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• Non-mathematical Project Euler (or similar)?

  - by Juha Untinen

  I checked the post (Where can I find programming puzzles and challenges?) where there's a lot of programming challenges and such, but after checking several of them, they all seem to be about algorithms and mathematics. Is there a similar site for purely logic/functionality-based challenges? For example: - Retrieve data using a web service - Generate output X from a CSV file - Protect this code against SQL injection - Make this code more secure - What is wrong with this code (where the error is in logic, not syntax) - Make this loop more efficient Does a challenge site like that exist? Especially one that provides hints and/or correct solutions. That would be a very helpful learning site.

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• Implementing `fling` logic without pan gesture recognizers

  - by KDiTraglia

  So I am trying to port over a simple game that I originally wrote to iphone into cocos2d-x. I've hit a minor bump however in implementing simple 'fling' logic I had in the iphone version that is difficult to port over to the c++. In iOS I could get the velocity of a pan gesture very easily: CGPoint velocity = [recognizer velocityInView:recognizer.view]; However now I basically only know where the touch began, where the touch ended, and all the touches that are logged in between. For now I logged all the pts onto a stack then pulled the last point and the 6th to last point (seemed to work the best), find the difference between those pts multiply by a constant and use that as the velocity. It works relatively well, but I'm wondering if anyone else has any better algorithms, when given a bunch of touch pts, to figure out a new speed upon releasing an object that feels natural (Note speed in my game is just a constant x and y, there's no drag or spin or anything tricky like that). Bonus points if anyone has figured out how to get pan gestures into the newest version (3.0 alpha) of cocos2d-x without losing ability to build cross platform.

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• Game with changing logic

  - by rsprat

  I'm planing to develop a puzzle like mobile game (android/ios) with a different logic for each puzzle. Say, for example one puzzle could be a Rubik's cube and another one a ball maze. Many more new puzzles will appear during the life of the game, and I want the users to be able to play those new puzzles. The standard way for managing this would be through application updates. Each time a new puzzle or bunch of puzzles appear, create a new update for the app that the user can download. However, I would like to do it in a more transparent way. When a new puzzle appears, the basic info of the puzzle would be displayed in the app menu, and the user would be able to play it by just clicking it. What comes to my mind is that the app would automatically download a .dll or .jar and inject it in the application at runtime. Is that even possible? Are there any restrictions from the OS? Is there a better way for solving it? Thanks alot

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• In separate data access & business logic layer, can I use entity frame work classes in business laye

  - by Greg

  In separate data access & business logic layer, can I use entity frame work classes in business layer?

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• I cant really wrap my head around BOOLEAN logic when I use NOT together with AND and OR

  - by Bq

  Im trying to understand how boolean logic works when I use NOT. To give an example using awk I have a text file containing CORE PORT CORE PORT COREPORT CORE COREPORT And I would like to remove all COREPORT lines. The way I thought I would do it was with (NOT CORE) AND (NOT PORT) eg awk '/!CORE/&&/!PORT/{print}' But when I try it out Im actually supposed to use OR instead of AND awk '/!CORE/||/!PORT/{print}' I would be really glad if some one could explain where my thinking is wrong and super glad if it could be visualized with a venn diagram or something like the boolean machine at kathyschrock

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• What's the right way to handle "One, Both, or None" logic?

  - by Stephen

  I have a logic situation that is best described as two "Teams" trying to win a task. The outcome of this task could be a single winner, a tie (draw), or no winner (stalemate). Currently, I'm using a nested if/else statement like so: // using PHP, but the concept seems language agnostic. if ($team_a->win()) { if ($team_b->win()) { // this is a draw } else { // team_a is the winner } } else { if ($team_b->win()) { // team_b is the winner } else { // This is a stalemate, no winner. } } This seems rather spaghetti-like and repetitive. Is there a more logical, DRY pattern I could use?

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• Repository, Service or Domain object - where does logic belong?

  - by betitall

  Take this simple, contrived example: UserRepository.GetAllUsers(); UserRepository.GetUserById(); Inevitably, I will have more complex "queries", such as: //returns users where active=true, deleted=false, and confirmed = true GetActiveUsers(); I'm having trouble determining where the responsibility of the repository ends. GetActiveUsers() represents a simple "query". Does it belong in the repository? How about something that involves a bit of logic, such as: //activate the user, set the activationCode to "used", etc. ActivateUser(string activationCode);

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• Business Objects - Containers or functional?

  - by Walter

  This is a question I asked a while back on SO, but it may get discussed better here... Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about another class to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense and why??

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• Question about separating game core engine from game graphics engine...

  - by Conrad Clark

  Suppose I have a SquareObject class, which implements IDrawable, an interface which contains the method void Draw(). I want to separate drawing logic itself from the game core engine. My main idea is to create a static class which is responsible to dispatch actions to the graphic engine. public static class DrawDispatcher<T> { private static Action<T> DrawAction = new Action<T>((ObjectToDraw)=>{}); public static void SetDrawAction(Action<T> action) { DrawAction = action; } public static void Dispatch(this T Obj) { DrawAction(Obj); } } public static class Extensions { public static void DispatchDraw<T>(this object Obj) { DrawDispatcher<T>.DispatchDraw((T)Obj); } } Then, on the core side: public class SquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<SquareObject>(); } #endregion } And on the graphics side: public static class SquareRender{ //stuff here public static void Initialize(){ DrawDispatcher<SquareObject>.SetDrawAction((Square)=>{//my square rendering logic}); } } Do this "pattern" follow best practices? And a plus, I could easily change the render scheme of each object by changing the DispatchDraw parameter, as in: public class SuperSquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<SquareObject>(); } #endregion } public class RedSquareObject: GameObject, IDrawable { #region Interface public void Draw() { this.DispatchDraw<RedSquareObject>(); } #endregion } RedSquareObject would have its own render method, but SuperSquareObject would render as a normal SquareObject I'm just asking because i do not want to reinvent the wheel, and there may be a design pattern similar (and better) to this that I may be not acknowledged of. Thanks in advance!

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• Can anyone explain this impossible bit of PHP logic?

  - by user268208

  I'm attempting to debug a simple PHP script. Essentially, there's a variable which is defined with: $variable = ($_GET['variable'] == 'true') ? TRUE : FALSE; Then, in the view file, the following code is meant to display a box if $variable == TRUE: <? if ($variable == true) { ?> <p class="box">You have imported a new plan.</p> <? } ?> Now, even when that $variable, as shown by var_dump($variable); == FALSE, that HTML is printed between the if { } tags. To me, this defies logic. I simply can't figure out this problem out. Furthermore, this code works fine on many PHP4 and PHP5 installations except for one particular server running PHP5.2. Any possible suggestions? Leads? I'm pulling out my hair trying to figure this one out. Thank you.

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• How accurate is "Business logic should be in a service, not in a model"?

  - by Jeroen Vannevel

  Situation Earlier this evening I gave an answer to a question on StackOverflow. The question: Editing of an existing object should be done in repository layer or in service? For example if I have a User that has debt. I want to change his debt. Should I do it in UserRepository or in service for example BuyingService by getting an object, editing it and saving it ? My answer: You should leave the responsibility of mutating an object to that same object and use the repository to retrieve this object. Example situation: class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } A comment I received: Business logic should really be in a service. Not in a model. What does the internet say? So, this got me searching since I've never really (consciously) used a service layer. I started reading up on the Service Layer pattern and the Unit Of Work pattern but so far I can't say I'm convinced a service layer has to be used. Take for example this article by Martin Fowler on the anti-pattern of an Anemic Domain Model: There are objects, many named after the nouns in the domain space, and these objects are connected with the rich relationships and structure that true domain models have. The catch comes when you look at the behavior, and you realize that there is hardly any behavior on these objects, making them little more than bags of getters and setters. Indeed often these models come with design rules that say that you are not to put any domain logic in the the domain objects. Instead there are a set of service objects which capture all the domain logic. These services live on top of the domain model and use the domain model for data. (...) The logic that should be in a domain object is domain logic - validations, calculations, business rules - whatever you like to call it. To me, this seemed exactly what the situation was about: I advocated the manipulation of an object's data by introducing methods inside that class that do just that. However I realize that this should be a given either way, and it probably has more to do with how these methods are invoked (using a repository). I also had the feeling that in that article (see below), a Service Layer is more considered as a façade that delegates work to the underlying model, than an actual work-intensive layer. Application Layer [his name for Service Layer]: Defines the jobs the software is supposed to do and directs the expressive domain objects to work out problems. The tasks this layer is responsible for are meaningful to the business or necessary for interaction with the application layers of other systems. This layer is kept thin. It does not contain business rules or knowledge, but only coordinates tasks and delegates work to collaborations of domain objects in the next layer down. It does not have state reflecting the business situation, but it can have state that reflects the progress of a task for the user or the program. Which is reinforced here: Service interfaces. Services expose a service interface to which all inbound messages are sent. You can think of a service interface as a façade that exposes the business logic implemented in the application (typically, logic in the business layer) to potential consumers. And here: The service layer should be devoid of any application or business logic and should focus primarily on a few concerns. It should wrap Business Layer calls, translate your Domain in a common language that your clients can understand, and handle the communication medium between server and requesting client. This is a serious contrast to other resources that talk about the Service Layer: The service layer should consist of classes with methods that are units of work with actions that belong in the same transaction. Or the second answer to a question I've already linked: At some point, your application will want some business logic. Also, you might want to validate the input to make sure that there isn't something evil or nonperforming being requested. This logic belongs in your service layer. "Solution"? Following the guidelines in this answer, I came up with the following approach that uses a Service Layer: class UserController : Controller { private UserService _userService; public UserController(UserService userService){ _userService = userService; } public ActionResult MakeHimPay(string username, int amount) { _userService.MakeHimPay(username, amount); return RedirectToAction("ShowUserOverview"); } public ActionResult ShowUserOverview() { return View(); } } class UserService { private IUserRepository _userRepository; public UserService(IUserRepository userRepository) { _userRepository = userRepository; } public void MakeHimPay(username, amount) { _userRepository.GetUserByName(username).makePayment(amount); } } class UserRepository { public User GetUserByName(string name){ // Get appropriate user from database } } class User { private int debt; // debt in cents private string name; // getters public void makePayment(int cents){ debt -= cents; } } Conclusion All together not much has changed here: code from the controller has moved to the service layer (which is a good thing, so there is an upside to this approach). However this doesn't look like it had anything to do with my original answer. I realize design patterns are guidelines, not rules set in stone to be implemented whenever possible. Yet I have not found a definitive explanation of the service layer and how it should be regarded. Is it a means to simply extract logic from the controller and put it inside a service instead? Is it supposed to form a contract between the controller and the domain? Should there be a layer between the domain and the service layer? And, last but not least: following the original comment Business logic should really be in a service. Not in a model. Is this correct? How would I introduce my business logic in a service instead of the model?

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• Using your own gameloop logic on iphone?

  - by kkan

  I'm currently working on moving some android-ndk code to the iphone and have hit a wall. I'm new to iphone development, and from looking at some samples it seems that the main loop is handled for you and all you've got to do is override the render method on the view to handle the rendering and add a selector to handle the update methods. The render method itself lookslike it's attached to the windows refresh. But in android I've got my own game loop that controls the rendering and updates using c++ time.h. is it possible to implement the same here bypassing apple's loop? I'd really like the keep the structures of the code similar. Thanks!

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• Programming logic to group a users activities like Facebook

  - by Chris Dowdeswell

  So I am trying to develop an activity feed for my site. Basically If I UNION a bunch of activities into a feed I would end up with something like the following. Chris is now friends with Mark Chris is now friends with Dave What I want though is a neater way of grouping these similar posts so the feed doesn't give information overload... E.g. Chris is now friends with Mark, Dave and 4 Others Any ideas on how I can approach this logically? I am using Classic ASP on SQL server. Here is the UNION statement I have so far: SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic,U.Fname + ' ' + U.Sname As FullName, 'said ' + WP.Post AS Activity, WP.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN WallPosts AS WP ON WP.userID = U.userID WHERE WP.Ctime IS NOT NULL UNION SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic,U.Fname + ' ' + U.Sname As FullName, 'commented ' + C.Comment AS Activity, C.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN Comments AS C ON C.UserID = U.userID WHERE C.Ctime IS NOT NULL UNION SELECT U.UserID As UserID, L.UN As UN,Left(U.UID,13) As ProfilePic, U.Fname + ' ' + U.Sname As FullName, 'connected with <a href="/profile.asp?un='+(SELECT Logins.un FROM Logins WHERE Logins.userID = Cn.ToUserID)+'">' + (SELECT Users.Fname + ' ' + Users.Sname FROM Users WHERE userID = Cn.ToUserID) + '</a>' AS Activity, Cn.Ctime FROM Users AS U LEFT JOIN Logins L ON L.userID = U.UserID LEFT OUTER JOIN Connections AS Cn ON Cn.UserID = U.userID WHERE CN.Ctime IS NOT NULL

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• How to abstract/generic WCF Service out of business logic

  Service Bus Architecture Based on WCF (2): Abstract WCF

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• How can I improve this collision detection logic?

  - by Dan

  I’m trying to make an android game and I’m having a bit of trouble getting the collision detection to work. It works sometimes but my conditions aren’t specific enough and my program gets it wrong. How could I improve the following if conditions? public boolean checkColisionWithPlayer( Player player ) { // Top Left // Top Right // Bottom Right // Bottom Left // int[][] PP = { { player.x, player.y }, { player.x + player.width, player.y }, {player.x + player.height, player.y + player.width }, { player.x, player.y + player.height } }; // TOP LEFT - PLAYER // if( ( PP[0][0] > x && PP[0][0] < x + width ) && ( PP[0][1] > y && PP[0][1] < y + height ) && ( (x - player.x) < 0 ) ) { player.isColided = true; //player.isSpinning = false; // Collision On Right if( PP[0][0] > ( x + width/2 ) && ( PP[0][1] - y < ( x + width ) - PP[0][0] ) ) { Log.i("Colision", "Top Left - Right Side"); player.x = ( x + width ) + 1; player.Vh = player.phy.getVelsoityWallColision(player.Vh, player.Cr); } // Collision On Bottom else if( PP[0][1] > ( y + height/2 ) ) { Log.i("Colision", "Top Left - Bottom Side"); player.y = ( y + height ) + 1; if( player.Vv > 0 ) player.Vv = 0; } return true; } // TOP RIGHT - PLAYER // else if( ( PP[1][0] > x && PP[1][0] < x + width ) && ( PP[1][1] > y && PP[1][1] < y + height ) && ( (x - player.x) > 0 ) ) { player.isColided = true; //player.isSpinning = false; // Collision On Left if( PP[1][0] < ( x + width/2 ) && ( PP[1][0] - x < PP[1][1] - y ) ) { Log.i("Colision", "Top Right - Left Side"); player.x = ( x ) + 1; player.Vh = player.phy.getVelsoityWallColision(player.Vh, player.Cr); } // Collision On Bottom else if( PP[1][1] > ( y + height/2 ) ) { Log.i("Colision", "Top Right - Bottom Side"); player.y = ( y + height ) + 1; if( player.Vv > 0 ) player.Vv = 0; } return true; } // BOTTOM RIGHT - PLAYER // else if( ( PP[2][0] > x && PP[2][0] < x + width ) && ( PP[2][1] > y && PP[2][1] < y + height ) ) { player.isColided = true; //player.isSpinning = false; // Collision On Left if( PP[2][0] < ( x + width/2 ) && ( PP[2][0] - x < PP[2][1] - y ) ) { Log.i("Colision", "Bottom Right - Left Side"); player.x = ( x ) + 1; player.Vh = player.phy.getVelsoityWallColision(player.Vh, player.Cr); } // Collision On Top else if( PP[2][1] < ( y + height/2 ) ) { Log.i("Colision", "Bottom Right - Top Side"); player.y = y - player.height; player.Vv = player.phy.getVelsoityWallColision(player.Vv, player.Cr); //player.Vh = -1 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); int rs = x - player.x; Log.i("RS", String.format("%d", rs)); if( rs > 0 ) { player.direction = -1; player.isSpinning = true; player.Vh = -0.5 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); } if( rs < 0 ) { player.direction = 1; player.isSpinning = true; player.Vh = 0.5 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); } player.rotateSpeed = 1 * rs; } return true; } // BOTTOM LEFT - PLAYER // else if( ( PP[3][0] > x && PP[3][0] < x + width ) && ( PP[3][1] > y && PP[3][1] < y + height ) )//&& ( (x - player.x) > 0 ) ) { player.isColided = true; //player.isSpinning = false; // Collision On Right if( PP[3][0] > ( x + width/2 ) && ( PP[3][1] - y < ( x + width ) - PP[3][0] ) ) { Log.i("Colision", "Bottom Left - Right Side"); player.x = ( x + width ) + 1; player.Vh = player.phy.getVelsoityWallColision(player.Vh, player.Cr); } // Collision On Top else if( PP[3][1] < ( y + height/2 ) ) { Log.i("Colision", "Bottom Left - Top Side"); player.y = y - player.height; player.Vv = player.phy.getVelsoityWallColision(player.Vv, player.Cr); //player.Vh = -1 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); int rs = x - player.x; //Log.i("RS", String.format("%d", rs)); //player.direction = -1; //player.isSpinning = true; if( rs > 0 ) { player.direction = -1; player.isSpinning = true; player.Vh = -1 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); } if( rs < 0 ) { player.direction = 1; player.isSpinning = true; player.Vh = 1 * ( player.phy.getVelsoityWallColision(player.Vv, player.Cr) ); } player.rotateSpeed = 1 * rs; } //try { Thread.sleep(1000, 0); } //catch (InterruptedException e) {} return true; } else { player.isColided = false; player.isSpinning = true; } return false; }

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• Logic behind a bejeweled-like game

  - by Joe

  In a prototype I am doing, there is a minigame similar to bejeweled. Using a grid that is a 2d array (int[,]) how can I go about know when the user formed a match? I only care about horizontally and vertically. Off the top of my head I was thinking I would just look each direction. Something like: int item = grid[x,y]; if(grid[x-1,y]==item) { int step=x; int matches =2; while(grid[step-1,y]==item) { step++; matches++ } if(matches>2) //remove all matching items } else if(grid[x+1,y]==item //.... else if(grid[x,y-1==item) //... else if(grid[x,y+1]==item) //... It seems like there should be a better way. Is there?

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• What is the kd tree intersection logic?

  - by bobobobo

  I'm trying to figure out how to implement a KD tree. On page 322 of "Real time collision detection" by Ericson The text section is included below in case Google book preview doesn't let you see it the time you click the link text section Relevant section: The basic idea behind intersecting a ray or directed line segment with a k-d tree is straightforward. The line is intersected against the node's splitting plane, and the t value of intersection is computed. If t is within the interval of the line, 0 <= t <= tmax, the line straddles the plane and both children of the tree are recursively descended. If not, only the side containing the segment origin is recursively visited. So here's what I have: (open image in new tab if you can't see the lettering) The logical tree Here the orange ray is going thru the 3d scene. The x's represent intersection with a plane. From the LEFT, the ray hits: The front face of the scene's enclosing cube, The (1) splitting plane The (2.2) splitting plane The right side of the scene's enclosing cube But here's what would happen, naively following Ericson's basic description above: Test against splitting plane (1). Ray hits splitting plane (1), so left and right children of splitting plane (1) are included in next test. Test against splitting plane (2.1). Ray actually hits that plane, (way off to the right) so both children are included in next level of tests. (This is counter-intuitive - shouldn't only the bottom node be included in subsequent tests) Can some one describe what happens when the orange ray goes through the scene correctly?

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• Logic to create common Serverlet3 Login

  - by user3696143

  I am using Servlet3 Login to Authenticate User in website I have these Login Website Normal Login(Fill the Sigup form) Facebook Login (From Facebook Id) Twitter Login (From Twitter) And I am already authenticate user by below code HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest(); request.login(username, password); And it is working fine for Website Login as user gave his/her EMailId and password and it store in DB. Now I modified table and added more columns to save Facebookid in same user table and also password for Facebook login FacebookId work as a Password as well. Same I will do for Twitter But I want the same Servlet3 to authenticate user. How can I achieve it? And also added context.xml file inside META-INF folder <Realm localDataSource="true" debug="99" className="org.apache.catalina.realm.JDBCRealm" connectionName="user" connectionPassword="password" connectionURL="jdbc:mysql://localhost:3306/ ccc" digest="md5" driverName="com.mysql.jdbc.Driver" roleNameCol="role_name" userCredCol="password" userNameCol="email_id" userRoleTable="users_list" userTable="user_list_view" /> Also it is possible to check which query fired by realm entry?

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• Use Oracle Product Hub Business Events to Integrate Additional Logic into Your Business Flows

  - by ToddAC-Oracle

  Business events provide a mechanism to plug-in and integrate some additional business processes or custom code into standard business flows.  You could send a notification to a business User, write to advanced queues or perform some custom processes. In-built business events are available specifically for each flow like Item Creation, Item Updation, User-Defined Attribute Changes, Change Order Creation, Change Order Status Changes and others.To get a list of business events, refer to the PIM implementation Guide or Using Business Events in PLM and PIM Data Librarian (Doc ID 372814.1) .If you are planning to use business events, Doc ID 1074754.1 walks you through a setup with examples. How to Subscribe and Use Product Hub (PIM / APC) Business Events [Video] ? (Doc ID 1074754.1). Review the 'Presentation' section of Doc ID 1074754.1 for complete information and best practices to follow while implementing code for subscriptions. Learn things you might want to avoid, like commit statements for instance. Doc ID 1074754.1 also provides sample code for testing, and can be used to troubleshoot missing setups or frequently experienced issues. Take advantage and run a test ahead of time with the sample code to isolate any issues from within business specific subscription code.Get more out of Oracle Product Hub by using Business Events!

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• Syntax logic suggestions

  - by Anna

  This syntax will be used inside HTML attributes. Here are a few examples of what I have so far: <input name="a" conditions="!b, c" /> <input name="b" /> <input name="c" /> This will make input "a" do something if b is not checked and c is checked (b and c are assumed to be checkboxes if they don't have a :value defined) <input name="a" conditions="!b:foo|bar, c:foo" /> <input name="b" /> <input name="c" /> This will make input "a" do something if bdoesn't have foo or bar values, and if c has the foo value. <input name="a" conditions="!b:EMPTY" /> <input name="b" /> Makes input "a" do something if b has a value assigned. So, essentially , acts as logical AND, : as equals (=), ! as NOT, and | as OR. The | (OR) is only needed between values (at least I think so), and AND is not needed between values for obvious reasons :) EMPTY means empty value, like <input value="" /> Do you have any suggestions on improving this syntax, like making it more human friendly? For example I think the "EMPTY" keyword is not really appropriate and should be replaced with a character, but I don't know which one to choose.

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• Which online form builders offer conditional logic/branching?

  - by Hari Sundararajan

  I have a survey with the following form fields: Country Age Male/Female Undergraduate/Graduate Question? Yes No If No, what about this and that? Yes No Google Forms and SurveyMonkey don't seem to allow things like the above. For question one I could ask, "What country are you from?" with a textbox as an answer section and work around it. But how do I go about creating questions five and six? I am not able to figure out how to do it except for having one more question that says "If your answer to the previous question was No, then blah blah (else skip this question)". Any suggestions, apart from creating my own custom website with JavaScript and a backend database?

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• Types of semantic bugs, logic errors [closed]

  - by C-Otto

  I am a PhD student and currently focus on automatically finding instances of new types of bugs in (Java) programs that cannot be found by existing tools like FindBugs. The existing tool currently is used to prove/disprove termination of (Java) programs. I have some ideas (see below), but I could need more input from you (experienced programmers, potential users of my tool). What kind of bugs do you wish to find? What types of bugs exist and might be suitable for my analysis? One strength of the approach I use is detailled information about the heap. So in contrast to FindBugs, I can work with knowledge of the form "variable x and variable y are disjoint on the heap" or "variable z is not cyclic". It is also possible to see if a method might have side effects (and if so, which variables may/may not be affected by it). Example 1: Vacuous call: Graph graphOne = createGraph(); Graph graphTwo = createGraph(); Node source = graphTwo.getRootNode(); for (Node n : graphOne.getNodes()) { if (areConnected(source, n)) { graphTwo.addNode(n); } } Imagine createGraph() creates a fresh graph, so that graphOne and graphTwo are disjoint on the heap. Then, because source is taken from graphTwo instead of graphOne, the call to areConnected always returns false. In this situation I could find out that the call areConnected is useless (because it does not have any side effect and the return value always is false) which helps finding the real bug (taking source from the wrong graph). For this the information that x and y are disjoint (because graphOne and graphTwo are disjoint) is crucial. This bug is related to calling x.equals(y) where x and y are objects of different classes. In this scenario, most implementations of equals() always return false, which most likely is not the intended result. FindBugs already finds this bug (hardcoded to equals(), semantics of implementation is not checked). Example 2: Useless code: someCode(); while (something()) { yetMoreSomething(); } moreCode(); In the case that the loop (so the code in something() and yetMoreSomething()) does not modify anything visible outside the loop, it does not make sense to run this code - the program has the same behaviour as someCode(); moreCode() (i.e., without the loop). To find this out, one needs detailled information about the side effects of the (possibly useless) code. If I can prove that the code does not have any side effect that can be observed afterwards (in the example: in moreCode() or later), then the code indeed is useless. Of course, here Input/Output of any form must be seen as a side effect, so that a System.out.println(...) is not considered useless. Example 3: Ignored return value: Instead of x = foo(); and making use of x, the method is called without storing the result: foo();. If the method does not have any side effect, its invocation is useless and can be dropped. Most likely, the bug here is that the returned value should have been used. Here, too, detailled information about side effects are needed. Can you think of similar types of bugs that might be detected (only) with detailled information about the heap, side effects, semantics of called methods, ...? Did you encounter bugs related to the ones shown below in "real life"? By the way, the tool is AProVE and Java related publications can be found on my homepage. Thanks a lot, Carsten

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• program logic of printing the prime numbers

  - by Vignesh Vicky

  can any body help to understand this java program it just print prime n.o ,as you enter how many you want and it works good class PrimeNumbers { public static void main(String args[]) { int n, status = 1, num = 3; Scanner in = new Scanner(System.in); System.out.println("Enter the number of prime numbers you want"); n = in.nextInt(); if (n >= 1) { System.out.println("First "+n+" prime numbers are :-"); System.out.println(2); } for ( int count = 2 ; count <=n ; ) { for ( int j = 2 ; j <= Math.sqrt(num) ; j++ ) { if ( num%j == 0 ) { status = 0; break; } } if ( status != 0 ) { System.out.println(num); count++; } status = 1; num++; } } } i dont understand this for loop condition for ( int j = 2 ; j <= Math.sqrt(num) ; j++ ) why we are taking sqrt of num...which is 3....why we assumed it as 3?

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• Sprites, Primitives and logic entity as structs

  - by Jeffrey

  I'm wondering would it be considered acceptable: The window class is responsible for drawing data, so it will have a method: Window::draw(const Sprite&); Window::draw(const Rect&); Window::draw(const Triangle&); Window::draw(const Circle&); and all those primitives + sprites would be just public struct. For example Sprite: struct Sprite { float x, y; // center float origin_x, origin_y; float width, height; float rotation; float scaling; GLuint texture; Sprite(float w, float h); Sprite(float w, float h, float a, float b); void useTexture(std::string file); void setOrigin(float a, float b); void move(float a, float b); // relative move void moveTo(float a, float b); // absolute move void rotate(float a); // relative rotation void rotateTo(float a); // absolute rotation void rotationReset(); void scale(float a); // relative scaling void scaleTo(float a); // absolute scaling void scaleReset(); }; So instead of having each primitive to call their draw() function, which is a little bit off topic for their object, I let the Window class handle all the OpenGL stuff and manipulate them as simple objects that will be drawn later on. Is this pattern used? Does it have any cons against it's primitives-draw-themself pattern? Are there any other related patterns?

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• Math > Logic for a Logarithmic Score Meter

  - by oodavid

  I'm trying to implement a score meter whereby I specify a maximum value (say 15,000) and I can render values on it in a logarithmic manner ie: +------+---+--+-++ +------+---+--+-++ |== | |====== | +------+---+--+-++ +------+---+--+-++ 200 pts 1,000 pts +------+---+--+-++ +------+---+--+-++ |============= | |================| +------+---+--+-++ +------+---+--+-++ 5,000 pts 15,000 pts + The upper bound needs to be variable, and need to be able to convert a score to a percentage, using the above mockup as an example: score2pct(15000, 200) = 0.2 score2pct(15000, 1000) = 0.4 score2pct(15000, 5000) = 0.8 score2pct(15000, 15000) = 1 Does anyone have any pointers for me?

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