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• TDD and UML together

  - by uther-lightbringer

  Hello, I'm new to TDD approach so I'm wondering if anyone experienced wit this could enlighten me a little. I would like to get some leads how to use UML and TDD methodology together. I've been used to: Design with UML -- Generate skeleton classes (and then keep it synchronized) - Implement and finally Test. I must admit that testing part was the worst one, so I started to look for something else - TDD. So I have some general knowledge what is it about but before I proceed further, I am interested knowing how it goes together with software design especially UML. So when I first design/create test, how can UML fit in? Would it be possible to design classes first, from them create skeleton classes, from them generate Unit tests which would be "filled" before actual implementation of UML pregenerated classes, would this approach break whole TDD? Or is there any other way that would keep UML and TDD together? Thanks everyone for answer.

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• Interview question: f(f(n)) == -n

  - by Hrvoje Prgeša

  A question I got on my last interview: Design a function f, such that: f(f(n)) == -n Where n is a 32 bit signed integer; you can't use complex numbers arithmetic. If you can't design such a function for the whole range of numbers, design it for the largest range possible. Any ideas?

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• Web application vs. linux multiuser application

  - by Eugene

  I have a web-based bussines application written in C#/ASP.NET Recently my boss start pushing to re-write the app as Linux multi-user desktop application. In his design users will need to connect to Linux server via VNC or alike to use the app. I am not familiar with this kind of application design. I'd appretiate any help explainig pros and cons of this approach vs. web and perhaps vs. traditional client-server design Thank you

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• jQuery featured content slider

  - by azz0r

  Hello, I have a content area that loops through divs and shows there content. I'm having trouble making it display the initial content, unfortunately it waits 5000 milliseconds before triggering the very first content area to display. Anyone spot an easy way to make it display the initial area, then slide to the next area and do them at 5000 milliseconds. JS Model.FeatureBar = { current:0, items:{}, init: function init(options){ var me = this; me.triggers = [] me.slides = [] this.container = jQuery('#features'); jQuery('.feature').each(function(i){ me.triggers[i] = {url: jQuery(this).children('.feature-title a').href, title: jQuery(this).children('.feature-title'),description:jQuery(this).children('.feature-description')} me.slides[i] = {image: jQuery(this).children('.feature-image')} }); for(var i in this.slides){ this.slides[i].image.hide(); this.triggers[i].description.hide(); } setInterval(function(){Model.FeatureBar.next()},5000); }, next: function next(){ var i = (this.current+1 < this.triggers.length) ? this.current+1 : 0; this.goToItem(i); }, previous: function previous(){ var i = (this.current-1 > 1) ? this.current-1 : this.triggers.length; this.goToItem(i); }, goToItem: function goToItem(i){ if(!this.slides[i]) throw 'Slide out of range'; this.triggers[this.current].description.slideUp(); this.triggers[i].description.slideDown(); this.slides[this.current].image.hide(); this.slides[i].image.show(); this.current = i; }, } html <div id="features"> <div class="feature current"> <div class="movie-cover"> <a href="/police/movie"><img title="" alt="" src="/design/images/four-oh-four.png"></a> </div> <div class="feature-image" style="display: none;"> <img src="/design/images/four-oh-four.png"> </div> <h2 class="feature-title"><a href="/police/movie">Police</a></h2> <p class="feature-description" style="overflow: hidden; display: block; height: 50.8604px; margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;">DESCRIPTION</p> </div> <div class="feature"> <div class="movie-cover"> <a href="/rude/movie"><img title="" alt="" src="/design/images/four-oh-four.png"></a> </div> <div class="feature-image" style="display: none;"> <img src="/design/images/four-oh-four.png"> </div> <h2 class="feature-title"><a href="/rude/movie">Rude</a></h2> <p class="feature-description" style="overflow: hidden; display: block; height: 18.3475px; margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;">DESCRIPTION</p> </div> <div class="feature"> <div class="movie-cover"> <a href="/brits/movie"><img title="" alt="" src="/design/images/four-oh-four.png"></a> </div> <div class="feature-image" style="display: block;"> <img src="/design/images/four-oh-four.png"> </div> <h2 class="feature-title"><a href="/brits/movie">Brits</a></h2> <p class="feature-description" style="overflow: hidden; display: block; height: 40.1549px; margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;">DESCRIPTION</p> </div> <div class="feature"> <div class="movie-cover"> <a href="/indie/movie"><img title="" alt="" src="/design/images/four-oh-four.png"></a> </div> <div class="feature-image" style="display: none;"> <img src="/design/images/four-oh-four.png"> </div> <h2 class="feature-title"><a href="/indie/movie">Indie</a></h2> <p class="feature-description" style="overflow: hidden; display: block; height: 42.4247px; margin-top: 0px; margin-bottom: 0px; padding-top: 0px; padding-bottom: 0px;">DESCRIPTION</p> </div>

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• How to Software Service Industry get their Client from or where do they look for their Clients ?

  - by Rachel

  This question is inclined more towards Business Side of Software Industry, I am sure that we have two types in Software Industry as with any other Industry, i.e, Service side and Product Side. Basically for Product based company, we are looking more into product features and to see if market if mature or not for particular product but as far as Service Based company goes (may be it can be big giants like Infosys, TCS or Sapient or some midsize or small companies which provide services like:Web Design,Website Design,Corporate Identity,Logo Design,Flash Design,Web Applications,Enterprise Portal,Rich Internet Applications,Business Applications,Technology Consulting,Ecommerce,Online Store Creations,Custom Shopping Carts,Ecommerce Hosting,Website Marketing,Organic SEO,Pay-Per-Click,Social Media Optimization,Mobile,Mobile Website and Mobile Applications) where do they look for Client and how do they manage to get one ? So my basic question is Where do Service Based Companies Look for Client or get their Clients Form ?

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• Select a particular column using awk or cut or perl

  - by javed abbas

  Have a requirement to select the 7th column. eg: cat filename | awk '{print $7}' The issue is that the data in the 4th column has multiple values with blank in between. example - The last line in the below output: user \Adminis FL_vol Design 0 - 1 - group 0 FL_vol Design 19324481 - 3014 - user \MAK FL_vol Design 16875161 - 2618 - tree 826 FL_vol Out Global Doc Mark 16875162 - 9618 - /vol/FL_vol/Out Global Doc Mark

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• How to Generate the .Form file using .java file in swings

  - by vamshikpd

  Hi all, I am using SunJavaStudio Enterprise 8 and Swing frame work In swing, In My source folder, I have Demo.java and Demo.form file. Demo.form file is the Design file. If both files in the Source folder,java file shows source and design view in IDE. If I delete the Demo.form in source folder,The Design view doesn't show. I have only Demo.java file,How can i generate the Demo.form ? please can u help me urgent

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• Sharing the same file between different projects

  - by selsine

  Hi Everyone, For version control we currently use Visual Source Safe and are thinking of migrating to another version control system (SVN, Mercurial, Git). Currently we use Visual Source Safe's "Shared" file feature quite heavily. This allows us to share code between design and runtimes of a single product, and between multiple products as well. For example: **Product One** - Design Login.cpp Login.h Helper.cpp Helper.h - Runtime Login.cpp Login.h Helper.cpp Helper.h **Product Two** - Design Login.cpp Login.h - Launcher Login.cpp Login.h - Runtime Login.cpp Login.h In this example Login.cpp and Login.h contain common code that all of our projects need, Helper.cpp and Helper.h is only used in Product One. In Visual Source Safe they are shared between the specific projects, which means that whenever the files are updated in one project they are updated in any project they are shared with. This is a simple example but hopefully it explains why we use the shared feature: to reduce the amount of duplicated code and ensure that when a bug is fixed all projects automatically have access to the new fixed code. After researching alternatives to Visual Source Safe it seems that most version control systems do not have the idea of shared files, instead they seem to use the idea of sub repositories. (http://mercurial.selenic.com/wiki/subrepos http://svnbook.red-bean.com/en/1.0/ch07s03.html) My question (after all of that) is about what the best practices for achieving this are using other version control systems? Should we restructure our projects so that two copies of the files do not exist and an include directory is used instead? e.g. Product One Design Login.cpp Login.h Runtime Login.cpp Login.h Common Helper.cpp Helper.h This still leaves what to do with Login.cpp and Logon.h Should the shared files be moved to their own repository and then compiled into a lib or dll? This would make bug fixing more time consuming as the lib projects would have to be edited and then rebuilt. Should we use externals or sub repositories? Should we combine our projects (i.e. runtime, design, and launcher) into one large project? Any help would be appreciated. We have the feeling that our project design has evolved based on the tools that we used and now that we are thinking of switching tools it's difficult for us to see how we can best modify our practices. Or maybe we are the only people are there doing this...? Also, we use Visual Studio for all of our stuff. Thanks.

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• Easily digestible UI tips for developers

  - by David

  What are some key UI design tips that every developer should know? While there are a number of UI resources for developers (for example, Joel Spolsky's User Interface Design for Programmers), I'm interested in more of a bullet list that can be communicated in 1 to 2 pages. I'm interested in more tactical, day-to-day UI tips, as opposed to overarching UI design goals that would be covered in a UI design meeting (presumably attended by at least one person with a good UI sense). A collection of these tips might cover about 80% of the cases that an everyday programmer would come across.

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• Controls on main window using Visual C++ designer?

  - by PatrickBateman

  Is is possible to draw controls using Visual C++ designer on the main window, in the same way you can design dialogs? I'd preferably like to be able to design the main window controls this way without using MFC, rather than creating them on WM_CREATE. EDIT: I don't want a dialog-based app, just to be able to design the main window graphically similar to what can be done using Windows Forms Designer in .NET?

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• Designing for varying mobile device resolutions, i.e. iPhone 4 & iPhone 3G

  - by Josh

  As the design community moves to design applications & interfaces for mobile devices, a new problem has arisen: Varying Screen DPI's. Here's the situation: Touch: * iPhone 3G/S ~ 160 dpi * iPhone 4 ~ 300 dpi * iPad ~ 126 dpi * Android device @ 480p ~ 200 dpi Point / click: * Laptop @ 720p ~ 96 dpi * Desktop @ 720p ~ 72 dpi There is certainly a clear distinction between desktop and mobile so having two separate front-ends to the same app is logical, especially when considering one is "touch"-based and the other is "point/click"-based. The challenge lies in designing static graphical elements that will scale between, say, 160 dpi and 300+ dpi, and get consistent and clean design across zoom levels. Any thoughts on how to approach this? Here are some scenarios, but each has drawbacks as well: * Design a single set of assets (high resolution), then adjust zoom levels based on detected resolution / device o Drawbacks: Performance caused by code layering, varying device support of Zoom * Develop & optimize multiple variations of image and CSS assets, then hide / show each based on device o Drawbacks: Extra work in design & QA. Anyone have thoughts or experience on how to deal with this? We should certainly be looking at methods that use / support HTML5 and CSS3.

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• How to change the default "double click" action of a web service in a class library (VS2010)?

  - by JL

  I have a web service defined as follows, residing in a class library: [WebService(Namespace = "http://comp.com/")] [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)] // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. // [System.Web.Script.Services.ScriptService] public class SendingItems_new : System.Web.Services.WebService When I double click it, instead of going to code view, it shows the design view. I NEVER use design view, so how can I get it to open up code view instead, its very annoying having to flick from design view each time. Thank you

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• How does braking assist of car racing games work?

  - by Ayush Khemka

  There are a lot of PC car racing games around which have this unique driving assist which helps brake your car so that you can safely turn it. While in some games it just an 'assist', it will just help your car brake but won't ensure a safe turn. While in others, the braking assist will help you get a safe turn. I was wondering on what could be the algorithm that is followed to achieve it. A very basic algorithm I could think of was, Pre-determine the braking distance of an ideal car for every turn of the track, depending on the radius of the turn, and then start braking the car accordingly. For example, for a turn of less than 90o, the car would start braking automatically at 50m distance from the start of the turn. A more advanced algorithm, which would ensure a safe turn, could be Pre-determine the speed of the car at the start of each turn, individually for each track, turn and car. Also, pre-determine the deceleration rate of each car individually, which varies because of the car's performance. The braking assist would keep recording the speed of the car at a certain instant of time. Start braking the car appropriately so that the car gets to the exact speed needed at the start of the turn. For example, let the speed of a particular car at the start of a turn 43m in radius, be 120km/h. Let the deceleration rate of the car be 200km/h2. If, at some instant of time, the speed of the car is 200km/h, then the car would automatically start braking at 400m from the start of the turn.

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• Is it illegal to rewrite every line of an open source project in a slightly different way, and use it in a closed source project?

  - by Chris Barry

  There is some code which is GPL or LGPL that I am considering using for an iPhone project. If I took that code (JavaScript) and rewrote it in a different language for use on the iPhone would that be a legal issue? In theory the process that has happened is that I have gone through each line of the project, learnt what it is doing, and then reimplemented the ideas in a new language. To me it seems this is like learning how to implement something, but then reimplementing it separately from the original licence. Therefore you have only copied the algorithm, which arguably you could have learnt from somewhere else other than the original project. Does the licence cover the specific implementation or the algorithm as well? EDIT------ Really glad to see this topic create a good conversation. To give a bit more backing to the project, the code involved does some kind of audio analysis. I believe it is non-trivial to learn or implement, although I was prepared to embark on this task (I'm at the level where I can implement an FFT algorithm, and this was going to go beyond that.) It is a fairly low LOC script, so I didn't think it would be too hard to do a straight port. I really like the idea of rereleasing my port as well as using it in the application. I don't see any problem with that, and it would be a great way to give something back to the community. I was going to add a line about not wanting to discuss the moral issues, but I'm quite glad I didn't as it seems to have fired the debate a bit. I still feel a bit odd about using open source code to learn from. Does this mean that anything one learns from an open source project is not allowed to be used in a closed source project? And how long after or different does an implementation have to be to not be considered violation of the licence? Murky! EDIT 2 -------- Follow up question

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• How to find the average color of an image.

  - by Edward Boyle

  Years ago I was the lead developer of a large Scrapbook Web Site. One of the things I implemented was to allow shoppers to find Scrapbook papers and embellishments of like colors (“more like this color”). Below is the base algorithm I wrote to extract the color from an image. It worked out pretty well. I took the returned values and stored them in an associated table for the products. Yet another algorithm was used to SELECT near matches. This algorithm has turned out to be very handy for me. I have used it for borders and subtle outlined text overlays. I am sure you will find more creative uses for it. Enjoy… private Color GetColor(Bitmap bmp) { int r = 0; int g = 0; int b = 0; Color mColor = System.Drawing.Color.White; for (int i = 1; i < bmp.Width; i++) { for (int x = 1; x < bmp.Height; x++) { mColor = bmp.GetPixel(i, x); r += mColor.R; g += mColor.G; b += mColor.B; } } r = (r / (bmp.Height * bmp.Width)); g = (g / (bmp.Height * bmp.Width)); b = (b / (bmp.Height * bmp.Width)); return System.Drawing.Color.FromArgb(r, g, b); } You could also get the RGB values by passing in the RGB by ref private Color GetColor(ref int r, ref int g, ref int b, Bitmap bmp) but that is a bit much as you can simply get it from the return value: mReturnedColor.R; mReturnedColor.G; mReturnedColor.B;

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• Continuous Physics Engine's Collision Detection Techniques

  - by Griffin

  I'm working on a purely continuous physics engine, and I need to choose algorithms for broad and narrow phase collision detection. "Purely continuous" means I never do intersection tests, but instead want to find ways to catch every collision before it happens, and put each into "planned collisions" stack that is ordered by TOI. Broad Phase The only continuous broad-phase method I can think of is encasing each body in a circle and testing if each circle will ever overlap another. This seems horribly inefficient however, and lacks any culling. I have no idea what continuous analogs might exist for today's discrete collision culling methods such as quad-trees either. How might I go about preventing inappropriate and pointless broad test's such as a discrete engine does? Narrow Phase I've managed to adapt the narrow SAT to a continuous check rather than discrete, but I'm sure there's other better algorithms out there in papers or sites you guys might have come across. What various fast or accurate algorithm's do you suggest I use and what are the advantages / disatvantages of each? Final Note: I say techniques and not algorithms because I have not yet decided on how I will store different polygons which might be concave, convex, round, or even have holes. I plan to make a decision on this based on what the algorithm requires (for instance if I choose an algorithm that breaks down a polygon into triangles or convex shapes I will simply store the polygon data in this form).

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• ADDS: 1 - Introducing and designing

  - by marc dekeyser

  Normal 0 false false false EN-GB X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} What is ADDS?  Every Microsoft oriented infrastructure in today's enterprises will depend largely on the active directory version built by Microsoft. It is the foundation stone on which all other products (Exchange, update services, office communicator, the system center family, etc) rely on to get their information. And that is just looking at it from an infrastructure perspective. A well designed and implemented Active Directory implementation makes life for IT personnel and user alike a lot easier. Centralised management and the abilities opened up  by having it in place are ample.  But what is Active Directory Domain Services? We can look at ADDS as a centralised directory containing all objects your infrastructure runs on in one way or another. Since it is a Microsoft product you'll obviously not be seeing linux or mac clients listed in here (exceptions exist) but in general we can say it contains everything your company has in place in one form or another.  The domain name services. The domain naming service (or DNS for short) is a service which translates IP address (the identifiers for each computer in your domain) into readable and easy to understand names. This service is a prequisite for ADDA to work and having wrong record in a DNS server will make any ADDS service fail. Generally speaking a DNS service will be run on the same server as the ADDS service but it is worth wile to remember that this is not necessary. You could, for example, run your DNS services on a linux box (which would need special preparing to host an ADDS integrated DNS zone) and run the ADDS service of another box… Where to start? If the aim is to put in place a first time implementation of ADDS in your enterprise there are plenty of things to consider depending on what you are going to do in the long run. Great care has to be taken when first designing and implementing as having it set up wrong will cause a headache down the line. It is for that reason that I like to start building from the bottom up and start with a generic installation of ADDS (which will still differ for every client) and make it adaptable for future services which can hook in to the existing environment. Adapting existing environments is out of scope for this document (and series) although it is possible to take the pointers and change your existing environment to run in a smoother manor. Take great care when changing things as one small slip of the hand can give you a forest wide failure… Whenever starting with an ADDS deployment I ask the client the following questions:  What are your long term plans and goals?  How flexible do you want it? Are you currently linux heavy and want to keep this or can we go for an all Microsoft design? Those three questions should give some sort of indicator what direction can be taken and if the client has thought about some things themselves :).  The technical side of things  What is next to consider is what kind of infrastructure is already in place. For these series I'll keep it simple and introduce some general concepts without going in to depth on integrating ADDS with other DNS services.  Building from the ground up means we need to consider our layers on which our infrastructure will rely. In my view that goes as follows:  Network (WAN/LAN links and physical sites DNS Namespacing All in one domain or split up in different domains/forests? Security (both for ADDS and physical sites) The network side of things  Looking at how the network is currently set up can potentially teach us a large deal about the client. Do they have multiple physical site? What network speeds exist between these sites, etc… Depending on this information we will design our site links (which controls replication) in future stages. DNS Namespacing Maybe the single most intresting thing to know is what the domain will be named (ADDS will need a DNS domain with the same name) and where this will be hosted. Note that active directory can be set up with a singe name (aka contoso instead of contoso.com) but it is highly recommended to never do this. If you do end up with a domain like that for some reason there will be a lot of services that are going to give you good grief in the future (exchange being one of them). So one of the best practises would be always to use a double name (contoso.com or contoso.lan for example). Internal namespace A single namespace is just what it sounds like. You have a DNS domain which is different internally from what the client has as an external namespace. f.e. contoso.com as an external name (out on the internet) and contoso.lan on the internal network. his setup is has its advantages in that you have more obscurity from the internet in the DNS side of this but it will require additional work to publish services to the web. External namespace Quite like the internal namespace only here you do not differ the internal namespace of the company from what is known on the internet. In this implementation you would host your own DNS servers for the external domain inside the network. Or in other words, any external computer doing a DNS lookup would contact your internal DNS server for the resolution. Generally speaking this set up is a bad idea from the security side of things. Split DNS Whilst using an external namespace design is fairly easy it involves a lot of security risks. Opening up you ADDS DSN servers for lookups exposes your entire network to the internet and should be avoided at any cost. And that is where the "split DNS" design comes in. In this setup up would still have the same namespace internally and externally but you would be using different DNS servers for lookups on the external network who have no records of your internal resources unless you explicitly publish them. All in one or not? In determining your active directory design you can look at the following possibilities:  Single forest, Single domain Single forest, multiple domains Multiple forests, multiple domains I've listed the possibilities for design in increasing order of administrative magnitude. Microsoft recommends trying to use a single forest, single domain in as much situations as possible. It is, however, always possible that you require your services to be seperated from your users in a resource forest with trusts set up between the different forests. To start out I would go with the single forest design to avoid complexity unless there are strict requirements to have multiple forests. Security What kind of security is required on the domain and does this reflect the physical security on the sites? Not every client can afford to have a domain controller in a secluded server room on every site and it is exactly for that reason that Microsoft introduced the RODC (read only domain controller). A RODC is a domain controller that has been limited in functionality, in essence it will only cache the data you explicitly tell it to cache and in the case of a DC compromise (it being stolen) only a limited number of accounts will need to be affected. Th- Th- Th- That’s all folks! Well at least for now! In future editions of this series we’ll be walking through the different task that need to be done and the thought which needs to be put in to it. But for all editions we’ll be going from the concept of running a single forest, single domain with a split DNS setup… See you next time!

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• How to practice object oriented programming?

  - by user1620696

  I've always programmed in procedural languages and currently I'm moving towards object orientation. The main problem I've faced is that I can't see a way to practice object orientation in an effective way. I'll explain my point. When I've learned PHP and C it was pretty easy to practice: it was just matter of choosing something and thinking about an algorithm for that thing. In PHP for example, it was matter os sitting down and thinking: "well, just to practice, let me build one application with an administration area where people can add products". This was pretty easy, it was matter of thinking of an algorithm to register some user, to login the user, and to add the products. Combining these with PHP features, it was a good way to practice. Now, in object orientation we have lots of additional things. It's not just a matter of thinking about an algorithm, but analysing requirements deeper, writing use cases, figuring out class diagrams, properties and methods, setting up dependency injection and lots of things. The main point is that in the way I've been learning object orientation it seems that a good design is crucial, while in procedural languages one vague idea was enough. I'm not saying that in procedural languages we can write good software without design, just that for sake of practicing it is feasible, while in object orientation it seems not feasible to go without a good design, even for practicing. This seems to be a problem, because if each time I'm going to practice I need to figure out tons of requirements, use cases and so on, it seems to become not a good way to become better at object orientation, because this requires me to have one whole idea for an app everytime I'm going to practice. Because of that, what's a good way to practice object orientation?

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• In the days of modern computing, in 'typical business apps' - why does performance matter?

  - by Prog

  This may seem like an odd question to some of you. I'm a hobbyist Java programmer. I have developed several games, an AI program that creates music, another program for painting, and similar stuff. This is to tell you that I have an experience in programming, but not in professional development of business applications. I see a lot of talk on this site about performance. People often debate what would be the most efficient algorithm in C# to perform a task, or why Python is slow and Java is faster, etc. What I'm trying to understand is: why does this matter? There are specific areas of computing where I see why performance matters: games, where tens of thousands of computations are happening every second in a constant-update loop, or low level systems which other programs rely on, such as OSs and VMs, etc. But for the normal, typical high-level business app, why does performance matter? I can understand why it used to matter, decades ago. Computers were much slower and had much less memory, so you had to think carefully about these things. But today, we have so much memory to spare and computers are so fast: does it actually matter if a particular Java algorithm is O(n^2)? Will it actually make a difference for the end users of this typical business app? When you press a GUI button in a typical business app, and behind the scenes it invokes an O(n^2) algorithm, in these days of modern computing - do you actually feel the inefficiency? My question is split in two: In practice, today does performance matter in a typical normal business program? If it does, please give me real-world examples of places in such an application, where performance and optimizations are important.

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• Automatic Appointment Conflict Resolution

  - by Thomas

  I'm trying to figure out an algorithm for resolving appointment times. I currently have a naive algorithm that pushes down conflicting appointments repeatedly, until there are no more appointments. # The appointment list is always sorted on start time appointment_list = [ <Appointment: 10:00 -> 12:00>, <Appointment: 11:00 -> 12:30>, <Appointment: 13:00 -> 14:00>, <Appointment: 13:30 -> 14:30>, ] Constraints are that appointments: cannot be after 15:00 cannot be before 9:00 This is the naive algorithm for i, app in enumerate(appointment_list): for possible_conflict in appointment_list[i+1:]: if possible_conflict.start < app.end: difference = app.end - possible_conflict.start possible_conflict.end += difference possible_conflict.start += difference else: break This results in the following resolution, which obviously breaks those constraints, and the last appointment will have to be pushed to the following day. appointment_list = [ <Appointment: 10:00 -> 12:00>, <Appointment: 12:00 -> 13:30>, <Appointment: 13:30 -> 14:30>, <Appointment: 14:30 -> 15:30>, ] Obviously this is sub-optimal, It performs 3 appointment moves when the confict could have been resolved with one: if we were able to push the first appointment backwards, we could avoid moving all the subsequent appointments down. I'm thinking that there should be a sort of edit-distance approach that would calculate the least number of appointments that should be moved in order to resolve the scheduling conflict, but I can't get the a handle on the methodology. Should it be breadth-first or depth first solution search. When do I know if the solution is "good enough"?

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• Obstacle Avoidance steering behavior: how can an entity avoid an obstacle while other forces are acting on the entity?

  - by Prog

  I'm trying to implement the Obstacle Avoidance steering behavior in my 2D game. Currently my approach is to apply a force on the entity, in the direction of the normal of the heading, scaled by a number that gets bigger the closer we are to the obstacle. This is supposed to push the entity to the side and avoid the obstacle that blocks it's way. However, in the same time that my entity tries to avoid an obstacle, it Seeks to a point more or less behind the obstacle (which is the reason it needs to avoid the obstacle in the first place). The Seek algorithm constantly applies a force on the entity that pushes it (more or less) in the direction of the obstacle, while the Obstacle Avoidance algorithm constantly applies a force that pushes the entity away (more accurately, to the side) of the obstacle. The result is that sometimes the entity succesfully avoids the obstacle, and sometimes it collides with it, depending on the strength of the avoidance force I'm applying. How can I make sure that a force will succeed in steering the entity in some direction, while other forces are currently acting on the entity? (And while still looking natural). I can't allow entities to collide with obstacles when realistically they should be able to easily avoid them, doesn't matter what they're currently doing. Also, the Obstacle Avoidance algorithm is made exactly for the case where another force is acting on the entity. Otherwise it wouldn't be moving and there would be no need to avoid anything. So maybe I'm missing something. Thanks

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• Finding header files

  - by rwallace

  A C or C++ compiler looks for header files using a strict set of rules: relative to the directory of the including file (if "" was used), then along the specified and default include paths, fail if still not found. An ancillary tool such as a code analyzer (which I'm currently working on) has different requirements: it may for a number of reasons not have the benefit of the setup performed by a complex build process, and have to make the best of what it is given. In other words, it may find a header file not present in the include paths it knows, and have to take its best shot at finding the file itself. I'm currently thinking of using the following algorithm: Start in the directory of the including file. Is the header file found in the current directory or any subdirectory thereof? If so, done. If we are at the root directory, the file doesn't seem to be present on this machine, so skip it. Otherwise move to the parent of the current directory and go to step 2. Is this the best algorithm to use? In particular, does anyone know of any case where a different algorithm would work better?

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• Mechanics of reasoning during programming interviews

  - by user129506

  This is not the usual "I don't want to write code during an interview", in this question the assumption is that I need to write code during an interview (think about the level of rewriting the quicksort or mergesort from scratch) I know how the algorithm work or I have a basic idea of how I should start working from there, i.e. I don't remember the algorithm by heart I noticed that even on a whiteboard, I always end up writing bugged code or code that doesn't compile. If there's a typo, whatever I usually live with that.. but when there's a crash due to some uncaught particular case I end up losing confidence in my skills. I realize that perhaps interviewers might want to look at how I write code and/or how I solve problems rather than proof-compiling my whiteboard code, but I'd like to ask how should I approach the above problem in mental terms, i.e. what mental steps should I follow when writing code for an interview with the two bullet points above. There must be a unique and agreed series of steps I should follow to avoid getting stuck/caught into particular exception cases (limit cases) that might end up wasting my time and my energies rather than focusing on the overall algorithm for the general case. I hope I made my point clear

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• Approach to Authenticate Clients to TCP Server

  - by dab

  I'm writing a Server/Client application where clients will connect to the server. What I want to do, is make sure that the client connecting to the server is actually using my protocol and I can "trust" the data being sent from the client to the server. What I thought about doing is creating a sort of hash on the client's machine that follows a particular algorithm. What I did in a previous version was took their IP address, the client version, and a few other attributes of the client and sent it as a calculated hash to the server, who then took their IP, and the version of the protocol the client claimed to be using, and calculated that number to see if they matched. This works ok until you get clients that connect from within a router environment where their internal IP is different from their external IP. My fix for this was to pass the client's internal IP used to calculate this hash with the authentication protocol. My fear is this approach is not secure enough. Since I'm passing the data used to create the "auth hash". Here's an example of what I'm talking about: Client IP: 192.168.1.10, Version: 2.4.5.2 hash = 2*4*5*1 * (1+9+2) * (1+6+8) * (1) * (1+0) Client Connects to Server client sends: auth hash ip version Server calculates that info, and accepts or denies the hash. Before I go and come up with another algorithm to prove a client can provide data a server (or use this existing algorithm), I was wondering if there are any existing, proven, and secure systems out there for generating a hash that both sides can generate with general knowledge. The server won't know about the client until the very first connection is established. The protocol's intent is to manage a network of clients who will be contributing data to the server periodically. New clients will be added simply by connecting the client to the server and "registering" with the server. So a client connects to the server for the first time, and registers their info (mac address or some other kind of unique computer identifier), then when they connect again, the server will recognize that client as a previous person and associate them with their data in the database.

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• How do I do high quality scaling of a image?

  - by pbhogan

  I'm writing some code to scale a 32 bit RGBA image in C/C++. I have written a few attempts that have been somewhat successful, but they're slow and most importantly the quality of the sized image is not acceptable. I compared the same image scaled by OpenGL (i.e. my video card) and my routine and it's miles apart in quality. I've Google Code Searched, scoured source trees of anything I thought would shed some light (SDL, Allegro, wxWidgets, CxImage, GD, ImageMagick, etc.) but usually their code is either convoluted and scattered all over the place or riddled with assembler and little or no comments. I've also read multiple articles on Wikipedia and elsewhere, and I'm just not finding a clear explanation of what I need. I understand the basic concepts of interpolation and sampling, but I'm struggling to get the algorithm right. I do NOT want to rely on an external library for one routine and have to convert to their image format and back. Besides, I'd like to know how to do it myself anyway. :) I have seen a similar question asked on stack overflow before, but it wasn't really answered in this way, but I'm hoping there's someone out there who can help nudge me in the right direction. Maybe point me to some articles or pseudo code... anything to help me learn and do. Here's what I'm looking for: 1. No assembler (I'm writing very portable code for multiple processor types). 2. No dependencies on external libraries. 3. I am primarily concerned with scaling DOWN, but will also need to write a scale up routine later. 4. Quality of the result and clarity of the algorithm is most important (I can optimize it later). My routine essentially takes the following form: DrawScaled( uint32 *src, uint32 *dst, src_x, src_y, src_w, src_h, dst_x, dst_y, dst_w, dst_h ); Thanks! UPDATE: To clarify, I need something more advanced than a box resample for downscaling which blurs the image too much. I suspect what I want is some kind of bicubic (or other) filter that is somewhat the reverse to a bicubic upscaling algorithm (i.e. each destination pixel is computed from all contributing source pixels combined with a weighting algorithm that keeps things sharp. EXAMPLE: Here's an example of what I'm getting from the wxWidgets BoxResample algorithm vs. what I want on a 256x256 bitmap scaled to 55x55. And finally: the original 256x256 image

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