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• Design pattern and best practices

  - by insane-36

  I am an iphone developer. I am quite confident on developing iphone application with some minimal feature. I would consider myself as a fair application developer but the code I write is not so much structured. I make vey little use of MVC because I dont seem to find places to impose MVC. Most of the time, I create application with viewcontrollers and very few models only. How could I improve the skill for making my code more reusable, standard, easy and maintainable. I have seen few books on design patterns and tried few chapters myself but I dont seem to skip my habit. I know few of them but I am not being able to apply those patterns into my app. What is the best way to learn the design patterns and coding habit. Any kind of suggestion is warmly welcomed.

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• What is the benefit of triple buffering?

  - by user782220

  I read everything written in a previous question. From what I understand in double buffering the program must wait until the finished drawing is copied or swapped before starting the next drawing. In triple buffering the program has two back buffers and can immediately start drawing in the one that is not involved in such copying. But with triple buffering if you're in a situation where you can take advantage of the third buffer doesn't that suggest that you are drawing frames faster than the monitor can refresh. So then you don't actually get a higher frame rate. So what is the benefit of triple buffering then?

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• If immutable objects are good, why do people keep creating mutable objects?

  - by Vinoth Kumar

  If immutable objects are good,simple and offers benefits in concurrent programming why do programmers keep creating mutable objects? I have four years of experience in Java programming and as I see it, the first thing people do after creating a class is generate getters and setters in the IDE (thus making it mutable). Is there a lack of awareness or can we get away with using mutable objects in most scenarios?

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• Turning your code inside out (functional style) compared to a OO paradigm

  - by Acaz Souza

  I have find this article Turning Your Code Inside Out and I want to know how this approach described in article is for OO programmers/languages. Is this style of design used in OO programmers/languages? What's downsides and goodsides of this approach in a OO language? Update: OO objects have state and behavior, the design explained in article is stateless. Is not only Single Responsability Principle. (If I'm talking shit, please explain to me instead of only downside/close votes)

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• Functional programming readability

  - by Jimmy Hoffa

  I'm curious about this because I recall before learning any functional languages, I thought them all horribly, awfully, terribly unreadable. Now that I know Haskell and f#, I find it takes a little longer to read less code, but that little code does far more than an equivalent amount would in an imperative language, so it feels like a net gain and I'm not extremely practiced in functional. Here's my question, I constantly hear from OOP folks that functional style is terribly unreadable. I'm curious if this is the case and I'm deluding myself, or if they took the time to learn a functional language, the whole style would no longer be more unreadable than OOP? Has anybody seen any evidence or got any anecdotes where they saw this go one way or another with frequency enough to possibly say? If writing functionally really is of lower readability than I don't want to keep using it, but I really don't know if that's the case or not..

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• How to explain OOP to a matlab programmer?

  - by Oak

  I have a lot of friends who come from electrical / physical / mechanical engineering background, and are curious about what is "OOP" all about. They all know Matlab quite well, so they do have basic programming background; but they have a very hard time grasping a complex type system which can benefit from the concepts OOP introduces. Can anyone propose a way I can try to explain it to them? I'm just not familiar with Matlab myself, so I'm having troubles finding parallels. I think using simple examples like shapes or animals is a bit too abstract for those engineers. So far I've tried using a Matrix interface vs array-based / sparse / whatever implementations, but that didn't work so well, probably because different matrix types are already well-supported in Matlab.

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• Help to understand the abstract factory pattern

  - by Chobeat

  I'm learning the 23 design patterns of the GoF. I think I've found a way to understand and simplify how the Abstract Factory works but I would like to know if this is a correct assumption or if I am wrong. What I want to know is if we can see the result of the Abstract Factory method as a matrix of possible products where there's a Product for every "Concrete Factory" x "AbstractProduct" where the Concrete Factory is a single implementation among the implementations of an AbstractFactory and an AbstractProduct is an interface among the interfaces to create Products. Is this correct or am I missing something?

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• Java Alphabetize Algorithm Insertion sort vs Bubble Sort

  - by Chris Okyen

  I am supposed to "Develop a program that alphabetizes three strings. The program should allow the user to enter the three strings, and then display the strings in alphabetical order." It's instructed that I need to use the String library compareTo()/charAt()/toLowerCase() to make all the characters lowercase so the Lexicon comparison is also a alphabetical comparison. Input Pseudo Code: String input[3]; Scanner keyboard = new Scanner(System.in); System.out.println("Enter three strings: "); for(byte i = 0; i < 3; i++) input[i] = keyboard.next() The sorting would be Insertion Sort: 321 2 3 1 2 31 231 1 23 1 2 3 1 23 1 23 123 Bubble Sort 321 231 213 123 Which would be more efficient in this case? The bubble sort seems to be more efficient though they seem to have equal stats for worst best and avg case, but I read the Insertion Sort is quicker for small amounts of data like my case.

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• EXALYTICS - If Oracle BI Server Does Not Fail Over to the TimesTen Instance

  - by Ahmed Awan

  If the BI Server does not fail over to the second TimesTen instance on the scaled-out node, then ensure that the logical table source (LTS) for the repository has mapped both TimesTen physical data sources. This mapping ensures that at the logical table source level, a mapping exists to both TimesTen instances. If one TimesTen instance is not available, then failover logic for the BI Server at the DSN level tries to connect to the other TimesTen instance. Reference: http://docs.oracle.com/cd/E23943_01/bi.1111/e24706/toc.htm

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• Ways to break the "Syndrome of the perfect programmer"

  - by Rushino

  I am probably not the only one that feel that way. But I have what I tend to call "The syndrome of the perfect programmer" which many might say is the same as being perfectionist but in this case it's in the domain of programming. However, the domain of programming is a bit problematic for such a syndrome. Have you ever felt that when you are programming you're not confident or never confident enought that your code is clean and good code that follows most of the best practices ? There so many rules to follow that I feel like being overwhelmed somehow. Not that I don't like to follow the rules of course I am a programmer and I love programming, I see this as an art and I must follow the rules. But I love it too, I mean I want and I love to follow the rules in order to have a good feeling of what im doing is going the right way.. but I only wish I could have everything a bit more in "control" regarding best practices and good code. Maybe it's a lack of organization? Maybe it's a lack of experience? Maybe a lack of practice? Maybe it's a lack of something else someone could point out? Is there any way to get rid of that syndrome somehow ?

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• SQL Azure Federations and Semantic Search by the SQL product team in London tonight (Monday)

  - by simonsabin

  Don’t forget that tonight we have Michael Rys from the SQL Server Product Team presenting on the Federation support coming to SQL Azure and the Semantic search coming in SQL Server Denali. This is a must attend evening for anyone that is serious about scaling SQL or doing search in SQL Server. Michael also has a few other hats including Microsoft’s representative on the W3C XML Query Working Group. To register go to http://sqlsocial20110613.eventbrite.com/   Ps Beer and Pizza will be laid on...(read more)

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• What is the best way to check if there is overlap between player and static, non-collidable items in bullet physic engine

  - by tigrou

  I'd like to add non collidable objects (eg: power ups, items, ...) in a game world using Bullet Physics Engine and to know if there is collision between player and them. Some info : there is a lot of items ( 1000), all are box shapes and they don't overlap. Here is things i have tried : btDbvt* bvtItems = new btDbvt(); //btDbvt is a hierachical AABB tree, used by Bullet foreach(var item ...) { btDbvtVolume volume = ... //compute item AABB; bvtItems->insert(volume, (void*)someExtraData); } Then, to find collisions between items and player : playerRigidBody->getAabb(min, max); btDbvtVolume playervolume = ... //compute player AABB bvtItems->collideTV(bvtItems->m_root, playervolume, *someCollisionHandler); This works fairly well (and its very fast), however, there is a problem : it only check items AABB against player AABB. That loss of precision is acceptable for items but not for player which is not a box. It would actually need another check to make sure player really collide with item but i don't know how to do this in Bullet. It would have been nice to have a function like this : playerRigidBody->checkCollisionWithAABB(); After doing trying that, I discovered that a btGhostObject exist and seems to have been made for that. I changed my code like this : foreach(var item...) { btCollisionObject* ghostObject = new btGhostObject(); ghostObject->setCollisionShape(boxShape); ghostObject->setCollisionFlags(ghostObject->getCollisionFlags() | btCollisionObject::CF_NO_CONTACT_RESPONSE); startTransform.setOrigin(...); //item position ghostObject->setWorldTransform(startTransform); dynamicsWorld->addCollisionObject(ghostObject, btBroadphaseProxy::SensorTrigger, btBroadphaseProxy:: CharacterFilter); } It also works ok, but there is a huge fps drop (almost ten times slower) which is not acceptable. Maybe there is something missing (forget set a flag) and Bullet is doing extra job for nothing or maybe all that ghostObjects are polluting broad phase and ghostObject is not the right thing for that. Any help would be appreciated.

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• C# vector class - Interpolation design decision

  - by Benjamin

  Currently I'm working on a vector class in C# and now I'm coming to the point, where I've to figure out, how i want to implement the functions for interpolation between two vectors. At first I came up with implementing the functions directly into the vector class... public class Vector3D { public static Vector3D LinearInterpolate(Vector3D vector1, Vector3D vector2, double factor) { ... } public Vector3D LinearInterpolate(Vector3D other, double factor { ... } } (I always offer both: a static method with two vectors as parameters and one non-static, with only one vector as parameter) ...but then I got the idea to use extension methods (defined in a seperate class called "Interpolation" for example), since interpolation isn't really a thing only available for vectors. So this could be another solution: public class Vector3D { ... } public static class Interpolation { public static Vector3D LinearInterpolate(this Vector3D vector, Vector3D other, double factor) { ... } } So here an example how you'd use the different possibilities: { var vec1 = new Vector3D(5, 3, 1); var vec2 = new Vector3D(4, 2, 0); Vector3D vec3; vec3 = vec1.LinearInterpolate(vec2, 0.5); //1 vec3 = Vector3D.LinearInterpolate(vec1, vec2, 0.5); //2 //or with extension-methods vec3 = vec1.LinearInterpolate(vec2, 0.5); //3 (same as 1) vec3 = Interpolation.LinearInterpolation(vec1, vec2, 0.5); //4 } So I really don't know which design is better. Also I don't know if there's an ultimate rule for things like this or if it's just about what someone personally prefers. But I really would like to hear your opinions, what's better (and if possible why ).

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• Very simple OOP question

  - by Mosty Mostacho

  I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram: Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more. Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this: Now I've been wondering: Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way? When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names? Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time? Any comment will be appreciated.

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• Pattern for a class that does only one thing

  - by Heinzi

  Let's say I have a procedure that does stuff: void doStuff(initalParams) { ... } Now I discover that "doing stuff" is quite a compex operation. The procedure becomes large, I split it up into multiple smaller procedures and soon I realize that having some kind of state would be useful while doing stuff, so that I need to pass less parameters between the small procedures. So, I factor it out into its own class: class StuffDoer { private someInternalState; public Start(initalParams) { ... } // some private helper procedures here ... } And then I call it like this: new StuffDoer().Start(initialParams); or like this: new StuffDoer(initialParams).Start(); And this is what feels wrong. When using the .NET or Java API, I always never call new SomeApiClass().Start(...);, which makes me suspect that I'm doing it wrong. Sure, I could make StuffDoer's constructor private and add a static helper method: public static DoStuff(initalParams) { new StuffDoer().Start(initialParams); } But then I'd have a class whose external interface consists of only one static method, which also feels weird. Hence my question: Is there a well-established pattern for this type of classes that have only one entry point and have no "externally recognizable" state, i.e., instance state is only required during execution of that one entry point?

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• Shared to Dedicated or Amazon CloudFront to improve performances and keep secured?

  - by user978548

  I have a Wordpress which currently takes about 1.8s to 2.5s for the home page to completely load in my country. The page weight is about 700Ko (static content included). In order to increase performances, I'm considering two solutions: Switching to a dedicated host. Using amazon s3 cloudfront to serve static contents. My current shared hosting have servers in a neighboring country but not exactly in mine, and both amazon and the dedicated hosting have some, so that's already an advantage. So considering all that, I still have three questions remaining: Currently having a low traffic (100 unique visitors/days, but growing) will it make a huge difference between my shared hosting and a dedicated server ? Knowing that I already use a cookie-less domain to deliver static contents (but using a redirection to the same server), would using amazon s3 make a real difference ? Talking about the cons of dedicated vs amazon s3, if I choose for the dedicated server something like Ubuntu server and do daily package updates and have only port 80 open, would it be sufficient in terms of security (in comparison with my current shared hosting which manage everything for me) ?

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• What is the best way to keep track of the median?

  - by Steven Mou

  I read a question in one book: Numbers are randomly generated and stored into an (expanding) array, How would you keep track of the median? There are two data structures can solve the problem. One is the balanced binary tree, the other is two heaps which keep trace of the biggest half and the smallest half of the elements. I think these two solutions has the same running time as O(n lg n), but I am not sure of my judgement. In your opinions, What is the best way to keep track of the median?

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• Liskov principle: violation by type-hinting

  - by Elias Van Ootegem

  According to the Liskov principle, a construction like the one below is invalid, as it strengthens a pre-condition. I know the example is pointless/nonsense, but when I last asked a question like this, and used a more elaborate code sample, it seemed to distract people too much from the actual question. //Data models abstract class Argument { protected $value = null; public function getValue() { return $this->value; } abstract public function setValue($val); } class Numeric extends Argument { public function setValue($val) { $this->value = $val + 0;//coerce to number return $this; } } //used here: abstract class Output { public function printValue(Argument $arg) { echo $this->format($arg); return $this; } abstract public function format(Argument $arg); } class OutputNumeric extends Output { public function format(Numeric $arg)//<-- VIOLATION! { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } My question is this: Why would this kind of "violation" be considered harmful? So much so that some languages, like the one I used in this example (PHP), don't even allow this? I'm not allowed to strengthen the type-hint of an abstract method but, by overriding the printValue method, I am allowed to write: class OutputNumeric extends Output { final public function printValue(Numeric $arg) { echo $this->format($arg); } public function format(Argument $arg) { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } But this would imply repeating myself for each and every child of Output, and makes my objects harder to reuse. I understand why the Liskov principle exists, don't get me wrong, but I find it somewhat difficult to fathom why the signature of an abstract method in an abstract class has to be adhered to so much stricter than a non-abstract method. Could someone explain to me why I'm not allowed to hind at a child class, in a child class? The way I see it, the child class OutputNumeric is a specific use-case of Output, and thus might need a specific instance of Argument, namely Numeric. Is it really so wrong of me to write code like this?

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• Examples of Liskov Substitution

  - by james lewis

  I'm facilitating a session next week on the Liskov Substitution Principle and I was wondering if anyone had any examples of violations 'from the trenches'? I'm looking for something other than uncle Bob's rectangle - square problem and the persistent set problem he talks about in A-PPP (although that is a great example). So far I'm using the example of a (very simple) List and an IndexedList as the 'correct' use of inheritance. And the addition of a Set to this hierarchy as a violation (as a Set is distinct; strengthening the pre condition of the Add method). I've also taken this great example and it's solution from this question Both those examples are great but I'm looking for something more subtle and harder to spot. So far I've come up with nothing so if you've got a great, subtle example post it up. Also, any metaphors you've come across that helped you understand LSP would be really useful too.

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• SharePoint Client Object Model: Step One

  - by PeterBrunone

  I almost didn't make it out alive.  I followed the instructions in every piece of sample code and every forum post by someone who had no idea why their client OM code wasn't working, and my code still wouldn't get past the page load.  I kept getting "'Type' is undefined" errors when sp.core.js tried to register the SP namespace.As it turns out, you need the help of the default master page (or one like it) to get the object model loaded.  Once I told my sample page to use the default master and modified everything accordingly, it hooked up and ran just fine.Now I can finally get some work done.

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• 'module' object has no attribute 'PY2'

  - by ManikandanV

  I am using ubuntu 14.04, was trying to install python-memcache. I have got an error like Downloading/unpacking python-memcached Downloading python-memcached-1.53.tar.gz Cleaning up... Exception: Traceback (most recent call last): File "/usr/lib/python2.7/dist-packages/pip/basecommand.py", line 122, in main status = self.run(options, args) File "/usr/lib/python2.7/dist-packages/pip/commands/install.py", line 278, in run requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle) File "/usr/lib/python2.7/dist-packages/pip/req.py", line 1229, in prepare_files req_to_install.run_egg_info() File "/usr/lib/python2.7/dist-packages/pip/req.py", line 292, in run_egg_info logger.notify('Running setup.py (path:%s) egg_info for package %s' % (self.setup_py, self.name)) File "/usr/lib/python2.7/dist-packages/pip/req.py", line 284, in setup_py if six.PY2 and isinstance(setup_py, six.text_type): AttributeError: 'module' object has no attribute 'PY2' Storing debug log for failure in /home/mani/.pip/pip.log I am getting the same error when installing Django-celery, pymongo etc

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• How did you get good practices for your OOP designs?

  - by Darf Zon

  I realized I have a difficulty creating OOP designs. I spent many time deciding if this property is correctly set it to X class. For example, this is a post which has a few days: http://codereview.stackexchange.com/questions/8041/how-to-improve-my-factory-design I'm not convinced of my code. So I want to improve my designs, take less time creating it. How did you learn creating good designs? Some books that you can recommend me?

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• Demantra Partitioning and the First PK Column

  - by user702295

    We have found that it is necessary in Demantra to have an index that matches the partition key, although it does not have to be the PK.  It is ok   to create a new index instead of changing the PK.   For example, if my PK on SALES_DATA is (ITEM_ID, LOCATION_ID, SALES_DATE) and I decide partition by SALES_DATE, then I should add an index starting   with the partition key like this: (SALES_DATE, ITEM_ID, LOCATION_ID).   * Note that the first column of the new index matches the partition key.   It might also be helpful to create a 2nd index with the other PK columns reversed (SALES_DATE, LOCATION_ID, ITEM_ID). Again, the first column   matches the partition key.

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• Java Spotlight Episode 98: Cliff Click on Benchmarkings

  - by Roger Brinkley

  Interview with Cliff Click of 0xdata on benchmarking. Recorded live at JFokus 2012. Right-click or Control-click to download this MP3 file. You can also subscribe to the Java Spotlight Podcast Feed to get the latest podcast automatically. If you use iTunes you can open iTunes and subscribe with this link:  Java Spotlight Podcast in iTunes. Show Notes News Bean Validation 1.1 Java EE 7 Roadmap Java JRE Update 7u7 and 6u35 available. Change to Java SE 7 and Java SE 6 Update Release Numbers JCP 2012 Award Nominations Announced Griffon JavaFX Plugin Events Sep 3-6, Herbstcampus, Nuremberg, Germany Sep 10-15, IMTS 2012 Conference,  Chicago Sep 12,  The Coming M2M Revolution: Critical Issues for End-to-End Software and Systems Development,  Webinar Sep 30-Oct 4, JavaONE, San Francisco Oct 3-4, Java Embedded @ JavaONE, San Francisco Oct 15-17, JAX London Oct 30-Nov 1, Arm TechCon, Santa Clara Oct 22-23, Freescale Technology Forum - Japan, Tokyo Nov 2-3, JMagreb, Morocco Nov 13-17, Devoxx, Belgium Feature Interview Cliff Click is the CTO and Co-Founder of 0xdata, a firm dedicated to creating a new way to think about web-scale data storage and real-time analytics. I wrote my first compiler when I was 15 (Pascal to TRS Z-80!), although my most famous compiler is the HotSpot Server Compiler (the Sea of Nodes IR). I helped Azul Systems build an 864 core pure-Java mainframe that keeps GC pauses on 500Gb heaps to under 10ms, and worked on all aspects of that JVM. Before that I worked on HotSpot at Sun Microsystems, and am at least partially responsible for bringing Java into the mainstream. I am invited to speak regularly at industry and academic conferences and has published many papers about HotSpot technology. I hold a PhD in Computer Science from Rice University and about 15 patents. What’s Cool Shaun Smith’s Devoxx 2011 talk "JPA Multi-Tenancy & Extensibility" now freely available at Parleys.

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