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• What is recursion? -- In plain english.

  - by Christopher Altman

  I hear this word everyday, but cannot give a meaningful, concise, or plain-english answer to what it is. Recursion is defined by the bastian of knowledge as: Recursion in computer science is a method where the solution to a problem depends on solutions to smaller instances of the same problem.1 The approach can be applied to many types of problems, and is one of the central ideas of computer science.[2] Source Is recursion simply something that repeats itself to get a solution? I am looking for a "Recursion for Dummies" definition, and maybe simple examples. My goal is to be able to understand and explain recursion in my own words. I do not like simply thinking I know the meaning of something because I hear it referenced daily, but have not paused to form my own understanding.

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• Why make anything internal?

  - by c-charp N00b

  I don't really see the point of making methods or classes internal. In my very limited understanding, all it does is make working with your code very difficult for other programmers. Say I write Big_Important_Class for Project A and make said class internal. Then Bob, working on Project B needs to use my class to have project B work with Project A, but since its internal he can't. As of now this is the only thing I have seen internals do, make things really complicated for the guy working on Project B. I know there has to be a good reason to use internals, but I don't see any. Could someone please explain how they can be a good thing?

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• BlackBerry project version number

  - by Seva Alekseyev

  I have a BlackBerry Java project in Eclipse. It has version number written down in four different spots: in the project properties, under "BlackBerry Project Settings/General" in the JAD file, under MIDlet-1 in the JAD file, under MIDlet-Version in the ALX file, under <version> And they seem uncorrelated. Changing either of these affects none of the rest. The third one is what the users sees during over-the-air setup and under Options/Advanced. Questions - why do we need all these? Are there contexts where numbers 1, 2, 4 come up? It's my understanding that the ALX is generated during compilation - where does the version # come from? Is there a way to learn at least one of those programmatically (without signing the app)?

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• How to implement a Google-chrome-like title bar for Java SWT application

  - by MartyC

  I have inherited development of a Java/SWT application running on Windows only. One of the feature requests that I need to scope is a Google-chrome-type title bar in place of the SWT windows title bar. The application's tabs appear at the same level as the window control buttons. My understanding is that I will need to: write a Windows widget capable of rendering the custom look and managing tabs as opposed to menus. expose the Windows widget as a dll for use in Java via JNI write a custom SWT widget to wrap it and expose the tab management interface. I have a lot of experience with Java programming, GUI programming with Swing/AWT, and non-GUI C# programming. Windows GUI programming and SWT are new to me so I'm not sure where to start. The best I have found so far is a 2001 article on writing your own SWT widget. My biggest unknown is the best way to implement a custom Windows application-window.

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• Using Geo APIs to pick a random town from anywhere in the world

  - by Dan Forys

  Hi all, I'm trying to use Yahoo's excellent GeoPlanet API: http://developer.yahoo.com/geo/geoplanet/guide/api-reference.html I would like to pick a random town from anywhere in the world but can't see an easy way to do it. I have tried querying by country and asking for children of type 'town', but can't seem to do that directly. Can anyone think of a way to pluck out a random town WOEID without having to query the country, then the admin regions, then the admin 2, then the admin 3 etc. I have also experimented using YQL, but don't have enough of an understanding about the available APIs.

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• What resources will help me understand the fundamentals of Relational Database Design.

  - by Rachel

  This are few of the fundamental database questions which has always given me trouble. I have tried using google and wiki but I somehow I miss out on understanding the functionality rather than terminology. If possible would really appreciate if someone can share more insights on this questions using some visual representative examples. What is a key? A candidate key? A primary key? An alternate key? A foreign key? What is an index and how does it help your database? What are the data types available and when to use which ones?

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• Modular enterprise architecture using MVC and Orchard CMS

  - by MrJD

  I'm making a large scale MVC application using Orchard. And I'm going to be separating my logic into modules. I'm also trying to heavily decouple the application for maximum extensibility and testability. I have a rudimentary understanding of IoC, Repository Pattern, Unit of Work pattern and Service Layer pattern. I've made myself a diagram. I'm wondering if it is correct and if there is anything I have missed regarding an extensible application. Note that each module is a separate project.

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• JavaFX - reduce() function to show how to pass functions as parameters

  - by Helper Method

  At the moment I'm writing a JavaFX guide for Java developers. In order to show how to pass a function to another funtion i adopted the reduce() function found in Effective Java: function reduce(seq: Integer[], f: function(: Integer, : Integer): Integer, init: Integer) { var result = init; for (i in seq) { result = f(i, result); } result } def nums = [1 .. 10]; println(reduce(nums, function(a: Integer, b: Integer) { a + b }, 0)); // prints 55 println(reduce(nums, function(a: Integer, b: Integer) { a * b }, 0)); // prints 3628800 Now I wonder if this example is not to hard for someone starting to learn JavaFX. The tutorial is targeted to programmers with a solid understanding of Java, yet I'm not quite sure about the usefulness of the example. Any ideas?

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• Using DataTypeAttribute to validate a date

  - by Andy Evans

  I'm having some difficulty understanding how to validate a date (DOB) using MVC2. What I want to do is 1. Is the date entered a valid date and, 2. Is the date at lease 13 years in the past. For example, to validate an email I use the following code: [Required(ErrorMessage = "Email address is required.")] [StringLength(320, ErrorMessage = "Email must be less than 320 characters.")] [Email(ErrorMessage = "This email address is invalid.")] public string email { get; set; } To validate the email I use: public class EmailAttribute : RegularExpressionAttribute { public EmailAttribute() : base("insert long regex expression here") { } } Any assistance would be greatly appreciated, thanks!

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• What Kind of Knowledge is Necessary For a Permon Who Does Not Have IT Background? [closed]

  - by skyflyer

  One of my colleagues joined our company, which by the way is a internet company, months ago as an on-line marketing specialist. He majored English in his college and has never deeply touched IT before. He says that to be a good on-line marketing specialist he needs to lean some basic IT skills in order to deliver superb work. According to him, things like Search Engine Optimization, monitoring competitors' web sites, design some functionality on web site and so on require IT entree-level knowledge. And he asks me what kind knowledge is helpful for him to do his job. I am stunted by his question. It is easy enough to answer, things like HTML, CSS, even Photo-shop are required in some job descriptions. Also, I believe some basic understanding of dynamic web site, static web site is helpful to him. On the other hand, as a techie I still feel my answer is awkward. What is your opinion on this? Always lot of thanks to you guys on SO.

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• How do I plot more than one series using qplot?

  - by celenius

  I'm trying to understand how to have more than one series on a plot, using the following data. Year <- c('1950', '1960', '1970', '1980') Bus <- c(10,20,30,40) Bus.sd <- c(1.1, 2.2, 3.3, 4.4) Car <- c(20, 20, 40, 40) Car.sd <- c(1.1, 2.2, 3.3, 4.4) sample_data = data.frame(Year, Bus, Bus.sd, Car, Car.sd) qplot(Year, Bus, data=sample_data, geom="pointrange", ymin = Bus - Bus.sd/2, ymax = Bus + Bus.sd/2) For example, using the above data, how do I show both sample_data$Bus and sample_data$Car on the same plot in different colors? What I tried doing was: p <- qplot(...) then p <- p + qplot(...) where I replicated the previous line, but this gave me an error. I don't fully understand how AES works. I have studied the ggplot2 examples, but have difficulty understanding the relevant examples here.

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• bytea type & nulls, Postgres

  - by Thanatos

  I'm using a bytea type in PostgreSQL, which, to my understanding, contains just a series of bytes. However, I can't get it to play well with nulls. For example: =# select length(E'aa\x00aa'::bytea); length -------- 2 (1 row) I was expecting 5. Also: =# select md5(E'aa\x00aa'::bytea); md5 ---------------------------------- 4124bc0a9335c27f086f24ba207a4912 (1 row) That's the MD5 of "aa", not "aa\x00aa". Clearly, I'm Doing It Wrong, but I don't know what I'm doing wrong. I'm also on an older version of Postgres (8.1.11) for reasons outside of my control. (I'll see if this behaves the same on the latest Postgres as soon as I get home...)

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• Doesn't JavaScript support closures with local variables?

  - by qollin

  I am very puzzled about this code: var closures = []; function create() { for (var i = 0; i < 5; i++) { closures[i] = function() { alert("i = " + i); }; } } function run() { for (var i = 0; i < 5; i++) { closures[i](); } } create(); run(); From my understanding it should print 0,1,2,3,4 (isn't this the concept of closures?). Instead it prints 5,5,5,5,5. I tried Rhino and Firefox. Could someone explain this behavior to me? Thx in advance.

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• Lifetime of javacript variables.

  - by The Machine

  What is the lifetime of a variable in javascript, declared with "var". I am sure, it is definitely not according to expectation. <script> function(){ var a; var fun=function(){ // a is accessed and modified } }(); </script> Here how and when does javascript garbage collect the variable a? Since 'a' is a part of the closure of the inner function, it ideally should never get garbage collected, since the inner function 'fun', may be passed as a reference to an external context.So 'fun' should still be able to access 'a', from the external context. If my understanding is correct, how does garbage collection happen then, and how does it ensure to have enough memory space, since keeping all variables in memory until the execution of the program might not be tenable ?

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• Question about best practices and Macros from the book 'C++ Coding Standards'

  - by Victor T.

  From Herb Sutter and Andrei Alexandrescu's 'C++ Coding Standards', Item 16: Avoid Macros under Exceptions for this guideline they wrote: For conditional compilation (e.g., system-dependent parts), avoid littering your code with #ifdefs. Instead, prefer to organize code such that the use of macros drives alternative implementations of one common interface, and then use the interface throughout. I'm having trouble understanding exactly what they mean by this. How can you drive alternate implementations without the use of #ifdef conditional compile macro directives? Can someone provide an example to help illustrate what's being proposed by the above paragraph? Thanks

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• Which set(s) of video lectures for computer science?

  - by SebKom

  As most of you know a couple of top universities (MIT, Stanford, etc) around the world are now publishing videos of their lectures online. I am advancing to the third and final year of my computer science degree this September and I was thinking about spending some time during the summer to watch a couple of lectures, in order to improve my understanding of algorithms, complexity, programming, software engineering, etc. Now I don't have infinite time to spend so I can't watch all of the lectures from all of the universities so I was wondering if you could suggest me which sets to watch from each one (something like "Algorithms from MIT", "Programming from Yale", etc).

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• Question about mysql indexes on low to medium cardinality columns

  - by Kevin J

  I have a general question about the way that database indexing works, particularly in mysql. Let's say I have a table with a million rows with a column "ClientID" that is distributed relatively equally among 30 values. Thus, this column is very low cardinality (30) relative to the primary key (1 million). Now, I understand that you shouldn't create indexes on low cardinality fields. However, in this case, queries are only ever done with one of the 30 clientIDs. Thus, wouldn't creating an index on ClientID be helpful, as the search space is automatically reduced to 1/30th what it normally would be? Or is my understanding of how the index works flawed? Thanks

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• Android: stack management for views in a tab?

  - by wei

  I see some answers here prefer views over activities as contents of tabs. Correct me if I am wrong. My understanding is that by switching out views, it's possible to keep the navigation flow inside a tab (more user friendly, I think). But I wonder how to manage the view stack then in case of the back button events. Also this could cause one giant Activity with large amount of views, which might not be good. So I wish to know why exactly views as contents is preferred before I change my current application to this. Thanks,

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• OpenAL device, buffer and context relationship

  - by Markus

  I'm trying to create an object oriented model to wrap OpenAL and have a little problem understanding the devices, buffers and contexts. From what I can see in the Programmer's Guide, there are multiple devices, each of which can have multiple contexts as well as multiple buffers. Each context has a listener, and the alListener*() functions all operate on the listener of the active context. (Meaning that I have to make another context active first if I wanted to change it's listener, if I got that right.) So far, so good. What irritates me though is that I need to pass a device to the alcCreateContext() function, but none to alGenBuffers(). How does this work then? When I open multiple devices, on which device are the buffers created? Are the buffers shared between all devices? What happens to the buffers if I close all open devices? (Or is there something I missed?)

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• Does the number of busy worker threads in the CLR ThreadPool affect performance of I/O threads?

  - by andrej351

  We have a Windows Service which hosts a number of WCF services and, in an unrelated part of the app, makes extensive use of the TPL Task class to asynchronously do relatively short bits of work. It is my understanding that WCF uses managed I/O threads from the ThreadPool to execute requests. I noticed that after deploying a feature which significantly raised the applications use of Tasks, and as such the use of ThreadPool worker threads as well, performance of a couple of web services has become very slow. We're talking minutes instead of less than a second. The number of Tasks actually trying to run at any one time can range between 20 and 1000, which makes me think that any new (last in) work needing some CPU time could be forced to wait for quite some time. Does the (in my case extremely large) number of busy ThreadPool worker threads affect the ThreadPool's managed I/O threads? Or could these two be connected in any way? Thanks!

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• Adding gwt project to existing java servlet 3 project

  - by Michael

  I have a standalone gwt project with RPC built with Maven. I also have java servlet 3.0 project. Both the servlet and gwt projects have war packaging but I want to have only one war file so I changed the packaging of the gwt project to jar and included it in my servlet project. Now I have a problem understanding how to wire everything together. Do I need to migrate gwt project's web.xml into the main project web.xml file ? How do I redirect to my gwt project entry index.html ? Thanks.

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• Perl : localtime with print

  - by kiruthika

  Hi all, I have used the following statements to get the current time. print "$query executed successfully at ",localtime; print "$query executed successfully at ",(localtime); print "$query executed successfully at ".(localtime); Output executed successfully at 355516731103960 executed successfully at 355516731103960 executed successfully at Wed Apr 7 16:55:35 2010 The first two statements are not printing the current time in a date format. Third statement only giving the correct output in a date format. My understanding is the first one is returning a value in scalar context,so it is returning numbers. Then in the second print I used localtime in list context only,why it's also giving number output.

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• What is the "task" in twitter Storm parallelism

  - by John Wang

  I'm trying to learn twitter storm by following the great article "Understanding the parallelism of a Storm topology" However I'm a bit confused by the concept of "task". Is a task an running instance of the component(spout or bolt) ? A executor having multiple tasks actually is saying the same component is executed for multiple times by the executor, am I correct ? Moreover in a general parallelism sense, Storm will spawn a dedicated thread(executor) for a spout or bolt, but what is contributed to the parallelism by an executor(thread) having multiple tasks ? I think having multiple tasks in a thread, since a thread executes sequentially, only make the thread a kind of "cached" resource, which avoids spawning new thread for next task run. Am I correct? I may clear those confusion by myself after taking more time to investigate, but you know, we both love stackoverflow ;-) Thanks in advance.

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• how to deal with a static analyzer output

  - by Jim

  We have started using a static analyzer (Coverity) on our code base. We were promptly stupefied by the sheer amount of warnings we received (its in the hundreds of thousands) , it will take the entire team a few mounts to clear them all (obliviously impossible). the options we discussed so far are 1) hire a contractor to sort out the warning and fix them - he drawback: we will probably need very experiences people to do all these modifications, and no contractor will have required understanding of the code. 2) filter out the warning and deal only with the dangerous ones - the problem here is that our static analysis output will always be cluttered by warning making it difficult for us to isolate problems. also the filtering of the warning is also a major effort. either way, bringing our code to a state when the static analyzer can be a useful tool for us seems a monumental task. so how is it possible to work with the static analyzer without braining current development efforts into a complete stand still?

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• Haskell: Pattern Matching with Lists

  - by user1670032

  I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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