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  • Is this use of PreparedStatements in a Thread in JAVA correct?

    - by Gormcito
    I'm still an undergrad just working part time and so I'm always trying to be aware of better ways to do things. Recently I had to write a program for work where the main thread of the program would spawn "task" threads (for each db "task" record) which would perform some operations and then update the record to say that it has finished. Therefore I needed a database connection object and PreparedStatement objects in or available to the ThreadedTask objects. This is roughly what I ended up writing, is creating a PreparedStatement object per thread a waste? I thought static PreparedStatments could create race conditions... Thread A stmt.setInt(); Thread B stmt.setInt(); Thread A stmt.execute(); Thread B stmt.execute(); A´s version never gets execed.. Is this thread safe? Is creating and destroying PreparedStatement objects that are always the same not a huge waste? public class ThreadedTask implements runnable { private final PreparedStatement taskCompleteStmt; public ThreadedTask() { //... taskCompleteStmt = Main.db.prepareStatement(...); } public run() { //... taskCompleteStmt.executeUpdate(); } } public class Main { public static final db = DriverManager.getConnection(...); }

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  • XSL(like) declarative language as MVC view over strongtyped model?

    - by Martin Kool
    As a huge XSL fan, I am very happy to use xsl as the view in our proprietary MVC framework on ASP.NET. Objects in the model are serialized under the hood using .NET's xml serializer, and we use quite atomic xsl templates to declare how each object or property should transform. For example: <xsl:template match="/Article"> <html> <body> <div class="article"> <xsl:apply-templates /> </div> </body> </html> </xsl:template> <xsl:template match="Article/Title"> <h1> <xsl:apply-templates /> </h1> </xsl:template> <xsl:template match="@*|text()"> <xsl:copy /> </xsl:template> This mechanism allows us to quickly override default matching templates, like having a template matching on the last item in a list, or the selected one, etc. Also, xsl extension objects in .NET allow us just the bit of extra grip that we need. Common shared templates can be split up and included. However Even though I can ignore the verbosity downside of xsl (because Visual Studio schema intellisense + snippets really is slick, praise to the VS-team), the downside of not having intellisense over strongtyped objects in the model is really something that's bugging me. I've seen ASP.NET MVC + user controls in action and really starting to love it, but I wonder; Is there a way of getting some sort of intellisense over XML that we're iterating over, or do you know of a language that offers the freedom and declarativeness of XSL but has the strongtype/intellisense benefits of say webforms/usercontrols/asp.net.mvc-view? (I probably know the answer: "no", and I'll find myself using Phil Haack's utterly cool mvc shizzle soon...)

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  • Python - How to wake up a sleeping process- multiprocessing?

    - by user1162512
    I need to wake up a sleeping process ? The time (t) for which it sleeps is calculated as t = D/S . Now since s is varying, can increase or decrease, I need to increase/decrease the sleeping time as well. The speed is received over a UDP procotol. So, how do I change the sleeping time of a process, keeping in mind the following:- If as per the previous speed `S1`, the time to sleep is `(D/S1)` . Now the speed is changed, it should now sleep for the new time,ie (D/S2). Since, it has already slept for D/S1 time, now it should sleep for D/S2 - D/S1. How would I do it? As of right now, I'm just assuming that the speed will remain constant all throughout the program, hence not notifying the process. But how would I do that according to the above condition? def process2(): p = multiprocessing.current_process() time.sleep(secs1) # send some packet1 via UDP time.sleep(secs2) # send some packet2 via UDP time.sleep(secs3) # send some packet3 via UDP Also, as in threads, 1) threading.activeCount(): Returns the number of thread objects that are active. 2) threading.currentThread(): Returns the number of thread objects in the caller's thread control. 3) threading.enumerate(): Returns a list of all thread objects that are currently active. What are the similar functions for getting activecount, enumerate in multiprocessing?

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  • Need help optimizing this Django aggregate query

    - by Chris Lawlor
    I have the following model class Plugin(models.Model): name = models.CharField(max_length=50) # more fields which represents a plugin that can be downloaded from my site. To track downloads, I have class Download(models.Model): plugin = models.ForiegnKey(Plugin) timestamp = models.DateTimeField(auto_now=True) So to build a view showing plugins sorted by downloads, I have the following query: # pbd is plugins by download - commented here to prevent scrolling pbd = Plugin.objects.annotate(dl_total=Count('download')).order_by('-dl_total') Which works, but is very slow. With only 1,000 plugins, the avg. response is 3.6 - 3.9 seconds (devserver with local PostgreSQL db), where a similar view with a much simpler query (sorting by plugin release date) takes 160 ms or so. I'm looking for suggestions on how to optimize this query. I'd really prefer that the query return Plugin objects (as opposed to using values) since I'm sharing the same template for the other views (Plugins by rating, Plugins by release date, etc.), so the template is expecting Plugin objects - plus I'm not sure how I would get things like the absolute_url without a reference to the plugin object. Or, is my whole approach doomed to failure? Is there a better way to track downloads? I ultimately want to provide users some nice download statistics for the plugins they've uploaded - like downloads per day/week/month. Will I have to calculate and cache Downloads at some point? EDIT: In my test dataset, there are somewhere between 10-20 Download instances per Plugin - in production I expect this number would be much higher for many of the plugins.

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  • Python & Pygame: Updating all elements in a list under a loop during iteration

    - by Unit978
    i am working on a program in Python and using Pygame. this is what the basic code looks like: while 1: screen.blit(background, (0,0)) for event in pygame.event.get(): if event.type == QUIT: pygame.quit() sys.exit() if event.type == KEYDOWN and event.key == K_c: circle_create = True circle_list.append(Circle()) if event.type == MOUSEBUTTONDOWN and circle_create == True: if clicks == 0: circle_list[i].center() clicks += 1 if event.type == MOUSEMOTION and clicks == 1 and circle_create == True: circle_list[i].stretch() these if statements are under the while loop not the for loop since they dont require input from the user if circle_create == True: circle_list[i].draw_circle() if clicks == 2: clicks = 0 i += 1 circle_create = False pygame.display.update() what i want to do is have the object's function of draw_circle() to be constantly updated by the loop so that the drawn circle is shown for all objects in the list, but since the list is iterated it updates the new object added and the objects already appended are not updated. The program, works, it draws the circles upon user input but the update problem is the only issue i need to solve. Is there any possible way to have all elements in the list of objects being updated by the while loop? i have tried for many days and i have not been able to find a good solution. any ideas are appreciated. Thanks

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  • Most Efficient way to deal with multiple CCSprites?

    - by nardsurfer
    I have four different types of objects within my environment(box2d), each type of object having multiple instances of itself, and would like to find the most efficient way to deal with adding and manipulating all the CCSprites. The sprites are all from different files, so would it be best to create each sprite and add it to a data structure (NSMutableArray) or would I use a CCSpriteBatchNode even though each CCSprite file is different (for each type of object)? Thanks. @interface LevelScene : CCLayer { b2World* world; GLESDebugDraw *m_debugDraw; CCSpriteBatchNode *ballBatch; CCSpriteBatchNode *blockBatch; CCSpriteBatchNode *springBatch; CCSprite *goal; } +(id) scene; // adds a new sprite at a given coordinate -(void) addNewBallWithCoords:(CGPoint)p; // loads the objects (blocks, springs, and the goal), returns the Level Object -(Level) loadLevel:(int)level; @end or using NSMutableArray objects within the Level object... @interface zLevel : zThing { NSMutableArray *springs; NSMutableArray *blocks; NSMutableArray *balls; zGoal *goal; int levelNumber; } @property(nonatomic,retain)NSMutableArray *springs; @property(nonatomic,retain)NSMutableArray *blocks; @property(nonatomic,retain)NSMutableArray *balls; @property(nonatomic,retain)zGoal *goal; @property(nonatomic,assign)int levelNumber; -(void)initWithLevel:(int)level; -(void)loadLevelThings; @end

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  • !gcroot output leads nowhere

    - by Jeff Costa
    I am troubleshooting memory fragmentation in an app pool, as evidenced by a small number of Free objects consuming the most space on the heap: 0x000007ff00256728 6,543 3,890,208 System.Collections.Hashtable+bucket[] 0x000007ff002649a8 7,297 22,979,560 System.Byte[] 0x000007ff001e0d90 251,347 30,374,304 System.String 0x0000000001d0c830 373 48,036,816 Free Running the !dumpgen 3 command reveals the fragmentation; There is a repeating pattern of Free and System.Object objects of the same size: 000000017feb7350 24 **** FREE **** 000000017feb7368 8192 System.Object[] 000000017feb9368 24 **** FREE **** 000000017feb9380 8192 System.Object[] 000000017febb380 24 **** FREE **** 000000017febb398 8192 System.Object[] 000000017febd398 24 **** FREE **** 000000017febd3b0 8192 System.Object[] 000000017febf3b0 24 **** FREE **** 000000017febf3c8 8192 System.Object[] 000000017fec13c8 24 **** FREE **** 000000017fec13e0 8192 System.Object[] 000000017fec33e0 24 **** FREE **** 000000017fec33f8 8192 System.Object[] 000000017fec53f8 24 **** FREE **** 000000017fec5410 14024 System.Object[] 000000017fec8ad8 24 **** FREE **** 000000017fec8af0 8192 System.Object[] 000000017fecaaf0 24 **** FREE **** 000000017fecab08 8192 System.Object[] 000000017feccb08 24 **** FREE **** 000000017feccb20 8192 System.Object[] 000000017feceb20 24 **** FREE **** 000000017feceb38 8192 System.Object[] 000000017fed0b38 24 **** FREE **** 000000017fed0b50 8192 System.Object[] 000000017fed2b50 24 **** FREE **** 000000017fed2b68 8192 System.Object[] When I try to obtain the root of one of the System.Objects with !gcroot, I get a pinned handle, but no additional stack data: Scan Thread 41 OSThread 1044 DOMAIN(0000000001D51330):HANDLE(Pinned):15217e8:Root: 000000017fe60fe8(System.Object[]) As you can see, there is no additional data to go on. Running a !handle command also yields nothing: 0:041> !handle 000000017fe7a068 ff Handle 000000017fe7a068 Type <Error retrieving type> unable to query object information unable to query object information No object specific information available How can I trace out this memory leak when I cannot find what is rooting System.Object?

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  • Should the program logic reside inside the gui object class or be external to the class?

    - by hd112
    I have a question about how to structure code in relation to GUI objects. Suppose I have a dialog that has a list control that has a bunch of names obtained from a database. The user can edit the names. Does the logic reside inside that dialog class or should it be from the outside. To illustrate what I mean, here’s some pseudo code showing the structure of the code when the logic is handled outside the dialog class: NamesDialog : wxDialog { Private: ..stuff.. Public: ... SetNames(wxStringArray names); wxStringArray GetNames(); ..stuff.. } So the user of the class would do something like: wxStringArray names = DatabaseManager::Get()->GetNames(); names.Sort(); NamesDialogObject.SetNames(names); NamesDialogObject.ShowModal(); wxStringArray modified_names = NamesDialogObject.GetNames(); AddToDatabase(modified_names); //or something like this. On the other hand, the database logic can reside inside the NamesDialog class itself. In the show method I can query the database for the names and as the user interacts with the controls (list control in this case), the database can be updated from the event handlers. As a result the NamesDialog class only has the Show() method as there is no need to use SetNames or GetNames() etc. Which method is generally preferred? I don’t have much work experience so I’m not sure which is the proper way to handle it. Sometimes it's easier to handle everything in the class but getting access to objects it interacts with can be challenging. Generally can do it by having the relevant objects be singletons like the database manager in the above example.

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  • HTML5 Canvas and Game Programming

    - by LemonBeagle
    I hope this isn't too open ended. I'm wondering if there is a better (more battery-friendly) way of doing this -- I have a small HTML 5 game, drawn in a canvas (let's say 500x500). I have some objects whose positions I update every 50ms or so. My current implementation re-draws the entire canvas every 50ms. I can't imagine that being very good for battery life on mobile platforms. Is there a better way to do this? This must be a common pattern with games. EDIT: as requested, here are some more updates: Right now, the objects are geometric primitives drawn via arcs and lines. I'm not opposed to making these small png/jpg/gif files instead of that'd help out. These are small graphics -- just 15x15 or so. As the game progresses, more and more of the screen changes at a time. However, at the start, the screen changes relatively slowly (the objects randomly moved a few pixels every 50ms).

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  • StackOverflow Error at java.util.AbstractColllection.<init>(Unknown Source)

    - by thebulge
    I fixed my prior problem yesterday by just separating all the classes into separate files. Nevertheless, I wrote all the code down and seeing no errors was able to compile the program. Or so I thought. Here's the error code: Exception in thread "main" java.lang.StackOverflowError at java.util.AbstractCollection.<init>(Unknown Source) at java.util.AbstractList.<init>(Unknown Source) at java.util.Vector.<init>(Unknown Source) at java.util.Vector.<init>(Unknown Source) at java.util.Vector.<init>(Unknown Source Here are the spots where my I get the errors(marked with problem?) public class GameWorld implements IObservable, IGameWorld { // create collections class public Vector<GameObject> GameObjectList = new Vector<GameObject>(); // PROBLEM private Vector<IObserver> ObserverList = new Vector<IObserver>(); // declare objects Tank pTank = new Tank(10, 10); // other objects and variables to declare public GameWorld() { // add objects to GameObjectList } // accessors/mutators } I get another error here public class Tank extends Movable implements ISteerable { private int armorStrength; private int missileCount; public Tank() {} public Tank(int armStr, int misslCt) // problem? { armorStrength = armStr; // default armorStrength missileCount = misslCt; // default missileCount } public void setDirection(int direction) { this.setDirection(direction); // get input from left turn or right turn // updateValues(); } // access/mutators here I'm stumped on what to do here.

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  • Could this C cast to avoid a signed/unsigned comparison make any sense?

    - by sharptooth
    I'm reviewing a C++ project and see effectively the following: std::vector<SomeType> objects; //then later int size = (int)objects.size(); for( int i = 0; i < size; ++i ) { process( objects[i] ); } Here's what I see. std::vector::size() returns size_t that can be of some size not related to the size of int. Even if sizeof(int) == sizeof(size_t) int is signed and can't hold all possible values of size_t. So the code above could only process the lower part of a very long vector and contains a bug. That said I'm curious of why the author might have written this? My only guess is that first he omitted the (int) cast and the compiler emitted something like Visual C++ C4018 warning: warning C4018: '<' : signed/unsigned mismatch so the author though that the best way to avoid the compiler warning would be to simply cast the size_t to int thus making the compiler shut up. Is there any other possible sane reason for that C cast?

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  • Java JCheckBox ArrayList help needed

    - by user2929626
    I'm new to Java and struggling with something which I'm sure must have a simple answer but I can't seem to find it. I have an array of checkbox objects defined as: ArrayList<JCheckBox> checkBoxList A JPanel is created with a grid layout and the checkboxes are added to the JPanel and the ArrayList: for (int i = 0; i < 256; i++) { JCheckBox c = new JCheckBox(); c.setSelected(false); checkBoxList.add(c); mainPanel.add(c); } Yes, there are 256 checkboxes! The panel is added to a JFrame and eventually the GUI is displayed. The user can select any combination of the 256 checkboxes. My class implements Serializable and this ArrayList of checkboxes can be saved and restored using 'Save' and 'Load' GUI buttons. My code to load the saved object is as below: public class LoadListener implements ActionListener { public void actionPerformed(ActionEvent a) { try { // Prompt the user for a load file JFileChooser fileLoad = new JFileChooser(); fileLoad.showOpenDialog(mainFrame); // Create a object/file input stream linking to the selected file ObjectInputStream is = new ObjectInputStream(new FileInputStream(fileLoad.getSelectedFile())); // Read the checkBox array list checkBoxList = (ArrayList<JCheckBox>) is.readObject(); is.close(); } catch (Exception ex) { ex.printStackTrace(); } } On loading the ArrayList object, the values of the checkboxes are correctly populated, however I want to update the checkboxes on the GUI to reflect this. Is there an easy way to do this? I assumed as the array of checkboxes had the correct values that I could just repaint the panel / frame but this doesn't work. I'd like to understand why - does my loaded array of checkbox objects no longer reflect the checkbox objects on the GUI? Any help would be much appreciated. Thanks!

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  • how to organize classes in ruby if they are literal subclasses

    - by RetroNoodle
    I know that title didn't make sense, Im sorry! Its hard to word what I am trying to ask. I had trouble googling it for the same reason. So this isn't even Ruby specific, but I am working in ruby and I am new to it, so bear with me. So you have a class that is a document. Inside each document, you have sentences, and each sentence has words. Words will have properties, like "noun" or a count of how many times they are used in the document, etc. I would like each of the elements, document, sentence, word be an object. Now, if you think literally - sentences are in documents, and words are in sentences. Should this be organized literally like this as well? Like inside the document class you will define and instantiate the sentence objects, and inside the sentence class you will define and instantiate the words? Or, should everything be separate and reference each other? Like the word class would sit outside the sentence class but the sentence class would be able to instantiate and work with words? This is a basic OOP question I guess, and I suppose you could argue to do it either way. What do you guys think? Each sentence in the document could be stored in a hash of sentence objects inside the document object, and each word in the sentence could be stored in a hash of word objects inside the sentence. I dont want to code myself into a corner here, thats why I am asking, plus I have wondered this before in other situations. Thank you!

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  • Storing same type but still getting an ArrayStoreException

    - by Firefoxx Pwnass
    I have strange problem. I have three classes. Book ( abstract ), and two subclasses ( Fiction, Nonfiction). I have created array of Book references. That array can hold both subclasse's objects. I'have following code for Fiction class. public class Fiction extends Book{ public Fiction(String title) { super(title); setPrice(); } public void setPrice() { super.price = 24.99; } } And the "same" code for Nonfiction class public class Nonfiction extends Book{ public Nonfiction(String title) { super(title); setPrice(); } public void setPrice() { super.price = 37.99; } } And this is Main program. import javax.swing.JOptionPane; public class Main { public static void main(String[] args) { Book[] book = new Fiction[6]; for(int i = 0; i<book.length; i++) { if(i<4) { String title = JOptionPane.showInputDialog("Enter fiction book, no "+i); book[i] = new Fiction(title); } else { String title = JOptionPane.showInputDialog("Enter non fiction book, no "+i); book[i] = new Nonfiction(title); } } for(int x = 0; x<book.length; x++) { System.out.println("Book named "+book[x].getTitle()+" costs "+book[x].getPrice()); } } } For any reason i'm getting ArrayStoreException on this line.. book[i] = new Nonfiction(title); But same code works for Fiction class. I checked java documentation and it says that this exception is thrown when i'm trying to store different objects in array ( like String and Int ), but in this case they are all the same objects. Both classes are children of superclass, that means, they are of the same type. I'm confsued. A little help here please?

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  • Slowing process creation under Java?

    - by oconnor0
    I have a single, large heap (up to 240GB, though in the 20-40GB range for most of this phase of execution) JVM [1] running under Linux [2] on a server with 24 cores. We have tens of thousands of objects that have to be processed by an external executable & then load the data created by those executables back into the JVM. Each executable produces about half a megabyte of data (on disk) that when read right in, after the process finishes, is, of course, larger. Our first implementation was to have each executable handle only a single object. This involved the spawning of twice as many executables as we had objects (since we called a shell script that called the executable). Our CPU utilization would start off high, but not necessarily 100%, and slowly worsen. As we began measuring to see what was happening we noticed that the process creation time [3] continually slows. While starting at sub-second times it would eventually grow to take a minute or more. The actual processing done by the executable usually takes less than 10 seconds. Next we changed the executable to take a list of objects to process in an attempt to reduce the number of processes created. With batch sizes of a few hundred (~1% of our current sample size), the process creation times start out around 2 seconds & grow to around 5-6 seconds. Basically, why is it taking so long to create these processes as execution continues? [1] Oracle JDK 1.6.0_22 [2] Red Hat Enterprise Linux Advanced Platform 5.3, Linux kernel 2.6.18-194.26.1.el5 #1 SMP [3] Creation of the ProcessBuilder object, redirecting the error stream, and starting it.

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  • Applying iterative algorithm to a set of rows from database

    - by Corvin
    Hello, this question may seem too basic to some, but please bear with be, it's been a while since I dealt with decent database programming. I have an algorithm that I need to program in PHP/MySQL to work on a website. It performs some computations iteratively on an array of objects (it ranks the objects based on their properties). In each iteration the algorithm runs through all collection a couple of times, accessing various data from different places of the whole collection. The algorithm needs several hundred iterations to complete. The array comes from a database. The straightforward solution that I see is to take the results of a database query and create an object for each row of the query, put the objects to an array and pass the array to my algorithm. However, I'm concerned with efficacy of such solution when I have to work with an array of several thousand of items because what I do is essentially mirror the results of a query to memory. On the other hand, making database query a couple of times on each iteration of the algorithm also seems wrong. So, my question is - what is the correct architectural solution for a problem like this? Is it OK to mirror the query results to memory? If not, which is the best way to work with query results in such an algorithm? Thanks!

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  • float** allocation limit + serialized struct problem. Need advice!

    - by jmgunn
    basically im getting an allocation limit error/warning when i create a float** array. the function i am calling to fill the float** retrieves data from a struct loaded from a file. The function works fine when i use one object but when i load 2 objects into memory i get the limit error. I am pretty sure this is to do with byte alignment or a similar thing because my struct is saved with a float** member which i am sure you are not susposed to do !?! Please confirm this! The next question i have now is how to save/serialize the float** member of this struct? I cant really afford to put an upper bound on the array ie "float [10000][3]" because i need/want to use this structure as a base for many other types of objects that may have well under the upper bound. Stroking my chin here! Any help/advice will recieve my highest gratitude. BTW these said struct objects will be used in a game/graphics package, the float** is a float[3] array for storing vertices in a model. Much thanks in advance

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  • Mysterious combination

    - by pstone
    I decided to learn concurrency and wanted to find out in how many ways instructions from two different processes could overlap. The code for both processes is just a 10 iteration loop with 3 instructions performed in each iteration. I figured out the problem consisted of leaving X instructions fixed at a point and then fit the other X instructions from the other process between the spaces taking into account that they must be ordered (instruction 4 of process B must always come before instruction 20). I wrote a program to count this number, looking at the results I found out that the solution is n Combination k, where k is the number of instructions executed throughout the whole loop of one process, so for 10 iterations it would be 30, and n is k*2 (2 processes). In other words, n number of objects with n/2 fixed and having to fit n/2 among the spaces without the latter n/2 losing their order. Ok problem solved. No, not really. I have no idea why this is, I understand that the definition of a combination is, in how many ways can you take k elements from a group of n such that all the groups are different but the order in which you take the elements doesn't matter. In this case we have n elements and we are actually taking them all, because all the instructions are executed ( n C n). If one explains it by saying that there are 2k blue (A) and red (B) objects in a bag and you take k objects from the bag, you are still only taking k instructions when 2k instructions are actually executed. Can you please shed some light into this? Thanks in advance.

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  • Trouble accessing Mutable array

    - by Jared Gross
    Im having trouble with my for loop where I am trying to index user names. I am able to separate my original array into individual objects but am not able to send the value to a new array that I need to reference later on. The value and count for userNames in my self.userNamesArray = userNames; line is correct. But right after that when I log self.userNamesArray, I get (null). Any tips cause I'm not completely sure I'm cheers! .h @property (nonatomic, copy) NSMutableArray *userNamesArray; .m - (void)viewWillAppear:(BOOL)animated { self.friendsRelation = [[PFUser currentUser] objectForKey:@"friendsRelation"]; PFQuery *query = [self.friendsRelation query]; [query orderByAscending:@"username"]; [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { if (error) { NSLog(@"Error: %@ %@", error, [error userInfo]); } else { self.friends = objects; NSArray *users = [self.friends valueForKey:@"username"]; NSLog(@"username:%@", users); //Create an array of name wrappers and pass to the root view controller. NSMutableArray *userNames = [[NSMutableArray alloc] initWithCapacity:[self.friends count]]; for (NSString *user in users) { componentsSeparatedByCharactersInSet:charSet]; NSArray *nameComponents = [user componentsSeparatedByString:@" "]; UserNameWrapper *userNameWrapper = [[UserNameWrapper alloc] initWithUserName:nil nameComponents:nameComponents]; [userNames addObject:userNameWrapper]; } self.userNamesArray = userNames; NSLog(@"userNamesArray:%@",self.userNamesArray); [self.tableView reloadData]; } Here's the code where I need to reference the self.userNamesArray where again, it is comping up nil. - (void)setUserNamesArray:(NSMutableArray *)newDataArray { if (newDataArray != self.userNamesArray) { self.userNamesArray = [newDataArray mutableCopy]; if (self.userNamesArray == nil) { self.sectionsArray = nil; NSLog(@"user names empty"); } else { [self configureSections]; } } }

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  • [Scala] Using overloaded, typed methods on a collection

    - by stephanos
    I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly. For example: def convert(doc: ClickDoc): ClickVO = doc match { case null => null case _ => val result = new ClickVO result.x = doc.x result.y = doc.y result } Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: MyBaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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  • How to improve my software project's speed?

    - by Blitzkr1eg
    I'm doing a school software project with my class mates in Java. We store the info on a remote db. When we start the application we pull all the information from the database and transform it into objects to use in our application (using java sql statemens). In the application we edit some of these objects and then when we exit the application we save or update information in the database using Hibernate. As you see we dont use Hibernate for pulling in information, we use it just for saving and updating. We have 2, but very similar problems. The loading of object(when we start the app) and the saving of objects(with Hibernate) in the db(when closing the app) is taking too much time. And our project its not a huge enterprise application, its a quite small app, we just manage some students, teachers, homeworks and tests. So our db is also very very small. How could we increase performance ? later edit: if we use a local database it runs very quick, it just runs slow on remote databases

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  • How to add a checkbox for each row in Rails 3.2 index page?

    - by user938363
    We would like to add a checkbox to each row on Rails index page to flag for the row. This checkbox is not part of the object (no checkbox boolean in database). When the index page shows, a user can check the box to trigger an event for the row in following process: #objects/checkbox_index.html.erb <table> <tr> <th>CheckBox</th> <th>Object Name</th> <th>Object ID</th> </tr> <%= @objects.each do |obj| %> <tr> <td><%= checkbox %></td> <td><%= obj.name %></td> <td><%= obj.id %></td> </tr> <% end %> </table> In controller, the process will be like this: @objects.each do |obj| some_event if obj.checked end There are a couple of questions we don't quite understand: 1. How to declare an array checkbox variable on the form and link it to each row of obj? We have been using `attr_accessor` to declare var for a form. 2. How to retrieve each row on checkbox_index form and pass them back to controller? We are using simple_form for new/edit. Can anyone point me towards any good examples of this sort of behavior, or suggest what we should be thinking about? Many Thanks.

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  • Why are my thread being terminated ?

    - by Sephy
    Hi, I'm trying to repeat calls to methods through 3 differents threads. But after I start my threads, during the next iteration of my loop, they are all terminated so nothing is executed... The code is as follows : public static void main(String[] args) { main = new Main(); pollingThread.start(); } static Thread pollingThread = new Thread() { @Override public void run() { while (isRunning) { main.poll(); // test the state of the threads try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }; }; public void poll() { if (clientThread == null) { clientThread = new Thread(new Runnable() { @Override public void run() { //create some objects } }); clientThread.start(); } else if (clientThread.isAlive()) { // do some treatment } if (gestionnaireThread == null) { gestionnaireThread = new Thread(new Runnable() { @Override public void run() { //create some objects }; }); gestionnaireThread.start(); } else if (gestionnaireThread.isAlive()) { // do some treatment } if (marchandThread == null) { marchandThread = new Thread(new Runnable() { @Override public void run() { // create some objects }; }); marchandThread.start(); } else if (marchandThread.isAlive()) { // do some treatment } } And for some reason, when I test the state of my different threads, they appear as runnable and then a the 2nd iteration, they are all terminated... What am I doing wrong? I actually have no error, but the threads are terminated and so my loop keeps looping and telling me the threads are terminated.... Thanks for any help.

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  • Change webserver used by Flex in FlexBuilder to .NET Framework 3.5

    - by Simon_Weaver
    I just had to reformat and reinstall Flex and reconstruct a project. The problem is i am using ASP.NET as my server side technology and using LINQ in my files. The version of WebDev.Webserver.exe that FlexBuilder starts up is the wrong version so I get this error : Compiler Error Message: CS0234: The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference?) Microsoft (R) Visual C# 2005 Compiler version 8.00.50727.3053 for Microsoft (R) Windows (R) 2005 Framework version 2.0.50727 Copyright (C) Microsoft Corporation 2001-2005. All rights reserved. I know that changing to the latest version of ASP.NET / Framework will fix this - but I just can't figure out HOW to make that change in Flexbuilder. I cant even remember if i ever successfully did it before or if I just created a virtual directory in IIS7. Where would I change the version?

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  • DataBinding: 'System.String' does not contain a property with the name 'dbMake'.

    - by marcmiki
    Hi , i am a newbie at ASP.net and after using sqldatasource with a listview to insert and show results from an SQL server db i want to try using the LINQ datasource since it seems to be more flexible in codebehind. My problem is this: i droped a listview control to the page and i created the Linq datasource in codebehind with vb. the issue that i am having when i ..Select d.columms name i get the error system.string does not contain a property with the name "columname".. if i ommit the column name then its works fine.. the funny part is the d.count works fine but after that i get the error.. please see my code below: vb code Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim rowsCount As Integer Dim showSearchForm As String showSearchForm = Request.QueryString("tab") If showSearchForm = "1" Then Dim db As New ASPNETDBDataContext() Dim q = From b In db.PassengerVehiclesTables Select b.dbMake rowsCount = q.Count MsgBox(rowsCount) lvMakes.DataSource = q lvMakes.DataBind() PnlPassengerVehiclesSearch.Visible = True ElseIf showSearchForm = "2" Then aspx code <asp:Panel ID="PnlPassengerVehiclesSearch" Visible="false" runat="server"> Search Passenger Vehicles Form.....<br /> <table style="width: 100%; border-style: solid; border-width: 1px"> <tr> <td> <asp:ListView ID="lvMakes" runat="server"> <LayoutTemplate> <asp:PlaceHolder runat="server" ID="itemPlaceholder" /> </LayoutTemplate> <ItemTemplate> <%#Eval("dbMake")%><br /> </ItemTemplate> </asp:ListView> </td> b.dbMake needs to work so that i can use Distinct ,, ia m using asp.net version:3.5 and IIS version 7.0 .. not sure what i am missing ,, but i did try alot of approaches,,1- checked the web.config file and it seems to have two assemblies and two namespaces for LINQ..2- used different databinding syntaxs,,and i searched a lot for the solution.. the last one i read the person ommited the name of the column,, i thought that wasnt the best solution.. also my dbMake column is comming up in the "intellisence" .. thank you in advance for your help..

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