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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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  • MidiSystem.getSequencer() returns Audio Device Unavailable

    - by ksemeks
    I've keep having an exception thrown, on and on. When i try to make a new Sequencer object, i keep getting the javax.sound.midi.MidiUnavailableException: Audio Device Unavailable exception. So, here's the code: import javax.sound.midi.*; public class MiniMusicPlayer1 { public static void main(String[] args) { try { Sequencer sequencer = MidiSystem.getSequencer(); sequencer.open(); Sequence seq = new Sequence(Sequence.PPQ, 4); Track track = seq.createTrack(); for (int i = 5; i < 61; i += 4) { track.add(makeEvent(144, 1, i, 100, i)); track.add(makeEvent(128, 1, i, 100, (i+2))); } sequencer.setSequence(seq); sequencer.setTempoInBPM(220); sequencer.start(); } catch (Exception e) { e.printStackTrace(); } } public static MidiEvent makeEvent(int comd, int chan, int one, int two, int tick) { MidiEvent event = null; try { ShortMessage a = new ShortMessage(); a.setMessage(comd, chan, one, two); event = new MidiEvent(a, tick); } catch (Exception e) { e.printStackTrace(); } return event; } } And here's the complete error (at compile): javax.sound.midi.MidiUnavailableException: Audio Device Unavailable at com.sun.media.sound.MixerSynth.implOpen(MixerSynth.java:165) at com.sun.media.sound.AbstractMidiDevice.doOpen(AbstractMidiDevice.java:144) at com.sun.media.sound.AbstractMidiDevice.openInternal(AbstractMidiDevice.java:134) at com.sun.media.sound.AbstractMidiDevice.getReceiverReferenceCounting(AbstractMidiDevice.java:339) at javax.sound.midi.MidiSystem.getReceiver(MidiSystem.java:243) at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:442) at javax.sound.midi.MidiSystem.getSequencer(MidiSystem.java:348) at MiniMusicPlayer1.main(MiniMusicPlayer1.java:9) First i was unable to play MIDI files on my pc, but then i got it to work, so now i can play MIDI files, that's okay. I tried even to close every process which uses my sound card, but the error is still there. Anyone can help me?

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  • How to save errors with the handleError in CakePHP 2.0?

    - by jags1988cr
    I have a big problem. Well, I'm trying to save the errors that happen in my web application. For example (only a example), if I make a division by zero, or happens an error in a query or something like that. So, I wanna catch that and save it in the database. But the handleError of CakePHP is static, so I can't use $this-MyModel-saveError(...). In my /app/Lib/AppError.php I have this: class AppError extends ErrorHandler { public $uses = array('Errors.Error'); public static function handleError($code, $description, $file = null, $line = null, $context = null) { //This print the error: echo "Code: ".$code." Description: ".$description." File: ".$file." Line: ".$line."<br>"; //I want to do this, (save to the database): $this->Error->saveError($code, $description, $file, $line); } } Without the $this-Error-saveError($code, $description, $file, $line); it works but I not only want to show the error. I think need an example or something like that. Please help me. Regards and thank you. Thanks... P.D.: Sorry for the English, I'm an english student...

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  • What's the deal with the hidden Throw when catching a ThreadAbortException?

    - by priehl
    I'm going through a book of general c# development, and I've come to the thread abort section. The book says something along the lines that when you call Thread.Abort() on another thread, that thread will throw a ThreadAbortException, and even if you tried to supress it it would automatically rethrow it, unless you did some bs that's generally frowned upon. Here's the simple example offered. using System; using System.Threading; public class EntryPoint { private static void ThreadFunc() { ulong counter = 0; while (true) { try { Console.WriteLine("{0}", counter++); } catch (ThreadAbortException) { // Attempt to swallow the exception and continue. Console.WriteLine("Abort!"); } } } static void Main() { try { Thread newThread = new Thread(new ThreadStart(EntryPoint.ThreadFunc)); newThread.Start(); Thread.Sleep(2000); // Abort the thread. newThread.Abort(); // Wait for thread to finish. newThread.Join(); } catch (Exception e) { Console.WriteLine(e.ToString()); } } } The book says: When your thread finishes processing the abort exception, the runtime implicitly rethrows it at the end of your exception handler. It’s the same as if you had rethrown the exception yourself. Therefore, any outer exception handlers or finally blocks will still execute normally. In the example, the call to Join won’t be waiting forever as initially expected. So i wrapped a try catch around the Thread.Abort() call and set a break point, expecting it to hit this, considering the text says "any outer exception handlers or finally blocks will still execute normally". BUT IT DOES NOT. I'm racking my brain to figure out why. Anyone have any thoughts on why this isn't the case? Is the book wrong? Thanks in advance.

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  • Refactoring. Your way to reduce code complexity of big class with big methods

    - by Andrew Florko
    I have a legacy class that is rahter complex to maintain: class OldClass { method1(arg1, arg2) { ... 200 lines of code ... } method2(arg1) { ... 200 lines of code ... } ... method20(arg1, arg2, arg3) { ... 200 lines of code ... } } methods are huge, unstructured and repetitive (developer loved copy/paste aprroach). I want to split each method into 3-5 small functions, whith one pulic method and several helpers. What will you suggest? Several ideas come to my mind: Add several private helper methods to each method and join them in #region (straight-forward refactoring) Use Command pattern (one command class per OldClass method in a separate file). Create helper static class per method with one public method & several private helper methods. OldClass methods delegate implementation to appropriate static class (very similiar to commands). ? Thank you in advance!

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  • Problem Binding to a Brush Property in WPF

    - by Krisc
    Working in WPF, writing a custom user control. I am trying to change the background property of the Border element when I change the value of a property of the class. Right now I am working on simply binding it to a DP, though if there is a better way I am open to suggestions. Here is the XAML for the UserControl <UserControl x:Class="MyProject.MyControl" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:js="clr-namespace:MyProject" mc:Ignorable="d" x:Name="MyControlRootLayout" Background="Transparent" d:DesignHeight="300" d:DesignWidth="300" Cursor="Hand"> <Border x:Name="RootBorder" Background="{Binding Path=CoreBackground, ElementName=MyControlRootLayout}" > </Border> </UserControl> And the code... public partial class MyControl : UserControl { public static DependencyProperty IsSelectedProperty = DependencyProperty.Register("IsSelected", typeof(bool), typeof(MyControl)); public static DependencyProperty CoreBackgroundProperty = DependencyProperty.Register("CoreBackground", typeof(Brush), typeof(MyControl)); public MyControl() { CoreBackground = new SolidColorBrush(Color.FromArgb(0, 255, 245, 104)); InitializeComponent(); Margin = new Thickness(5); } public Brush CoreBackground { get { return (Brush)GetValue(CoreBackgroundProperty); } set { SetValue(CoreBackgroundProperty, value); } } public bool IsSelected { get { return (bool)GetValue(IsSelectedProperty); } private set { SetValue(IsSelectedProperty, value); } } } Instead, the background comes out as transparent.

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  • Does declaring many identical anonymous classes waste memory in java?

    - by depsypher
    I recently ran across the following snippet in an existing codebase I'm working on and added the comment you see there. I know this particular piece of code can be rewritten to be cleaner, but I just wonder if my analysis is correct. Will java create a new class declaration and store it in perm gen space for every call of this method, or will it know to reuse an existing declaration? protected List<Object> extractParams(HibernateObjectColumn column, String stringVal) { // FIXME: could be creating a *lot* of anonymous classes which wastes perm-gen space right? return new ArrayList<Object>() { { add(""); } }; }

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  • How to create a String Array and link it to a Grade array

    - by user1861544
    I have a project that I need to create 2 Arrays, one to hold Student Names and one to hold Student Scores. The user inputs the size of the array, and the array needs to be sorted using BubbleSort (putting the high scores at the top). I have started the project, created the first array for scores, I have successfully done bubble sort and sorted the grades. Now I can't figure out how to make an array for Names, and once I do how do I make the names array correspond to the Grades array BubbleSort? Here is the code I have so far. import java.util.Scanner; public class Grades { public static void main(String[]args){ { Scanner UserIn = new Scanner(System.in); System.out.print( "How many students are there? " ); int[]GradeArray = new int[UserIn.nextInt()]; for( int i=0 ; i<GradeArray.length ; i++ ) { System.out.print( "Enter Grade for Student " + (i+1) + ": " ); GradeArray[i] = UserIn.nextInt(); } bubbleSort(GradeArray); for( int i : GradeArray ) System.out.println( i ); System.out.println(); } } private static void bubbleSort(int[]GradeArray){ int n = GradeArray.length; int temp = 0; String temp2; for(int i=0; i<n; i++){ for(int j=1; j<(n-i);j++){ if(GradeArray[j-1]<GradeArray[j]){ //swap temp=GradeArray[j-1]; GradeArray[j-1]=GradeArray[j]; GradeArray[j]=temp; } } } } } Also how do I change the grades to Double? I started with Int and when I try to change everything to double I get an error saying "Found Double, expected Int".

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  • Java Detect Variable Change Using PropertyChangeSupport and PropertyChangeListener

    - by Sam
    I'm trying to print out debug statements when some third party code changes a variable. For example, consider the following: public final class MysteryClass { private int secretCounter; public synchronized int getCounter() { return secretCounter; } public synchronized void incrementCounter() { secretCounter++; } } public class MyClass { public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // add code here to detect calls to incrementCounter and print a debug message } I don't have the ability to change the 3rd party MysteryClass, so I thought that I could use PropertyChangeSupport and PropertyChangeListener to detect changes to the secretCounter: public class MyClass implements PropertyChangeListener { private PropertyChangeSupport propertySupport = new PropertyChangeSupport(this); public MyClass() { propertySupport.addPropertyChangeListener(this); } public void propertyChange(PropertyChangeEvent evt) { System.out.println("property changing: " + evt.getPropertyName()); } public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // do logic which involves increment and getting the value of MysteryClass } } Unfortunately, this did not work and I have no debug messages printed out. Does anyone see what is wrong with my implementation of the PropertyChangeSupport and Listener interfaces? I want to print a debug statement whenever incrementCounter is called or the value of secretCounter changes.

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  • Endless saving of CoreData Context

    - by Robert
    Sometimes I noticed that a 'save:' operation an a ManagedObjectContext never returns and consumes 100% CPU. I'm using an SQL Store in a GarbageCollected environment (Mac OS X 10.6.3). The disk activity shows about 700 KB/s writing. While having a look at the folder that contains the sqlite database file the "-journal" file appears and disappears, appears and disappears, ... This is part of the call graph from the process analysis: 2203 -[NSManagedObjectContext save:] 1899 -[NSPersistentStoreCoordinator(_NSInternalMethods) executeRequest:withContext:] 1836 -[NSSQLCore executeRequest:withContext:] 1836 -[NSSQLCore saveChanges:] 1479 -[NSSQLCore performChanges] ... 335 -[NSSQLCore recordChangesInContext:] ... 20 -[NSSQLCore rollbackChanges] ... 2 -[NSSQLCore prepareForSave:] ... 62 -[NSPersistentStoreCoordinator(_NSInternalMethods) _checkRequestForStore:originalRequest:andOptimisticLocking:] ... 1 -[NSPersistentStore(_NSInternalMethods) _preflightCrossCheck] ... 184 -[NSMergePolicy resolveConflicts:] ... 120 -[NSManagedObjectContext(_NSInternalChangeProcessing) _prepareForPushChanges:] ... Everything a happening in the main GUI thread. Any ideas what I can to do to resolve the problem?

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  • joining programming projects for free

    - by josephj1989
    Hi All Not sure if this is an appropriate question for the forum. I an experienced software developer with over 15 years in design and development of systems -mostly using Oracle software and ERP solutions using Oracle Apps. But due to some personal reasons I had to stay away from work for a period of 5 years.Now I am finding it hard to get back in. I have trained myself thoroughly in microsoft technologies C#,.NET,SQL SERVER,ASP .NET and also certified in these areas.Now I want to gain some practical experience with these technologies.I am very willing to take up some project work for free so that I can gain some experience and also add to my portfolio. Is any of you in a position to give me some voluntary work. I did try to find open source work but none is available. I can do the following very well. Analysis/Design Oracle Database PLSQL/SQL SQL Server TSQL C# .NET and .NET Platform ASP.NET I can also do Web Development HTML,CSS, JAVASCRIPT,JQUERY Unix Shell Scripting Java Swing Development Thanks

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  • How do I pass three arrays from on method to another?

    - by user2966716
    I have a method studentSummary, that scans the input and creates three arrays examMark,courseworkMark and courseworkWeight. I need these arrays passing over to a different method, so I can use them to calculate moduleResult. heres my code: public static int[] studentSummary(int[] courseworkWeight2, int [] examMark2 , int [] courseworkMark2){ int examMark[] = { 0, 0, 0, 0, 0, 0 }; int courseworkMark[] = { 0, 0, 0, 0, 0, 0 }; Scanner resultInput = new Scanner(System.in); int courseworkWeight[] = { 0, 0, 0, 0, 0, 0 }; for (int k = 1; k < 7; k++) { System.out.print("Please enter exam marks for module " + k + ":"); examMark[k - 1] = resultInput.nextInt(); System.out.print("Please enter Coursework marks for module " + k + ":"); courseworkMark[k - 1] = resultInput.nextInt(); System.out.print("Please enter Coursework weighting for module " + k + ":"); courseworkWeight[k - 1] = resultInput.nextInt(); } Calculator method: public static int[] markCalculator() { int[] courseworkWeight = new int [6]; int[] courseworkMark = new int [6]; int[] examMark = new int [6]; for (int i = 0; i < 6; i++) { computedModuleMark = ((courseworkMark[i] * courseworkWeight[i]) + (examMark[i] * (100 - courseworkWeight[i]))) / 100; if ((computedModuleMark) < 35) { if (examMark[i]<35){ } } moduleMark[i] = computedModuleMark; } computeResult(moduleMark); StudentChart.draw(moduleMark); StudentChart.printSummary(moduleMark); return moduleMark; }

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  • Best way to run multiple queries per second on database, performance wise?

    - by Michael Joell
    I am currently using Java to insert and update data multiple times per second. Never having used databases with Java, I am not sure what is required, and how to get the best performance. I currently have a method for each type of query I need to do (for example, update a row in a database). I also have a method to create the database connection. Below is my simplified code. public static void addOneForUserInChannel(String channel, String username) throws SQLException { Connection dbConnection = null; PreparedStatement ps = null; String updateSQL = "UPDATE " + channel + "_count SET messages = messages + 1 WHERE username = ?"; try { dbConnection = getDBConnection(); ps = dbConnection.prepareStatement(updateSQL); ps.setString(1, username); ps.executeUpdate(); } catch(SQLException e) { System.out.println(e.getMessage()); } finally { if(ps != null) { ps.close(); } if(dbConnection != null) { dbConnection.close(); } } } And my DB connection private static Connection getDBConnection() { Connection dbConnection = null; try { Class.forName(DB_DRIVER); } catch (ClassNotFoundException e) { System.out.println(e.getMessage()); } try { dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,DB_PASSWORD); return dbConnection; } catch (SQLException e) { System.out.println(e.getMessage()); } return dbConnection; } This seems to be working fine for now, with about 1-2 queries per second, but I am worried that once I expand and it is running many more, I might have some issues. My questions: Is there a way to have a persistent database connection throughout the entire run time of the process? If so, should I do this? Are there any other optimizations that I should do to help with performance? Thanks

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  • Maintaining traceability up-to-date as project evolves

    - by Catalin Piti?
    During various projects, I needed to make sure that the use case model I developed during the analysis phase is covering the requirements of the project. For that, I was able to have some degree of traceability between requirement statements (uniquely identified) and use cases (also uniquely identified). In some cases, enabling traceability implied some additional effort that I considered (and later proved) to be a good investment. Now, the biggest problem I faced was to maintain this traceability later, when things started to change (as a result of change requests, or as a result of use case changes). Any ideas of best practices for traceability maintenance? (It can apply to other items in the project - e.g. use cases and test cases, or requirements and acceptance test cases) Later edit Tools might help, but they can't detect gaps or errors in traceability. Navigation... maybe, but no warranty that the traceability is up-to-date or correct after applying the changes.

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  • How to check if a child-object is populated

    - by TheQ
    How can i check if a child-object of a linq-object is populated or not? Example code below. My model have two methods, one joins data, and the other does not: public static Member GetMemberWithPhoto(Guid memberId) { using (DataContext db = new DataContext()) { DataLoadOptions dataLoadOptions = new DataLoadOptions(); dataLoadOptions.LoadWith<Member>(x => x.UserPhoto); db.LoadOptions = dataLoadOptions; var query = from x in db.Members where x.MemberId == memberId select x; return query.FirstOrDefault(); } } public static Member GetMember(Guid memberId) { using (DataContext db = new DataContext()) { var query = from x in db.Members where x.MemberId == memberId select x; return query.FirstOrDefault(); } } Then my control have the following code: Member member1 = Member.GetMemberWithPhoto(memberId); Member member2 = Member.GetMember(memberId); Debug.WriteLine(member1.UserPhoto.ToString()); Debug.WriteLine(member2.UserPhoto.ToString()); The last line will generate a "Cannot access a disposed object" exception. I know that i can get rid of that exception just by not disposing the datacontext, but then the last line will generate a new query to the database, and i don't want that. What i would like is something like: Debug.WriteLine((member1.UserPhoto.IsPopulated()) ? member1.UserPhoto.ToString() : "none"); Debug.WriteLine((member2.UserPhoto.IsPopulated()) ? member2.UserPhoto.ToString() : "none"); Is it possible?

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  • Value of A.S. Degree in Programming

    - by MiseryIndex
    I am in a quite unusual family situation. For the next two years, I have to stay at home where the only post-secondary institution available is a community college. After two years, I will have to start earning a living. I do not really have any real-world programming experience to put on my résumé. I did some not-too-advanced work in PHP for family and friends, and I’m pretty sure that I want to program for a living. I have been working on an A.S. Degree in Computer Programming and Analysis since fall. My question regarding the degree is: is it worth anything to potential employers or am I just wasting my time? Is there a better way to spend the oncoming two years? If I could get an internship and some experience, would that hold more weight than a two-year degree without experience?

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  • Controlling race condition at startup.

    - by Will Hartung
    I have some code that I want to have some one time initialisation performed. But this code doesn't have a definite lifecycle, so my logic can be potentially invoked by multiple threads before my initialisation is done. So, I want to basically ensure that my logic code "waits" until initialisation is done. This is my first cut. public class MyClass { private static final AtomicBoolean initialised = new AtomicBoolean(false); public void initialise() { synchronized(initialised) { initStuff(); initialised.getAndSet(true); initialised.notifyAll(); } } public void doStuff() { synchronized(initialised) { if (!initialised.get()) { try { initialised.wait(); } catch (InterruptedException ex) { throw new RuntimeException("Uh oh!", ex); } } } doOtherStuff(); } } I basically want to make sure this is going to do what I think it's going to do -- block doStuff until the initialised is true, and that I'm not missing a race condition where doStuff might get stuck on a Object.wait() that will never arrive. Edit: I have no control over the threads. And I want to be able to control when all of the initialisation is done, which is why doStuff() can't call initialise(). I used an AtomicBoolean as it was a combination of a value holder, and an object I could synchronize. I could have also simply had a "public static final Object lock = new Object();" and a simple boolean flag. AtomicBoolean conveniently gave me both. A Boolean can not be modified. The CountDownLatch is exactly what I was looking for. I also considered using a Sempahore with 0 permits. But the CountDownLatch is perfect for just this task.

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  • Is it a good practice for a .js file to rely on variables declared in the including html

    - by Bozho
    In short: <script type="text/javascript"> var root = '${config.root}'; var userLanguage = '${config.language}'; var userTimezone = '${config.timezone}'; </script> <script type="text/javascript" src="js/scripts.js"></script> And then, in scripts.js, rely on these variables: if (userLanguage == 'en') { .. } The ${..} is simply a placeholder for a value in the script that generates the page. It can be php, jsp, asp, whatever. The point is - it is dynamic, and hence it can't be part of the .js file (which is static). So, is it OK for the static javascript file to rely on these externally defined configuration variables? (they are mainly configuration, of course). Or is it preferred to make the .js file be served dynamically as well (i.e. make it a .php / .jsp, with the proper Content-Type), and have these values defined in there.

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  • How does Contract.Exists add value?

    - by Scott Bilas
    I am just starting to learn about the code contracts library that comes standard with VS2010. One thing I am running into right away is what some of the contract clauses really mean. For example, how are these two statements different? Contract.Requires(!mycollection.Any(a => a.ID == newID)); Contract.Requires(!Contract.Exists(mycollection, a => a.ID == newID)); In other words, what does Contract.Exists do in practical purposes, either for a developer using my function, or for the static code analysis system?

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  • C#: Passing data to forms UI using BeginInvoke

    - by Bi
    Hi I am a C# newbie and have a class that needs to pass row information to a grid in the windows form. What is the best way to do it? I have put in some example code for better understanding. Thanks. public class GUIController { private My_Main myWindow; public GUIController( My_Main window ) { myWindow = window; } public void UpdateProducts( List<myProduct> newList ) { object[] row = new object[3]; foreach (myProduct product in newList) { row[0] = product.Name; row[1] = product.Status; row[2] = product.Day; //HOW DO I USE BeginInvoke HERE? } } } And the form class below: public class My_Main : Form { //HOW DO I GO ABOUT USING THIS DELEGATE? public delegate void ProductDelegate( string[] row ); public static My_Main theWindow = null; static void Main( ) { Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); theWindow = new My_Main(); Application.Run(theWindow); } private void My_Main_Load( object sender, EventArgs e ) { /// Create GUIController and pass the window object gui = new GUIController( this ); } public void PopulateGrid( string[] row ) { ProductsGrid.Rows.Add(row); ProductsGrid.Update(); } } Thanks!

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  • Why aren't my threads start at the same time? Java

    - by Ada
    Hi, I have variable number of threads which are used for parallel downloading. I used this, for(int i = 0; i< sth; i++){ thrList.add(new myThread (parameters)); thrList.get(i).start(); thrList.get(i).join(); } I don't know why but they wait for each other to complete. When using threads, I am supposed get mixed print outs, since right then there are several threads running that code. However, when I print them out, they are always in order and one thread waits for the previous one to finish first. I only want them to join the main thread, not wait for each other. I noticed that when I measured time while downloading in parallel. How can I fix this? Why are they doing it in order? In my .java, there is MyThread class with run and there is Downloader class with static methods and variables. Would they be the cause of this? The static methods and variables? How can I fix this problem?

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  • Mono Develop 2.4.1 + linq error.

    - by Nev_Rahd
    I just started to learn Mono Develop Installed Mono Develop 2.4.1 and trial version of Mono Touch. my Code: using System; using System.Xml.Linq; using System.Collections.Generic; namespace RSSReader { public static class RSSRepository { public static IList<FeedItem> GetFeeds(string url) { XDocument rssFeed = XDocument.Load(url); Console.Write(rssFeed.ToString()); var feeds = new List<FeedItem>(); try { var query = from item in rssFeed.Descendants("item") select new FeedItem { Title = item.Element("title").Value, Published = DateTime.Parse(item.Element("pubDate").Value), Url = item.Element("link").Value }; feeds = query.ToList(); } catch (Exception ex){ Console.WriteLine(ex.Message); } return feeds; } } } This is throwing an error: An implementation of 'select' query expression pattern could not be found. Are you missing 'System.linq' using directive or 'System.Core.dll' assembly reference? I got both references to System.Xml.Linq and System.Core What am i missing ?

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  • c++ Sorting a vector based on values of other vector, or what's faster?

    - by pollux
    Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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  • Saving associated domain classes in Grails

    - by Cesar
    I'm struggling to get association right on Grails. Let's say I have two domain classes: class Engine { String name int numberOfCylinders = 4 static constraints = { name(blank:false, nullable:false) numberOfCylinders(range:4..8) } } class Car { int year String brand Engine engine = new Engine(name:"Default Engine") static constraints = { engine(nullable:false) brand(blank:false, nullable:false) year(nullable:false) } } The idea is that users can create cars without creating an engine first, and those cars get a default engine. In the CarController I have: def save = { def car = new Car(params) if(!car.hasErrors() && car.save()){ flash.message = "Car saved" redirect(action:index) }else{ render(view:'create', model:[car:car]) } } When trying to save, I get a null value exception on the Car.engine field, so obviously the default engine is not created and saved. I tried to manually create the engine: def save = { def car = new Car(params) car.engine = new Engine(name: "Default Engine") if(!car.hasErrors() && car.save()){ flash.message = "Car saved" redirect(action:index) }else{ render(view:'create', model:[car:car]) } } Didn't work either. Is Grails not able to save associated classes? How could I implement such feature?

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  • Cast exception being generated when using the same type of object

    - by David Tunnell
    I was previously using static variables to hold variable data that I want to save between postbacks. I was having problems and found that the data in these variables is lost when the appdomain ends. So I did some research and decided to go with ViewStates: static Dictionary<string, linkButtonObject> linkButtonDictonary; protected void Page_Load(object sender, EventArgs e) { if (ViewState["linkButtonDictonary"] != null) { linkButtonDictonary = (Dictionary<string, linkButtonObject>)ViewState["linkButtonDictonary"]; } else { linkButtonDictonary = new Dictionary<string, linkButtonObject>(); } } And here is the very simple class I use: [Serializable] public class linkButtonObject { public string storyNumber { get; set; } public string TaskName { get; set; } } I am adding to linkButtonDictionary as a gridview is databound: protected void hoursReportGridView_OnRowDataBound(Object sender, GridViewRowEventArgs e) { if (e.Row.RowType == DataControlRowType.DataRow) { LinkButton btn = (LinkButton)e.Row.FindControl("taskLinkButton"); linkButtonObject currentRow = new linkButtonObject(); currentRow.storyNumber = e.Row.Cells[3].Text; currentRow.TaskName = e.Row.Cells[5].Text; linkButtonDictonary.Add(btn.UniqueID, currentRow); } } It appears that my previous issues are resolved however a new one has arisin. Sometime when I postback I am getting this error: [A]System.Collections.Generic.Dictionary2[System.String,linkButtonObject] cannot be cast to [B]System.Collections.Generic.Dictionary2[System.String,linkButtonObject]. Type A originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' at location 'C:\Windows\Microsoft.Net\assembly\GAC_32\mscorlib\v4.0_4.0.0.0__b77a5c561934e089\mscorlib.dll'. Type B originates from 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' in the context 'LoadNeither' at location 'C:\Windows\Microsoft.Net\assembly\GAC_32\mscorlib\v4.0_4.0.0.0__b77a5c561934e089\mscorlib.dll'. I don't understand how there can be a casting issue when I am using the same class everywhere. What am I doing wrong and how do I fix it?

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