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  • [java] Efficiency of while(true) ServerSocket Listen

    - by Submerged
    I am wondering if a typical while(true) ServerSocket listen loop takes an entire core to wait and accept a client connection (Even when implementing runnable and using Thread .start()) I am implementing a type of distributed computing cluster and each computer needs every core it has for computation. A Master node needs to communicate with these computers (invoking static methods that modify the algorithm's functioning). The reason I need to use sockets is due to the cross platform / cross language capabilities. In some cases, PHP will be invoking these java static methods. I used a java profiler (YourKit) and I can see my running ServerSocket listen thread and it never sleeps and it's always running. Is there a better approach to do what I want? Or, will the performance hit be negligible? Please, feel free to offer any suggestion if you can think of a better way (I've tried RMI, but it isn't supported cross-language. Thanks everyone

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  • Algorithm to determine coin combinations

    - by A.J.
    I was recently faced with a prompt for a programming algorithm that I had no idea what to do for. I've never really written an algorithm before, so I'm kind of a newb at this. The problem said to write a program to determine all of the possible coin combinations for a cashier to give back as change based on coin values and number of coins. For example, there could be a currency with 4 coins: a 2 cent, 6 cent, 10 cent and 15 cent coins. How many combinations of this that equal 50 cents are there? The language I'm using is C++, although that doesn't really matter too much. edit: This is a more specific programming question, but how would I analyze a string in C++ to get the coin values? They were given in a text document like 4 2 6 10 15 50 (where the numbers in this case correspond to the example I gave)

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  • Call a function by its name, given from string java

    - by Joao
    Hello, I would like to be able to call a function based on its name provided by a string. Something like public void callByName(String funcName){ this.(funcName)(); } I have searched a bit into lambda funcions but they are not supported. I was thinking about going for Reflection, but I am a bit new to programming, so I am not so familiar with the subject. This whole question was brought up on my java OOP class, when I started GUI (Swing, swt) programming, and events. I found that using object.addActionCommand() is very ugly, because I would later need to make a Switch and catch the exact command I wanted. I would rather do something like object.attachFunction(btn1_click), so that it would call the btn1_click function when the event click was raised. Thank you Joao

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  • Default Database Collations PenTesting Env

    - by dominicdinada
    I am using Ubuntu 9.10 with XAMPP ( Lampp "MYSQL 5.1.45 PHPMYADMIN 3.3.1 PHP 5.3.2 ) What my problem is, is that I set up my testing env to debug my scripts locally and when I did so there arose a problem. This problem is that I used firefox's addon SQLinject ME to test for weakness' and upon doing so it caused mysql to change the default local collations; character sets dir /opt/lampp/share/mysql/charsets/ collation connection latin1_general_ci (Global value) latin1_swedish_ci collation database latin1_swedish_ci collation server latin1_swedish_ci I have searched for quite sometime in regards to a solution to this problem and have come up with searching for the db.opt file which stores this information without success. Upon not finding a solution I removed lampp with the "sudo rm -fR /opt" command and reinstall and the problem still persists. I have tried to change the collations manually and still come up with the database displaying latin1_swedish_ci as the default language. Why is this a problem?? Why is it a problem with mysql? Because the application I am testing and debugging locally is built on the CodeIgnitor with Smarty framework and since this combination of framework is built to detect the LOCALES, Rather what the database defaults are I keep getting errors saying no language file for swedish...... Of course I could get the swedish language file to work around this problem but I do not feel the need to make this work around a perminant solution as with time when I move on to projects I will run into simular problems every time that A; When importing database files, backups etc it will default to import such databases as the locale swedish. B; As time passes on I might completly forget of this error and will be back to square one. I have found this code in searches for a fix,which seems to alter the tables to a desired Collaion; $value) { mysql_query("ALTER TABLE $value COLLATE latin1_general_ci"); }} echo "The collation of your database has been successfully changed!"; ? Which is handy to switch collations in One Schema at a time however this is not a fix when a framework doesnt care that the said database is in one langugae. It tests for the Default of the entire server. Someone with any knowledge of a purge or fix to this I would greatly appricate the help. One more final note is that when I was testing I only figured to back up the applications DataBase and not the entire Schema of the install. No matter if I uninstall or reinstall the database still seems to carry these problems.

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  • C# Training Quizzes

    - by John Sheppard
    Hello there, I have been programming 10 years, mostly in vba and vb.net but I know c# well enough to program what I normally do. I yesterday was applying for a Senior c# position and I did so poorly on the induction test its not funny :) I have always found that for me the best way to learn and recall is via question's and answers (multichoice and short answer). That is, a question is posed and after I answer instant feedback is given as to whether I choose right or wrong and the reasons why. As such I was wondering if anyone knew of or could recommend a C# quiz website. Something like a daily c# quiz to keep my brain up to date and fresh if I'm not always programming in it. Not something wimpy either. Something that does everything. Paying is not an obstacle, id prefer to pay for a good resource than muck around. Thank you

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  • What does Ruby have that Python doesn't, and vice versa?

    - by Lennart Regebro
    There is a lot of discussions of Python vs Ruby, and I all find them completely unhelpful, because they all turn around why feature X sucks in language Y, or that claim language Y doesn't have X, although in fact it does. I also know exactly why I prefer Python, but that's also subjective, and wouldn't help anybody choosing, as they might not have the same tastes in development as I do. It would therefore be interesting to list the differences, objectively. So no "Python's lambdas sucks". Instead explain what Ruby's lambdas can do that Python's can't. No subjectivity. Example code is good! Don't have several differences in one answer, please. And vote up the ones you know are correct, and down those you know are incorrect (or are subjective). Also, differences in syntax is not interesting. We know Python does with indentation what Ruby does with brackets and ends, and that @ is called self in Python. UPDATE: This is now a community wiki, so we can add the big differences here. Ruby has a class reference in the class body In Ruby you have a reference to the class (self) already in the class body. In Python you don't have a reference to the class until after the class construction is finished. An example: class Kaka puts self end self in this case is the class, and this code would print out "Kaka". There is no way to print out the class name or in other ways access the class from the class definition body in Python. All classes are mutable in Ruby This lets you develop extensions to core classes. Here's an example of a rails extension: class String def starts_with?(other) head = self[0, other.length] head == other end end Ruby has Perl-like scripting features Ruby has first class regexps, $-variables, the awk/perl line by line input loop and other features that make it more suited to writing small shell scripts that munge text files or act as glue code for other programs. Ruby has first class continuations Thanks to the callcc statement. In Python you can create continuations by various techniques, but there is no support built in to the language. Ruby has blocks With the "do" statement you can create a multi-line anonymous function in Ruby, which will be passed in as an argument into the method in front of do, and called from there. In Python you would instead do this either by passing a method or with generators. Ruby: amethod { |here| many=lines+of+code goes(here) } Python: def function(here): many=lines+of+code goes(here) amethod(function) Interestingly, the convenience statement in Ruby for calling a block is called "yield", which in Python will create a generator. Ruby: def themethod yield 5 end themethod do |foo| puts foo end Python: def themethod(): yield 5 for foo in themethod: print foo Although the principles are different, the result is strikingly similar. Python has built-in generators (which are used like Ruby blocks, as noted above) Python has support for generators in the language. In Ruby you could use the generator module that uses continuations to create a generator from a block. Or, you could just use a block/proc/lambda! Moreover, in Ruby 1.9 Fibers are, and can be used as, generators. docs.python.org has this generator example: def reverse(data): for index in range(len(data)-1, -1, -1): yield data[index] Contrast this with the above block examples. Python has flexible name space handling In Ruby, when you import a file with require, all the things defined in that file will end up in your global namespace. This causes namespace pollution. The solution to that is Rubys modules. But if you create a namespace with a module, then you have to use that namespace to access the contained classes. In Python, the file is a module, and you can import its contained names with from themodule import *, thereby polluting the namespace if you want. But you can also import just selected names with from themodule import aname, another or you can simply import themodule and then access the names with themodule.aname. If you want more levels in your namespace you can have packages, which are directories with modules and an __init__.py file. Python has docstrings Docstrings are strings that are attached to modules, functions and methods and can be introspected at runtime. This helps for creating such things as the help command and automatic documentation. def frobnicate(bar): """frobnicate takes a bar and frobnicates it >>> bar = Bar() >>> bar.is_frobnicated() False >>> frobnicate(bar) >>> bar.is_frobnicated() True """ Python has more libraries Python has a vast amount of available modules and bindings for libraries. Python has multiple inheritance Ruby does not ("on purpose" -- see Ruby's website, see here how it's done in Ruby). It does reuse the module concept as a sort of abstract classes. Python has list/dict comprehensions Python: res = [x*x for x in range(1, 10)] Ruby: res = (0..9).map { |x| x * x } Python: >>> (x*x for x in range(10)) <generator object <genexpr> at 0xb7c1ccd4> >>> list(_) [0, 1, 4, 9, 16, 25, 36, 49, 64, 81] Ruby: p = proc { |x| x * x } (0..9).map(&p) Python: >>> {x:str(y*y) for x,y in {1:2, 3:4}.items()} {1: '4', 3: '16'} Ruby: >> Hash[{1=>2, 3=>4}.map{|x,y| [x,(y*y).to_s]}] => {1=>"4", 3=>"16"} Python has decorators Things similar to decorators can be created in Ruby, and it can also be argued that they aren't as necessary as in Python.

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  • What is the best API/framework/platform you ever worked with?

    - by Yuval A
    Most programming is done on an existing framework or platform, and using various APIs which make your programming job much more convenient. It can either be a superbly designed set of APIs, or a nice framework which you managed to get really cool things done really fast. All answers should give concrete examples of why that framework is so awesome, or examples of cool stuff you did with it. What existing framework really inspired you to do some awesome work? I know this is subjective, but I think we can get some cool ideas from this question. Please be easy on the "close" link :) Also - commun-ikified in advance.

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  • grails metaprogramming

    - by Don
    Hi, My understanding is that there are two obvious places in a Grails app where one can do meta-programming: The init closure of Bootstrap.groovy The doWithDynamicMethods closure of a plugin The meta-programming I'm referring to here should be visible throughout the metaprogramming, typical examples include adding (or replacing) methods of 3rd party classes. String.metaClass.myCustomMethod = { /* implementation omitted */ } The disadvantage of (1), is that the metaprogramming won't be applied when the application is dynamically reloaded. The disadvantage of (2) is that I need to create and maintain an entire plugin just for the sake of a little metaprogramming. Is there a better place to do this kind of metaprogramming? Thanks, Don

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  • Intel Assembler optimization

    - by Søren Haagerup
    I'm currently trying to optimize the code emitted from a home-made compiler, for a home-made language. I've tried out Intel VTune to see where the bottlenecks are: http://www.imada.sdu.dk/~sorenh07/misc/vtune-assembly-optimization.png I find it very impressive that a "subl"-instruction is responsible for over 38% of the clockticks in a program running for 30-90 seconds! Can anybody give an explanation why? The "optimization report" feature in VTune apparently doesn't exist for programs not compiled with icc. Does there exist a program which suggests optimization for assembler code? (that is, not code coming from a high-level language).

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  • What (kind of) project could I create to learn JavaScript?

    - by Aziz Light
    Hello, I started learning JavaScript a while ago. It's a fairly easy programming language considering that I learned Java in university, that I know php pretty well and that I already played around with python and ruby. The problem is that to properly learn a programming language I usually create a project. In javascript, I just don't know what kind of project I could create - that is, a project that is not web-based or related to the web browser. Can I create javascript shell scripts? Where is javascript commonly used beside the web browsers? So, can someone actually give me some ideas please?

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  • How are you using IronPython?

    - by Will Dean
    I'm keen to drink some modern dynamic language koolaid, so I've believed all the stuff on Michael Foord's blog and podcasts, I've bought his book (and read some of it), and I added an embedded IPy runtime to a large existing app a year or so ago (though that was for someone else and I didn't really use it myself). Now I need to do some fairly simple code generation stuff, where I'm going to call a few methods on a few .net objects (custom, C#-authored objects), create a few strings, write some files, etc. The experience of trying this leaves me feeling like the little boy who thinks he's the only one who can see that The Emperor has no clothes on. If you're using IronPython, I'd really appreciate knowing how you deal with the following aspects of it: Code editing - do you use the .NET framework without Intellisense? Refactoring - I know a load of 'refactoring' is about working around language-related busywork, so if Python is sufficiently lightweight then we won't need that, But things like renames seem to me to be essential to iteratively developing quality code regardless of language. Crippling startup time - One of the things which is supposed to be good about interpreted languages is the lack of compile time leading to fast interactive development. Unfortunately I can compile a C# application and launch it quicker than IPy can start up. Interactive hacking - the IPy console/repl is supposed to be good for this, but I haven't found a good way to take the code you've interactively arrived at and persist it into a file - cut and paste from the console is fairly miserable. And the console seems to hold references to .NET assemblies you've imported, so you have to quit it and restart it if you're working on the C# stuff as well. Hacking on C# in something like LinqPad seems a much faster and easier way to try things out (and has proper Intellisense). Do you use the console? Debugging - what's the story here? I know someone on the IPy team is working on a command-line hobby-project, but let's just say I'm not immediately attracted to a command line debugger. I don't really need a debugger from little Python scripts, but I would if I were to use IPy for scripting unit tests, for example. Unit testing - I can see that dynamic languages could be great for this, but is there any IDE test-runner integration (like for Resharper, etc). The Foord book has a chapter about this, which I'll admit I have not yet read properly, but it does seem to involve driving a console-mode test-runner from the command prompt, which feels to be an enormous step back from using an integrated test runner like TestDriven.net or Resharper. I really want to believe in this stuff, so I am still working on the assumption that I've missed something. I would really like to know how other people are dealing with IPy, particularly if they're doing it in a way which doesn't feel like we've just lost 15 years'-worth of tool development.

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  • How beneficial is this subject combination for an undergrad CS student?

    - by Maxood
    I'm an undergrad Computer Science student and studying online. There is a lot of self study, independent research and practice i have to do myself. I wonder how beneficial would it be to choose this subject combination in programming: Data Structures OOP Assembly Language & Computer Architecture Although i also have the option to take DLD (Digital Logic Design) or Data communication courses instead of Assembly Language. My interest lies in programming and i'm also working as a programmer at local software house. Can anyone give me some good advice and suggestions.

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  • Why exactly is eval evil?

    - by Jay
    I know that Lisp and Scheme programmers usually say that eval should be avoided unless strictly necessary. I´ve seen the same recommendation for several programming languages, but I´ve not yet seen a list of clear arguments against the use of eval. Where can I find an account of the potential problems of using eval? For example, I know the problems of GOTO in procedural programming (makes programs unreadable and hard to maintain, makes security problems hard to find, etc), but I´ve never seen the arguments against eval. Interestingly, the same arguments against GOTO should be valid against continuations, but I see that Shemers, for example, won´t say that continuations are "evil" -- you should just be careful when using them. They´re much more likely to frown upon code using eval than upon code using continuations (as far as I can see -- I could be wrong).

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  • Android-iPhone single codebase cross development

    - by Lorenzo
    Is there a way, apart from using HTML and JavaScript on a web control, to have an (almost) single codebase for an application that should run on iOS and Android? The big issue is of course that they use a different language (Java for Android, Objective-C for iOS) for application development. It would be nice to have some sort of meta-language that will be translated in Java and in Objective-C. What about Flash? Adobe wasn't supposed to release a tool to create flash-based apps in iOS? Update: based on current answers, the best cross platform development tool for iOS and Android seems to be Titanium appcelerator. I suspect that this topic will evolve overtime, so feel free to contribute with new information and comments. Thank you!

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  • Does Objective-C have a Standard Library?

    - by Roman A. Taycher
    Most somewhat modern programming languages have a standard library? It is my impression is that there isn't a decent sized standard library for Obj-C , rather that it relies mostly/all on Cocoa and that (plus people not wanting to use GNUstep) is why Obj-C is only used on macs)? Is this true/to what extent? Are there any standard obj-c collections? (note I haven't done any Obj-C programming and am not to likely to try it in the near future, I'm just curious). P.S. are there a any decent non-Cocoa/Gnustep Libraries? are they non-apple, are they open source, well documented?

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  • Any good books out there for advanced concepts like lambdas, delegates, events etc?

    - by they_soft
    I've read about these features but I don't think I've seen enough to consistently apply them in my coding, eg "This would be better done with a delegate than with my other, outdated approach". I know what they do, but I want more examples of use cases, or want some heuristic to help me think in terms of such features. All the books I've seen either focus only on the basics or just mention the features as part of the language. Is there any book out there that deals with this? Preferably C# or language agnostic.

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  • How to access a SIM card programatically?

    - by mawg
    Just any old GSM compatible SIM card (bonus for 3G USIM). I presume I need some hardware? Can anyone recommend something cheap for hobbyist, and something more professional? I presume that there will be full docs of an API with the h/w, so maybe this should be tagged "no-programming-related"? Sorry, if so. Any good URLs or books (I am conversant with the 3GPP standards). I'm not (black hat) hacking, don't worry, just not pleased with the likes of SIM Card Secretary, Data Doctor Recovery, etc, so would like to code my own, but might turn it commercial, or offer SIM card programming services (data recover from damaged card, etc) as a sideline.

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  • What should I call the operation that limit a string's length?

    - by egarcia
    This is a language-agnostic question - unless you count English as a language. I've got this list of items which can have very long names. For aesthetic purposes, these names must be made shorter in some cases, adding dots (...) to indicate that the name is longer. So for example, if article.name returns this: lorem ipsum dolor sit amet I'd like to get this other output. lorem ipsum dolor ... I can program this quite easily. My question is: how should I call that shortening operation? I mean the name, not the implementation. Is there a standard English name for it?

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