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  • Java Thread - Synchronization issue

    - by Yatendra Goel
    From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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  • Streaming large result sets with MySQL

    - by configurator
    I'm developing a spring application that uses large MySQL tables. When loading large tables, I get an OutOfMemoryException, since the driver tries to load the entire table into application memory. I tried using statement.setFetchSize(Integer.MIN_VALUE); but then every ResultSet I open hangs on close(); looking online I found that that happens because it tries loading any unread rows before closing the ResultSet, but that is not the case since I do this: ResultSet existingRecords = getTableData(tablename); try { while (existingRecords.next()) { // ... } } finally { existingRecords.close(); // this line is hanging, and there was no exception in the try clause } The hangs happen for small tables (3 rows) as well, and if I don't close the RecordSet (which happened in one method) then connection.close() hangs.

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  • Why use constants in programming?

    - by Adam N
    I've just been going back over a bit of C studying using Ivor Horton's Beginning C book. I got to the bit about declaring constants which seems to get mixed up with variables in the same sentence. Just to clarify, what is the difference in specifying constants and variables in C, and really, when do you need to use a constant instead of a variable? I know folks say to use a constant when the information doesn't change during program execution but I can't really think of a time when a variable couldn't be used instead. Thanks

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  • method returning wrong variable

    - by cocoanewbie
    This class I'm working with has three instance variables I'm interested in, NSmutablearrays xArray yArray and zArray, there are also other NSmutablearrays, a, bArray and c. I just added accessors - (NSMutableArray *) xArray { return xArray; } ditto for y and z. However, it's returning yArray, zArray and bArray for some reason. Why is that happening? Okay, I just changed the names of the methods to GetXArray and everything seems to be returning the right variables. Now I'm really confused. How the heck did this happen and how do I prevent this from happening in the future?

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  • How to make my WPF application as FAST as Outlook

    - by Raul Otaño
    The commons WPF applications take some time for loading medium complex views, once the view is loaded it works fine. For example in a Master - Detail view, if the Detail view is very complex and use different DataTemplates take some seconds (2-3 seconds) for load the view. When i open the Outlook application, for instance, it renders complex views and it is relative much more fast. Is there a way for increase the performance of my WPF application? Maybe a way for not loading the template's data every time that change the "master" item, and load it only one time in the app time live? i will appreciate any suggestion.

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  • C# Different class objects in one list

    - by jeah_wicer
    I have looked around some now to find a solution to this problem. I found several ways that could solve it but to be honest I didn't realize which of the ways that would be considered the "right" C# or OOP way of solving it. My goal is not only to solve the problems but also to develop a good set of code standards and I'm fairly sure there's a standard way to handle this problem. Let's say I have 2 types of printer hardwares with their respective classes and ways of communicating: PrinterType1, PrinterType2. I would also like to be able to later on add another type if neccessary. One step up in abstraction those have much in common. It should be possible to send a string to each one of them as an example. They both have variables in common and variables unique to each class. (One for instance communicates via COM-port and has such an object, while the other one communicates via TCP and has such an object). I would however like to just implement a List of all those printers and be able to go through the list and perform things as "Send(string message)" on all Printers regardless of type. I would also like to access variables like "PrinterList[0].Name" that are the same for both objects, however I would also at some places like to access data that is specific to the object itself (For instance in the settings window of the application where the COM-port name is set for one object and the IP/port number for another). So, in short something like: In common: Name Send() Specific to PrinterType1: Port Specific to PrinterType2: IP And I wish to, for instance, do Send() on all objects regardless of type and the number of objects present. I've read about polymorphism, Generics, interfaces and such, but I would like to know how this, in my eyes basic, problem typically would be dealt with in C# (and/or OOP in general). I actually did try to make a base class, but it didn't quite seem right to me. For instance I have no use of a "string Send(string Message)" function in the base class itself. So why would I define one there that needs to be overridden in the derived classes when I would never use the function in the base class ever in the first place? I'm really thankful for any answers. People around here seem very knowledgeable and this place has provided me with many solutions earlier. Now I finally have an account to answer and vote with too. EDIT: To additionally explain, I would also like to be able to access the objects of the actual printertype. For instance the Port variable in PrinterType1 which is a SerialPort object. I would like to access it like: PrinterList[0].Port.Open() and have access to the full range of functionality of the underlaying port. At the same time I would like to call generic functions that work in the same way for the different objects (but with different implementations): foreach (printer in Printers) printer.Send(message)

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  • Why do I get strange output from Perl using SQL?

    - by benjamin button
    Here is my Perl code: foreach my $line (@tmp_field_validation) { chomp $line; my ($cycle_code,$cycle_month,$cycle_year)= split /\s*\|\s*/, $line; $cycle_code=~ s/^\s*(.*)\s*$/$1/; $cycle_month=~ s/^\s*(.*)\s*$/$1/; $cycle_year=~ s/^\s*(.*)\s*$/$1/; print "$line\n"; print "$cycle_code|$cycle_month|$cycle_year"; } Here is the output: 1 10 2009 1 10 2009|| What's wrong over here? I expected the pipes to be between the variables. Why are the pipes getting printed after all the three variables?

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  • Member variable in C++ class that is always constant for all objects of that class?

    - by user1799323
    I'm constructing a class where I have three member variables that I want to always be the same value NO MATTER WHAT. I have class foo{ public: double var_1, var_2, var_3; double x=1, y=2, z=3; [functions go here] }; that gave me an error since I can't initialize a variable like that. But I want x, y and z to always be 1, 2 and 3 respectively. I tried defining them outside the class but that doesn't work since I want them to be member variables of the class. How do I do this?

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  • Find a variable with a given value in VS2008

    - by Aaron
    I have an instance variable with several members, many of which have their own members and so on. Using the debugger and watch variables, I found a string variable with a specific value that I need by diving into this variable's members. However, after spending some time on other things and coming back to this, I am now unable to find where this value is located. When I have my application paused, is there a way to search the values of variables in the current context for a given value? To clarify, if I have the given structure: myVariable | |--aMember1 | |--subMember = "A value" | |--aMember2 |--subMember = "Another value" Is there a way (possibly using the watch list in VS debugger) to search myVariable for any member or submember with the value "A value", returning to me the path myVariable->aMember->subMember?

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  • Performance implications of using a variable versus a magic number

    - by Nathan
    I'm often confused by this. I've always been taught to name numbers I use often using variables or constants, but if it reduces the efficiency of the program, should I still do it? Heres an example: private int CenterText(Font font, PrintPageEventArgs e, string text) { int recieptCenter = 125; int stringLength = Convert.ToInt32(e.Graphics.MeasureString(text, font)); return recieptCenter - stringLength / 2; } The above code is using named variables, but runs slower then this code: private int CenterText(Font font, PrintPageEventArgs e, string text) { return 125 - Convert.ToInt32(e.Graphics.MeasureString(text, font) / 2); } In this example, the difference in execution time is minimal, but what about in larger blocks of code?

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  • Which is the best Linux C/C++ debugger (or front-end to gdb) to help teaching programming?

    - by omer.gimenez
    I teach a sort of "lite" C++ programming course to novices ("lite" meaning no pointers, no classes, just plain old C, plus references and STL string and vectors). Students have no previous experience in programming, so I believe that using an interactive debugger would help them understand program flow, variables, and recursion. The course is taught in Linux. Teaching them to use gdb is just overkill (they will not use nor understand most features). I just need something simple but easy to use: to see at which line the program is now, what is in the stack (local variables, previous calls, etc.). I look something similar to old Turbo Pascal or Turbo C++ Borland's debugger, or Visual Studio debugger. Thank you,

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  • Call an anonymous function defined in a setInterval

    - by Tominator
    Hi, I've made this code: window.setInterval(function(){ var a = doStuff(); var b = a + 5; }, 60000) The actual contents of the anonymous function is of course just for this small example as it doesn't matter. What really happens is a bunch of variables get created in the scope of the function itself, because I don't need/want to pollute the global space. But as you all know, the doStuff() function won't be called until 60 seconds in the page. I would also like to call the function right now, as soon as the page is loaded, and from then on every 60 seconds too. Is it somehow possible to call the function without copy/pasting the inside code to right after the setInterval() line? As I said, I don't want to pollute the global space with useless variables that aren't needed outside the function.

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  • How to setup Math program

    - by Miles
    I'm needing to write a program (C#) that will allow the user to create generic formulas with variables and numbers. For example: D = A + (A - C / X)(7.8 - 6.6) F = E + (E - C / X)(7.8 - 6.6) FinalResult = (A + D)(0.9) + (E + F)(0.32) + B(0.1) + .023 where all variables would mean for me to go to a database and look something up based on values and return a number in its place. So A would be 2.12 for example (and the same for C and E) Whats the best way to structure this program? How would I make my program read these formulas? I've seen a little bit of the MathML but not sure how to get that started (or an example of it)

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  • Hibernate one-to-one: getId() without fetching entire object

    - by Rob
    I want to fetch the id of a one-to-one relationship without loading the entire object. I thought I could do this using lazy loading as follows: class Foo { @OneToOne(fetch = FetchType.LAZY, optional = false) private Bar bar; } Foo f = session.get(Foo.class, fooId); // Hibernate fetches Foo f.getBar(); // Hibernate fetches full Bar object f.getBar().getId(); // No further fetch, returns id I want f.getBar() to not trigger another fetch. I want hibernate to give me a proxy object that allows me to call .getId() without actually fetching the Bar object. What am I doing wrong?

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  • Prism for Silverlight: How to maintain views in a specific order inside a region.

    - by ArielBH
    Hi I am creating sort of a "Navigation panel" (which is actually an ItemControl) for SL and using Regions to allow each module to add his link to the panel. Problem is that modules loading is inconsistent and thus order of links in the panel can change according to modules loading order. Restricting the modules order is out of the question. Other feasible option is the order the region's Views Collection that is binded to the ItemControl, the problem is that ViewCollection is very limited, so ordering it is pretty hard. Did I miss an option, do you have an idea? Thanks Ariel

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  • How to call a Zend lucene search function?

    - by stef
    I inherited a Zend project devoid of comments and I didn't get to talk to the previous developer. Since I have no Zend experience I'm having some issues :) I'd like to print out some variables inside an function that indexes items from the site using Zend_Search_Lucene because I think something is going wrong here. From what I've read, ::create creates a new index and ::open updates it. So it's in this ::open function I'd like to print out some variables. The name and params of the function are below. Does anyone have any idea how this function can be called so I can run some tests? private function search($category,$string,$page = 1,$itemsByPage = 5) EDIT: OR, is there a way I can nuke the existing index and force it to be rebuilt completely, for example by deleting the index files on the FS and then performing some searches?

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  • Remembering Form information

    - by Pete Herbert Penito
    Hi everyone! I'm sorry if this has been asked before but I feel my situation is a little different... I have a huge form (like 50 questions involving checkboxes, drop downs, text boxes and textareas) When a user submits a form and the validation page throws an error, is there an easy way to keep the info they entered? My intitial form is on form.php and then the form action is form_posted.php, before anything is run on form_posted.php I have my validation code which sends the user back to form.php with an error number (eg. form.php?error=3) if there was a problem with any in particular. This is done with header("form.php?error=3") so on form.php do the posted variables exist? even tho the page wasn't specifically sent with any posted variables. Also if this is the case, is it completely secure to be making the value of a textbox what it was before? like <input type="text" value="php echo $_POSTED["username"] ?>">

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  • Understanding configuration for parallel calling in web app (IIS + MS SQL)

    - by mmcteam.com.ua
    We have an ASP.NET MVC application + IIS 7.5 + SQL Server 2008 R2. We have to load a lot of aggregate counters on the each page. We decided to use ajax and call with javascript for each counter or groups of counters and return them as JSON result. We solve the problem that user doesn't wait for page loading, page loads fast. User waits for counters loading while seeing other page content. But we thought that if we make calls from javascript - our queries will be make async, but we notice, that it is not. All our javascipt calls runs immediately, but action that they invoke are in queue. If we use Async Controller ability - all counters calculating simultaneously, but user has to wait for the longest counter calculating before page loads. The question: We want to understand what is happens if we use ajax and call two or more actions simultaneously. And how can we configuring this. (also in each action we make some queries to sql server)

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  • Propor usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something? Cheers.

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  • Access static constant variable from multiple threads in C

    - by user325519
    I have some experience with multithread programming under Linux (C/C++ & POSIX threads), however most obvious cases are sometimes very complicated. I have several static constant variables (global and function local) in my code, can I access them simultaneously from multiple threads without using mutexes? Because I don't modify them it should be ok, but it's always better to ask. I have to do heavy speed optimization, so even as fast operations as mutex lock/unlock are quite expensive for me, especially because my application is going to access these variables form long loops.

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  • Proper usage of double and single quotes?

    - by Phox
    I'm talking about the performance increase here. From all I know you can echo variables in double quotes ("), like so: <?php echo "You are $yourAge years old"; ?> But single quotes will just return You are $yourAge years old. But what about performance differences? I've always gone by the rule that single quotes are faster because the PHP interpreter doesn't have to search through the string for variables. But I'm seeing more and more blog and forum posts on the web saying differently. Does anyone actually have any information on this subject? Perhaps benchmark tests or something?

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  • How to animate the command line?

    - by The.Anti.9
    I have always wondered how people update a previous line in a command line. a great example of this is when using the wget command in linux. It creates an ASCII loading bar of sorts that looks like this: [======                    ] 37% and of course the loading bar moves and the percent changes, But it doesn't make a new line. I cannot figure out how to do this. Can someone point me in the right direction?

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  • Is there a %in% operator accros multiple columns

    - by RobinLovelace
    Imagine you have two data frames df1 <- data.frame(V1 = c(1, 2, 3), v2 = c("a", "b", "c")) df2 <- data.frame(V1 = c(1, 2, 2), v2 = c("b", "b", "c")) Here's what they look like, side by side: > cbind(df1, df2) V1 v2 V1 v2 1 1 a 1 b 2 2 b 2 b 3 3 c 2 c You want to know which observations are duplicates, across all variables. This can be done by pasting the cols together and then using %in%: df1Vec <- apply(df1, 1, paste, collapse= "") df2Vec <- apply(df2, 1, paste, collapse= "") df2Vec %in% df1Vec [1] FALSE TRUE FALSE The second observation is thus the only one in df2 and also in df1. Is there no faster way of generating this output - something like %IN%, which is %in% across multiple variables, or should we just be content with the apply(paste) solution?

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  • Codeigniter pre_system hook for DB driven dynamic controller selection - best approach?

    - by Andy
    Although I can tentatively see a solution to this, I was wondering if there may be a glaringly obvious simpler approach. My aim is to use the first segment of a given URI to query the DB as to which controller should be run. I assume I would have to reform the URI with the resultant controller name in segment 1, then allow the system to continue processing as normal (hence a pre_system hook). Although not essential I would also like to hold a couple of other variables from the same DB request to be used later in the call stack, and assume this would have to be done using global variables? Any better suggestions would be gladly received. Thanks.

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