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• Looking for a real-world example illustrating that composition can be superior to inheritance

  - by Job

  I watched a bunch of lectures on Clojure and functional programming by Rich Hickey as well as some of the SICP lectures, and I am sold on many concepts of functional programming. I incorporated some of them into my C# code at a previous job, and luckily it was easy to write C# code in a more functional style. At my new job we use Python and multiple inheritance is all the rage. My co-workers are very smart but they have to produce code fast given the nature of the company. I am learning both the tools and the codebase, but the architecture itself slows me down as well. I have not written the existing class hierarchy (neither would I be able to remember everything about it), and so, when I started adding a fairly small feature, I realized that I had to read a lot of code in the process. At the surface the code is neatly organized and split into small functions/methods and not copy-paste-repetitive, but the flip side of being not repetitive is that there is some magic functionality hidden somewhere in the hierarchy chain that magically glues things together and does work on my behalf, but it is very hard to find and follow. I had to fire up a profiler and run it through several examples and plot the execution graph as well as step through a debugger a few times, search the code for some substring and just read pages at the time. I am pretty sure that once I am done, my resulting code will be short and neatly organized, and yet not very readable. What I write feels declarative, as if I was writing an XML file that drives some other magic engine, except that there is no clear documentation on what the XML should look like and what the engine does except for the existing examples that I can read as well as the source code for the 'engine'. There has got to be a better way. IMO using composition over inheritance can help quite a bit. That way the computation will be linear rather than jumping all over the hierarchy tree. Whenever the functionality does not quite fit into an inheritance model, it will need to be mangled to fit in, or the entire inheritance hierarchy will need to be refactored/rebalanced, sort of like an unbalanced binary tree needs reshuffling from time to time in order to improve the average seek time. As I mentioned before, my co-workers are very smart; they just have been doing things a certain way and probably have an ability to hold a lot of unrelated crap in their head at once. I want to convince them to give composition and functional as opposed to OOP approach a try. To do that, I need to find some very good material. I do not think that a SCIP lecture or one by Rich Hickey will do - I am afraid it will be flagged down as too academic. Then, simple examples of Dog and Frog and AddressBook classes do not really connivence one way or the other - they show how inheritance can be converted to composition but not why it is truly and objectively better. What I am looking for is some real-world example of code that has been written with a lot of inheritance, then hit a wall and re-written in a different style that uses composition. Perhaps there is a blog or a chapter. I am looking for something that can summarize and illustrate the sort of pain that I am going through. I already have been throwing the phrase "composition over inheritance" around, but it was not received as enthusiastically as I had hoped. I do not want to be perceived as a new guy who likes to complain and bash existing code while looking for a perfect approach while not contributing fast enough. At the same time, my gut is convinced that inheritance is often the instrument of evil and I want to show a better way in a near future. Have you stumbled upon any great resources that can help me?

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• Why appending to a list in Scala should have O(n) time complexity?

  - by Jubbat

  I am learning Scala at the moment and I just read that the execution time of the append operation for a list (:+) grows linearly with the size of the list. Appending to a list seems like a pretty common operation. Why should the idiomatic way to do this be prepending the components and then reversing the list? It can't also be a design failure as implementation could be changed at any point. From my point of view, both prepending and appending should be O(1). Is there any legitimate reason for this?

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• Cron Script to Delete Folder Contents Every 5 Minutes on Media Temple

  - by Brian Iannone

  I'm not familiar with server-side scripting, but I'm currently using a PHP application on Media Temple to cache JPEGs from four webcams hosted on a server located in the middle of the Indian Ocean. (Hence my reason for caching them in the US.) The webcams are updated every five minutes. The PHP application stores the cached images in http://static.rigic.co/cache/. I would like to create a cron script to automatically delete the contents of "cache" (not the folder itself; just the files inside) at a regular interval.

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• Preferred lambda syntax?

  - by Roger Alsing

  I'm playing around a bit with my own C like DSL grammar and would like some oppinions. I've reserved the use of "(...)" for invocations. eg: foo(1,2); My grammar supports "trailing closures" , pretty much like Ruby's blocks that can be passed as the last argument of an invocation. Currently my grammar support trailing closures like this: foo(1,2) { //parameterless closure passed as the last argument to foo } or foo(1,2) [x] { //closure with one argument (x) passed as the last argument to foo print (x); } The reason why I use [args] instead of (args) is that (args) is ambigious: foo(1,2) (x) { } There is no way in this case to tell if foo expects 3 arguments (int,int,closure(x)) or if foo expects 2 arguments and returns a closure with one argument(int,int) - closure(x) So thats pretty much the reason why I use [] as for now. I could change this to something like: foo(1,2) : (x) { } or foo(1,2) (x) -> { } So the actual question is, what do you think looks best? [...] is somewhat wrist unfriendly. let x = [a,b] { } Ideas?

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• Designing call center applications, what to consider.

  - by Espen Schulstad

  We have customers calling in to place orders. What sort of considerations should I make when building a call center application. Speed is a factor here. We had a powerbuilder application that was extremly fast for a trained user. We want to have the same sort of speed in our new production system. So some thoughts I've made are: Hotkeys are important. Is it faster to use a "wizard", step by step, or should I try to place everything important about the order logically on one sceen and have another screen where you do all searches, pertinent for that order?

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• How do I use an API?

  - by GRardB

  Background I have no idea how to use an API. I know that all APIs are different, but I've been doing research and I don't fully understand the documentation that comes along with them. There's a programming competition at my university in a month and a half that I want to compete in (revolved around APIs) but nobody on my team has ever used one. We're computer science majors, so we have experience programming, but we've just never been exposed to an API. I tried looking at Twitter's documentation, but I'm lost. Would anyone be able to give me some tips on how to get started? Maybe a very easy API with examples, or explaining essential things about common elements of different APIs? I don't need a full-blown tutorial on Stack Overflow; I just need to be pointed in the right direction. Update The programming languages that I'm most fluent in are C (simple text editor usually) and Java (Eclipse). In an attempt to be more specific with my question: I understand that APIs (and yes, external libraries are what I was referring to) are simply sets of functions. Question I guess what I'm trying to ask is how I would go about accessing those functions. Do I need to download specific files and include them in my programs, or do they need to be accessed remotely, etc.?

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• Why don't languages include implication as a logical operator?

  - by Maciej Piechotka

  It might be a strange question, but why there is no implication as a logical operator in many languages (Java, C, C++, Python Haskell - although as last one have user defined operators its trivial to add it)? I find logical implication much clearer to write (particularly in asserts or assert-like expressions) then negation with or: encrypt(buf, key, mode, iv = null) { assert (mode != ECB --> iv != null); assert (mode == ECB || iv != null); assert (implies(mode != ECB, iv != null)); // User-defined function }

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• How to make a queue switches from FIFO mode to priority mode?

  - by enzom83

  I would like to implement a queue capable of operating both in the FIFO mode and in the priority mode. This is a message queue, and the priority is first of all based on the message type: for example, if the messages of A type have higher priority than the messages of the B type, as a consequence all messages of A type are dequeued first, and finally the messages of B type are dequeued. Priority mode: my idea consists of using multiple queues, one for each type of message; in this way, I can manage a priority based on the message type: just take first the messages from the queue at a higher priority and progressively from lower priority queues. FIFO mode: how to handle FIFO mode using multiple queues? In other words, the user does not see multiple queues, but it uses the queue as if it were a single queue, so that the messages leave the queue in the order they arrive when the priority mode is disabled. In order to achieve this second goal I have thought to use a further queue to manage the order of arrival of the types of messages: let me explain better with the following code snippet. int NUMBER_OF_MESSAGE_TYPES = 4; int CAPACITY = 50; Queue[] internalQueues = new Queue[NUMBER_OF_MESSAGE_TYPES]; Queue<int> queueIndexes = new Queue<int>(CAPACITY); void Enqueue(object message) { int index = ... // the destination queue (ie its index) is chosen according to the type of message. internalQueues[index].Enqueue(message); queueIndexes.Enqueue(index); } object Dequeue() { if (fifo_mode_enabled) { // What is the next type that has been enqueued? int index = queueIndexes.Dequeue(); return internalQueues[index].Dequeue(); } if (priority_mode_enabled) { for(int i=0; i < NUMBER_OF_MESSAGE_TYPES; i++) { int currentQueueIndex = i; if (!internalQueues[currentQueueIndex].IsEmpty()) { object result = internalQueues[currentQueueIndex].Dequeue(); // The following statement is fundamental to a subsequent switching // from priority mode to FIFO mode: the messages that have not been // dequeued (since they had lower priority) remain in the order in // which they were queued. queueIndexes.RemoveFirstOccurrence(currentQueueIndex); return result; } } } } What do you think about this idea? Are there better or more simple implementations?

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• If the model is validating the data, shouldn't it throw exceptions on bad input?

  - by Carlos Campderrós

  Reading this SO question it seems that throwing exceptions for validating user input is frowned upon. But who should validate this data? In my applications, all validations are done in the business layer, because only the class itself really knows which values are valid for each one of its properties. If I were to copy the rules for validating a property to the controller, it is possible that the validation rules change and now there are two places where the modification should be made. Is my premise that validation should be done on the business layer wrong? What I do So my code usually ends up like this: <?php class Person { private $name; private $age; public function setName($n) { $n = trim($n); if (mb_strlen($n) == 0) { throw new ValidationException("Name cannot be empty"); } $this->name = $n; } public function setAge($a) { if (!is_int($a)) { if (!ctype_digit(trim($a))) { throw new ValidationException("Age $a is not valid"); } $a = (int)$a; } if ($a < 0 || $a > 150) { throw new ValidationException("Age $a is out of bounds"); } $this->age = $a; } // other getters, setters and methods } In the controller, I just pass the input data to the model, and catch thrown exceptions to show the error(s) to the user: <?php $person = new Person(); $errors = array(); // global try for all exceptions other than ValidationException try { // validation and process (if everything ok) try { $person->setAge($_POST['age']); } catch (ValidationException $e) { $errors['age'] = $e->getMessage(); } try { $person->setName($_POST['name']); } catch (ValidationException $e) { $errors['name'] = $e->getMessage(); } ... } catch (Exception $e) { // log the error, send 500 internal server error to the client // and finish the request } if (count($errors) == 0) { // process } else { showErrorsToUser($errors); } Is this a bad methodology? Alternate method Should maybe I create methods for isValidAge($a) that return true/false and then call them from the controller? <?php class Person { private $name; private $age; public function setName($n) { $n = trim($n); if ($this->isValidName($n)) { $this->name = $n; } else { throw new Exception("Invalid name"); } } public function setAge($a) { if ($this->isValidAge($a)) { $this->age = $a; } else { throw new Exception("Invalid age"); } } public function isValidName($n) { $n = trim($n); if (mb_strlen($n) == 0) { return false; } return true; } public function isValidAge($a) { if (!is_int($a)) { if (!ctype_digit(trim($a))) { return false; } $a = (int)$a; } if ($a < 0 || $a > 150) { return false; } return true; } // other getters, setters and methods } And the controller will be basically the same, just instead of try/catch there are now if/else: <?php $person = new Person(); $errors = array(); if ($person->isValidAge($age)) { $person->setAge($age); } catch (Exception $e) { $errors['age'] = "Invalid age"; } if ($person->isValidName($name)) { $person->setName($name); } catch (Exception $e) { $errors['name'] = "Invalid name"; } ... if (count($errors) == 0) { // process } else { showErrorsToUser($errors); } So, what should I do? I'm pretty happy with my original method, and my colleagues to whom I have showed it in general have liked it. Despite this, should I change to the alternate method? Or am I doing this terribly wrong and I should look for another way?

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• What is the worst programmer habit?

  - by 0x4a6f4672

  Many people get into programming because programming is fun. At least in the beginning. After some time doing it professionally, programming is no longer fun, often just hard work. Sometimes we develop bad habits along the way to make it fun again. Some bad habits of programmers are well known, for example the "I fix that in a second" habit, the "reinvent the wheel" practice or the "all code except mine is crap" attitude (which often leads to "I will re-write the entire program from scratch" syndrome). There are things which a programmer should never do. What is the worst programmer habit?

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• How do I use an API?

  - by GRardB

  Background I have no idea how to use an API. I know that all APIs are different, but I've been doing research and I don't fully understand the documentation that comes along with them. There's a programming competition at my university in a month and a half that I want to compete in (revolved around APIs) but nobody on my team has ever used one. We're computer science majors, so we have experience programming, but we've just never been exposed to an API. I tried looking at Twitter's documentation, but I'm lost. Would anyone be able to give me some tips on how to get started? Maybe a very easy API with examples, or explaining essential things about common elements of different APIs? I don't need a full-blown tutorial on Stack Overflow; I just need to be pointed in the right direction. Update The programming languages that I'm most fluent in are C (simple text editor usually) and Java (Eclipse). In an attempt to be more specific with my question: I understand that APIs (and yes, external libraries are what I was referring to) are simply sets of functions. Question I guess what I'm trying to ask is how I would go about accessing those functions. Do I need to download specific files and include them in my programs, or do they need to be accessed remotely, etc.?

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• Why the static data members have to be defined outside the class separately in C++ (unlike Java)?

  - by iammilind

  class A { static int foo () {} // ok static int x; // <--- needed to be defined separately in .cpp file }; I don't see a need of having A::x defined separately in a .cpp file (or same file for templates). Why can't be A::x declared and defined at the same time? Has it been forbidden for historical reasons? My main question is, will it affect any functionality if static data members were declared/defined at the same time (same as Java) ?

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• When should one use "out" parameters?

  - by qegal

  In Objective-C, there are several methods like initWithContentsOfFile:encoding:error: where one passes in a reference to an NSError object for the error: parameter. In this example, the value of the NSError object passed in can change based on what goes on at runtime when the method is being called and whether the body of the method was executed in a certain way successfully. In a way I think of this NSError object as sort of like a second return value from the method, and only differs from an object anObject in the statement return anObject; in that when this statement is called, execution leaves the method. So my question is, not only in the context of error handling in Objective-C, but in general, when should one use an "out" parameter in place of returning said value in a return statement?

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• TDD, new tests while old ones not implemented yet

  - by liori

  I am experimenting with test-driven development, and I found that I often come to a following situation: I write tests for some functionality X. Those tests fail. While trying to implement X, I see that I need to implement some feature Y in a lower layer of my code. So... I write tests for Y. Now both tests for X and Y fail. Once I had 4 features in different layers of code being worked on at the same time, and I was losing my focus on what I am actually doing (too many tests failing at the same time). I think I could solve this by putting more effort into planning my tasks even before I start writing tests. But in some cases I didn't know that I will need to go deeper, because e.g. I didn't know the API of lower layer very well. What should I do in such cases? Does TDD have any recommendations?

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• Why do programming languages allow shadowing/hiding of variables and functions?

  - by Simon

  Many of the most popular programming languges (such as C++, Java, Python etc.) have the concept of hiding / shadowing of variables or functions. When I've encountered hiding or shadowing they have been the cause of hard to find bugs and I've never seen a case where I found it necessary to use these features of the languages. To me it would seem better to disallow hiding and shadowing. Does anybody know of a good use of these concepts?

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• Why are slower programming languages considered worse than faster ones?

  - by Emanuil

  Here's how I see it. There's machine code and it's all that the computers needs in order to run something. The computers don't care about programming languages. It doesn't matter to them if the machine code comes from Perl, Python or PHP. Programming languages exist to serve programmers. Some programming languages run slower then others but that's not because there is something wrong with them. It's often because they do more things that otherwise programmers would do and by doing these things, they do better what they are supposed to do - serve programmers. So why are slower programming languages considered worse than faster ones?

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• How did we get saddled with the (hierarchical) filesystem as the basic data structure?

  - by user1936

  I'm self-taught and I don't have a CS degree. The more I've been learning about data structure, the more I wonder, in this day and age, how are we still saddled with the filesystem, with directories and files, as the basic data storage structure on the OS? I understand the simplicity of it, but it seems nowadays that there could be more options available natively. As far as I'm aware, the only project to improve the basic functionality of the filesystem was ReiserFS, where you could tell what line of a file was changed by whom, and when. For instance, if I could have native tagging for files, where I could tag images, diagrams, word-processing documents, an entire code repository, all as belonging to a single project, that would really be helpful to me. Since I'm stuck in the filesystem paradigm, I know that I could put all those into a single folder/directory, but what if they already exist in disparate directories, and they need to stay there? I know there are programs out there that can do this, but why aren't they on the filesystem? Something that would be nice to have is some kind of relational feature in the filesystem, like you get with RDBMSes. I understand that that was supposed to be part of Vista/7, but that fell off the feature list too. Sure, any program can store a binary file and have any data structure it wants in it, by why couldn't the OS offer more complex ways of storing data, beyond the simple heirarchy of the filesystem?

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• What is the program "Additional Drivers" (jockey-gtk) talking me about?

  - by Robert Vila

  The program says: "No proprietary drivers are in use on this system" But it doesn't say if it is talking about graphical drivers only or what. Then, it lists two drivers: NVIDIA accelerated graphics driver (version 173). NVIDIA accelerated graphics driver (version current) [recomended] Both have exactly the same description. What is the difference then? When I select the 1st one, it says: "This river is not activated",and there's a button to "activate" it. When I select the 2nd one, it says: "This river is activated but it is not currently in use", and the button is to "remove". So which one is in use? Why or what for should I have activated (enabled) and not in use? If it is in use it is activated? What is the difference between activate and remove? and what is the relationship between installed, activated, in use, enabled and removed, disabled, inactive and not-installed? Why can I activate the inactivated and remove (but not deactivate) the activated that is not in use? All this is very puzzling... What other drivers can I use for an Apple MacBook pro 3,1 and how? I see that there's a nouveau and I heard that there was going to be a new open source even better. > -display > description: VGA compatible controller > product: G84 [GeForce 8600M GT] > vendor: nVidia Corporation

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• Why is x=x++ undefined?

  - by ugoren

  It's undefined because the it modifies x twice between sequence points. The standard says it's undefined, therefore it's undefined. That much I know. But why? My understanding is that forbidding this allows compilers to optimize better. This could have made sense when C was invented, but now seems like a weak argument. If we were to reinvent C today, would we do it this way, or can it be done better? Or maybe there's a deeper problem, that makes it hard to define consistent rules for such expressions, so it's best to forbid them? So suppose we were to reinvent C today. I'd like to suggest simple rules for expressions such as x=x++, which seem to me to work better than the existing rules. I'd like to get your opinion on the suggested rules compared to the existing ones, or other suggestions. Suggested Rules: Between sequence points, order of evaluation is unspecified. Side effects take place immediately. There's no undefined behavior involved. Expressions evaluate to this value or that, but surely won't format your hard disk (strangely, I've never seen an implementation where x=x++ formats the hard disk). Example Expressions x=x++ - Well defined, doesn't change x. First, x is incremented (immediately when x++ is evaluated), then it's old value is stored in x. x++ + ++x - Increments x twice, evaluates to 2*x+2. Though either side may be evaluated first, the result is either x + (x+2) (left side first) or (x+1) + (x+1) (right side first). x = x + (x=3) - Unspecified, x set to either x+3 or 6. If the right side is evaluated first, it's x+3. It's also possible that x=3 is evaluated first, so it's 3+3. In either case, the x=3 assignment happens immediately when x=3 is evaluated, so the value stored is overwritten by the other assignment. x+=(x=3) - Well defined, sets x to 6. You could argue that this is just shorthand for the expression above. But I'd say that += must be executed after x=3, and not in two parts (read x, evaluate x=3, add and store new value). What's the Advantage? Some comments raised this good point. It's not that I'm after the pleasure of using x=x++ in my code. It's a strange and misleading expression. What I want is to be able to understand complicated expressions. Normally, a complicated expression is no more than the sum of its parts. If you understand the parts and the operators combining them, you can understand the whole. C's current behavior seems to deviate from this principle. One assignment plus another assignment suddenly doesn't make two assignments. Today, when I look at x=x++, I can't say what it does. With my suggested rules, I can, by simply examining its components and their relations.

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• Chrome not accepting international dead keys 14.04

  - by D3L

  Every other application on 14.04 accepts that I have selected US international with dead keys as my keyboard layout option, and accepts text input as it should. Chrome however fails to recognise what keyboard I have set in system settings and blindly uses "US keyboard". Looking for a solution to force Chrome to accept dead key input. AFAIK it used to work, but something has messed up recently with updates to Chrome

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• I want to be a developer (website and web application) and want to choose asp.net as a programming lang

  - by jeet

  I want to be a developer (website and web application) and want to choose asp.net as a programming lang. I am currently an intermediate web designer. My friend told me that there are many things in asp.net My question is I am interested in website and web application development Is there any specific thing I have to learn to be a web developer or I have to learn the whole. Also, what does a developer has to do? key skills if he choose asp.net? Thanks :)

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• Do you write unit tests for all the time in TDD?

  - by mcaaltuntas

  I have been designing and developing code with TDD style for a long time. What disturbs me about TDD is writing tests for code that does not contain any business logic or interesting behaviour. I know TDD is a design activity more than testing but sometimes I feel it's useless to write tests in these scenarios. For example I have a simple scenario like "When user clicks check button, it should check file's validity". For this scenario I usually start writing tests for presenter/controller class like the one below. @Test public void when_user_clicks_check_it_should_check_selected_file_validity(){ MediaService service =mock(MediaService); View view =mock(View); when(view.getSelectedFile).thenReturns("c:\\Dir\\file.avi"); MediaController controller =new MediaController(service,view); controller.check(); verify(service).check("c:\\Dir\\file.avi"); } As you can see there is no design decision or interesting code to verify behaviour. I am testing values from view passed to MediaService. I usually write but don't like these kind of tests. What do yo do about these situations ? Do you write tests for all the time ? UPDATE : I have changed the test name and code after complaints. Some users said that you should write tests for the trivial cases like this so in the future someone might add interesting behaviour. But what about “Code for today, design for tomorrow.” ? If someone, including myself, adds more interesting code in the future the test can be created for it then. Why should I do it now for the trivial cases ?

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• What do you do when working with multiple languages with different capitalization schemes?

  - by dvcolgan

  I'm making a webapp using Django. The Python convention for naming variables is lowercase_with_underscores, but the Javascript convention is camelCase. In addition, I've seen many people use lowercase-with-hyphens for CSS identifiers. Would you suggest using all three naming conventions where appropriate, or picking one and using it, even if the other two recommend something else? Switching back and forth isn't a huge problem, but it can still be mental overhead.

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• Which platform to choose from .Net or Java [closed]

  - by SahilMahajanMj

  I know that there is a lot healthy discussion about this topic. but my case is entirely different from these discussions. I have just passed out my graduation. During the graduation period, i had done C#.net and java as well. Now i am working as Android programmer in a company. In the recent times, i have heard a lot about pros and cons of these platforms. What our seniors used to suggest that, ASP.net is a lot better than JSP for website developement. .net provides us lot of in built tools and API's for building powerfull applications. Java's platform independancy has always been issue among them. Security fetures are more in java. .Net has more powerfull IDE's. Now i am a bit confused on which platform to choose from these. I found java better from two, so did i prefer to choose android. Also, the discussion always ends with an issue that java has no scope for job as far has .net does. I would like to hear suggestions on this topic, but it would be better, if you consider indian IT market for this discussion.

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• Why use other number bases when programming

  - by JMD

  My coworkers and I have been bending our minds to figuring out why anyone would go out of their way to program numbers in a base other than base 10. I suggested that perhaps you could optimize longer equations by putting the variables in the correct base you are working with (for instance, if you have only sets of 5 of something with no remainders you could use base 5), but I'm not sure if that's true. Any thoughts?

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