green one at Z = -1 everything works perfectly BUT you may need up to 3 key presses Q/E to see the other quad. Why is that happening?

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• Jumping Physics

  - by CogWheelz

  With simplicity, how can I make a basic jump without the weird bouncing? It jumps like 2 pixels and back Here's what I use y += velY x += velX then keypresses MAX_SPEED = 180; falling = true; if(Gdx.input.isKeyPressed(Keys.W)) {//&& !jumped && !p.falling) { p.y += 20; } if(!Gdx.input.isKeyPressed(Keys.W)) p.velY = 0; if(Gdx.input.isKeyPressed(Keys.D)) p.velX = 5; if(!Gdx.input.isKeyPressed(Keys.D) && !(Gdx.input.isKeyPressed(Keys.A))) p.velX = 0; if(Gdx.input.isKeyPressed(Keys.A)) p.velX = -5; if(!Gdx.input.isKeyPressed(Keys.A) && !(Gdx.input.isKeyPressed(Keys.D))) p.velX = 0; if(p.falling == true || p.jumping == true) { p.velY -= 2; } if(p.velY > MAX_SPEED) p.velY = MAX_SPEED; if(p.velX > MAX_SPEED) p.velX = MAX_SPEED;

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• Is there a pattern to restrict which classes can update another class?

  - by Mike

  Say I have a class ImportantInfo with a public writable property Data. Many classes will read this property but only a few will ever set it. Basically, if you want to update Data you should really know what you're doing. Is there a pattern I could use to make this explicit other than by documenting it? For example, some way to enforce that only classes that implement IUpdateImportantData can do it (this is just an example)? I'm not talking about security here, but more of a "hey, are you sure you want to do that?" kind of thing.

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• Provide A Scrolling "Camera" View Over A 2D Game Map

  - by BitCrash

  I'm in the process of attempting to create a 2D MMO type game with Kryonet and some basic sprites, mostly for my own learning. I have the back end set up great (By my standards) and I'm moving on to actually getting some things drawn onto the map. I cannot for the life of me figure out a solid way to have a "Camera" follow a player around a large area. The view pane for the game is 640 x 480 pixels, and each tile is 32x32 pixels (Thats 20 tiles wide and 15 high for the viewpane) I have tried a couple things to do this, but they did not seem to work out so well. I had a JScrollPane with 9 "Viewpane"-sized canvases in it, and tried to have the JScrollPane move in accordance with the player. The issue came when I reached the end of the JScrollPane. I tried to "Flip" canvases, sending the canvas currrently drawing the player to the middle of the 9 and load the corresponding maps onto the other ones. It was slow and worked poorly. I'm looking for any advice or previous experience with this; any ideas? Thank you! Edit and Clarification: I did not mean to mention Kryonet, I was merely providing peripheral information in case there was something that would help which I could not foresee. Instead of having an array of 9 canvases, why not just have one large canvas loading a large map every once in a while? I'm willing to have "load times" where as with the canvas array I would have none (in theory) to give the user a smooth experience. I could just change the size and location of the map with a modified setBounds() call on the canvas in a layered pane (layered because I have hidden swing items, like inventories and stuff) I'll try it out and post here how it goes for people asking the same question.

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• LIbgdx and android scaling

  - by petervaz

  Following my previous question, I decided to migrate my andengine game to libdgx to have the desktop option. The game assets were planned, at first, to use a 1080x600 resolution and I raised that to 1200x800 which is native for many tablets and would look better on monitors. I followed this blog aproach regarding aspect ratio, which worked nicely on the desktop version, but running the android version (on my smaller tablet), the background would still appear on the original size being cropped by the smaller screen size. How can I force the resize of the background (or for what matter, of everything) on android to fit the screen?

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• How to make an Image still when at position at Slick 2D?

  - by SystemNetworks

  For example, I want to put a building down. if I press 2, it will show the building near the character and it is moving with my character. I have done that. Now I wanted to know how do i put it down and stop following my character? I have something called shiftX and shiftY (Which is the position of my character) And my character looks like it is moving because the map and images itself is moving which i call, probePositionX and probePositionY.

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• mobile apllication building

  - by Tekwane Mwendwa

  I got this from a guy thats to build a mobile application what does most of it mean purpose (what problem does your application solve) Audience (who will use your app? what are some examples of user cases?) platforms (iOS, Android, web/responsive web, etc) detailed feature requirements (consider both front and back end, if you can) what services you need from Sourcebits (design & engineering?) any important technical details (existing dependencies such as a server that your app will need to interface with, custom APIs, etc etc any wireframes or other visual assets? any existing apps with similar purpose / design / interactive sense budget/funding limitations development timeframe

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• Recommended design pattern for object with optional and modifiable attributtes? [on hold]

  - by Ikuzen

  I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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• How do I split a texture into differently shaped pieces with libgdx?

  - by VictorB

  I want to split a texture into variously shaped pieces with libgdx, like the pieces of a puzzle game. TextureRegion.split() is not an option, as it splits into equally sized rectangular texture regions. The "Similar Questions" section here is helpful (particularly this question How do I break an image into 6 or 8 pieces of different shapes?), but I'm not sure yet if it's possible to implement the solution with libgdx. Any pointers?

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• Get all triangles that are < N dist from you?

  - by CyanPrime

  Does anyone know of a way I could add a radius to this code for p? Like basically saying "this is true if the triangle is < N dist from the point" public boolean isPointInTriangle( Vector3f p, Vector3f a, Vector3f b, Vector3f c ) { return ( pointsAreOnSameSide(p, a, b, c) && pointsAreOnSameSide(p, b, a, c) && pointsAreOnSameSide(p, c, a, b) ); } public boolean pointsAreOnSameSide( Vector3f p1, Vector3f p2, Vector3f a, Vector3f b ) { Vector3f diffba = new Vector3f(0,0,0); Vector3f.sub( b, a, diffba ); Vector3f diffp1a = new Vector3f(0,0,0); Vector3f.sub( p1, a, diffp1a ); Vector3f diffp2a = new Vector3f(0,0,0); Vector3f.sub( p2, a, diffp2a ); Vector3f cross1 = Vector3f.cross(diffba, diffp1a); Vector3f cross2 = Vector3f.cross(diffba, diffp2a); return ( Vector3f.dot( cross1, cross2 ) >= 0 ); }

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• How can I set the rotation of a shape to the same as my image?

  - by BleedObsidian

  The way you set rotations of images is different from setting shape rotations. So how can I make the shape have the same rotation as my image? This is how my image rotates: if(input.isKeyDown(Input.KEY_RIGHT)) { rotate += rotateSpeed * delta; image.rotate(rotate - image.getRotation()); } How can I get the same effect but with a shape? For example: How can I get that rectangle to be at the same rotation as the car?

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• Vector normalization gives very imprecise results

  - by Kipras

  When I normalize vectors I receive very strange results. The lengths of the normalized vectors range from 1.0 to almost 1.5. The functions are all written by me, but I just can't find a mistake in my algorithm. When I normalize I just divide all components of the vector by the vector's length. public double length(){ return Math.sqrt(x*x + y*y); } public void normalize(){ if(length() > 0){ x /= length(); y /= length(); } } Is this supposed to happen? I mean I can see the length ranging from 0.9 to 1.1 at worst, but this is just overwhelming. Cheers

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• SQL RDBMS : one query or multiple calls

  - by None None

  After looking around the internet, I decided to create DAOs that returned objects (POJOs) to the calling business logic function/method. For example: a Customer object with a Address reference would be split in the RDBMS into two tables; Customer and ADDRESS. The CustomerDAO would be in charge of joining the data from the two tables and create both an Address POJO and Customer POJO adding the address to the customer object. Finally return the fulll Customer POJO. Simple, however, now i am at a point where i need to join three or four tables and each representing an attribute or list of attributes for the resulting POJO. The sql will include a group by but i will still result with multiple rows for the same pojo, because some of the tables are joining a one to many relationship. My app code will now have to loop through all the rows trying to figure out if the rows are the same with different attributes or if the record should be a new POJO. Should I continue to create my daos using this technique or break up my Pojo creation into multiple db calls to make the code easier to understand and maintain?

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• Static vs. dynamic memory allocation - lots of constant objects, only small part of them used at runtime

  - by k29

  Here are two options: Option 1: enum QuizCategory { CATEGORY_1(new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...), CATEGORY_2(new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...), ... ; public MyCollection<Question> collection; private QuizCategory(MyCollection<Question> collection) { this.collection = collection; } public Question getRandom() { return collection.getRandomQuestion(); } } Option 2: enum QuizCategory2 { CATEGORY_1 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_A) .add(Question.QUESTION_B) .add...; } }, CATEGORY_2 { @Override protected MyCollection<Question> populateWithQuestions() { return new MyCollection<Question>() .add(Question.QUESTION_B) .add(Question.QUESTION_C) .add...; } }; public Question getRandom() { MyCollection<Question> collection = populateWithQuestions(); return collection.getRandomQuestion(); } protected abstract MyCollection<Question> populateWithQuestions(); } There will be around 1000 categories, each containing 10 - 300 questions (100 on average). At runtime typically only 10 categories and 30 questions will be used. Each question is itself an enum constant (with its fields and methods). I'm trying to decide between those two options in the mobile application context. I haven't done any measurements since I have yet to write the questions and would like to gather more information before committing to one or another option. As far as I understand: (a) Option 1 will perform better since there will be no need to populate the collection and then garbage-collect the questions; (b) Option 1 will require extra memory: 1000 categories x 100 questions x 4 bytes for each reference = 400 Kb, which is not significant. So I'm leaning to Option 1, but just wondered if I'm correct in my assumptions and not missing something important? Perhaps someone has faced a similar dilemma? Or perhaps it doesn't actually matter that much?

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• Design application to send messages by marking circle on the map where you want to send message

  - by jhamb

  This is question asked to me by an interviewer, in which a map of world is given, and for those country you want to send message, just marked circle on that area, and just send to all the people comes in that area. Question visual link is : Design this application The approach that I told him: Firstly build whole person's data (contacts , place information and all) Then where you mark on the map, just build a cluster of that country using Hadoop and fire the message to all the person's contact comes in that cluster. So help me for better understandings of this problem, and if have another good approach (all back-end ad front-end) , then please tell me or discuss here with me. Thanks in advance.

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• What is the best practice for reading a large number of custom settings from a text file?

  - by jawilmont

  So I have been looking through some code I wrote a few years ago for an economic simulation program. Each simulation has a large number of settings that can be saved to a file and later loaded back into the program to re-run the same/similar simulation. Some of the settings are optional or depend on what is being simulated. The code to read back the parameters is basically one very large switch statement (with a few nested switch statements). I was wondering if there is a better way to handle this situation. One line of the settings file might look like this: #RA:1,MT:DiscriminatoryPriceKDoubleAuction,OF:Demo Output.csv,QM:100,NT:5000,KP:0.5 //continues... And some of the code that would read that line: switch( Character.toUpperCase( s.charAt(0) ) ) { case 'R': randSeed = Integer.valueOf( s.substring(3).trim() ); break; case 'M': marketType = s.substring(3).trim(); System.err.println("MarketType: " + marketType); break; case 'O': outputFileName = s.substring(3).trim() ; break; case 'Q': quantityOfMarkets = Integer.valueOf( s.substring(3).trim() ); break; case 'N': maxTradesPerRound = Integer.valueOf( s.substring(3).trim() ); break; case 'K': kParameter = Float.valueOf( s.substring(3).trim() ); break; // continues... }

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• Should Business Interfaces be part of the Model layer?

  - by Mik378

  In an oriented-services enterprise application, isn't it an antipattern to mix Service APIs (containing interface that external users depends on) with Model objects (entities, custom exceptions objects etc...) ? According to me, Services should only depends on Model layer but never mixed with it. In fact, my colleague told me that it doesn't make sense to separate it since client need both. (model and service interfaces) But I notice that everytime a client asks for some changes, like adding a new method in some interface (means a new service), Model layer has to be also delivered... Thus, client who has not interested by this "addition" is constrained to be concerned by this update of Model... and in a large enterprise application, this kind of delivery is known to be very risked... What is the best practice ? Separate services(only interfaces so) and model objects or mix it ?

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• way to do if(x > x2) x = x2 with rotation?

  - by CyanPrime

  Alright, so I got this walking code, and some collision detection, now the collision detection returns a Vector3f of the closest point on the triangle that the projected position is at (pos + move), so then I project my position again in the walking method/function and if the projected position's x is the nearest point'x the projected position's x becomes the nearist point's x. same with their z points, but if I'm moving in a different direction from 0 degrees XZ how would I rotate the equation/condition? Here is what I got so far, and it's not working, as I go through walls, and such. Vector3f move = new Vector3f(0,0,0); move.x = (float)-Math.cos(Math.toRadians(yaw)); move.z = (float)-Math.sin(Math.toRadians(yaw)); // System.out.println("slopeNormal.z: " + slopeNormal.z + "move.z: " + move.z); move.normalise(); move.scale(movementSpeed * delta); float horizontaldotproduct = move.x * slopeNormal.x + move.z * slopeNormal.z; move.y = -horizontaldotproduct * slopeNormal.y; Vector3f dest = colCheck(pos, move, model, drawDist, movementSpeed, delta); Vector3f projPos = new Vector3f(pos); Vector3f.add(projPos, move, projPos); if(projPos.x > 0 && dest.x > 0 && projPos.x < dest.x) projPos.x = dest.x; else if(projPos.x < 0 && dest.x < 0 && projPos.x > dest.x) projPos.x = dest.x; if(projPos.z > 0 && dest.z > 0 && projPos.z < dest.z) projPos.z = dest.z; else if(projPos.z < 0 && dest.z < 0 && projPos.z > dest.z) projPos.z = dest.z; pos = new Vector3f(projPos);

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• What is the primary use of Vertex Buffer Objects?

  - by sensae

  From what I've read, it seems VBOs are purely for performance. I'm working on a very rudimentary learning project in lwjgl and I'm just trying to figure out what more advanced features of the library I should be delving into, and what their use is. My understanding is that VBOs allow a person to keep vertexes in VRAM while they aren't currently being drawn in a scene. In my case, I'm just drawing quads and performance probably isn't a concern at all, but I'm trying to piece together what's happening under the hood. If I'm drawing quads directly, I'm drawing from the CPU memory, correct? Also, if I'm not doing any checks for visibility, does that mean I'm rendering absolutely everything in the "scene", regardless of whether its in view? Are VBOs a way to store objects and only render what's needed?

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• How to use Twitter4j With JSF2 for Login? [on hold]

  - by subodh

  I am trying to do login with Twitter and using Twitter4j for that and wrote this code In JSF <h:commandButton id="twitterbutton" value="Sign up with Twitter" action="#{twitterLoginBean.redirectTwitterLogin}" immediate="true" styleClass="twitterbutton"/> In ManagedBean public String redirectTwitterLogin() throws ServletException, IOException, TwitterException { HttpServletRequest request = (HttpServletRequest) FacesContext .getCurrentInstance().getExternalContext().getRequest(); HttpServletResponse response = (HttpServletResponse) FacesContext .getCurrentInstance().getExternalContext().getResponse(); Twitter twitter = TwitterFactory.getSingleton(); twitter.setOAuthConsumer(apiKey, apiSecret); RequestToken requestToken = twitter.getOAuthRequestToken(); if (requestToken != null) { AccessToken accessToken = null; BufferedReader br = new BufferedReader(new InputStreamReader( System.in)); while (null == accessToken) { try { String pin = br.readLine(); accessToken = twitter .getOAuthAccessToken(requestToken, pin); } catch (TwitterException te) { System.out .println("Failed to get access token, caused by: " + te.getMessage()); System.out.println("Retry input PIN"); } } request.setAttribute(IS_AUTHENTICATED, true); if (accessToken != null) { LOGGER.debug("We have a valid oauth token! Make the facebook request"); doApiCall(twitter, request, response); return null; } } else { LOGGER.debug("We don't have auth code yet, fetching the Authorization URL..."); String authorizationUrl = requestToken.getAuthorizationURL(); LOGGER.debug("Redirecting to the Authorization URL: {}", authorizationUrl); request.setAttribute(IS_AUTHENTICATED, false); redirect(authorizationUrl, response); return null; } return null; } In above code i want first Login window of twitter will show and then again same method will call and after user will login i can show user information userId,Handel,location etc. Redirect private void redirect(String url, HttpServletResponse response) throws IOException { String urlWithSessionID = response.encodeRedirectURL(url); response.sendRedirect(urlWithSessionID); } But this code is not working Can anyone tell better Solution for this ?

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• How should I implement Transaction database EJB 3.0

  - by JamesBoyZ

  In the CustomerTransactions entity, I have the following field to record what the customer bought: @ManyToMany private List<Item> listOfItemsBought; When I think more about this field, there's a chance it may not work because merchants are allowed to change item's information (e.g. price, discount, etc...). Hence, this field will not be able to record what the customer actually bought when the transaction occurred. At the moment, I can only think of 2 ways to make it work. I will record the transaction details into a String field. I feel that this way would be messy if I need to extract some information about the transaction later on. Whenever the merchant changes an item's information, I will not update directly to that item's fields. Instead, I will create another new item with all the new information and keep the old item untouched. I feel that this way is better because I can easily extract information about the transaction later on. However, the bad side is that my Item table may contain a lot of rows. I'd be very grateful if someone could give me an advice on how I should tackle this problem. UPDATE: I'd like to add more information about the current design. public class Customer implements Serializable { @OneToMany private List<CustomerTransactions> listOfTransactions; } public class CustomerTransactions implements Serializable { @ManyToMany private List<Item> listOfItemsBought; } public class Merchant implements Serializable { @OneToMany private List<Item> listOfSellingItems; }

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