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• Object-Oriented Operating System

  - by nmagerko

  As I thought about writing an operating system, I came across a point that I really couldn't figure out on my own: Can an operating system truly be written in an Object-Oriented Programming (OOP) Language? Being that these types of languages do not allow for direct accessing of memory, wouldn't this make it impossible for a developer to write an entire operating system using only an OOP Language? Take, for example, the Android Operating System that runs many phones and some tablets in use around the world. I believe that this operating system uses only Java, an Object-Oriented language. In Java, I have been unsuccessful in trying to point at and manipulate a specific memory address that the run-time environment (JRE) has not assigned to my program implicitly. In C, C++, and other non-OOP languages, I can do this in a few lines. So this makes me question whether or not an operating system can be written in an OOP, especially Java. Any counterexamples or other information is appreciated.

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• What is the intention behind asking weight of plane?

  - by AKS

  I was asked this question "How would you find weight of Aeroplane" in an interview and I am not sure why this question was one of the two question asked in the interview. I tried to answer it using all possible ways but could not give the correct answer.(found the correct answer after google search) How much such questions decide your selection in the interview? Here was my approach: 1. If measurement of plane is given then i will calculate volume and multiply by density, will consider fuel weight plus other dead weight. 2. Using water displacement method if i can put plane in water and somehow measure how much water is displaced. But found using google search that right approach was to put place on a ship and mark the level of water on the hull, then remove plane and then ship will go up. And start putting weight on the ship till marked hull reaches the water level.

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• Small-scale database options for .NET

  - by raney

  I have a .NET 4.0/WPF based application I've developed and maintain for my company that acts as a friendly GUI central-point-of-information, combining information pulled from a couple of SQL databases, as well as CSV exports from a few other applications. I would like to build out my own database to support the entirety of the information that the application accesses, so that I could have a service running on my server that would read in necessary remote SQL info and file exports, to provide the user's application with a single database to connect to, as well as to remove all of the file handling currently involved in the program (copying new CSV resources from network location, reading them into memory each launch.) I have complete control and flexibility here as long as the user's experience isn't affected, and this is as much a learning experience as it is tidying up. Caveat being, I don't have much in the way of a budget. Right now I recognize my options to be: SQL Express - I'm comfortable with the server setup, I like ADO.NET and LINQ to SQL. I feel that I have the least to learn here, but it would let me focus on SQL in a familiar environment. Perhaps in conjunction with Entity Framework? MongoDB - I don't know a whole lot about, but I've heard the name enough to make me curious. Brief research seems friendly enough, and there is .NET support. I like working with open source projects. My questions are: What's popular and extensible right now? I'm not far from starting to job-hunt, and I'd like this project to be relevant going forward. What am I missing? Pros, cons? Other options? What plays well with .NET? What are the things I should be considering, the questions I should be asking, when making a decision like this? Thanks for your time.

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• Experience vs. versatility

  - by Florin Bombeanu

  Let's say a .NET programmer works at a company which provides software on demand, not as a product. The programmer works in WPF for a period of time and he/she invests lots of time in it. He/she get very good at WPF and Windows Forms and desktop development in general. But the company has to provide a web application now, so the developer has to learn MVC or Web Forms. He/she is not experienced in web development so he/she starts investing time in this new technology and in time they get good at it. But this time the company has to provide a Sharepoint solution, and so on. What is more important: Being very very good at a certain technology, Or be as versatile as possible knowing less in each technology but covering a greater area of expertise? Should the programmer keep studying and working in WPF until he/she reaches a guru level or is it a good thing that they had to learn other technologies as well? I agree with those of you who will say that when learning different technologies you will also learn things which are useful no matter the technology you're programming in. But eventually, when the programmer will want to change jobs, will it matter more that he/she knows some WPF, MVC or Sharepoint than the fact that he/she is insanely good at one of them? I would think the second one is more important since most companies are looking for a developer for a certain technology. I don't think there are many companies looking for technical know-it-all people. What do you think?

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• How is architectural design done in an agile environment?

  - by B?????

  I have read Principles for the Agile Architect, where they defined next principles : Principle #1 The teams that code the system design the system. Principle #2 Build the simplest architecture that can possibly work. Principle #3 When in doubt, code it out. Principle #4 They build it, they test it. Principle #5 The bigger the system, the longer the runway. Principle #6 System architecture is a role collaboration. Principle #7 There is no monopoly on innovation. The paper says that most of the architecture design is done during the coding phase, and only system design before that. That is fine. So, how is the system design done? Using UML? Or a document that defines interfaces and major blocks? Maybe something else?

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• Absolute beginner to app developement [closed]

  - by Andrew Johnston

  I have two app ideas that I am trying to build. I have started at the Facebook developement pages and done the Heroku/Git thing. However, I have absolutely no idea of what I am doing. When they say on the developer page: follow these quick easy steps Are they assuming that they are talking to a programmer/developer? I believe my apps have huge potential but I don't want to disclose my ideas. Any advice? I also would like to know how does one make money from Facebook applications?

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• OpenGL CPU vs. GPU

  - by Nitrex88

  So I've always been under the impression that doing work on the GPU is always faster than on the CPU. Because of this, in OpenGL, I usually try to do intensive tasks in shaders so they get the speed boost from the GPU. However, now I'm starting to realize that some things simply work better on the CPU and actually perform worse on the GPU (particularly when a geometry shader is involved). For example, in a recent project I did involving procedurally generated terrain, I tried passing a grid of single triangles into a geometry shader, and tesselated each of these triangles into quads with 400 vertices whose height was determined by a noise function. This worked fine, and looked great, but easily maxed out the GPU with only 25 base triangles and caused a very slow framerate. I then discovered that tesselating on the CPU instead, and setting the height (using noise function) in the vertex shader was actually faster! This prompted me to question the benefits of using the GPU as much as possible... So, I was wondering if someone could describe the general pros and cons of using the GPU vs CPU for intensive graphics tasks. I know this mainly comes down to what your trying to achieve, so if necessary, use the above scenario to discuss why the "CPU + vertex shader" was actually faster than doing everything in the geometry shader on the GPU. It's possible my hardware (newest macbook pro) isn't optomized well for the geometry shader (thus causing the slow framerate). Also, I read that the vertex shader is very good with parallelism, and would love a quick explanation of how this may have played a role in speeding up my procedural terrain. Any info/advice about CPU/GPU/shaders would be awesome!

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• How to implement a safe password history

  - by Lorenzo

  Passwords shouldn't be stored in plain text for obvious security reasons: you have to store hashes, and you should also generate the hash carefully to avoid rainbow table attacks. However, usually you have the requirement to store the last n passwords and to enforce minimal complexity and minimal change between the different passwords (to prevent the user from using a sequence like Password_1, Password_2, ..., Password_n). This would be trivial with plain text passwords, but how can you do that by storing only hashes? In other words: how it is possible to implement a safe password history mechanism?

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• Something confusing about Single Responsibility Principle

  - by user1483278

  1) In fact if two responsibilities are always expected to change at the same time you arguably should not separate them into different classes as this would lead, to quote Martin, to a "smell of Needless Complexity". The same is the case for responsibilities that never change - the behavior is invariant, and there is no need to split it. I assume even if non-related responsibilities are always expected to change for the same reason ( or if they never change ), we still shouldn't put them in the same class, since this would still violate high cohesion principle? 2) I've found two quite different definitions for SRP: Single Responsibility Principle says that a subsystem, module, class, or even a function, should not have more than one reason to change. and There should never be more than one reason for a class to change Doesn't the latter definition narrow SRP to a class level? If so, isn't first quote wrong by claiming that SRP can also be applied at subsystem, module and function levels? thank you

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• What simple techniques do you use to improve performance?

  - by Cristian

  I'm talking about the way we write simple routines in order to improve performance without making your code harder to read... for instance, this is the typical for we learned: for(int i = 0; i < collection.length(); i++ ){ // stuff here } But, I usually do this when a foreach is not applicable: for(int i = 0, j = collection.length(); i < j; i++ ){ // stuff here } I think this is a better approach since it will call the length method once only... my girlfriend says it's cryptic though. Is there any other simple trick you use on your own developments?

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• Should I ditch AJAX in client side web development when I've got a web-socket open?

  - by jt0dd

  I was thinking that maybe I should forget AJAX (HTTP) requests when I've got a web-socket open between client and server, but I decided I should ask here to check if this could be a bad practice for some reason that I'm not thinking of. Once the socket is open, there's less syntax (often meaning simpler error handling) involved in passing information between client and server with Socket.io (just one example of a web-socket). Is there some obvious situation where a web-socket (Socket.io for example) isn't going to be capable of handling a functionality that an AJAX request could do easily?

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• How to prepare for a programming competition? Graphs, Stacks, Trees, oh my! [closed]

  - by Simucal

  Last semester I attended ACM's (Association for Computing Machinery) bi-annual programming competition at a local University. My University sent 2 teams of 3 people and we competed amongst other schools in the mid-west. We got our butts kicked. You are given a packet with about 11 problems (1 problem per page) and you have 4 hours to solve as many as you can. They'll run your program you submit against a set of data and your output must match theirs exactly. In fact, the judging is automated for the most part. In any case.. I went there fairly confident in my programming skills and I left there feeling drained and weak. It was a terribly humbling experience. In 4 hours my team of 3 people completed only one of the problems. The top team completed 4 of them and took 1st place. The problems they asked were like no problems I have ever had to answer before. I later learned that in order to solve them some of them effectively you have to use graphs/graph algorithms, trees, stacks. Some of them were simply "greedy" algo's. My question is, how can I better prepare for this semesters programming competition so I don't leave there feeling like a complete moron? What tips do you have for me to be able to answer these problems that involve graphs, trees, various "well known" algorithms? How can I easily identify the algorithm we should implement for a given problem? I have yet to take Algorithm Design in school so I just feel a little out of my element. Here are some examples of the questions asked at the competitions: ACM Problem Sets Update: Just wanted to update this since the latest competition is over. My team placed 1st for our small region (about 6-7 universities with between 1-5 teams each school) and ~15th for the midwest! So, it is a marked improvement over last years performance for sure. We also had no graduate students on our team and after reviewing the rules we found out that many teams had several! So, that would be a pretty big advantage in my own opinion. Problems this semester ranged from about 1-2 "easy" problems (ie bit manipulation, string manipulation) to hard (graph problems involving fairly complex math and network flow problems). We were able to solve 4 problems in our 5 hours. Just wanted to thank everyone for the resources they provided here, we used them for our weekly team practices and it definitely helped! Some quick tips that I have that aren't suggested below: When you are seated at your computer before the competition starts, quickly type out various data structures that you might need that you won't have access to in your languages libraries. I typed out a Graph data-structure complete with floyd-warshall and dijkstra's algorithm before the competition began. We ended up using it in our 2nd problem that we solved and this is the main reason why we solved this problem before anyone else in the midwest. We had it ready to go from the beginning. Similarly, type out the code to read in a file since this will be required for every problem. Save this answer "template" someplace so you can quickly copy/paste it to your IDE at the beginning of each problem. There are no rules on programming anything before the competition starts so get any boilerplate code out the way. We found it useful to have one person who is on permanent whiteboard duty. This is usually the person who is best at math and at working out solutions to get a head start on future problems you will be doing. One person is on permanent programming duty. Your fastest/most skilled "programmer" (most familiar with the language). This will save debugging time also. The last person has several roles between assessing the packet of problems for the next "easiest" problem, helping the person on the whiteboard work out solutions and helping the person programming work out bugs/issues. This person needs to be flexible and be able to switch between roles easily.

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• Nearly technical books that you enjoyed reading

  - by pablo

  I've seen questions about "What books you recommend" in several of the Stack Exchange verticals. Perhaps these two questions (a and b) are the most popular. But, I'd like to ask for recommendations of a different kind of books. I have read in the past "The Passionate Programmer" and I am now reading "Coders at Work". Both of them I would argue that are almost a biography (or biographies in the "Coders at work") or even a bit of "self-help" book (that is more the case of the "Passionate programmer"). And please don't get me wrong. I loved reading the first one, and I am loving reading the second one. There's a lot of value in it, mostly in "lessons of the trade" kind of way. So, here is what I'd like to know. What other books that you read that are similar to these ones in intent that you enjoyed? Why?

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• Benchmarking CPU processing power

  - by Federico Zancan

  Provided that many tools for computers benchmarking are available already, I'd like to write my own, starting with processing power measurement. I'd like to write it in C under Linux, but other language alternatives are welcome. I thought starting from floating point operations per second, but it is just a hint. I also thought it'd be correct to keep track of CPU number of cores, RAM amount and the like, to more consistently associate results with CPU architecture. How would you proceed to the task of measuring CPU computing power? And on top of that: I would worry about a properly minimum workload induced by concurrently running services; is it correct to run benchmarking as a standalone (and possibly avulsed from the OS environment) process?

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• Large sparse (stiff) ODE system needed for testing

  - by macydanim

  I hope this is the right place for this question. I have been working on a sparse stiff implicit ODE solver and have finished the code so far. I now tested the solver with the Van der Pol equation, and another stiff problem, which is of dimension 4. But to perform better tests I am searching for a bigger system. I'm thinking of the order N = 100...1000, if possible stiff and sparse. Does anybody have an example I could use? I really don't know where to search.

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• How to fill certain application design learning "gaps"?

  - by e4rthdog

  In life it doesnt matter if you do one thing for 15 years. You will end up waking one day and asking stuff that are equal to "how do i walk?" :) My specific question is that as a new entrant to C# and OOP i am stepping into many little "details" that need to be addressed. Written a lot of code in VB.NET / cobol / simple php e.t.c surely does not help much into the OOP world... So , even after reading entry level books for C# and watching some videos i recently found out about the "factory model design" for applications. I would appreciate if any of you guys recomment some reading on application design architecture for further reading...

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• What is the oldest living piece of unaltered production code? [closed]

  - by user1598390

  It's come to my mind that parts of the code in, say, Unix, has maybe passed unaltered from one version or flavor into another. Maybe some pieces of the source code of the ls command is the same, unaltered, than was written years ago. Have any of you read or learn about this ? What would be the oldest living piece of unaltered production code still running, passing from version through version of a program or system ? Will the code we write outlive us for decades ?

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• Reuse the data CRUD methods in data access layer, but they are updated too quickly

  - by ValidfroM

  I agree that we should put CRUD methods in a data access layer, However, in my current project I have some issues. It is a legacy system, and there are quite a lot CRUD methods in some concrete manager classes. People including me seem to just add new methods to it, rather than reuse the existing methods. Because We don't know whether the existing method is what we need Even if we have source code, do we really need read other's code then make decision? It is updated too quickly. Do not have time get familiar with the DAO API. Back to the question, how do you solve that in your project? If we say "reuse", it really needs to be reusable rather than just an excuse.

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• I'm a CS student, and honestly I don't understand Knuth's books..

  - by Raymond Ho

  I stumbled this quote from Bill Gates: "You should definitely send me a resume if you can read the whole thing." He was talking about The Art of Programming books.. So I was pretty curious and want to read it all but honestly, I don't understand it at all.. I'm really not that highly intellectual being.. So this should be the reason why I can't understand it, but I am eager to learn.. I'm currently reading volume 1 about fundamental algo.. So is there any books out there that are friendly to novice/slow people like me? So I can build up myself and hopefully in the future I can read Knuth's book at ease..

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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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• what's included in a typical computer architecture class? [closed]

  - by sq1020

  Does this description fit what's usually included in a computer architecture class? Computer Organization and Assembly Language An introduction to the hardware organization and assembly language of the Intel processor. Topics include memory hierarchy and design- CPU design- pipelining- addressing modes- subroutine linkage- polled input/output- interrupts- high level language interfacing and macros.

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• Switch vs Polymorphism when dealing with model and view

  - by Raphael Oliveira

  I can't figure out a better solution to my problem. I have a view controller that presents a list of elements. Those elements are models that can be an instance of B, C, D, etc and inherit from A. So in that view controller, each item should go to a different screen of the application and pass some data when the user select one of them. The two alternatives that comes to my mind are (please ignore the syntax, it is not a specific language) 1) switch (I know that sucks) //inside the view controller void onClickItem(int index) { A a = items.get(index); switch(a.type) { case b: B b = (B)a; go to screen X; x.v1 = b.v1; // fill X with b data x.v2 = b.v2; case c: go to screen Y; etc... } } 2) polymorphism //inside the view controller void onClickItem(int index) { A a = items.get(index); Screen s = new (a.getDestinationScreen()); //ignore the syntax s.v1 = a.v1; // fill s with information about A s.v2 = a.v2; show(s); } //inside B Class getDestinationScreen(void) { return Class(X); } //inside C Class getDestinationScreen(void) { return Class(Y); } My problem with solution 2 is that since B, C, D, etc are models, they shouldn't know about view related stuff. Or should they in that case?

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• TypeScript or JavaScript for noob web developer [closed]

  - by Phil Murray

  Following the recent release by Microsoft of TypeScript I was wondering if this is something that should be considered for a experienced WinForm and XAML developer looking to get into more web development. From reviewing a number of sites and videos online it appears that the type system for TypeScript makes more sense to me as a thick client developer than the dynamic type system in Javascript. I understand that Typescript compiles down to JavaScript but it appears that the learning curve is shallower due to the current tooling provided by Microsoft. What are your thoughts?

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• Changing from Frontend Development to .Net

  - by Ivo

  On of my colleagues is going to change jobs from full time frontend developer(jquery, css,html) to 50% frontend 50% .Net (MVC 3 with razor) What are good techniques to get him up to speed asap. I have the following idea's myself Read Clean Code Read/Pratice with the book Pro ASP.NET MVC 3 Framework Watch Asp.net video's http://www.asp.net/mvc/videos Do the nerd dinner intro http://www.asp.net/mvc/videos Start building the json services from jQuery 0.5/1 day of pair programming with an experienced .Net developer each week Is this a good way to go? Is it totally wrong? Any other tips

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• Imitating Exchange Server's "RBAC AuthZ" in my own application... (is there something similar?)

  - by makerofthings7

  Exchange 2010 has a delegation model where groups of winrm cmdlets are essentally grouped into roles, and the roles assigned to a user. (Image source) This is a great & flexible model considering how I can leverage all the benefits of PowerShell, while using the right low level technologies (WCF, SOAP etc), and requiring no additional software on the client side. (Image source) Question(s) Is there a way for me to leverage Exchange's delegation model in my .NET application? Has anyone attempted to imitate this model? If I must start from scratch, how would I go about imitating this approach?

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