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• Do you leverage the benefits of the open-closed principle?

  - by Kaleb Pederson

  The open-closed principle (OCP) states that an object should be open for extension but closed for modification. I believe I understand it and use it in conjunction with SRP to create classes that do only one thing. And, I try to create many small methods that make it possible to extract out all the behavior controls into methods that may be extended or overridden in some subclass. Thus, I end up with classes that have many extension points, be it through: dependency injection and composition, events, delegation, etc. Consider the following a simple, extendable class: class PaycheckCalculator { // ... protected decimal GetOvertimeFactor() { return 2.0M; } } Now say, for example, that the OvertimeFactor changes to 1.5. Since the above class was designed to be extended, I can easily subclass and return a different OvertimeFactor. But... despite the class being designed for extension and adhering to OCP, I'll modify the single method in question, rather than subclassing and overridding the method in question and then re-wiring my objects in my IoC container. As a result I've violated part of what OCP attempts to accomplish. It feels like I'm just being lazy because the above is a bit easier. Am I misunderstanding OCP? Should I really be doing something different? Do you leverage the benefits of OCP differently? Update: based on the answers it looks like this contrived example is a poor one for a number of different reasons. The main intent of the example was to demonstrate that the class was designed to be extended by providing methods that when overridden would alter the behavior of public methods without the need for changing internal or private code. Still, I definitely misunderstood OCP.

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• What type of pattern would be used in this case

  - by Admiral Kunkka

  I want to know how to tackle this type of scenario. We are building a person's background, from scratch, and I want to know, conceptually, how to proceed with a secure object pattern in both design and execution... I've been reading on Factory patterns, Model-View-Controller types, Dependency injection, Singleton approaches... and I can't seem to grasp or 'fit' these types of designs decisions into what I'm trying to do.. First and foremost, I started with having a big jack-of-all-trades class, then I read some more, and some tips were to make sure your classes only have a single purpose.. which makes sense and I started breaking down certain things into other classes. Okay, cool. Now I'm looking at dependency injection and kind of didn't really know what's going on. Example/insight of what kind of heirarchy I need to accomplish... class Person needs to access and build from a multitude of different classes. class Culture needs to access a sub-class for culture benefits class Social needs to access class Culture, and other sub-classes class Birth needs to access Social, Culture, and other sub-classes class Childhood/Adolescence/Adulthood need to access everything. Also, depending on different rolls, this class heirarchy needs to create multiple people as well, such as Family, and their backgrounds using some, if not all, of these same classes. Think of it as a people generator, all random, with backgrounds and things that happen to them. Ageing, death of loved ones, military careers, e.t.c. Most of the generation is done randomly, making calls to a mt_rand function to pick from most of the selections inside the classes, guaranteeing the data to be absolutely random. I have most of the bulk-data down, and was looking for some insight from fellow programmers, what do you think?

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• Do objects maintain identity under all non-cloning conditions in PHP?

  - by Buttle Butkus

  PHP 5.5 I'm doing a bunch of passing around of objects with the assumption that they will all maintain their identities - that any changes made to their states from inside other objects' methods will continue to hold true afterwards. Am I assuming correctly? I will give my basic structure here. class builder { protected $foo_ids = array(); // set in construct protected $foo_collection; protected $bar_ids = array(); // set in construct protected $bar_collection; protected function initFoos() { $this->foo_collection = new FooCollection(); foreach($this->food_ids as $id) { $this->foo_collection->addFoo(new foo($id)); } } protected function initBars() { // same idea as initFoos } protected function wireFoosAndBars(fooCollection $foos, barCollection $bars) { // arguments are passed in using $this->foo_collection and $this->bar_collection foreach($foos as $foo_obj) { // (foo_collection implements IteratorAggregate) $bar_ids = $foo_obj->getAssociatedBarIds(); if(!empty($bar_ids) ) { $bar_collection = new barCollection(); // sub-collection to be a component of each foo foreach($bar_ids as $bar_id) { $bar_collection->addBar(new bar($bar_id)); } $foo_obj->addBarCollection($bar_collection); // now each foo_obj has a collection of bar objects, each of which is also in the main collection. Are they the same objects? } } } } What has me worried is that foreach supposedly works on a copy of its arrays. I want all the $foo and $bar objects to maintain their identities no matter which $collection object they become of a part of. Does that make sense?

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• Are there design patterns or generalised approaches for particle simulations?

  - by romeovs

  I'm working on a project (for college) in C++. The goal is to write a program that can more or less simulate a beam of particles flying trough the LHC synchrotron. Not wanting to rush into things, me and my team are thinking about how to implement this and I was wondering if there are general design patterns that are used to solve this kind of problem. The general approach we came up with so far is the following: there is a World that holds all objects you can add objects to this world such as Particle, Dipole and Quadrupole time is cut up into discrete steps, and at each point in time, for each Particle the magnetic and electric forces that each object in the World generates are calculated and summed up (luckily electro-magnetism is linear). each Particle moves accordingly (using a simple estimation approach to solve the differential movement equations) save the Particle positions repeat This seems a good approach but, for instance, it is hard to take into account symmetries that might be present (such as the magnetic field of each Quadrupole) and is this thus suboptimal. To take into account such symmetries as that of the Quadrupole field, it would be much easier to (also) make space discrete and somehow store form of the Quadrupole field somewhere. (Since 2532 or so Quadrupoles are stored this should lead to a massive gain of performance, not having to recalculate each Quadrupole field) So, are there any design patterns? Is the World-approach feasible or is it old-fashioned, bad programming? What about symmetry, how is that generally taken into acount?

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• How to store a list of Objects that might change in future?

  - by Amogh Talpallikar

  I have set of Objects of the same class which have different values of their attributes. and I need to find the best match from a function under given scenarios out of these objects. In future these objects might increase as well. Quite similar to the way we have Color class in awt. we have some static color objects in the class with diff rgb values. But in my case say, I need to chose the suitable color out of these static ones based on certain criteria. So should I keep them in an arrayList or enum or keep them as static vars as in case of Colors. because I will need to parse through all of them and decide upon the best match. so I need them in some sort of collection. But in future if I need to add another type I will have to modify the class and add another list.add(object) call for this one and then it will violate the open-close principle. How should I go about it ?

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• FP for simulation and modelling

  - by heaptobesquare

  I'm about to start a simulation/modelling project. I already know that OOP is used for this kind of projects. However, studying Haskell made me consider using the FP paradigm for modelling a system of components. Let me elaborate: Let's say I have a component of type A, characterised by a set of data (a parameter like temperature or pressure,a PDE and some boundary conditions,etc.) and a component of type B, characterised by a different set of data(different or same parameter, different PDE and boundary conditions). Let's also assume that the functions/methods that are going to be applied on each component are the same (a Galerkin method for example). If I were to use an OOP approach, I would create two objects that would encapsulate each type's data, the methods for solving the PDE(inheritance would be used here for code reuse) and the solution to the PDE. On the other hand, if I were to use an FP approach, each component would be broken down to data parts and the functions that would act upon the data in order to get the solution for the PDE. This approach seems simpler to me assuming that linear operations on data would be trivial and that the parameters are constant. What if the parameters are not constant(for example, temperature increases suddenly and therefore cannot be immutable)? In OOP, the object's (mutable) state can be used. I know that Haskell has Monads for that. To conclude, would implementing the FP approach be actually simpler,less time consuming and easier to manage (add a different type of component or new method to solve the pde) compared to the OOP one? I come from a C++/Fortran background, plus I'm not a professional programmer, so correct me on anything that I've got wrong.

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• Should I build a multi-threaded system that handles events from a game and sorts them, independently, into different threads based on priority?

  - by JonathonG

  Can I build a multi-threaded system that handles events from a game and sorts them, independently, into different threads based on priority, and is it a good idea? Here's more info: I am about to begin work on porting a mid-sized game from Flash/AS3 to Java so that I can continue development with multi-threading capabilities. Here's a small bit of background about the game: The game contains numerous asynchronous activities, such as "world updating" (the game environment is constantly changing based on a set of natural laws and forces), procedural generation of terrain, NPCs, quests, items, etc., and on top of that, the effects of all of the player's interactions with his environment are programmatically calculated in real time, based on a set of constantly changing "stats" and once again, natural laws and forces. All of these things going on at once, in an asynchronous manner, seem to lend themselves to multi-threading very well. My question is: Can I build some kind of central engine that handles the "stacking" of all of these events as they are triggered, and dynamically sorts them out amongst the available threads, and would it be a good idea? As an example: Essentially, every time something happens (IE, a magic missile being generated by a spell, or a bunch of plants need to grow to their next stage), instead of just processing that task right then and adding the new object(s) to a list of managed objects, send a reference to that event to a core "event handler" that throws it into a stack of all other currently queued events, which then sorts them out and orders them according to urgency, splits them between a number of available threads for as-fast-as-possible multithreaded execution.

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• Help with design structure choice: Using classes or library of functions

  - by roverred

  So I have GUI Class that will call another class called ImageProcessor that contains a bunch functions that will perform image processing algorithms like edgeDetection, gaussianblur, contourfinding, contour map generations, etc. The GUI passes an image to ImageProcessor, which performs one of those algorithm on it and it returns the image back to the GUI to display. So essentially ImageProcessor is a library of independent image processing functions right now. It is called in the GUI like so Image image = ImageProcessor.EdgeDetection(oldImage); Some of the algorithms procedures require many functions, and some can be done in a single function or even one line. All these functions for the algorithms jam packed into ImageProcessor can be pretty messy, and ImageProcessor doesn't sound it should be a library. So I was thinking about making every algorithm be a class with a shared interface say IAlgorithm. Then I pass the IAlgorithm interface from the GUI to the ImageProcessor. public interface IAlgorithm{ public Image Process(); } public class ImageProcessor{ public Image Process(IAlgorithm TheAlgorithm){ return IAlgorithm.Process(); } } Calling in the GUI like so Image image = ImageProcessor.Process(new EdgeDetection(oldImage)); I think it makes sense in an object point of view, but the problem is I'll end up with some classes that are just one function. What do you think is a better design, or are they both crap and you have a much better idea? Thanks!

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• Avoiding bloated Domain Objects

  - by djcredo

  We're trying to move data from our bloated Service layer into our Domain layer using a DDD approach. We currently have a lot of business logic in our services, which is spread out all over the place and doesn't benefit from inheritance. We have a central Domain class which is the focus of most of our work - a Trade. The Trade object will know how to price itself, how to estimate risk, validate itself, etc. We can then replace conditionals with polymorphism. Eg: SimpleTrade will price itself one way, but ComplexTrade will price itself another. However, we are worried that this will bloat the Trade class(s). It really should be in charge of its own processing but the class size is going to increase exponentially as more features are added. So we have choices: Put processing logic in Trade class. Processing logic is now polymorphic based on the type of the trade, but Trade class is now has multiple responsibilites (pricing, risk, etc) and is large Put processing logic into other class such as TradePricingService. No longer polymorphic with the Trade inheritance tree, but classes are smaller and easier to test. What would be the suggested approach?

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• What OO Design to use ( is there a Design Pattern )?

  - by Blundell

  I have two objects that represent a 'Bar/Club' ( a place where you drink/socialise). In one scenario I need the bar name, address, distance, slogon In another scenario I need the bar name, address, website url, logo So I've got two objects representing the same thing but with different fields. I like to use immutable objects, so all the fields are set from the constructor. One option is to have two constructors and null the other fields i.e: class Bar { private final String name; private final Distance distance; private final Url url; public Bar(String name, Distance distance){ this.name = name; this.distance = distance; this.url = null; } public Bar(String name, Url url){ this.name = name; this.distance = null; this.url = url; } // getters } I don't like this as you would have to null check when you use the getters In my real example the first scenario has 3 fields and the second scenario has about 10, so it would be a real pain having two constructors, the amount of fields I would have to declare null and then when the object are in use you wouldn't know which Bar you where using and so what fields would be null and what wouldn't. What other options do I have? Two classes called BarPreview and Bar? Some type of inheritance / interface? Something else that is awesome?

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• Do I suffer from encapsulation overuse?

  - by Florenc

  I have noticed something in my code in various projects that seems like code smell to me and something bad to do, but I can't deal with it. While trying to write "clean code" I tend to over-use private methods in order to make my code easier to read. The problem is that the code is indeed cleaner but it's also more difficult to test (yeah I know I can test private methods...) and in general it seems a bad habit to me. Here's an example of a class that reads some data from a .csv file and returns a group of customers (another object with various fields and attributes). public class GroupOfCustomersImporter { //... Call fields .... public GroupOfCustomersImporter(String filePath) { this.filePath = filePath; customers = new HashSet<Customer>(); createCSVReader(); read(); constructTTRP_Instance(); } private void createCSVReader() { //.... } private void read() { //.... Reades the file and initializes the class attributes } private void readFirstLine(String[] inputLine) { //.... Method used by the read() method } private void readSecondLine(String[] inputLine) { //.... Method used by the read() method } private void readCustomerLine(String[] inputLine) { //.... Method used by the read() method } private void constructGroupOfCustomers() { //this.groupOfCustomers = new GroupOfCustomers(**attributes of the class**); } public GroupOfCustomers getConstructedGroupOfCustomers() { return this.GroupOfCustomers; } } As you can see the class has only a constructor which calls some private methods to get the job done, I know that's not a good practice not a good practice in general but I prefer to encapsulate all the functionality in the class instead of making the methods public in which case a client should work this way: GroupOfCustomersImporter importer = new GroupOfCustomersImporter(filepath) importer.createCSVReader(); read(); GroupOfCustomer group = constructGoupOfCustomerInstance(); I prefer this because I don't want to put useless lines of code in the client's side code bothering the client class with implementation details. So, Is this actually a bad habit? If yes, how can I avoid it? Please note that the above is just a simple example. Imagine the same situation happening in something a little bit more complex.

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• SQL Developer Data Modeler: On Notes, Comments, and Comments in RDBMS

  - by thatjeffsmith

  Ah the beautiful data model. They say a picture is worth a 1,000 words. And then we have our diagrams, how many words are they worth? Our friends from the Human Relations sample schema So our models describe how the data ‘works’ – whether that be at a logical-business level, or a technical-physical level. Developers like to say that their code is self-documenting. These would be very lazy or very bad (or both) developers. Models are the same way, you should document your models with comments and notes! I have 3 basic options: Comments Comments in RDBMS Notes So what’s the difference? Comments You’re describing the entity/table or attribute/column. This information will NOT be published in the database. It will only be available to the model, and hence, folks with access to the model. Table Comments (in the design only!) Comments in RDBMS You’re doing the same thing as above, but your words will be stored IN the data dictionary of the database. Oracle allows you to store comments on the table and column definitions. So your awesome documentation is going to be viewable to anyone with access to the database. RDBMS is an acronym for Relational Database Management System – of which Oracle is one of the first commercial examples If the DDL is produced and ran against a database, these comments WILL be stored in the data dictionary. Notes A place for you to add notes, maybe from a design meeting. Or maybe you’re using this as a to-do or requirements list. Basically it’s for anything that doesn’t literally describe the object at hand – that’s what the comments are for. I totally made these up. Now these are free text fields and you can put whatever you want here. Just make sure you put stuff here that’s worth reading. And it will live on…forever.

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• SQL SERVER – Validating Spatial Object with IsValidDetailed Function

  - by pinaldave

  What do you prefer – error or warning indicating error may happen with the reason for the error. While writing the previous statement I remember the movie “Minory Report”. This blog post is not about minority report but I will still cover the concept in a single statement “Let us predict the future and prevent the crime which is about to happen in future”. (Please feel free to correct me if I am wrong about the movie concept, I really do not want to hurt your sentiment if you are dedicated fan). Let us switch to the SQL Server world. Spatial data types are interesting concepts. I love writing about spatial data types because it allows me to be creative with shapes (just like toddlers). When working with Spatial Datatypes it is all good when the spatial object works fine. However, when the spatial object has issue or it is created with invalid coordinates it used to give a simple error that there is an issue with the object but did not provide much information. This made it very difficult to debug. If this spatial object was used in the big procedure and while this big procedural error out because of the invalid spatial object, it is indeed very difficult to debug it. I always wished that the more information provided regarding what is the problem with spatial datatype. SQL Server 2012 has introduced the new function IsValidDetailed(). This function has made my life very easy. In simple words this function will check if the spatial object passed is valid or not. If it is valid it will give information that it is valid. If the spatial object is not valid it will return the answer that it is not valid and the reason for the same. This makes it very easy to debug the issue and make the necessary correction. DECLARE @p GEOMETRY = 'Polygon((2 2, 6 6, 4 2, 2 2))' SELECT @p.IsValidDetailed() GO DECLARE @p GEOMETRY = 'Polygon((2 2, 3 3, 4 4, 5 5, 6 6, 2 2))' SELECT @p.IsValidDetailed() GO DECLARE @p GEOMETRY = 'Polygon((2 2, 4 4, 4 2, 2 3, 2 2))' SELECT @p.IsValidDetailed() GO DECLARE @p GEOMETRY = 'CIRCULARSTRING(2 2, 4 4, 0 0)' SELECT @p.IsValidDetailed() GO DECLARE @p GEOMETRY = 'CIRCULARSTRING(2 2, 4 4, 0 0)' SELECT @p.IsValidDetailed() GO DECLARE @p GEOMETRY = 'LINESTRING(2 2, 4 4, 0 0)' SELECT @p.IsValidDetailed() GO Here is the resultset of the above query. You can see any valid query and some invalid query. If the query is invalid it also demonstrates the reason along with the error message. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Spatial Database, SQL Spatial

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• Is throwing an error in unpredictable subclass-specific circumstances a violation of LSP?

  - by Motti Strom

  Say, I wanted to create a Java List<String> (see spec) implementation that uses a complex subsystem, such as a database or file system, for its store so that it becomes a simple persistent collection rather than an basic in-memory one. (We're limiting it specifically to a List of Strings for the purposes of discussion, but it could extended to automatically de-/serialise any object, with some help. We can also provide persistent Sets, Maps and so on in this way too.) So here's a skeleton implementation: class DbBackedList implements List<String> { private DbBackedList() {} /** Returns a list, possibly non-empty */ public static getList() { return new DbBackedList(); } public String get(int index) { return Db.getTable().getRow(i).asString(); // may throw DbExceptions! } // add(String), add(int, String), etc. ... } My problem lies with the fact that the underlying DB API may encounter connection errors that are not specified in the List interface that it should throw. My problem is whether this violates Liskov's Substitution Principle (LSP). Bob Martin actually gives an example of a PersistentSet in his paper on LSP that violates LSP. The difference is that his newly-specified Exception there is determined by the inserted value and so is strengthening the precondition. In my case the connection/read error is unpredictable and due to external factors and so is not technically a new precondition, merely an error of circumstance, perhaps like OutOfMemoryError which can occur even when unspecified. In normal circumstances, the new Error/Exception might never be thrown. (The caller could catch if it is aware of the possibility, just as a memory-restricted Java program might specifically catch OOME.) Is this therefore a valid argument for throwing an extra error and can I still claim to be a valid java.util.List (or pick your SDK/language/collection in general) and not in violation of LSP? If this does indeed violate LSP and thus not practically usable, I have provided two less-palatable alternative solutions as answers that you can comment on, see below. Footnote: Use Cases In the simplest case, the goal is to provide a familiar interface for cases when (say) a database is just being used as a persistent list, and allow regular List operations such as search, subList and iteration. Another, more adventurous, use-case is as a slot-in replacement for libraries that work with basic Lists, e.g if we have a third-party task queue that usually works with a plain List: new TaskWorkQueue(new ArrayList<String>()).start() which is susceptible to losing all it's queue in event of a crash, if we just replace this with: new TaskWorkQueue(new DbBackedList()).start() we get a instant persistence and the ability to share the tasks amongst more than one machine. In either case, we could either handle connection/read exceptions that are thrown, perhaps retrying the connection/read first, or allow them to throw and crash the program (e.g. if we can't change the TaskWorkQueue code).

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• When following SRP, how should I deal with validating and saving entities?

  - by Kristof Claes

  I've been reading Clean Code and various online articles about SOLID lately, and the more I read about it, the more I feel like I don't know anything. Let's say I'm building a web application using ASP.NET MVC 3. Let's say I have a UsersController with a Create action like this: public class UsersController : Controller { public ActionResult Create(CreateUserViewModel viewModel) { } } In that action method I want to save a user to the database if the data that was entered is valid. Now, according to the Single Responsibility Principle an object should have a single responsibility, and that responsibility should be entirely encapsulated by the class. All its services should be narrowly aligned with that responsibility. Since validation and saving to the database are two separate responsibilities, I guess I should create to separate class to handle them like this: public class UsersController : Controller { private ICreateUserValidator validator; private IUserService service; public UsersController(ICreateUserValidator validator, IUserService service) { this.validator = validator; this.service= service; } public ActionResult Create(CreateUserViewModel viewModel) { ValidationResult result = validator.IsValid(viewModel); if (result.IsValid) { service.CreateUser(viewModel); return RedirectToAction("Index"); } else { foreach (var errorMessage in result.ErrorMessages) { ModelState.AddModelError(String.Empty, errorMessage); } return View(viewModel); } } } That makes some sense to me, but I'm not at all sure that this is the right way to handle things like this. It is for example entirely possible to pass an invalid instance of CreateUserViewModel to the IUserService class. I know I could use the built in DataAnnotations, but what when they aren't enough? Image that my ICreateUserValidator checks the database to see if there already is another user with the same name... Another option is to let the IUserService take care of the validation like this: public class UserService : IUserService { private ICreateUserValidator validator; public UserService(ICreateUserValidator validator) { this.validator = validator; } public ValidationResult CreateUser(CreateUserViewModel viewModel) { var result = validator.IsValid(viewModel); if (result.IsValid) { // Save the user } return result; } } But I feel I'm violating the Single Responsibility Principle here. How should I deal with something like this?

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• Help with Collision of spawned object(postion fixed) with objects that there are translating on screen

  - by Amrutha

  Hey guys I am creating a game using Corona SDK and so coding it in Lua. So there are 2 separate functions, To translate the hit objects and change their color when they are tapped The link below is the code I am using to for the first function http://developer.anscamobile.com/sample-code/fishies Spawn objects that will hit the translating objects on collision. Alos on collision the spawned object disappears and the translating object bears a color(indicating the collision). In addition the size of this spawned object is dependent on i/p volume level. The function I have written is as follows: --VOICE INPUT CODE local r = media.newRecording() r:startRecording() r:startTuner() --local function newBar() -- local bar = display.newLine( 0, 0, 1, 0 ) -- bar:setColor( 0, 55, 100, 20 ) -- bar.width = 5 -- bar.y=400 -- bar.x=20 -- return bar --end local c1 = display.newImage("str-minion-small.png") c1.isVisible=false local c2 = display.newImage("str-minion-mid.png") c2.isVisible=false local c3 = display.newImage("str-minion-big.png") c3.isVisible=false --SPAWNING local function spawnDisk( event ) local phase = event.phase local volumeBar = display.newLine( 0, 0, 1, 0 ) volumeBar.y = 400 volumeBar.x = 20 --volumeBar.isVisible=false local v = 20*math.log(r:getTunerVolume()) local MINTHRESH = 30 local LEFTMARGIN = 20 local v2 = MINTHRESH + math.max (v, -MINTHRESH) v2 = (display.contentWidth - 1 * LEFTMARGIN ) * v2 / MINTHRESH volumeBar.xScale = math.max ( 20, v2 ) local l = volumeBar.xScale local cnt1 = 0 local cnt2 = 0 local cnt3 = 0 local ONE =1 local val = event.numTaps --local px=event.x --local py=event.y if "ended" == phase then --audio.play( popSound ) --myLabel.isVisible = false if l > 50 and l <=150 then --c1:setFillColor(10,105,0) --c1.isVisible=false c1.x=math.random( 10, 450 ) c1.y=math.random( 10, 300 ) physics.addBody( c1, { density=1, radius=10.0 } ) c1.isVisible=true cnt1= cnt1+ ONE return c1 elseif l > 100 and l <=250 then --c2:setFillColor(200,10,0) c2.x=math.random( 10, 450 ) c2.y=math.random( 10, 300 ) physics.addBody( c2, { density=2, radius=9000.0 } ) c2.isVisible=true cnt2= cnt2+ ONE return c2 elseif l >=250 then c3.x=math.random( 40, 450 ) c3.y=math.random( 40, 300 ) physics.addBody( c3, { density=2, radius=7000.0 , bounce=0.0 } ) c3.isVisible=true cnt3= cnt3+ ONE return c3 end end end buzzR:addEventListener( "touch", spawnDisk ) -- touch the screen to create disks Now both functions work fine independently but there is no collision happening. Its almost as if the translating object and the spawn object are on different layers. The translating object passes through the spawn object freely. Can anyone please tell me how to resolve this problem. And how can I get them to collide. Its my first attempt at game development, that too for a mobile platform so would appreciate all help. Also if I have not been specific do let me know. I'll try to frame the query better :). Thanks in advance.

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• Help with Collision of spawned object(postion fixed) with objects that there are translating on screen

  - by Amrutha

  Hey guys I am creating a game using Corona SDK and so coding it in Lua. So there are 2 separate functions, To translate the hit objects and change their color when they are tapped The link below is the code I am using to for the first function http://developer.anscamobile.com/sample-code/fishies Spawn objects that will hit the translating objects on collision. Alos on collision the spawned object disappears and the translating object bears a color(indicating the collision). In addition the size of this spawned object is dependent on i/p volume level. The function I have written is as follows, --VOICE INPUT CODE local r = media.newRecording() r:startRecording() r:startTuner() --local function newBar() -- local bar = display.newLine( 0, 0, 1, 0 ) -- bar:setColor( 0, 55, 100, 20 ) -- bar.width = 5 -- bar.y=400 -- bar.x=20 -- return bar --end local c1 = display.newImage("str-minion-small.png") c1.isVisible=false local c2 = display.newImage("str-minion-mid.png") c2.isVisible=false local c3 = display.newImage("str-minion-big.png") c3.isVisible=false --SPAWNING local function spawnDisk( event ) local phase = event.phase local volumeBar = display.newLine( 0, 0, 1, 0 ) volumeBar.y = 400 volumeBar.x = 20 -- volumeBar.isVisible=false local v = 20*math.log(r:getTunerVolume()) local MINTHRESH = 30 local LEFTMARGIN = 20 local v2 = MINTHRESH + math.max (v, -MINTHRESH) v2 = (display.contentWidth - 1 * LEFTMARGIN ) * v2 / MINTHRESH volumeBar.xScale = math.max ( 20, v2 ) local l = volumeBar.xScale local cnt1 = 0 local cnt2 = 0 local cnt3 = 0 local ONE =1 local val = event.numTaps --local px=event.x --local py=event.y if "ended" == phase then --audio.play( popSound ) --myLabel.isVisible = false if l > 50 and l <=150 then -- c1:setFillColor(10,105,0) -- c1.isVisible=false c1.x=math.random( 10, 450 ) c1.y=math.random( 10, 300 ) physics.addBody( c1, { density=1, radius=10.0 } ) c1.isVisible=true cnt1= cnt1+ ONE return c1 elseif l > 100 and l <=250 then --c2:setFillColor(200,10,0) c2.x=math.random( 10, 450 ) c2.y=math.random( 10, 300 ) physics.addBody( c2, { density=2, radius=9000.0 } ) c2.isVisible=true cnt2= cnt2+ ONE return c2 elseif l >=250 then c3.x=math.random( 40, 450 ) c3.y=math.random( 40, 300 ) physics.addBody( c3, { density=2, radius=7000.0 , bounce=0.0 } ) c3.isVisible=true cnt3= cnt3+ ONE return c3 end end end buzzR:addEventListener( "touch", spawnDisk ) -- touch the screen to create disks Now both functions work fine independently but there is no collision happening. Its almost as if the translating object and the spawn object are on different layers. The translating object passes through the spawn object freely. Can anyone please tell me how to resolve this problem. And how can I get them to collide. Its my first attempt at game development, that too for a mobile platform so would appreciate all help. Also if I have not been specific do let me know. I ll try to frame the query better :). Thanks in advance.

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• Confusion about inheritance

  - by Samuel Adam

  I know I might get downvoted for this, but I'm really curious. I was taught that inheritance is a very powerful polymorphism tool, but I can't seem to use it well in real cases. So far, I can only use inheritance when the base class is an abstract class. Examples : If we're talking about Product and Inventory, I quickly assumed that a Product is an Inventory because a Product must be inventorized as well. But a problem occured when user wanted to sell their Inventory item. It just doesn't seem to be right to change an Inventory object to it's subtype (Product), it's almost like trying to convert a parent to it's child. Another case is Customer and Member. It is logical (at least for me) to think that a Member is a Customer with some more privileges. Same problem occurred when user wanted to upgrade an existing Customer to become a Member. A very trivial case is the Employee case. Where Manager, Clerk, etc can be derived from Employee. Still, the same upgrading issue. I tried to use composition instead for some cases, but I really wanted to know if I'm missing something for inheritance solution here. My composition solution for those cases : Create a reference of Inventory inside a Product. Here I'm making an assumption about that Product and Inventory is talking in a different context. While Product is in the context of sales (price, volume, discount, etc), Inventory is in the context of physical management (stock, movement, etc). Make a reference of Membership instead inside Customer class instead of previous inheritance solution. Therefor upgrading a Customer is only about instantiating the Customer's Membership property. This example is keep being taught in basic programming classes, but I think it's more proper to have those Manager, Clerk, etc derived from an abstract Role class and make it a property in Employee. I found it difficult to find an example of a concrete class deriving from another concrete class. Is there any inheritance solution in which I can solve those cases? Being new in this OOP thing, I really really need a guidance. Thanks!

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• How to do pixel per pixel modeling in unity3d?

  - by Kabumbus

  So generally I want to have api like pixels.addPixel3D(new Pixel3D(0xFF0000, 100, 100,100)); (color, position) where pixels is some abstraction on 3d sceen objet.So to say point cloud. It would have grate use in deep space/stars modeling... I want to set each pixel by hand (having no image base or any automatic thing)... So point is modeling something like Or look at alive flash analog here How to do such thing in unity?

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• How far should an entity take care of its properties values by itself?

  - by Kharlos Dominguez

  Let's consider the following example of a class, which is an entity that I'm using through Entity Framework. - InvoiceHeader - BilledAmount (property, decimal) - PaidAmount (property, decimal) - Balance (property, decimal) I'm trying to find the best approach to keep Balance updated, based on the values of the two other properties (BilledAmount and PaidAmount). I'm torn between two practices here: Updating the balance amount every time BilledAmount and PaidAmount are updated (through their setters) Having a UpdateBalance() method that the callers would run on the object when appropriate. I am aware that I can just calculate the Balance in its getter. However, it isn't really possible because this is an entity field that needs to be saved back to the database, where it has an actual column, and where the calculated amount should be persisted to. My other worry about the automatically updating approach is that the calculated values might be a little bit different from what was originally saved to the database, due to rounding values (an older version of the software, was using floats, but now decimals). So, loading, let's say 2000 entities from the database could change their status and make the ORM believe that they have changed and be persisted back to the database the next time the SaveChanges() method is called on the context. It would trigger a mass of updates that I am not really interested in, or could cause problems, if the calculation methods changed (the entities fetched would lose their old values to be replaced by freshly recalculated ones, simply by being loaded). Then, let's take the example even further. Each invoice has some related invoice details, which also have BilledAmount, PaidAmount and Balance (I'm simplifying my actual business case for the sake of the example, so let's assume the customer can pay each item of the invoice separately rather than as a whole). If we consider the entity should take care of itself, any change of the child details should cause the Invoice totals to change as well. In a fully automated approach, a simple implementation would be looping through each detail of the invoice to recalculate the header totals, every time one the property changes. It probably would be fine for just a record, but if a lot of entities were fetched at once, it could create a significant overhead, as it would perform this process every time a new invoice detail record is fetched. Possibly worse, if the details are not already loaded, it could cause the ORM to lazy-load them, just to recalculate the balances. So far, I went with the Update() method-way, mainly for the reasons I explained above, but I wonder if it was right. I'm noticing I have to keep calling these methods quite often and at different places in my code and it is potential source of bugs. It also has a detrimental effect on data-binding because when the properties of the detail or header changes, the other properties are left out of date and the method has no way to be called. What is the recommended approach in this case?

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• Should library classes be wrapped before using them in unit testing?

  - by Songo

  I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework. Example: class Logger{ private $mailer; function __construct(Zend_Mail $mail){ $this->mail=$mail; } function toBeTestedFunction(){ //Some code $this->mail->setTo('some value'); $this->mail->setSubject('some value'); $this->mail->setBody('some value'); $this->mail->send(); //Some } } However, Unit testing demands that I test one component at a time, so I need to mock the Zend_Mail class. In addition I'm violating the Dependency Inversion principle as my Logger class now depends on concretion not abstraction. Does that mean that I can never use a library class directly and must always wrap it in a class of my own? Example: interface Mailer{ public function setTo($to); public function setSubject($subject); public function setBody($body); public function send(); } class MyMailer implements Mailer{ private $mailer; function __construct(){ $this->mail=new Zend_Mail; //The class isn't injected this time } function setTo($to){ $this->mailer->setTo($to); } //implement the rest of the interface functions similarly } And now my Logger class can be happy :D class Logger{ private $mailer; function __construct(Mailer $mail){ $this->mail=$mail; } //rest of the code unchanged } Questions: Although I solved the mocking problem by introducing an interface, I have created a totally new class Mailer that now needs to be unit tested although it only wraps Zend_Mail which is already unit tested by the Zend team. Is there a better approach to all this? Zend_Mail's send() function could actually have a Zend_Transport object when called (i.e. public function send($transport = null)). Does this make the idea of a wrapper class more appealing? The code is in PHP, but answers doesn't have to be. This is more of a design issue than a language specific feature

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• PHP - Internal APIs/Libraries - What makes sense?

  - by Mark Locker

  I've been having a discussion lately with some colleagues about the best way to approach a new project, and thought it'd be interesting to get some external thoughts thrown into the mix. Basically, we're redeveloping a fairly large site (written in PHP) and have differing opinions on how the platform should be setup. Requirements: The platform will need to support multiple internal websites, as well as external (non-PHP) projects which at the moment consist of a mobile app and a toolbar. We have no plans/need in the foreseeable future to open up an API externally (for use in products other than our own). My opinion: We should have a library of well documented native model classes which can be shared between projects. These models will represent everything in our database and can take advantage of object orientated features such as inheritance, traits, magic methods, etc. etc. As well as employing ORM. We can then add an API layer on top of these models which can basically accept requests and route them to the appropriate methods, translating the response so that it can be used platform independently. This routing for each method can be setup as and when it's required. Their opinion: We should have a single HTTP API which is used by all projects (internal PHP ones or otherwise). My thoughts: To me, there are a number of issues with using the sole HTTP API approach: It will be very expensive performance wise. One page request will result in several additional http requests (which although local, are still ones that Apache will need to handle). You'll lose all of the best features PHP has for OO development. From simple inheritance, to employing the likes of ORM which can save you writing a lot of code. For internal projects, the actual process makes me cringe. To get a users name, for example, a request would go out of our box, over the LAN, back in, then run through a script which calls a method, JSON encodes the output and feeds that back. That would then need to be JSON decoded, and be presented as an array ready to use. Working with arrays, as appose to objects, makes me sad in a modern PHP framework. Their thoughts (and my responses): Having one method of doing thing keeps things simple. - You'd only do things differently if you were using a different language anyway. It will become robust. - Seeing as the API will run off the library of models, I think my option would be just as robust. What do you think? I'd be really interested to hear the thoughts of others on this, especially as opinions on both sides are not founded on any past experience.

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• Does OO, TDD, and Refactoring to Smaller Functions affect Speed of Code?

  - by Dennis

  In Computer Science field, I have noticed a notable shift in thinking when it comes to programming. The advice as it stands now is write smaller, more testable code refactor existing code into smaller and smaller chunks of code until most of your methods/functions are just a few lines long write functions that only do one thing (which makes them smaller again) This is a change compared to the "old" or "bad" code practices where you have methods spanning 2500 lines, and big classes doing everything. My question is this: when it call comes down to machine code, to 1s and 0s, to assembly instructions, should I be at all concerned that my class-separated code with variety of small-to-tiny functions generates too much extra overhead? While I am not exactly familiar with how OO code and function calls are handled in ASM in the end, I do have some idea. I assume that each extra function call, object call, or include call (in some languages), generate an extra set of instructions, thereby increasing code's volume and adding various overhead, without adding actual "useful" code. I also imagine that good optimizations can be done to ASM before it is actually ran on the hardware, but that optimization can only do so much too. Hence, my question -- how much overhead (in space and speed) does well-separated code (split up across hundreds of files, classes, and methods) actually introduce compared to having "one big method that contains everything", due to this overhead? UPDATE for clarity: I am assuming that adding more and more functions and more and more objects and classes in a code will result in more and more parameter passing between smaller code pieces. It was said somewhere (quote TBD) that up to 70% of all code is made up of ASM's MOV instruction - loading CPU registers with proper variables, not the actual computation being done. In my case, you load up CPU's time with PUSH/POP instructions to provide linkage and parameter passing between various pieces of code. The smaller you make your pieces of code, the more overhead "linkage" is required. I am concerned that this linkage adds to software bloat and slow-down and I am wondering if I should be concerned about this, and how much, if any at all, because current and future generations of programmers who are building software for the next century, will have to live with and consume software built using these practices. UPDATE: Multiple files I am writing new code now that is slowly replacing old code. In particular I've noted that one of the old classes was a ~3000 line file (as mentioned earlier). Now it is becoming a set of 15-20 files located across various directories, including test files and not including PHP framework I am using to bind some things together. More files are coming as well. When it comes to disk I/O, loading multiple files is slower than loading one large file. Of course not all files are loaded, they are loaded as needed, and disk caching and memory caching options exist, and yet still I believe that loading multiple files takes more processing than loading a single file into memory. I am adding that to my concern.

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• Oracle SQL Developer Data Modeler: What Tables Aren’t In At Least One SubView?

  - by thatjeffsmith

  Organizing your data model makes the information easier to consume. One of the organizational tools provided by Oracle SQL Developer Data Modeler is the ‘SubView.’ In a nutshell, a SubView is a subset of your model. The Challenge: I’ve just created a model which represents my entire ____________ application. We’ll call it ‘residential lending.’ Instead of having all 100+ tables in a single model diagram, I want to break out the tables by module, e.g. appraisals, credit reports, work histories, customers, etc. I’ve spent several hours breaking out the tables to one or more SubViews, but I think i may have missed a few. Is there an easy way to see what tables aren’t in at least ONE subview? The Answer Yes, mostly. The mostly comes about from the way I’m going to accomplish this task. It involves querying the SQL Developer Data Modeler Reporting Schema. So if you don’t have the Reporting Schema setup, you’ll need to do so. Got it? Good, let’s proceed. Before you start querying your Reporting Schema, you might need a data model for the actual reporting schema…meta-meta data! You could reverse engineer the data modeler reporting schema to a new data model, or you could just reference the PDFs in \datamodeler\reports\Reporting Schema diagrams directory. Here’s a hint, it’s THIS one The Query Well, it’s actually going to be at least 2 queries. We need to get a list of distinct designs stored in your repository. For giggles, I’m going to get a listing including each version of the model. So I can query based on design and version, or in this case, timestamp of when it was added to the repository. We’ll get that from the DMRS_DESIGNS table: SELECT DISTINCT design_name, design_ovid, date_published FROM DMRS_designs Then I’m going to feed the design_ovid, down to a subquery for my child report. select name, count(distinct diagram_id) from DMRS_DIAGRAM_ELEMENTS where design_ovid = :dESIGN_OVID and type = 'Table' group by name having count(distinct diagram_id) < 2 order by count(distinct diagram_id) desc Each diagram element has an entry in this table, so I need to filter on type=’Table.’ Each design has AT LEAST one diagram, the master diagram. So any relational table in this table, only having one listing means it’s not in any SubViews. If you have overloaded object names, which is VERY possible, you’ll want to do the report off of ‘OBJECT_ID’, but then you’ll need to correlate that to the NAME, as I doubt you’re so intimate with your designs that you recognize the GUIDs So I’m going to cheat and just stick with names, but I think you get the gist. My Model Of my almost 90 tables, how many of those have I not added to at least one SubView? Now let’s run my report! Voila! My ‘BEER2′ table isn’t in any SubView! It says ’1′ because the main model diagram counts as a view. So if the count came back as ’2′, that would mean the table was in the main model diagram and in 1 SubView diagram. And I know what you’re thinking, what kind of residential lending program would have a table called ‘BEER2?’ Let’s just say, that my business model has some kinks to work out!

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• How to Create Views for All Tables with Oracle SQL Developer

  - by thatjeffsmith

  Got this question over the weekend via a friend and Oracle ACE Director, so I thought I would share the answer here. If you want to quickly generate DDL to create VIEWs for all the tables in your system, the easiest way to do that with SQL Developer is to create a data model. Wait, why would I want to do this? StackOverflow has a few things to say on this subject… So, start with importing a data dictionary. Step One: Open of Create a Model In SQL Developer, go to View – Data Modeler – Browser. Then in the browser panel, expand your design and create a new Relational Model. Step Two: Import your Data Dictionary This is a fancy way of saying, ‘suck objects out of the database into my model’ This will open a wizard to connect, select your schema(s), objects, etc. Once they’re in your model, you’re ready to cook with gas I’m using HR (Human Resources) for this example. You should end up with something that looks like this. Our favorite HR model Now we’re ready to generate the views! Step Three: Auto-generate the Views Go to Tools – Data Modeler – Table to View Wizard. I don’t want all my tables included, and I want to change the naming standard Decide if you want to change the default generated view names By default the views will be created as ‘V_TABLE_NAME.’ If you don’t like the ‘V_’ you can enter your own. You also can reference the object and model name with variables as shown in the screenshot above. I’m going to go with something a little more personal. The views are the little green boxes in the diagram Can’t find your views? They should be grouped together in your diagram. Don’t forget to use the Navigator to easily find and navigate to those model diagram objects! Step Four: Generate the DDL Ok, let’s use the Generate DDL button on the toolbar. Un-check everything but your views If you used a prefix, take advantage of that to create a filter. You might have existing views in your model that you don’t want to include, right? Once you click ‘OK’ the DDL will be generated. -- Generated by Oracle SQL Developer Data Modeler 4.0.0.825 -- at: 2013-11-04 10:26:39 EST -- site: Oracle Database 11g -- type: Oracle Database 11g CREATE OR REPLACE VIEW HR.TJS_BLOG_COUNTRIES ( COUNTRY_ID , COUNTRY_NAME , REGION_ID ) AS SELECT COUNTRY_ID , COUNTRY_NAME , REGION_ID FROM HR.COUNTRIES ; CREATE OR REPLACE VIEW HR.TJS_BLOG_EMPLOYEES ( EMPLOYEE_ID , FIRST_NAME , LAST_NAME , EMAIL , PHONE_NUMBER , HIRE_DATE , JOB_ID , SALARY , COMMISSION_PCT , MANAGER_ID , DEPARTMENT_ID ) AS SELECT EMPLOYEE_ID , FIRST_NAME , LAST_NAME , EMAIL , PHONE_NUMBER , HIRE_DATE , JOB_ID , SALARY , COMMISSION_PCT , MANAGER_ID , DEPARTMENT_ID FROM HR.EMPLOYEES ; CREATE OR REPLACE VIEW HR.TJS_BLOG_JOBS ( JOB_ID , JOB_TITLE , MIN_SALARY , MAX_SALARY ) AS SELECT JOB_ID , JOB_TITLE , MIN_SALARY , MAX_SALARY FROM HR.JOBS ; CREATE OR REPLACE VIEW HR.TJS_BLOG_JOB_HISTORY ( EMPLOYEE_ID , START_DATE , END_DATE , JOB_ID , DEPARTMENT_ID ) AS SELECT EMPLOYEE_ID , START_DATE , END_DATE , JOB_ID , DEPARTMENT_ID FROM HR.JOB_HISTORY ; CREATE OR REPLACE VIEW HR.TJS_BLOG_LOCATIONS ( LOCATION_ID , STREET_ADDRESS , POSTAL_CODE , CITY , STATE_PROVINCE , COUNTRY_ID ) AS SELECT LOCATION_ID , STREET_ADDRESS , POSTAL_CODE , CITY , STATE_PROVINCE , COUNTRY_ID FROM HR.LOCATIONS ; CREATE OR REPLACE VIEW HR.TJS_BLOG_REGIONS ( REGION_ID , REGION_NAME ) AS SELECT REGION_ID , REGION_NAME FROM HR.REGIONS ; -- Oracle SQL Developer Data Modeler Summary Report: -- -- CREATE TABLE 0 -- CREATE INDEX 0 -- ALTER TABLE 0 -- CREATE VIEW 6 -- CREATE PACKAGE 0 -- CREATE PACKAGE BODY 0 -- CREATE PROCEDURE 0 -- CREATE FUNCTION 0 -- CREATE TRIGGER 0 -- ALTER TRIGGER 0 -- CREATE COLLECTION TYPE 0 -- CREATE STRUCTURED TYPE 0 -- CREATE STRUCTURED TYPE BODY 0 -- CREATE CLUSTER 0 -- CREATE CONTEXT 0 -- CREATE DATABASE 0 -- CREATE DIMENSION 0 -- CREATE DIRECTORY 0 -- CREATE DISK GROUP 0 -- CREATE ROLE 0 -- CREATE ROLLBACK SEGMENT 0 -- CREATE SEQUENCE 0 -- CREATE MATERIALIZED VIEW 0 -- CREATE SYNONYM 0 -- CREATE TABLESPACE 0 -- CREATE USER 0 -- -- DROP TABLESPACE 0 -- DROP DATABASE 0 -- -- REDACTION POLICY 0 -- -- ERRORS 0 -- WARNINGS 0 You can then choose to save this to a file or not. This has a few steps, but as the number of tables in your system increases, so does the amount of time this feature can save you!

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