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  • Solving a probabilistic problem

    - by ????????????
    So I am interested in Computational Investing and came across this problem on a wiki page: Write a program to discover the answer to this puzzle:"Let's say men and women are paid equally (from the same uniform distribution). If women date randomly and marry the first man with a higher salary, what fraction of the population will get married?" I don't have much knowledge in probability theory, so I'm not really sure how to implement this in code. My thinking: Populate two arrays(female,male) with random salary values from a uniform distribution. Randomly pair one female and one male array element and see if condition of higher salary is met. If it is, increment a counter. Divide counter by population and get percentage. Is this the correct logic? Do woman continually date until there is no males left with higher salaries than women?

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  • New "delay" keyword for JavaScript

    - by Van Coding
    I had a great idea for a new javascript keyword "delay", but I don't know what I can do to bring it to the new specification. Also I want to know what you guys think about it and if it's even realistic. What does the delay keyword ? The delay keyword does nothing more than stop the execution of the current stack and immediately continues to the next "job" in the queue. But that's not all! Instead of discarding the stack, it adds it to the end of the queue. After all "jobs" before it are done, the stack continues to execute. What is it good for? delay could help make blocking code non-blocking while it still looks like synchronous code. A short example: setTimeout(function(){ console.log("two"); },0); console.log("one"); delay; //since there is currently another task in the queue, do this task first before continuing console.log("three"); //Outputs: one, two, three This simple keyword would allow us to create a synchronous-looking code wich is asynchronous behind the scenes. Using node.js modules, for example, would no longer be impossible to use in the browser without trickery. There would be so many possibilites with such a keyword! Is this pattern useful? What can I do to bring this into the new ECMAscript specification? Note: I asked this previously on Stack Overflow, where it was closed.

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  • Prevent Click Fraud in Advertisement system with PHP and Javascript

    - by CodeDevelopr
    I would like to build an Advertising project with PHP, MySQL, and Javascript. I am talking about something like... Google Adsense BuySellAds.com Any other advertising platform My question is mainly, what do I need to look out for to prevent people cheating the system and any other issues I may encounter? My design concept. An Advertisement is a record in the Database, when a page is loaded, using Javascript, it calls my server which in turn will use a PHP script to query the Database and get a random Advertisement. (It may do kore like get an ad based on demographics or other criteria as well) The PHP script will then return the Advertisement to the server/website that is calling it and show it on the page as an Image that will have a special tracking link. I will need to... Count all impressions (when the Advertisement is shown on the page) Count all clicks on the Advertisement link Count all Unique clicks on the Advertisement link My question is purely on the query and displaying of the Advertisement and nothing to do with the administration side. If there is ever money involved with my Advertisement buying/selling of adspace, then the stats need to be accurate and make sure people can't easily cheat the system. Is tracking IP address really the only way to try to prevent click fraud? I am hoping someone with some experience can clarify I am on the right track? As well as give me any advice, tips, or anything else I should know about doing something like this?

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  • Database for survey

    - by zfm
    One of my job now is to design a database for a survey. Let's say we have a series of questions (web-based), in which one page contains one question. Not every person will be given the same questions, those are based on their previous answers and also randomness. I would like to know whether it is better to have database like this user question answer userX question1 answer1A userX question2 answer2C userX question5 answer5F userY question1 answer1B userY question3 answer3B userY question6 answer6D ... or user q1 q2 q3 q4 q5 q6 userX 1A 2C null null 5F null userY 1B null 3B null null 6D ... My idea here is, using the second approach seems better, however I would like to know whether updating the table is (much) slower than inserting a new row? Also with the first approach, I can omit having some null answers. The total questions given are fix, the client wont add any more question later on. So my question is, what will you do if you were me?

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  • Program instantly closing [migrated]

    - by Ben Clayton
    I made this program and when I compiled it there were no errors but the program just instantly closed, any answers would be appreciated. #include <iostream> //Main commands #include <string> // String commands #include <windows.h> // Sleep using namespace std; int main () { //Declaring variables float a; bool end; std::string input; end = false; // Making sure program doesn't end instantly cout << "Enter start then the number you want to count down from." << ".\n"; while (end = false){ cin >> input; cout << ".\n"; if (input.find("end") != std::string::npos) // Ends the program if user types end end = true; else if (input.find("start" || /* || is or operator*/ "restart") != std::string::npos) // Sets up the countdown timer if the user types start { cin >> a; cout << ".\n"; while (a>0){ Sleep(100); a = a - 0.1; cout << a << ".\n"; } cout << "Finished! Enter restart and then another number, or enter end to close the program" << ".\n"; } else // Tells user to start program cout << "Enter start"; } return 0; // Ends program when (end = true) }

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  • How to deal with almost the same enums?

    - by reza
    I need to define enums in several classes. The majority of fields are the same in all of the enums. But one has one or two more fields, another has fewer fields. Now I wonder what is the best way to deal with this? Create separate enums public enum Foo {field1, field2, field5 }; public enum Bar {field1, field2, field3, field4 }; or use a general enum for them all public enum FooBar {field1, field2, field3, field4 , field5}; The enumerations contain the list of actions available for each class.

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  • Floating point undesireable in highly critical code?

    - by Kirt Undercoffer
    Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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  • Script/tool to import series of snapshots, each being a new edition, into GIT, populating source tree?

    - by Rob
    I've developed code locally and taken a fairly regular snapshot whenever I reach a significant point in development, e.g. a working build. So I have a long-ish list of about 40 folders, each folder being a snapshot e.g. in ascending date YYYYMMDD order, e.g.:- 20100523 20100614 20100721 20100722 20100809 20100901 20101001 20101003 20101104 20101119 20101203 20101218 20110102 I'm looking for a script to import each of these snapshots into GIT. The end result being that the latest code is the same as the last snapshot, and other editions are accessible and are as numbered. Some other requirements: that the latest edition is not cumulative of the previous snapshots, i.e., files that appeared in older snapshots but which don't appear in later ones (e.g. due to refactoring etc.) should not appear in the latest edition of the code. meanwhile, there should be continuity between files that do persist between snapshots. I would like GIT to know that there are previous editions of these files and not treat them as brand new files within each edition. Some background about my aim: I need to formally revision control this work rather than keep local private snapshot copies. I plan to release this work as open source, so version controlling would be highly recommended I am evaluating some of the current popular version control systems (Subversion and GIT) BUT I definitely need a working solution in GIT as well as subversion. I'm not looking to be persuaded to use one particular tool, I need a solution for each tool I am considering. (I haved posted an answer separately for each tool so separate camps of folks who have expertise in GIT and Subversion will be able to give focused answers on one or the other). The same but separate question for Subversion: Script/tool to import series of snapshots, each being a new revision, into Subversion, populating source tree?

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  • Developing Salesforce apps in Ruby on Rails

    - by Robert S.
    I want to build a web app that uses Salesforce.com data, and I want to build it fast. I'm a .NET developer (WPF, C#, ASP.NET MVC). I understand Ruby and RoR fairly well, but I haven't delivered any Rails apps. I'm wondering, is Ruby on Rails a suitable tool for rapidly building Salesforce apps, or is it better for the "traditional" web2.0 stuff like Groupon and Twitter? In other words, would using RoR help me achieve my fast (e.g., three months) goal over using .NET, which I already know?

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  • Constructive ways to answer "What was your most challenging project? and why?"

    - by tau
    I am asked this question many times in the interviews. What was your most challenging project -- and why? I get confused about which project to tell them and why some project would look challenging or non-challenging. What are they looking for in the answer? Any software is a challenge before it gets started and it becomes a normal software engineering task after it has finished. All softwares I made were challenging until they got finished. Do I misunderstood the word "challenge"? What's wrong in my thinking? What's an appropriate and constructive way to approach this question?

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  • Pointers in C vs No pointers in PHP

    - by AnnaBanana
    Both languages have the same syntax. Why does C have the weird * character that denotes pointers (which is some kind of memory address of the variable contents?), when PHP doesn't have it and you can do pretty much the same things in PHP that you can do in C, without pointers? I guess the PHP compiler handles this internally, why doesn't C do the same? Doesn't this add unneeded complexity in C? For example I don't understand them :)

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  • How to implement a no-login authentication system

    - by mrwooster
    I am looking to build a very loose authentication system that can track a user and link submitted data/comments to a specific user. The submissions are essentially anonymous, but a user may want to edit his submission/comment at a later date. I want the experience to be as smooth as possible so do not want to ask users to sign up for an account and then login each time. There is no point as their submissions are not in their name and to another user browsing the site, there is no way of linking a submission to a specific user (think anonymous comments on a blog post or pastie). However, the user should have the ability to edit (at least in the short term) the content they have posted. The way I imagine doing this would be to place a unique identifier in a cookie on the users machine. This would enable me to link a submission to a user, and while that cookie remained on the users machine, I would allow them to edit their content. Of course, if the cookie is lost, or the user accesses the site from a different browser, then they would not be able to edit their content, but this is not really an issue, they can always resubmit a new piece of content. Is there a better way of doing this? How can I implement this so that the user can edit their data for the longest possible amount of time.

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  • How do you structure your shared code so that it is "re-findable" for new developers?

    - by awmckinley
    I started working at my current job about 8 months ago, and its been one of the best experiences I've had as a young programmer. It's a small company, and both my co-developers are brilliant guys. One of the practices that they both have been encouraging is lots of code-reuse. Our code base is mainly C#, and we're using a centralized revision control system. The way the repository is currently structured, there is a single folder in which all shared class libraries are placed (along with unit tests for each library), and our revision control system allows for sharing or linking those libraries out to other projects. What I'm trying to understand at this point is how the current structure of the folder can be made more conducive for finding those libraries again. I've talked to the other developers about this, and they agree that it's gotten a little messy. I find that I am sometimes "reinventing the wheel" because I didn't realize that there was an existing piece of code that solved a particular problem. The issue is complicated further by the fact that we're sharing some code between ASP.NET MVC2, WinForms, and Windows CE projects, and sharing code between applications built against multiple versions of .NET. How do other people approach this? Is the answer in naming the libraries in a certain way or is it preferable to invest in some code-search software? Is the answer in doc comments? Should we be sharing libraries at all or should we simply branch the class libraries for re-use? Thanks for any and all help!

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  • How to define template directives (from an API perspective)?

    - by Ralph
    Preface I'm writing a template language (don't bother trying to talk me out of it), and in it, there are two kinds of user-extensible nodes. TemplateTags and TemplateDirectives. A TemplateTag closely relates to an HTML tag -- it might look something like div(class="green") { "content" } And it'll be rendered as <div class="green">content</div> i.e., it takes a bunch of attributes, plus some content, and spits out some HTML. TemplateDirectives are a little more complicated. They can be things like for loops, ifs, includes, and other such things. They look a lot like a TemplateTag, but they need to be processed differently. For example, @for($i in $items) { div(class="green") { $i } } Would loop over $items and output the content with the variable $i substituted in each time. So.... I'm trying to decide on a way to define these directives now. Template Tags The TemplateTags are pretty easy to write. They look something like this: [TemplateTag] static string div(string content = null, object attrs = null) { return HtmlTag("div", content, attrs); } Where content gets the stuff between the curly braces (pre-rendered if there are variables in it and such), and attrs is either a Dictionary<string,object> of attributes, or an anonymous type used like a dictionary. It just returns the HTML which gets plunked into its place. Simple! You can write tags in basically 1 line. Template Directives The way I've defined them now looks like this: [TemplateDirective] static string @for(string @params, string content) { var tokens = Regex.Split(@params, @"\sin\s").Select(s => s.Trim()).ToArray(); string itemName = tokens[0].Substring(1); string enumName = tokens[1].Substring(1); var enumerable = data[enumName] as IEnumerable; var sb = new StringBuilder(); var template = new Template(content); foreach (var item in enumerable) { var templateVars = new Dictionary<string, object>(data) { { itemName, item } }; sb.Append(template.Render(templateVars)); } return sb.ToString(); } (Working example). Basically, the stuff between the ( and ) is not split into arguments automatically (like the template tags do), and the content isn't pre-rendered either. The reason it isn't pre-rendered is because you might want to add or remove some template variables or something first. In this case, we add the $i variable to the template variables, var templateVars = new Dictionary<string, object>(data) { { itemName, item } }; And then render the content manually, sb.Append(template.Render(templateVars)); Question I'm wondering if this is the best approach to defining custom Template Directives. I want to make it as easy as possible. What if the user doesn't know how to render templates, or doesn't know that he's supposed to? Maybe I should pass in a Template instance pre-filled with the content instead? Or maybe only let him tamper w/ the template variables, and then automatically render the content at the end? OTOH, for things like "if" if the condition fails, then the template wouldn't need to be rendered at all. So there's a lot of flexibility I need to allow in here. Thoughts?

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  • Saving Dragged Dropped items position on postback in asp.net [closed]

    - by Deeptechtons
    Ok i saw many post's on how to serialize the value of dragged items to get hash and they tell how to save them. Now the question is how do i persist the dragged items the next time when user log's in using the has value that i got eg: <ul class="list"> <li id="id_1"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_2"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_3"> <div class="item ui-corner-all ui-widget ui-widget-content"> </div> </li> <li id="id_4"> <div class="item ui-corner-all ui-widget"> </div> </li> </ul> which on serialize will give "id[]=1&id[]=2&id[]=3&id[]=4" Now think that i saved it to Sql server database in a single field called SortOrder. Now how do i get the items to these order again ? the code to make these sort is below,without which people didn't know which library i had used to sort and serialize <script type="text/javascript"> $(document).ready(function() { $(".list li").css("cursor", "move"); $(".list").sortable(); }); </script>

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  • The code works but when using printf it gives me a weird answer. Help please [closed]

    - by user71458
    //Programmer-William Chen //Seventh Period Computer Science II //Problem Statement - First get the elapsed times and the program will find the //split times for the user to see. // //Algorithm- First the programmer makes the prototype and calls them in the //main function. The programmer then asks the user to input lap time data. //Secondly, you convert the splits into seconds and subtract them so you can //find the splits. Then the average is all the lap time's in seconds. Finally, //the programmer printf all the results for the user to see. #include <iostream> #include <stdlib.h> #include <math.h> #include <conio.h> #include <stdio.h> using namespace std; void thisgetsElapsedTimes( int &m1, int &m2, int &m3, int &m4, int &m5, int &s1, int &s2, int &s3, int &s4, int &s5); //this is prototype void thisconvertstoseconds ( int &m1, int &m2, int &m3, int &m4, int &m5, int &s1, int &s2, int &s3, int &s4, int &s5, int &split1, int &split2, int &split3, int &split4, int &split5);//this too void thisfindsSplits(int &m1, int &m2, int &m3, int &m4, int &m5, int &split1, int &split2, int &split3, int &split4, int &split5, int &split6, int &split7, int &split8, int &split9, int &split10);// this is part of prototype void thisisthesecondconversation (int &split1M, int &split2M, int &split3M, int &split4M, int &split5M, int &split1S,int &split2S, int &split3S, int &split4S, int &split5S, int &split1, int &split2, int &split3, int &split4, int &split5);//this gets a value void thisfindstheaverage(double &average, int &split1, int &split2, int &split3, int &split4, int &split5);//and this void thisprintsstuff( int &split1M, int &split2M, int &split3M, int &split4M, int &split5M, int &split1S, int &split2S, int &split3S, int &split4S, int &split5S, double &average); //this prints int main(int argc, char *argv[]) { int m1, m2, m3, m4, m5, s1, s2, s3, s4, s5, split1, split2, split3, split4, split5, split1M, split2M, split3M, split4M, split5M, split1S, split2S, split3S, split4S, split5S; int split6, split7, split8, split9, split10; double average; char thistakescolon; thisgetsElapsedTimes ( m1, m2, m3, m4, m5, s1, s2, s3, s4, s5); thisconvertstoseconds ( m1, m2, m3, m4, m5, s1, s2, s3, s4, s5, split1, split2, split3, split4, split5); thisfindsSplits ( m1, m2, m3, m4, m5, split1, split2, split3, split4, split5, split6, split7, split8, split9, split10); thisisthesecondconversation ( split1M, split2M, split3M, split4M, split5M, split1S, split2S, split3S, split4S, split5S, split1, split2, split3, split4, split5); thisfindstheaverage ( average, split1, split2, split3, split4, split5); thisprintsstuff ( split1M, split2M, split3M, split4M, split5M, split1S, split2S, split3S, split4S, split5S, average); // these are calling statements and they call from the main function to the other functions. system("PAUSE"); return 0; } void thisgetsElapsedTimes(int &m1, int &m2, int &m3, int &m4, int &m5, int &s1, int &s2, int &s3, int &s4, int &s5) { char thistakescolon; cout << "Enter the elapsed time:" << endl; cout << " Kilometer 1 "; cin m1 thistakescolon s1; cout << " Kilometer 2 "; cin m2 thistakescolon s2; cout << " Kilometer 3 " ; cin m3 thistakescolon s3; cout << " Kilometer 4 "; cin m4 thistakescolon s4; cout << " Kilometer 5 "; cin m5 thistakescolon s5; // this gets the data required to get the results needed for the user to see // . } void thisconvertstoseconds (int &m1, int &m2, int &m3, int &m4, int &m5, int &s1, int &s2, int &s3, int &s4, int &s5, int &split1, int &split2, int &split3, int &split4, int &split5) { split1 = (m1 * 60) + s1;//this converts for minutes to seconds for m1 split2 = (m2 * 60) + s2;//this converts for minutes to seconds for m2 split3 = (m3 * 60) + s3;//this converts for minutes to seconds for m3 split4 = (m4 * 60) + s4;//this converts for minutes to seconds for m4 split5 = (m5 * 60) + s5;//this converts for minutes to seconds for m5 } void thisfindsSplits (int &m1, int &m2, int &m3, int &m4, int &m5,int &split1, int &split2, int &split3, int &split4, int &split5, int &split6, int &split7, int &split8, int &split9, int &split10)//this is function heading { split6 = split1; //this is split for the first lap. split7 = split2 - split1;//this is split for the second lap. split8 = split3 - split2;//this is split for the third lap. split9 = split4 - split3;//this is split for the fourth lap. split10 = split5 - split4;//this is split for the fifth lap. } void thisfindstheaverage(double &average, int &split1, int &split2, int &split3, int &split4, int &split5) { average = (split1 + split2 + split3 + split4 + split5)/5; // this finds the average from all the splits in seconds } void thisisthesecondconversation (int &split1M, int &split2M, int &split3M, int &split4M, int &split5M, int &split1S,int &split2S, int &split3S, int &split4S, int &split5S, int &split1, int &split2, int &split3, int &split4, int &split5) { split1M = split1 * 60; //this finds the split times split1S = split1M - split1 * 60; //then this finds split2M = split2 * 60; //and all of this split2S = split2M - split2 * 60; //does basically split3M = split3 * 60; //the same thing split3S = split3M - split3 * 60; //all of it split4M = split4 * 60; //it's also a split4S = split4M - split4 * 60; //function split5M = split5 * 60; //and it finds the splits split5S = split5M - split5 * 60; //for each lap. } void thisprintsstuff (int &split1M, int &split2M, int &split3M, int &split4M, int &split5M, int &split1S, int &split2S, int &split3S, int &split4S, int &split5S, double &average)// this is function heading { printf("\n kilometer 1 %d" , ":02%d",'split1M','split1S'); printf("\n kilometer 2 %d" , ":02%d",'split2M','split2S'); printf("\n kilometer 3 %d" , ":02%d",'split3M','split3S'); printf("\n kilometer 4 %d" , ":02%d",'split4M','split4S'); printf("\n kilometer 5 %d" , ":02%d",'split5M','split5S'); printf("\n your average pace is ",'average',"per kilometer \n", "William Chen\n"); // this printf so the programmer // can allow the user to see // the results from the data gathered. }

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  • Interview Questions in OOP

    - by Fero
    Hi all, I faced the below interview questions in OOP under PHP language. Kindly clear my clarifications regarding this. I am very confused. As i am a beginner to OOP i got too confused. Could anyone clarify these things clearly? Difference between Abstract class and interface. Interviewer : Let us consider abstract class contains three abstract methods such as a,b,c and interface contains three methods a,b,c. In this case these do the same functionality. Then why are going for abstract and why are we going for interface. Me : ? static keyword. Interviewer: We call static method without creating object by using scope resolution operator in PHP. As well as we can able to call concrete methods also. Then what is need of static keyword there? Me : .... final keyword. Interviewer: Give me any scenario of using final keyword. Me : For db connection related method Interviewer: Other than that? Me: ... Constructor. Interviewer: What is the use of constructor? Me : There is no need for object to access this. It will call automatically when the class calls. Interviewer: Other than that? Me : .... Thanks in advance...

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  • Interacting with IE using sendkeys from Excel

    - by Thomas Egan
    I'm trying to write an application which uses values from excel and then switches to a web application using sendkeys. The problem I am having is that I cannot used sendkeys ("{ENTER}") or sendkeys ("^o") as I don't have the access for that. I'm trying to automate a very trivial admin task. I've thought about using the mouse to interact with the links as well as pausing and waiting for the user to just hit return but so far have been unable to come up with a solution. Do you think there is anyway around this? I have some VBA knowledge (enough to get me this far) but not a great deal.

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  • Does an inexperienced programmer need an IDE?

    - by Torben Gundtofte-Bruun
    Reading this other question makes me wonder if I (as an absolute beginner PHP programmer) should stick with WAMP and Notepad++ or to switch to some IDE like Eclipse. It's understandable that skilled developers will benefit from a big shiny IDE. But why should an absolute beginner use an IDE? Do the benefits outweigh the extra challenge of learning the IDE on top of learning to develop? Update for clarification: My goal is to get some basic programming experience. By choosing PHP and WAMP (and FogBugz and Kiln) I hope to avoid having to navigate the tricky / messy OS specifics and compiling etc. and just focus on basic functionality like an online user registration form. I've got lots of theoretical understanding from university a decade ago but no practical experience. I want to remedy that with a hobby project that would be similar to a real-world sellable web app. There are so many questions to ask. So many pitfalls I probably have to blunder into. This question is just one piece (my first!) of that puzzle.

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  • WCF web service with Neural Network

    - by Gary Frank
    I am developing a web service that performs object recognition. It will be available for testing as soon as enough code has been developed, and then officially when it is finished. It is based on a radically new type of artificial neural network that I designed. Its goal is to recognize any type of object within an image. Besides the WCF web service, the project will also create a website to test and demonstrate the web service. Here is a link with more information. http://www.indiegogo.com/VOR

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  • Compute the AES-encryption key given the plaintext and its ciphertext?

    - by Null Pointers etc.
    I'm tasked with creating database tables in Oracle which contain encrypted strings (i.e., the columns are RAW). The strings are encrypted by the application (using AES, 128-bit key) and stored in Oracle, then later retrieved from Oracle and decrypted (i.e., Oracle itself never sees the unencrypted strings). I've come across this one column that will be one of two strings. I'm worried that someone will notice and presumably figure out what those two values to figure out the AES key. For example, if someone sees that the column is either Ciphertext #1 or #2: Ciphertext #1: BF,4F,8B,FE, 60,D8,33,56, 1B,F2,35,72, 49,20,DE,C6. Ciphertext #2: BC,E8,54,BD, F4,B3,36,3B, DD,70,76,45, 29,28,50,07. and knows the corresponding Plaintexts: Plaintext #1 ("Detroit"): 44,00,65,00, 74,00,72,00, 6F,00,69,00, 74,00,00,00. Plaintext #2 ("Chicago"): 43,00,68,00, 69,00,63,00, 61,00,67,00, 6F,00,00,00. can he deduce that the encryption key is "Buffalo"? 42,00,75,00, 66,00,66,00, 61,00,6C,00, 6F,00,00,00. I'm thinking that there should be only one 128-bit key that could convert Plaintext #1 to Ciphertext #1. Does this mean I should go to a 192-bit or 256-bit key instead, or find some other solution? (As an aside, here are two other ciphertexts for the same plaintexts but with a different key.) Ciphertext #1 A ("Detroit"): E4,28,29,E3, 6E,C2,64,FA, A1,F4,F4,96, FC,18,4A,C5. Ciphertext #2 A ("Chicago"): EA,87,30,F0, AC,44,5D,ED, FD,EB,A8,79, 83,59,53,B7.

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  • Optimizing a thread safe Java NIO / Serialization / FIFO Queue [migrated]

    - by trialcodr
    I've written a thread safe, persistent FIFO for Serializable items. The reason for reinventing the wheel is that we simply can't afford any third party dependencies in this project and want to keep this really simple. The problem is it isn't fast enough. Most of it is undoubtedly due to reading and writing directly to disk but I think we should be able to squeeze a bit more out of it anyway. Any ideas on how to improve the performance of the 'take'- and 'add'-methods? /** * <code>DiskQueue</code> Persistent, thread safe FIFO queue for * <code>Serializable</code> items. */ public class DiskQueue<ItemT extends Serializable> { public static final int EMPTY_OFFS = -1; public static final int LONG_SIZE = 8; public static final int HEADER_SIZE = LONG_SIZE * 2; private InputStream inputStream; private OutputStream outputStream; private RandomAccessFile file; private FileChannel channel; private long offs = EMPTY_OFFS; private long size = 0; public DiskQueue(String filename) { try { boolean fileExists = new File(filename).exists(); file = new RandomAccessFile(filename, "rwd"); if (fileExists) { size = file.readLong(); offs = file.readLong(); } else { file.writeLong(size); file.writeLong(offs); } } catch (FileNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } channel = file.getChannel(); inputStream = Channels.newInputStream(channel); outputStream = Channels.newOutputStream(channel); } /** * Add item to end of queue. */ public void add(ItemT item) { try { synchronized (this) { channel.position(channel.size()); ObjectOutputStream s = new ObjectOutputStream(outputStream); s.writeObject(item); s.flush(); size++; file.seek(0); file.writeLong(size); if (offs == EMPTY_OFFS) { offs = HEADER_SIZE; file.writeLong(offs); } notify(); } } catch (IOException e) { throw new RuntimeException(e); } } /** * Clears overhead by moving the remaining items up and shortening the file. */ public synchronized void defrag() { if (offs > HEADER_SIZE && size > 0) { try { long totalBytes = channel.size() - offs; ByteBuffer buffer = ByteBuffer.allocateDirect((int) totalBytes); channel.position(offs); for (int bytes = 0; bytes < totalBytes;) { int res = channel.read(buffer); if (res == -1) { throw new IOException("Failed to read data into buffer"); } bytes += res; } channel.position(HEADER_SIZE); buffer.flip(); for (int bytes = 0; bytes < totalBytes;) { int res = channel.write(buffer); if (res == -1) { throw new IOException("Failed to write buffer to file"); } bytes += res; } offs = HEADER_SIZE; file.seek(LONG_SIZE); file.writeLong(offs); file.setLength(HEADER_SIZE + totalBytes); } catch (IOException e) { throw new RuntimeException(e); } } } /** * Returns the queue overhead in bytes. */ public synchronized long overhead() { return (offs == EMPTY_OFFS) ? 0 : offs - HEADER_SIZE; } /** * Returns the first item in the queue, blocks if queue is empty. */ public ItemT peek() throws InterruptedException { block(); synchronized (this) { if (offs != EMPTY_OFFS) { return readItem(); } } return peek(); } /** * Returns the number of remaining items in queue. */ public synchronized long size() { return size; } /** * Removes and returns the first item in the queue, blocks if queue is empty. */ public ItemT take() throws InterruptedException { block(); try { synchronized (this) { if (offs != EMPTY_OFFS) { ItemT result = readItem(); size--; offs = channel.position(); file.seek(0); if (offs == channel.size()) { truncate(); } file.writeLong(size); file.writeLong(offs); return result; } } return take(); } catch (IOException e) { throw new RuntimeException(e); } } /** * Throw away all items and reset the file. */ public synchronized void truncate() { try { offs = EMPTY_OFFS; file.setLength(HEADER_SIZE); size = 0; } catch (IOException e) { throw new RuntimeException(e); } } /** * Block until an item is available. */ protected void block() throws InterruptedException { while (offs == EMPTY_OFFS) { try { synchronized (this) { wait(); file.seek(LONG_SIZE); offs = file.readLong(); } } catch (IOException e) { throw new RuntimeException(e); } } } /** * Read and return item. */ @SuppressWarnings("unchecked") protected ItemT readItem() { try { channel.position(offs); return (ItemT) new ObjectInputStream(inputStream).readObject(); } catch (ClassNotFoundException e) { throw new RuntimeException(e); } catch (IOException e) { throw new RuntimeException(e); } } }

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  • Should I use structure from a core library graphic toolkit in my domain?

    - by Laurent Bourgault-Roy
    In java (and many other programming language), there are often structure to deal with graphic element : Colour, Shape, etc. Those are most often in a UI toolkit and thus have a relatively strong coupling with UI element. Now, in the domain of my application, we often deal with colour, shape, etc, to display statistic information on an element. Right now all we do with it is display/save those element with little or no behaviour. Would it make sense to avoid "reinventing the wheel" and directly use the structures in java.awt.* or should I make my own element and avoid a coupling to this toolkit? Its not like those element are going away anytime soon (they are part of the core java library after all), but at the same time it feel weird to import java.awt.* server side. I have no problem using java.util.List everywhere. Should I feel different about those class? What would be the "recommended" practice in that case?

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  • Understanding and memorizing git rebase parameters

    - by Robert Dailey
    So far the most confusing portion of git is rebasing onto another branch. Specifically, it's the command line arguments that are confusing. Each time I want to rebase a small piece of one branch onto the tip of another, I have to review the git rebase documentation and it takes me about 5-10 minutes to understand what each of the 3 main arguments should be. git rebase <upstream> <branch> --onto <newbase> What is a good rule of thumb to help me memorize what each of these 3 parameters should be set to, given any kind of rebase onto another branch? Bear in mind I have gone over the git-rebase documentation again, and again, and again, and again (and again), but it's always difficult to understand (like a boring scientific white-paper or something). So at this point I feel I need to involve other people to help me grasp it. My goal is that I should never have to review the documentation for these basic parameters. I haven't been able to memorize them so far, and I've done a ton of rebases already. So it's a bit unusual that I've been able to memorize every other command and its parameters so far, but not rebase with --onto.

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  • How to refactor my design, if it seems to require multiple inheritance?

    - by Omega
    Recently I made a question about Java classes implementing methods from two sources (kinda like multiple inheritance). However, it was pointed out that this sort of need may be a sign of a design flaw. Hence, it is probably better to address my current design rather than trying to simulate multiple inheritance. Before tackling the actual problem, some background info about a particular mechanic in this framework: It is a simple game development framework. Several components allocate some memory (like pixel data), and it is necessary to get rid of it as soon as you don't need it. Sprites are an example of this. Anyway, I decided to implement something ala Manual-Reference-Counting from Objective-C. Certain classes, like Sprites, contain an internal counter, which is increased when you call retain(), and decreased on release(). Thus the Resource abstract class was created. Any subclass of this will obtain the retain() and release() implementations for free. When its count hits 0 (nobody is using this class), it will call the destroy() method. The subclass needs only to implement destroy(). This is because I don't want to rely on the Garbage Collector to get rid of unused pixel data. Game objects are all subclasses of the Node class - which is the main construction block, as it provides info such as position, size, rotation, etc. See, two classes are used often in my game. Sprites and Labels. Ah... but wait. Sprites contain pixel data, remember? And as such, they need to extend Resource. But this, of course, can't be done. Sprites ARE nodes, hence they must subclass Node. But heck, they are resources too. Why not making Resource an interface? Because I'd have to re-implement retain() and release(). I am avoiding this in virtue of not writing the same code over and over (remember that there are multiple classes that need this memory-management system). Why not composition? Because I'd still have to implement methods in Sprite (and similar classes) that essentially call the methods of Resource. I'd still be writing the same code over and over! What is your advice in this situation, then?

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