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• What is the difference between all-static-methods and applying a singleton pattern?

  - by shahensha

  I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. regards shahensha P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

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• What is wrong with Unix/linux

  - by John Smith

  This is a genuine question motivated by Ideal Operating System When I moved from DOS to Linux in the late 90s it was an eye opener for me. Long file names, arbitrarily many extensions etc... Now I look at Linux and Unix and see all sorts of issues. Here are things I see which could be fixed. Too much depends on root, and rootly powers cannot be voluntarily delegated over several users. (I would love to give up my power to manager printers and delegate the job to another account) File permissions are very limited, and there is not much metadata to go with files. The "everything is a file" metaphor is not true, Plan 9 gets it right(er).

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• Mounting of UDF Bluray in Linux Mint 17

  - by user134885

  I am running Linux mint 17 Cinnamon 64 Bit 2.2.13 - 3.13.0-27 Kernal My machine is a Clevo - fitted with a bluray burner I have tried the following line sudo mount -t udf /dev/scd0 /media/bluray /dev/sr0 But to no avail. Can anyone help me with how to initiate / mount a Bluray on my machine? Thank you to anyone who can give me feedback may sanity and get it going - all works well in windows, but nothing in Linux?

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• Which numeral systems are useful in computer science?

  - by authchir

  I am wondering which numeral system different programmers are using, or would use if their language has support for them. As an example, in C++ we can use: Octal by prefixing with 0 (e.g. 0377) Decimal by default (e.g. 255) Hexadecimal by prefixing with 0x (e.g. 0xff) When working with bitmask, I am using hexadecimal but would sometimes want to be able to express binary numbers directly. I know some programming language support it with 0b syntax (e.g. 0b11111111). Is there any other numeric system useful in some computer science domain (e.g. cryptography, codecs, 3D graphics, etc)?

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• Changelog Management

  - by Gnial0id

  I'm currently developing a WinForm application. In order to inform the client about the improvements and corrections made during the last version, I would like to manage and display a changelog. I mostly found existing changelog on website (the term changelog is pretty used) or explanation on how to manage the release numbers, which I don't care. So, these are my questions: How do I manage a changelog (using XML, pure text in the app, etc.) in a desktop application? How do I present it to the user (external website, inside the winform application)?

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• What is the best website width? [on hold]

  - by Salvis Dišlers

  What is the best website width? I can't decide between 1200px max-width and 1236px....with 300px sidebar as enough or 320px? I personally like wide website, my current website is 1236px; but I hear it's considered very wide for eyesight and all those gadgets keeping in mind... The website is for reading - I mean, mostly articles with around 3000 words on average per page, so no matter - whether they look wide, whether they love to scroll down :) Also - what to decide about Banner size / sidebar? Probably the 300px I can put a 300px banner, but on 320px sidebar I could put 336px banner, if necessary...

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• How do they keep track of the NPCs in Left 4 Dead?

  - by f20k

  How do they keep track of the NPC zombies in Left 4 Dead? I am talking about the NPCs that just walk into walls or wander around aimlessly. Even though the players cannot see them, they are there (say inside rooms or behind doors). Let's say there's about 10 or so zombies in a hallway and inside rooms. Does the game keep all of those zombies in a list and iterate through giving them commands? Do they just spawn when the user is within a certain radius or reached a special location? Say you placed the 4 units (controlled by players) on completely different places throughout the map. Let's assume you aren't being swarmed and then you have not killed any of these aimless NPCs. Would the game be keeping track of 10 x 4 = 40 zombies in total? Or is my understanding completely off? The reason I ask is if I were to implement something similar on a mobile device, keeping track of 40 or more NPCs might not be such a great idea.

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• Given a RGB color x, how to find the most contrasting color y?

  - by Arthur Wulf White

  I have to mark a certain item in a way that will make it stick-out in the background. I need it to be surrounded with the color that contrasts the background as much as possible so it will pop out and easily noticeable by the player. Lets say I know the background is color 'x', how do I find 'y' such that it will be very contrasting to 'x' and easy to notice in a background where 'x' is a dominant color? I first thought about inverting color 'x' and then I noticed that when 'x' is a medium shade of gray, if I invert 'x' to get 'y', then 'y' is also a medium shade of gray which does not work.

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• AngularJS: structuring a web application with multiple ng-apps

  - by mg1075

  The blogosphere has a number of articles on the topic of AngularJS app structuring guidelines such as these (and others): http://www.johnpapa.net/angular-app-structuring-guidelines/ http://codingsmackdown.tv/blog/2013/04/19/angularjs-modules-for-great-justice/ http://danorlando.com/angularjs-architecture-understanding-modules/ http://henriquat.re/modularizing-angularjs/modularizing-angular-applications/modularizing-angular-applications.html However, one scenario I have yet to come across for guidelines and best practices is the case where you have a large web application containing multiple "mini-spa" apps, and the mini-spa apps all share a certain amount of code. I am not referring to the case of trying to have multiple ng-app declarations on the same page; rather, I mean different sections of a large site that have their own, unique ng-app declaration. As Scott Allen writes in his OdeToCode blog: One scenario I haven't found addressed very well is the scenario where multiple apps exist in the same greater web application and require some shared code on the client. Are there any recommended approaches to take, pitfalls to avoid, or good sample structures of this scenario that you can point to?

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• Acceptable placement of the composition root using dependency injection and inversion of control containers

  - by Lumirris

  I've read in several sources including Mark Seemann's 'Ploeh' blog about how the appropriate placement of the composition root of an IoC container is as close as possible to the entry point of an application. In the .NET world, these applications seem to be commonly thought of as Web projects, WPF projects, console applications, things with a typical UI (read: not library projects). Is it really going against this sage advice to place the composition root at the entry point of a library project, when it represents the logical entry point of a group of library projects, and the client of a project group such as this is someone else's work, whose author can't or won't add the composition root to their project (a UI project or yet another library project, even)? I'm familiar with Ninject as an IoC container implementation, but I imagine many others work the same way in that they can scan for a module containing all the necessary binding configurations. This means I could put a binding module in its own library project to compile with my main library project's output, and if the client wanted to change the configuration (an unlikely scenario in my case), they could drop in a replacement dll to replace the library with the binding module. This seems to avoid the most common clients having to deal with dependency injection and composition roots at all, and would make for the cleanest API for the library project group. Yet this seems to fly in the face of conventional wisdom on the issue. Is it just that most of the advice out there makes the assumption that the developer has some coordination with the development of the UI project(s) as well, rather than my case, in which I'm just developing libraries for others to use?

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• Resize broswer window below 400px on OS X

  - by David

  Resizing Firefox windows (by dragging) works fine, up until the window is about 400 px wide, at which point the width of the web page content cease to follow the window with. I'm pretty sure it's not a CSS issue, and the same thing goes for Chrome and Safari as well (they won't even let me resize the window < 400 px wide). I can't understand where this limitation comes from. Is it a setting in the browser? A bug? A limitation of the OS?

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• can you have too many dto/bo - mapping method

  - by Fredou

  I have a windows service, 2 web services and a web interface that need to follow the same path (data wise). So I came up with two ways of creating my solution. My concern is the fact that the UI/WS/etc will have their own kind of DTO (let's say the model in ASP.Net MVC) that should be mapped to a DTO so the SL can then map it to a BO then mapping it to the proper EF6 DTO so that I can save it in a database. So I'm thinking of doing it this way to remove one level of mapping. Which one should I take? Or is there a 3rd solution?

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• How can I gather client's data on Google App Engine without using Datastore/Backend Instances too much?

  - by ruslan

  One of the projects I'm working on is online survey engine. It's my first big commercial project on Google App Engine. I need your advice on how to collect stats and efficiently record them in DataStore without bankrupting me. Initial requirements are: After user finishes survey client sends list of pairs [ID (int) + PercentHit (double)]. This list shows how close answers of this user match predefined answers of reference answerers (which identified by IDs). I call them "target IDs". Creator of the survey wants to see aggregated % for given IDs for last hour, particular timeframe or from the beginning of the survey. Some surveys may have thousands of target/reference answerers. So I created entity public class HitsStatsDO implements Serializable { @Id transient private Long id; transient private Long version = (long) 0; transient private Long startDate; @Parent transient private Key parent; // fake parent which contains target id @Transient int targetId; private double avgPercent; private long hitCount; } But writing HitsStatsDO for each target from each user would give a lot of data. For instance I had a survey with 3000 targets which was answered by ~4 million people within one week with 300K people taking survey in first day. Even if we assume they were answering it evenly for 24 hours it would give us ~1040 writes/second. Obviously it hits concurrent writes limit of Datastore. I decided I'll collect data for one hour and save that, that's why there are avgPercent and hitCount in HitsStatsDO. GAE instances are stateless so I had to use dynamic backend instance. There I have something like this: // Contains stats for one hour private class Shard { ReadWriteLock lock = new ReentrantReadWriteLock(); Map<Integer, HitsStatsDO> map = new HashMap<Integer, HitsStatsDO>(); // Key is target ID public void saveToDatastore(); public void updateStats(Long startDate, Map<Integer, Double> hits); } and map with shard for current hour and previous hour (which doesn't stay here for long) private HashMap<Long, Shard> shards = new HashMap<Long, Shard>(); // Key is HitsStatsDO.startDate So once per hour I dump Shard for previous hour to Datastore. Plus I have class LifetimeStats which keeps Map<Integer, HitsStatsDO> in memcached where map-key is target ID. Also in my backend shutdown hook method I dump stats for unfinished hour to Datastore. There is only one major issue here - I have only ONE backend instance :) It raises following questions on which I'd like to hear your opinion: Can I do this without using backend instance ? What if one instance is not enough ? How can I split data between multiple dynamic backend instances? It hard because I don't know how many I have because Google creates new one as load increases. I know I can launch exact number of resident backend instances. But how many ? 2, 5, 10 ? What if I have no load at all for a week. Constantly running 10 backend instances is too expensive. What do I do with data from clients while backend instance is dead/restarting?

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• I know how to program, and how to learn how to program, but how/where do you learn how to make systems properly?

  - by Ryan

  There are many things that need to be considered when making a system, let's take for example a web based system where users log in and interact with each other, creating and editing content. Now I have to think about security, validation (I don't even think I am 100% sure what that entails), "making sure users don't step on each others feet" (term for this?), preventing errors in many cases, making sure database data doesn't become problematic through unexpected... situations? All these things I don't know how or where to learn, is there a book on this kind of stuff? Like I said there seems to be a huge difference between writing code and actually writing the right code, know what I mean? I feel like my current programming work lacks much of what I have described and I can see the problems it causes later, and then the problems are much harder to solve because data exists and people are using it. So can anyone point me to books or resources or the proper subset of programming(?) for this type of learning? PS: feel free to correct my tags, I don't know what I am talking about. Edit: I assume some of the examples I wrote apply to other types of systems too, I just don't know any other good examples because I've been mostly involved in web work.

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• How can I store all my level data in a single file instead of spread out over many files?

  - by Jon

  I am currently generating my level data, and saving to disk to ensure that any modifications done to the level are saved. I am storing "chunks" of 2048x2048 pixels into a file. Whenever the player moves over a section that doesn't have a file associated with the position, a new file is created. This works great, and is very fast. My issue, is that as you are playing the file count gets larger and larger. I'm wondering what are techniques that can be used to alleviate the file count, without taking a performance hit. I am interested in how you would store/seek/update this data in a single file instead of multiple files efficiently.

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• How is intermediate data organized in MapReduce?

  - by Pedro Cattori

  From what I understand, each mapper outputs an intermediate file. The intermediate data (data contained in each intermediate file) is then sorted by key. Then, a reducer is assigned a key by the master. The reducer reads from the intermediate file containing the key and then calls reduce using the data it has read. But in detail, how is the intermediate data organized? Can a data corresponding to a key be held in multiple intermediate files? What happens when there is too much data corresponding to one key to be held by a single file? In short, how do intermediate partitions differ from intermediate files and how are these differences dealt with in the implementation?

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• Writing selenium tests, should I just get it done or get it right?

  - by Peter Smith

  I'm attempting to drive my user interface (heavy on javascript) through selenium. I've already tested the rest of my ajax interaction with selenium successfully. However, this one particular method seems to be eluding me because I can't seem to fake the correct click event. I could solve this problem by simply waiting in the test for the user to click a point and then continuing with the test but this seems like a cop out. But I'm really running out of time on my deadline to have this done and working. Should I just get this done and move on or should I spend the extra (unknown) amount of time to fix this problem and be able to have my selenium tests 100% automated?

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• Comparison of languages by usage type? [closed]

  - by Tom

  Does anyone know of a good place to go find comparisons of programming languages by the intended platform/usage? Basically, what I want to know, is of the more popular languages, which ones are meant for high level application development, low level system development, mobile development, web, etc. If there's a good listing out there already, I'm not finding it so far. Does anyone know of a place that would have this? Thanks.

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• Speaking this week at Richmond SQL Server User Group

  - by drsql

  Thursday night, at 6:00 (or so) I will be speaking in Richmond ( http://richmondsql.org/cs2007/ ), talking about How to Implement a Hierarchy using SQL Server. The abstract is: One of the most common structures you will come across in the real world is a hierarchy (either a single parent "tree" or a multi-parent "graph"). Many systems will implement the obvious examples, such as a corporate managerial structure or a bill of materials. It turns out that almost any many-to-many relationship can be...(read more)

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• Keep user and user profile in different tables?

  - by Andrey

  I have seen in a couple of projects that developers prefer to keep essential user info in one table (email/login, password hash, screen name) and rest of the non essential user profile in another (creation date, country, etc). By non-essential I mean that this data is needed only occasionally. Obvious benefit is that if you are using ORM querying less fields is obviously good. But then you can have two entities mapped to same table and this will save you from querying stuff you don't need (while being more convenient). Does anybody know any other advantage of keeping these things in two tables?

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• Recommendations for a web-based help system

  - by ggkmath

  Hi Experts, I'm putting together a fairly large GUI. I'm a tech person, but more on the hardware side, not software. I'm wondering what software package would be best suited to enable me to generate a web-based help-system. Preferably it takes care of a lot of coding, allowing me to focus on the content. For example, the user would click on a link in the GUI when they have a question, that brings them to a web-based Help Guide, for example, providing an overview of how to use the GUI, perhaps a searchable index (key-word based index), table of contents, etc, for navigating through the Help Guide. My first thought was to program everything in XHTML using Dreamweaver, but my layout requirements are fairly modest (just figures and text, maybe a few equations), and I'd prefer not to spend a lot of time concentrating on the programming. Was wondering if any software existed that made generating web-based navigatable pages easy to create/publish. Again, I'm not really a programmer, so if there's something obvious out there, I'm probably not aware of it. Any advice much appreciated! Thanks in advance.

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• Drawing large 2D sidescroller level terrain

  - by Yar

  I'm a relatively good programmer but now that it comes to add some basic levels to my 2D game I'm kinda stuck. What I want to do: An acceptable, large (8000 * 1000 pixels) "green hills" test level for my game. What is the best way for me to do this? It doesn't have to look great, it just shouldn't look like it was made in MS paint with the line and paint bucket tool. Basically it should just mud with grass on top of it, shaped in some form of hills. But how should I draw it, I can't just take out the pencil tool and start drawing it pixel per pixel, can I?

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• Game ideas for a platformer

  - by user5925

  I have created a platformer which currently has the features listed below. I would greatly appreciate any further ideas which I could implement! (I don't play a lot of games which is why I require help) -- Walking/jumping/movement -- player can shoot lasers -- enemies also walk, fly, and shoot lasers -- water (you can swim in this) -- mud (slows you down on contact, and stops you from jumping) -- ladders -- damage when falling from a large height, unless falling into water -- moving platforms -- springboards (jumping on them shoot you into the air) -- growing platforms (allow you to reach new places) -- key and door system -- gem and coin collection system

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• Where can I find "magic numbers" for classic game play mechanics?

  - by MrDatabase

  I'd like to find some "magic numbers" for the classic helicopter game. For example the numbers that determine how fast the helicopter accelerates up and down. Also perhaps the "randomness" of the obstacles (uniformly distributed? Gaussian?). Where can I find these numbers? p.s. I don't care about the particular platform... Flash on the desktop browser is just as good as some implementation on a mobile device.

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• How many tiers should my models have in a DB driven web app?

  - by Hanno Fietz

  In my experience, the "Model" in MVC is often not really a single layer. I would regularly have "backend" models and "frontend" models, where the backend ones would have properties that I want to hide from the UI code, and the frontend ones have derived or composite properties which are more meaningful in the context of the UI. Recently, I have started to introduce a third layer in between when database normalization created tables that did not really match the conceptual domain objects anymore. In those projects I have model classes that are equivalent with the DB structure, these become components of objects that represent the domain model, and finally these are filtered and amended for displaying information to the user. Are there patterns or guidelines for how, when and why to organize the data model across application layers?

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