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  • How do you make your Java application memory efficient?

    - by Boune
    How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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  • C++: Can a macro expand "abc" into 'a', 'b', 'c'?

    - by Peter Alexander
    I've written a variadic template that accepts a variable number of char parameters, i.e. template <char... Chars> struct Foo; I was just wondering if there were any macro tricks that would allow me to instantiate this with syntax similar to the following: Foo<"abc"> or Foo<SOME_MACRO("abc")> or Foo<SOME_MACRO(abc)> etc. Basically, anything that stops you from having to write the characters individually, like so Foo<'a', 'b', 'c'> This isn't a big issue for me as it's just for a toy program, but I thought I'd ask anyway.

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  • IOS SDK : first advices for beginners

    - by VdesmedT
    I too often answer the same kind of questions regarding basic topics like memory management, UITableView, Interface Orientation, MVC, etc... I understand very well that everyone starting with that SDK is too exited about getting its hand on it but a few reading would save them hours of debugging and the frustration that come along with the feeling that "We miss something here". I'd like experience users to share the few small articles, white papers, docs, book chapters that helps other save their time and avoid frustration. My first vote would be for : IOS Memory Management Guide View Controller Programming Guide Table View Guide And as a General recommendation, read the Overview section that come along with every class documention in the reference library, they contains most of what you need to know to avoid big traps !

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  • What is faster: multiple `send`s or using buffering?

    - by dauerbaustelle
    I'm playing around with sockets in C/Python and I wonder what is the most efficient way to send headers from a Python dictionary to the client socket. My ideas: use a send call for every header. Pros: No memory allocation needed. Cons: many send calls -- probably error prone; error management should be rather complicated use a buffer. Pros: one send call, error checking a lot easier. Cons: Need a buffer :-) malloc/realloc should be rather slow and using a (too) big buffer to avoid realloc calls wastes memory. Any tips for me? Thanks :-)

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  • Is it a good practice to pass struct object as parameter to a function in c++?

    - by tsubasa
    I tried an example live below: typedef struct point { int x; int y; } point; void cp(point p) { cout<<p.x<<endl; cout<<p.y<<endl; } int main() { point p1; p1.x=1; p1.y=2; cp(p1); } The result thats printed out is: 1 2 which is what I expected. My question is: Does parameter p get the full copy of object p1? If so, I wonder if this is a good practice? (I assumed when the struct gets big in size, this will create a lot of copy overhead).

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  • Help me refactor this nasty Ruby if/else statement

    - by Suborx
    Hello, so I have this big method in my application for newsletter distribution. Method is for updating rayons and I need to assign a user to rayon. I have relation n:n through table colporteur_in_rayons which has attributes since_date and until_date. I am a junior programmer and I know this code is pretty dummy :) I appreciate every suggestion. def update rayon = Rayon.find(params[:id]) if rayon.update_attributes(params[:rayon]) if params[:user_id] != "" unless rayon.users.empty? unless rayon.users.last.id.eql?(params[:user_id]) rayon.colporteur_in_rayons.last.update_attributes(:until_date => Time.now) Rayon.assign_user(rayon.id,params[:user_id]) flash[:success] = "Rayon #{rayon.name} has been succesuly assigned to #{rayon.actual_user.name}." return redirect_to rayons_path end else Rayon.assign_user(rayon.id,params[:user_id]) flash[:success] = "Rayon #{rayon.name} has been successfully assigned to #{rayon.actual_user.name}." return redirect_to rayons_path end end flash[:success] = "Rayon has been successfully updated." return redirect_to rayons_path else flash[:error] = "Rayon has not been updated." return redirect_to :back end end

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  • mysql multiple where and inner join query combination

    - by bandhunt
    I'm a little lost as how to run two mysql queries as one(return one result set to be sorted etc). I understand how to do multiple JOINS but need to combine the below which is more than just a multiple join - it would include a multiple where etc. 1st query sql = "SELECT s.id, s.song_name FROM `songs` as s INNER JOIN `artists` as a ON s.artist_id = a.id WHERE ((`a`.id = #{search}))" 2nd query sql = "SELECT s.id, s.song_name FROM `songs` as s INNER JOIN `similarments` as si ON s.artist_id = si.artist_id WHERE ((`si`.similar_id = #{search}))" And then run both queries at once so I can ORDER them etc. Or combine them as one big query (maybe put an OR somewhere)? Thanks!

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  • What is the best way to read files in an EventMachine-based app?

    - by Theo
    In order not to block the reactor I would like to read files asynchronously, but I've found no obvious way of doing it using EventMachine. I've tried a few different approaches, but none of them feels right: Just read the file, it'll block the reactor, but what the hell, it's not that slow (unless it's a big file, and then it definitely is). Open the file for reading and read a chunk on each tick (but how much to read? too much and it'll block the reactor, too little and reading will get slower than necessary). EM.popen('cat some/file', FileReader) feels really weird, but works better than the alternatives above. In combination with the LineAndTextProtocol it reads lines pretty swiftly. EM.attach, but I haven't found any examples of how to use it, and the only thing I've found on the mailing list is that it's deprecated in favour of… EM.watch, which I've found no examples of how to use for reading files. How do you read files within a EventMachine reactor loop?

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  • second sorting with php usort

    - by bluedaniel
    So Ive got a pretty big array of data and need to sort them by two criteria. There is variable $data['important'] and $data['basic']. They are simple numbers and I am using uasort to sort $data firstly by important and then by basic. So Important | Basic 10 | 8 9 | 9 9 | 7 7 | 9 The usort function is a simple public function sort_by_important($a, $b) { if ($a[important] > $b[important]) { return -1; } elseif ($b[important] > $a[important]) { return 1; } else { return 0; } } How can I re-sort the array to the second variable and keep the Important ordering? Thanks everyone. EDIT How about adding a third sorting option after this even? So Important Basic Less

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  • Using opencv in Win32 application for image show

    - by erjik
    Is it possible to output images so that they all will be inside a single window? Before, I used to output data using only opencv functions: cvNamedWindow("Image 1"); cvShowImage("Image 1", img); So I change image, then call: cvShowImage function and so on. But If I want to look at more than one image, then every new image needs its own window to be shown there And what I want is to put every such an output opencv's window inside one big main window. Is it possible to do it? And how?

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  • A 110 kb .NET 4.0 app needs 10 seconds for a cold start, thats not acceptable !

    - by msfanboy
    Hello, I am using the .NET 4.0 client profile for my app and I run a dual core with 4 GB Ram and a fast hard disk. nothing big is done at the start just showing a generic List in a wpf listview. How can I make the cold start faster of my assembly ? I have done now again a cold start and run the windowsapplication.exe in my \obj\x86\Debug folder and my harddisk run like hell and it took 10,5 seconds ??? What is wrong? The warm start after the cold one took 1 second. Java 6 apps has not that problem, not at all just to compare...

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  • passing variable to a batch file

    - by sushant
    i am calling a batch file for xcopy. i have the path of the file to b copied in variable a. my code is: dim shell,z z="for.bat " & a & " " & b & " " & c set shell=createobject("wscript.shell") shell.Run z, 1, true where for.bat is: for %%f in (%1,%2,%3) do xcopy %%f D:\shipment\ /e when 'a' has small path like D:\flexcube, it works. but if i put some big path, say: D:\flexcube1\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder\New Folder it does not work. is their some length restriction on %1 type variables or is this some other problem? any help is really appreciated.

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  • Handling exceptions, is this a good way?

    - by Jorge Córdoba
    We're struggling with a policy to correctly handle exceptions in our application. Here's our goals for it (summarized): Handle only specific exceptions. Handle only exceptions that you can correct Log only once. We've come out with a solution that involves a generic Application Specific Exception and works like this in a piece of code: try { // Do whatever } catch(ArgumentNullException ane) { // Handle, optinally log and continue } catch(AppSpecificException) { // Rethrow, don't log, don't do anything else throw; } catch(Exception e) { // Log, encapsulate (so that it won't be logged again) and throw Logger.Log("Really bad thing", e.Message, e); throw new AppSpecificException(e) } All exception is logged and then turned to an AppSpecificException so that it won't be logged again. Eventually it will reach the last resort event handler that will deal with it if it has to. I don't have so much experience with exception handling patterns... Is this a good way to solve our goals? Has it any major drawbacks or big red warnings?

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  • C, reading multiple numbers from single input line (scanf?)

    - by michal
    Hi, I'm writing an app in pure C which expects two line at input: first one, which tells how big an array of int will be, and the second, which contains values, separated by space. So, for the following input 5 1 2 3 4 99 I need to create an array containing {1,2,3,4,99} Now, my question is - what is the fastest (yet easy ;)) way to do so? My problem is "how to read multiple numbers without looping through the whole string checking if it's space or a number" ? Thanks m.

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  • how to write floating value accurately to a bin file.

    - by user319873
    Hi I am trying to dump the floating point values from my program to a bin file. Since I can't use any stdlib function, I am thinking of writting it char by char to a big char array which I am dumping in my test application to a file. It's like float a=3132.000001; I will be dumping this to a char array in 4 bytes. Code example would be:- if((a < 1.0) && (a > 1.0) || (a > -1.0 && a < 0.0)) a = a*1000000 // 6 bit fraction part. Can you please help me writting this in a better way.

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  • What's the deal with char.GetNumericValue?

    - by mgroves
    I was working on Project Euler 40, and was a bit bothered that there was no int.Parse(char). Not a big deal, but I did some asking around and someone suggested char.GetNumericValue. GetNumericValue seems like a very odd method to me: Takes in a char as a parameter and returns...a double? Returns -1.0 if the char is not '0' through '9' So what's the reasoning behind this method, and what purpose does returning a double serve? I even fired up Reflector and looked at InternalGetNumericValue, but it's just like watching Lost: every answer just leads to another question.

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  • Is SHA sufficient for checking file duplication? (sha1_file in PHP)

    - by wag2639
    Suppose you wanted to make a file hosting site for people to upload their files and send a link to their friends to retrieve it later and you want to insure files are duplicated where we store them, is PHP's sha1_file good enough for the task? Is there any reason to not use md5_file instead? For the frontend, it'll be obscured using the original file name store in a database but some additional concerns would be if this would reveal anything about the original poster. Does a file inherit any meta information with it like last modified or who posted it or is this stuff based in the file system? Also, is using a salt frivolous since security in regards of rainbow table attack mean nothing to this and the hash could later be used as a checksum? One last thing, scalability? initially, it's only going to be used for small files a couple of megs big but eventually... Edit 1: The point of the hash is primarily to avoid file duplication, not to create obscurity.

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  • How to check with PHP does a SQL database already have

    - by Dan Horvat
    I've tried to find the answer to this question but none of the answers fit. I have two databases, one has 15.000.000 entries and I want to extract the necessary data and store it in a much smaller database with around 33.000 entries. Both databases are open at the same time. Or at least they should be. While having the big database open and extracting the entries from it, is it possible to check whether the value already exists in the smaller database? I just need some generic way which checks that.

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  • how to force ejb3 to reload value from data base and not use those of the context

    - by Kohan95
    Hello here I have a big problem that I hope to find help here I have two entities @Entity @Inheritance(strategy=InheritanceType.JOINED) @DiscriminatorColumn(name="Role", discriminatorType=DiscriminatorType.STRING) public class Utilisateur implements Serializable { private static final long serialVersionUID = 1L; @Id @GeneratedValue(strategy = GenerationType.IDENTITY) @Column(name="id") private Long id; @Column(name="nom",nullable=false) private String nom; @Column(name="Role",nullable=false, insertable=false) private String Role ; //... } @Entity @Table(name="ResCom") @DiscriminatorValue("ResCom") public class ResCom extends Utilisateur { /... } the first thing I do ResCom rsCom= new ResCom(nom,prenom, email,civilite, SysQl.crypePasse(pass)); gr.create(rsCom); I check my database I see that property is ResCom insert but when I check the value of role I get null Utilisateur tets= gr.findByEmail(email); message=tets.getEmail()+" and Role :"+tets.getRole()+""; but in my bass it ResCom !!!!! the problem disappears when I deploy the project again I hope you have a solution And thank you in advance sorry for my English

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  • iPhone. How to intercept system dialogs?

    - by Sjakelien
    My app offers the user the opportunity to put an event in his native calendar. For that, I refer to an online webcal:// URL. Since the underlying .ics file is quite big (containing quite a few events), it sometimes (also depending on the network performance)takes a while before the "Do you want to subscribe"-dialog sequence kicks in. I would like to give the user some feedback in the mean time, like a spinner, or a changing graphic, for him to know that something is going to happen. Question: how does my app know, that the "Do you want to subscribe"-dialog has been shown, and that the user has chosen either a Cancel of OK button in that dialog, so I can stop the spinner?

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  • REST authentication S3 like hmac sha1 signature vs symetric data encryption.

    - by coulix
    Hello stackers, I was arguing about an S3 like aproach using authorization hash with a secret key as the seed and some data on the request as the message signed with hmac sha1 (Amazon S3 way) vs an other developer supporting symetric encryption of the data with a secret key known by the emiter and the server. What are the advantage of using signed data with hmac sha1 vs symetric key other than the fact that with the former, we do not need to encrypt the username or password. What would be the hardest to break ? symetric encryption or sha1 hashing at la S3 ? If all big players are using oauth and similar without symetric key it is sure that there are obvious advantages, what are those ?

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  • Git: Stage into Commit, what is the right workflow?

    - by Lukasz Lew
    I just created a big piece of code I want to commit in several separate commits. So I can stage relevant parts, commit, stage, commit, ... and so on until I have all my changes commited. The missing part is how can I test whether I split the commit correcty. I.e. whether the part that is in staging area at least compiles? To do that I must somehow bring my work tree to be in sync with index (staging area) without losing the changes to be committed later. What is the right way to do it? What is the quickest way to do it? Update: How to do it with magit?

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  • What are the common patterns in web programming?

    - by lankerisms
    I have been trying to write my first big web app (more than one cgi file) and as I kept moving forward with the rough prototype, paralelly trying to predict more tasks, this is the todo that got accumulated (In no particular order). * Validations and input sanitizations * Object versioning (to avoid edit conflicts. I dont want hard locks) * Exception handling * memcache * xss and injection protections * javascript * html * ACLs * phonetics in search, match and find duplicates (for form validation) * Ajaxify!!! (I have snipped off the project specific items.) I know that each todo will be quite tied up to its project and technologies used. What I am wondering though, is if there is a pattern in your todo items as well as the sequence in which you experienced guys have come across them.

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  • Would you hire a foreigner ? [closed]

    - by user229999
    Hi! I'd like to dedicate this question (hope it's not a subjective) especially to people who own their companies. Would you (and why) hire a foreigner, which experience is documented in CV and portfolio, which can communicate in english (with grammar mistakes, but still)? I am writing in the name of all these guys looking for great opportunities abroad, living in countries which do not give you any opportunities at all. Is it real, to be hired like a programmer (PHP, Ruby, Python, C#) in country like UK, USA, Nederland, Sweeden or even Germany, if you're a foreigner? Please response in two categories: a) foreigner with engineer degree, zend certificate, few open source projects b) foreigner without any degree, with nice portfolio, and few big projects created Also, does First Certificate in English aka FCE matter for you ?

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  • Joomla article not showing in the frontend but its visible in administrative part.

    - by user248674
    I have a very big article to be put into our joomla site. At first I was getting "Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to allocate 285487 bytes) in..." . But then I increased the memory_limit in php.ini . And I was able to create the article. Now I can view the article by logging into backend. But the article is not at all visible in the front end. If I click on the menu item pointing to that article, all I can see is a blank page with nothing in it. All other articles in the site are visible properly. Any idea? ps: I have enabled the error reporting to maximum, also ran the site in debugging mode. But saw nothing unusual.

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