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• no appropriate default constructor available . (when creating a child class)

  - by numerical25

  I am creating some custom exception classes doing the following class GXException { public: GXException(LPCWSTR pTxt):pReason(pTxt){}; LPCWSTR pReason; }; class GXVideoException : GXException { public: GXVideoException(LPCWSTR pTxt):pReason(pTxt){}; LPCWSTR pReason; }; When I created GXVideoException to extend GXException, I get the following error 1>c:\users\numerical25\desktop\intro todirectx\godfiles\gxrendermanager\gxrendermanager\gxrendermanager\gxexceptions.h(14) : error C2512: 'GXException' : no appropriate default constructor available

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• Impossible to use ref and out in Extension methods?

  - by Hun1Ahpu

  Why is it forbidden to call Extension method with ref modifier? This one is possible: public static void Change(ref TestClass testClass, TestClass testClass2) { testClass = testClass2; } And this one not: public static void ChangeWithExtensionMethod(this ref TestClass testClass, TestClass testClass2) { testClass = testClass2; } But why?

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• Unrequired property keeps getting data-val-required attribute

  - by frennky

  This is the model with it's validation: [MetadataType(typeof(TagValidation))] public partial class Tag { } public class TagValidation { [Editable(false)] [HiddenInput(DisplayValue = false)] public int TagId { get; set; } [Required] [StringLength(20)] [DataType(DataType.Text)] public string Name { get; set; } //... } Here is the view: <h2>Create</h2> <script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script> <script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script> @using (Html.BeginForm()) { @Html.ValidationSummary(true) <fieldset> <legend>Tag</legend> <div>@Html.EditorForModel()</div> <p> <input type="submit" value="Create" /> </p> </fieldset> } <div> @Html.ActionLink("Back to List", "Index") </div> And here is what get's renderd: <form action="/Tag/Create" method="post"> <fieldset> <legend>Tag</legend> <div><input data-val="true" data-val-number="The field TagId must be a number." data-val-required="The TagId field is required." id="TagId" name="TagId" type="hidden" value="" /> <div class="editor-label"><label for="Name">Name</label></div> <div class="editor-field"><input class="text-box single-line" data-val="true" data-val-length="The field Name must be a string with a maximum length of 20." data-val-length-max="20" data-val-required="The Name field is required." id="Name" name="Name" type="text" value="" /> <span class="field-validation-valid" data-valmsg-for="Name" data-valmsg-replace="true"></span></div> ... </fieldset> </form> The problem is that TagId validation gets generated althoug thare is no Required attribute set on TagId property. Because of that I can't even pass the client-side validation in order to create new Tag in db. What am I missing?

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• remove duplicate code in java

  - by Anantha Kumaran

  class A extends ApiClass { public void duplicateMethod() { } } class B extends AnotherApiClass { public void duplicateMethod() { } } I have two classes which extend different api classes. The two class has some duplicate methods(same method repeated in both class) and how to remove this duplication? Edit The ApiClass is not under my control

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• Exception in thread "main" java.lang.NoSuchMethodError: main

  - by David

  when i try to compile this: public class Risk { } class territory { public static void main (String[]arg) { System.out.println ("hi") ; } } I get this error message: Exception in thread "main" java.lang.NoSuchMethodError: main whats going wrong here?

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• Implementing a robust async stream reader for a console

  - by Jon

  I recently provided an answer to this question: C# - Realtime console output redirection. As often happens, explaining stuff (here "stuff" was how I tackled a similar problem) leads you to greater understanding and/or, as is the case here, "oops" moments. I realized that my solution, as implemented, has a bug. The bug has little practical importance, but it has an extremely large importance to me as a developer: I can't rest easy knowing that my code has the potential to blow up. Squashing the bug is the purpose of this question. I apologize for the long intro, so let's get dirty. I wanted to build a class that allows me to receive input from a Stream in an event-based manner. The stream, in my scenario, is guaranteed to be a FileStream and there is also an associated StreamReader already present to leverage. The public interface of the class is this: public class MyStreamManager { public event EventHandler<ConsoleOutputReadEventArgs> StandardOutputRead; public void StartSendingEvents(); public void StopSendingEvents(); } Obviously this specific scenario has to do with a console's standard output. StartSendingEvents and StopSendingEvents do what they advertise; for the purposes of this discussion, we can assume that events are always being sent without loss of generality. The class uses these two fields internally: protected readonly StringBuilder inputAccumulator = new StringBuilder(); protected readonly byte[] buffer = new byte[256]; The functionality of the class is implemented in the methods below. To get the ball rolling: public void StartSendingEvents(); { this.stopAutomation = false; this.BeginReadAsync(); } To read data out of the Stream without blocking, and also without requiring a carriage return char, BeginRead is called: protected void BeginReadAsync() { if (!this.stopAutomation) { this.StandardOutput.BaseStream.BeginRead( this.buffer, 0, this.buffer.Length, this.ReadHappened, null); } } The challenging part: BeginRead requires using a buffer. This means that when reading from the stream, it is possible that the bytes available to read ("incoming chunk") are larger than the buffer. Since we are only handing off data from the stream to a consumer, and that consumer may well have inside knowledge about the size and/or format of these chunks, I want to call event subscribers exactly once for each chunk. Otherwise the abstraction breaks down and the subscribers have to buffer the incoming data and reconstruct the chunks themselves using said knowledge. This is much less convenient to the calling code, and detracts from the usefulness of my class. Edit: There are comments below correctly stating that since the data is coming from a stream, there is absolutely nothing that the receiver can infer about the structure of the data unless it is fully prepared to parse it. What I am trying to do here is leverage the "flush the output" "structure" that the owner of the console imparts while writing on it. I am prepared to assume (better: allow my caller to have the option to assume) that the OS will pass me the data written between two flushes of the stream in exactly one piece. To this end, if the buffer is full after EndRead, we don't send its contents to subscribers immediately but instead append them to a StringBuilder. The contents of the StringBuilder are only sent back whenever there is no more to read from the stream (thus preserving the chunks). private void ReadHappened(IAsyncResult asyncResult) { var bytesRead = this.StandardOutput.BaseStream.EndRead(asyncResult); if (bytesRead == 0) { this.OnAutomationStopped(); return; } var input = this.StandardOutput.CurrentEncoding.GetString( this.buffer, 0, bytesRead); this.inputAccumulator.Append(input); if (bytesRead < this.buffer.Length) { this.OnInputRead(); // only send back if we 're sure we got it all } this.BeginReadAsync(); // continue "looping" with BeginRead } After any read which is not enough to fill the buffer, all accumulated data is sent to the subscribers: private void OnInputRead() { var handler = this.StandardOutputRead; if (handler == null) { return; } handler(this, new ConsoleOutputReadEventArgs(this.inputAccumulator.ToString())); this.inputAccumulator.Clear(); } (I know that as long as there are no subscribers the data gets accumulated forever. This is a deliberate decision). The good This scheme works almost perfectly: Async functionality without spawning any threads Very convenient to the calling code (just subscribe to an event) Maintains the "chunkiness" of the data; this allows the calling code to use inside knowledge of the data without doing any extra work Is almost agnostic to the buffer size (it will work correctly with any size buffer irrespective of the data being read) The bad That last almost is a very big one. Consider what happens when there is an incoming chunk with length exactly equal to the size of the buffer. The chunk will be read and buffered, but the event will not be triggered. This will be followed up by a BeginRead that expects to find more data belonging to the current chunk in order to send it back all in one piece, but... there will be no more data in the stream. In fact, as long as data is put into the stream in chunks with length exactly equal to the buffer size, the data will be buffered and the event will never be triggered. This scenario may be highly unlikely to occur in practice, especially since we can pick any number for the buffer size, but the problem is there. Solution? Unfortunately, after checking the available methods on FileStream and StreamReader, I can't find anything which lets me peek into the stream while also allowing async methods to be used on it. One "solution" would be to have a thread wait on a ManualResetEvent after the "buffer filled" condition is detected. If the event is not signaled (by the async callback) in a small amount of time, then more data from the stream will not be forthcoming and the data accumulated so far should be sent to subscribers. However, this introduces the need for another thread, requires thread synchronization, and is plain inelegant. Specifying a timeout for BeginRead would also suffice (call back into my code every now and then so I can check if there's data to be sent back; most of the time there will not be anything to do, so I expect the performance hit to be negligible). But it looks like timeouts are not supported in FileStream. Since I imagine that async calls with timeouts are an option in bare Win32, another approach might be to PInvoke the hell out of the problem. But this is also undesirable as it will introduce complexity and simply be a pain to code. Is there an elegant way to get around the problem? Thanks for being patient enough to read all of this.

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• How to display specific data from a file

  - by user1067332

  My program is supposed to ask the user for firstname, lastname, and phone number till the users stops. Then when to display it asks for the first name and does a search in the text file to find all info with the same first name and display lastname and phones of the matches. import java.util.*; import java.io.*; import java.util.Scanner; public class WritePhoneList { public static void main(String[] args)throws IOException { BufferedWriter output = new BufferedWriter(new FileWriter(new File( "PhoneFile.txt"), true)); String name, lname, age; int pos,choice; try { do { Scanner input = new Scanner(System.in); System.out.print("Enter First name, last name, and phone number "); name = input.nextLine(); output.write(name); output.newLine(); System.out.print("Would you like to add another? yes(1)/no(2)"); choice = input.nextInt(); }while(choice == 1); output.close(); } catch(Exception e) { System.out.println("Message: " + e); } } } Here is the display code, when i search for a name, it finds a match but displays the last name and phone number of the same name 3 times, I want it to display all of the possible matches with the first name. import java.util.*; import java.io.*; import java.util.Scanner; public class DisplaySelectedNumbers { public static void main(String[] args)throws IOException { String name; String strLine; try { FileInputStream fstream = new FileInputStream("PhoneFile.txt"); // Get the object of DataInputStream DataInputStream in = new DataInputStream(fstream); BufferedReader br = new BufferedReader(new InputStreamReader(in)); Scanner input = new Scanner(System.in); System.out.print("Enter a first name"); name = input.nextLine(); strLine= br.readLine(); String[] line = strLine.split(" "); String part1 = line[0]; String part2 = line[1]; String part3 = line[2]; //Read File Line By Line while ((strLine= br.readLine()) != null) { if(name.equals(part1)) { // Print the content on the console System.out.print("\n" + part2 + " " + part3); } } }catch (Exception e) {//Catch exception if any System.out.println("Error: " + e.getMessage()); } } }

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• Understanding SingleTableEntityPersister n QueryLoader

  - by Iapilgrim

  Hi, I have the Hibernate model @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Node extends StatefulEntity implements Inheritable, Cloneable { private Node _parent; private List<Node> _childNodes; .. } @Cache(usage = CacheConcurrencyStrategy.NONE, region = SitesConstants.CACHE_REGION) public class Page extends Node implements Defaultable, Securable { private RootZone _rootZone; ...... @OneToOne(fetch = FetchType.LAZY) @JoinColumn(name = "root_zone_id", insertable = false, updatable = false) public RootZone getRootZone() { return _rootZone; } public void setRootZone(RootZone rootZone) { if (rootZone != null) { rootZone.setPageId(this.getId()); _rootZone = rootZone; } } I want to get all pages ( call getSiteTree), so I using this query String hpql = "SELECT n FROM Node n "; See the trace I find Page.setRootZone(RootZone) line: 155 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 BasicPropertyAccessor$BasicSetter.set(Object, Object, SessionFactoryImplementor) line: 66 PojoEntityTuplizer(AbstractEntityTuplizer).setPropertyValues(Object, Object[]) line: 352 PojoEntityTuplizer.setPropertyValues(Object, Object[]) line: 232 SingleTableEntityPersister(AbstractEntityPersister).setPropertyValues(Object, Object[], EntityMode) line: 3580 TwoPhaseLoad.initializeEntity(Object, boolean, SessionImplementor, PreLoadEvent, PostLoadEvent) line: 152 QueryLoader(Loader).initializeEntitiesAndCollections(List, Object, SessionImplementor, boolean) line: 877 QueryLoader(Loader).doQuery(SessionImplementor, QueryParameters, boolean) line: 752 QueryLoader(Loader).doQueryAndInitializeNonLazyCollections(SessionImplementor, QueryParameters, boolean) line: 259 QueryLoader(Loader).doList(SessionImplementor, QueryParameters) line: 2232 QueryLoader(Loader).listIgnoreQueryCache(SessionImplementor, QueryParameters) line: 2129 QueryLoader(Loader).list(SessionImplementor, QueryParameters, Set, Type[]) line: 2124 QueryLoader.list(SessionImplementor, QueryParameters) line: 401 QueryTranslatorImpl.list(SessionImplementor, QueryParameters) line: 363 HQLQueryPlan.performList(QueryParameters, SessionImplementor) line: 196 SessionImpl.list(String, QueryParameters) line: 1149 QueryImpl.list() line: 102 QueryImpl.getResultList() line: 67 NodeDaoImpl.getSiteTree(long) line: 358 PageNodeServiceImpl.getSiteTree(long) line: 797 NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method] NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39 DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25 Method.invoke(Object, Object...) line: 597 AopUtils.invokeJoinpointUsingReflection(Object, Method, Object[]) line: 307 JdkDynamicAopProxy.invoke(Object, Method, Object[]) line: 198 $Proxy100.getSiteTree(long) line: not available the calling setRootZone in Page makes Hibernate issue a hit to database. I don't want this. So my question is + Why query String hpql = "SELECT n FROM Node n "; issues un-expected trace logs like above. Why the query String hpql = "SELECT n.nodename FROM Node n " not? What is the mechanism behind? Note: Im using hibernate caching level 2. In case I don't want to see that trace logs. I mean I just get Node data only. How to do ? Thanks for your help. Sorry for my bad english :( Van

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• Using auto-generated event handler in both class and it's superclass

  - by abatishchev

  I have a abstract class: public abstract class MySuperControl : UserControl { protected void Page_PreRender(object sender, EventArgs e) { // do something in super } } and a class that is code-behind for a designed UserControl: public partial class MyControl : MySuperControl { protected void Page_PreRender(object sender, EventArgs e) { // do something in class } } how do declare both of them to nest automated call?

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• Qt - problem appending to QList of QList

  - by bullettime

  I'm trying to append items to a QList at runtime, but I'm running on a error message. Basically what I'm trying to do is to make a QList of QLists and add a few customClass objects to each of the inner lists. Here's my code: widget.h: class Widget : public QWidget { Q_OBJECT public: Widget(QWidget *parent = 0); ~Widget(); public slots: static QList<QList<customClass> > testlist(){ QList<QList<customClass> > mylist; for(int w=0 ; w<5 ; w++){ mylist.append(QList<customClass>()); } for(int z=0 ; z<mylist.size() ; z++){ for(int x=0 ; x<10 ; x++){ customClass co = customClass(); mylist.at(z).append(co); } } return mylist; } }; customclass.h: class customClass { public: customClass(){ this->varInt = 1; this->varQString = "hello world"; } int varInt; QString varQString; }; main.cpp: int main(int argc, char *argv[]) { QApplication a(argc, argv); Widget w; QList<QList<customClass> > list; list = w.testlist(); w.show(); return a.exec(); } But when I try to run the application, it gives off this error: error: passing `const QList<customClass>' as `this' argument of `void List<T>::append(const T&) [with T = customClass]' discards qualifiers I also tried inserting the objects using foreach: foreach(QList<customClass> list, mylist){ for(int x=0 ; x<10 ; x++){ list.append(customClass()); } } The error was gone, but the customClass objects weren't appended, I could verify that by using a debugging loop in main that showed the inner QLists sizes as zero. What am I doing wrong?

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• Is it possible to use pure Encoding and Decoding keys in asymmetric cryptography instead of private

  - by macropas

  Is it possible to use pure Encoding and Decoding keys instead of private and public keys? As I know in .Net asymmetric RSA implementation private key RSAParameters parameters = (new RSACryptoServiceProvider()).ExportParameters(true) is a superset of public key. And using private key we can both encode and decode our data. But I need key only for decoding data. How to do it? I experimented on nulling RSAParameters fields, but RSACryptoServiceProvider object can't import such parameters.

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• How do I create a M2Crypto DSA object given parameters and key values?

  - by casey

  Using M2Crypto I'd like to create a DSA_pub object for verifying a DSA signature. I know q, p, g, and the public key, but the only way I know to instantiate a DSA object is using: dsa = DSA.set_params(q,p,g) dsa.gen_key() How do I assign the known public key?

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• PHP sessions and class members.

  - by JDW

  Ok, messing about with classes in PHP and can't get it to work the way I'm used to as a C++/Java-guy. In the "_init" funtion, if I run a query at the "// query works here" line", everythong works, but in the "getUserID" function, all that happens is said warning... "getUserID" gets called from login.php (they are in the same dir): login.php <?php include_once 'sitehandler.php'; include_once 'dbhandler.php'; session_start(); #TODO: Safer input handling $t_userName = $_POST["name"]; $t_userId = $_SESSION['handler']['db']->getUserID($t_userName); if ($t_userId != -1) { $_SESSION['user']['name'] = $t_userName; $_SESSION['user']['id'] = $t_userId; } //error_log("user: " . $_SESSION['user']['name'] . ", id: ". $_SESSION['user']['id']); header("Location: " . $_SERVER["HTTP_REFERER"]); ? dbhandler.php <?php include_once 'handler.php'; class DBHandler extends HandlerAbstract { private $m_handle; function __construct() { parent::__construct(); } public function test() { #TODO: isdir liquibase #TODO: isfile liquibase-195/liquibase + .bat + execrights $this->m_isTested = true; } public function _init() { if (!$this->isTested()) $this->test(); if (!file_exists('files/data.db')) { #TODO: How to to if host is Windows based? exec('./files/liquibase-1.9.5/liquibase --driver=org.sqlite.JDBC --changeLogFile=files/data_db.xml --url=jdbc:sqlite:files/data.db update'); #TODO: quit if not success } #TODO: Set with default data try { $this->m_handle = new SQLite3('files/data.db'); } catch (Exception $e) { die("<hr />" . $e->getMessage() . "<hr />"); } // query works here $this->m_isSetup = true; } public function teardown() { } public function getUserID($name) { // PHP Warning: SQLite3::prepare(): The SQLite3 object has not been correctly initialised in $t_statement = $this->m_handle->prepare("SELECT id FROM users WHERE name = :name"); $t_statement->bindValue(":name", $name, SQLITE3_TEXT); $t_result = $t_statement->execute(); //var_dump($this->m_handle); return ($t_result)? (int)$t_result['id']: -1; } }

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• C# monkey patching - is it possible?

  - by Adal

  Is it possible to write a C# assembly which when loaded will inject a method into a class from another assembly? If yes, will the injected method be available from languages using DLR, like IronPython? namespace IronPython.Runtime { public class Bytes : IList<byte>, ICodeFormattable, IExpressionSerializable { internal byte[] _bytes; //I WANT TO INJECT THIS METHOD public byte[] getbytes() { return _bytes; } } } I need that method, and I would like to avoid recompiling IronPython if possible.

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• Mouse event in Java

  - by Harish

  I am trying to move a JComponent say a label over a table.I am tracking this event using MouseMotionListener's mouseDragged method.This method perfectly helps me in tracking the item.Is there a way to track the mouse release after dragging is complete(.ie the dropping event). tktLabel1.addMouseMotionListener(new MouseMotionListener() { public void mouseDragged(MouseEvent arg0) { tktLabel1.setBounds(tktLabel1.getX() + arg0.getX(), tktLabel1.getY() + arg0.getY(), width, height); } public void mouseMoved(MouseEvent arg0) { } });

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• Initialize static members in PHP

  - by Senthil

  class Person { public static function ShowQualification() { } } class School { public static $Headmaster = new Person(); // NetBeans complains about this line } Why is this not possible? I want to be able to use this like School::Headmaster::ShowQualification(); ..without instantiating any class. How can I do it?

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• Strange results - I obtain same value for all keys

  - by Pietro Luciani

  I have a problem with mapreduce. Giving as input a list of song ("Songname"#"UserID"#"boolean") i must have as result a song list in which is specified how many time different useres listen them... so a output ("Songname","timelistening"). I used hashtable to allow only one couple . With short files it works well but when I put as input a list about 1000000 of records it returns me the same value (20) for all records. This is my mapper: public static class CanzoniMapper extends Mapper<Object, Text, Text, IntWritable>{ private IntWritable userID = new IntWritable(0); private Text song = new Text(); public void map(Object key, Text value, Context context) throws IOException, InterruptedException { /*StringTokenizer itr = new StringTokenizer(value.toString()); while (itr.hasMoreTokens()) { word.set(itr.nextToken()); context.write(word, one); }*/ String[] caratteri = value.toString().split("#"); if(caratteri[2].equals("1")){ song.set(caratteri[0]); userID.set(Integer.parseInt(caratteri[1])); context.write(song,userID); } } } This is my reducer: public static class CanzoniReducer extends Reducer<Text,IntWritable,Text,IntWritable> { private IntWritable result = new IntWritable(); public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException { Hashtable<IntWritable,Text> doppioni = new Hashtable<IntWritable,Text>(); for (IntWritable val : values) { doppioni.put(val,key); } result.set(doppioni.size()); //doppioni.clear(); context.write(key,result); } } and main: Configuration conf = new Configuration(); Job job = new Job(conf, "word count"); job.setJarByClass(Canzoni.class); job.setMapperClass(CanzoniMapper.class); //job.setCombinerClass(CanzoniReducer.class); //job.setNumReduceTasks(2); job.setReducerClass(CanzoniReducer.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); FileInputFormat.addInputPath(job, new Path(args[0])); FileOutputFormat.setOutputPath(job, new Path(args[1])); System.exit(job.waitForCompletion(true) ? 0 : 1); Any idea???

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• DriverManager always returns my custom driver regardless of the connection URL

  - by JGB146

  I am writing a driver to act as a wrapper around two separate MySQL connections (to distributed databases). Basically, the goal is to enable interaction with my driver for all applications instead of requiring the application to sort out which database holds the desired data. Most of the code for this is in place, but I'm having a problem in that when I attempt to create connections via the MySQL Driver, the DriverManager is returning an instance of my driver instead of the MySQL Driver. I'd appreciate any tips on what could be causing this and what could be done to fix it! Below is a few relevant snippets of code. I can provide more, but there's a lot, so I'd need to know what else you want to see. First, from MyDriver.java: public MyDriver() throws SQLException { DriverManager.registerDriver(this); } public Connection connect(String url, Properties info) throws SQLException { try { return new MyConnection(info); } catch (Exception e) { return null; } } public boolean acceptsURL(String url) throws SQLException { if (url.contains("jdbc:jgb://")) { return true; } return false; } It is my understanding that this acceptsURL function will dictate whether or not the DriverManager deems my driver a suitable fit for a given URL. Hence it should only be passing connections from my driver if the URL contains "jdbc:jgb://" right? Here's code from MyConnection.java: Connection c1 = null; Connection c2 = null; /** *Constructors */ public DDBSConnection (Properties info) throws SQLException, Exception { info.list(System.out); //included for testing Class.forName("com.mysql.jdbc.Driver").newInstance(); String url1 = "jdbc:mysql://server1.com/jgb"; String url2 = "jdbc:mysql://server2.com/jgb"; this.c1 = DriverManager.getConnection( url1, info.getProperty("username"), info.getProperty("password")); this.c2 = DriverManager.getConnection( url2, info.getProperty("username"), info.getProperty("password")); } And this tells me two things. First, the info.list() call confirms that the correct user and password are being sent. Second, because we enter an infinite loop, we see that the DriverManager is providing new instances of my connection as matches for the mysql URLs instead of the desired mysql driver/connection. FWIW, I have separately tested implementations that go straight to the mysql driver using this exact syntax (al beit only one at a time), and was able to successfully interact with each database individually from a test application outside of my driver.

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• How do I destruct data associated with an object after the object no longer exists?

  - by Phineas

  I'm creating a class (say, C) that associates data (say, D) with an object (say, O). When O is destructed, O will notify C that it soon will no longer exist :( ... Later, when C feels it is the right time, C will let go of what belonged to O, namely D. If D can be any type of object, what's the best way for C to be able to execute "delete D;"? And what if D is an array of objects? My solution is to have D derive from a base class that C has knowledge of. When the time comes, C calls delete on a pointer to the base class. I've also considered storing void pointers and calling delete, but I found out that's undefined behavior and doesn't call D's destructor. I considered that templates could be a novel solution, but I couldn't work that idea out. Here's what I have so far for C, minus some details: // This class is C in the above description. There may be many instances of C. class Context { public: // D will inherit from this class class Data { public: virtual ~Data() {} }; Context(); ~Context(); // Associates an owner (O) with its data (D) void add(const void* owner, Data* data); // O calls this when he knows its the end (O's destructor). // All instances of C are now aware that O is gone and its time to get rid // of all associated instances of D. static void purge (const void* owner); // This is called periodically in the application. It checks whether // O has called purge, and calls "delete D;" void refresh(); // Side note: sometimes O needs access to D Data *get (const void *owner); private: // Used for mapping owners (O) to data (D) std::map _data; }; // Here's an example of O class Mesh { public: ~Mesh() { Context::purge(this); } void init(Context& c) const { Data* data = new Data; // GL initialization here c.add(this, new Data); } void render(Context& c) const { Data* data = c.get(this); } private: // And here's an example of D struct Data : public Context::Data { ~Data() { glDeleteBuffers(1, &vbo); glDeleteTextures(1, &texture); } GLint vbo; GLint texture; }; }; P.S. If you're familiar with computer graphics and VR, I'm creating a class that separates an object's per-context data (e.g. OpenGL VBO IDs) from its per-application data (e.g. an array of vertices) and frees the per-context data at the appropriate time (when the matching rendering context is current).

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• How to load a springframework ApplicationContext from Jython

  - by staticman

  I have a class that loads a springframework application context like so: package com.offlinesupport; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class OfflineScriptSupport { private static ApplicationContext appCtx; public static final void initialize() { appCtx = new ClassPathXmlApplicationContext( new String[] { "mycontext.spring.xml" } ); } public static final ApplicationContext getApplicationContext() { return appCtx; } public static final void main( String[] args ) { System.out.println( "Starting..." ); initialize(); System.out.println( "loaded" ); } } The class OfflineScriptSupport, and the file mycontext.spring.xml are each deployed into separate jars (along with other classes and resources in their respective modules). Lets say the jar files are OfflineScriptSupport.jar and *MyContext.jar". mycontext.spring.xml is put at the root of the jar. In a Jython script (*myscript.jy"), I try to call the initialize method to create the application context: from com.offlinesupport import OfflineScriptSupport OfflineScriptSupport.initialize(); I execute the Jython script with the following command (from Linux): jython -Dpython.path=spring.jar:OfflineScriptSupport.jar:MyContext.jar myscript.jy The Springframework application context cannot find the mycontext.spring.xml file. It displays the following error: java.io.FileNotFoundException: class path resource [mycontext.spring.xml] cannot be opened because it does not exist at org.springframework.core.io.ClassPathResource.getInputStream(ClassPathResource.java:137) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:167) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:148) at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:126) at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:142) at org.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(AbstractXmlApplicationContext.java:113) at org.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(AbstractXmlApplicationContext.java:81) at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:89) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:269) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:87) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:72) at com.offlinesupport.OfflineScriptSupport.initialize(OfflineScriptSupport.java:27) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) If I run the jar directly from Java (using the main entry point in OfflineScriptSupport) it works and there is no error thrown. Is there something special about the way Jython handles classpaths making the Springframework's ClassPathXmlApplicationContext not work (i.e. not be able to find resource files in the classpath)?

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• LINQ group by and getting latest value

  - by gregmac

  Say I have a structure like: class SomeObject Public Name as String Public Created as Date ... end class I have a List(of SomeObject), which has multiple entries for each name with different times. I'd like to select the newest (largest Created value) object for each Name. Given: Name Created A 2010-04-16 * A 2010-04-15 B 2010-04-12 B 2010-04-13 * C 2010-04-16 * I'd like to pick the objects with the * beside them. Is this possible using LINQ?

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• How safe is my safe rethrow?

  - by gustafc

  (Late edit: This question will hopefully be obsolete when Java 7 comes, because of the "final rethrow" feature which seems like it will be added.) Quite often, I find myself in situations looking like this: do some initialization try { do some work } catch any exception { undo initialization rethrow exception } In C# you can do it like this: InitializeStuff(); try { DoSomeWork(); } catch { UndoInitialize(); throw; } For Java, there's no good substitution, and since the proposal for improved exception handling was cut from Java 7, it looks like it'll take at best several years until we get something like it. Thus, I decided to roll my own: (Edit: Half a year later, final rethrow is back, or so it seems.) public final class Rethrow { private Rethrow() { throw new AssertionError("uninstantiable"); } /** Rethrows t if it is an unchecked exception. */ public static void unchecked(Throwable t) { if (t instanceof Error) throw (Error) t; if (t instanceof RuntimeException) throw (RuntimeException) t; } /** Rethrows t if it is an unchecked exception or an instance of E. */ public static <E extends Exception> void instanceOrUnchecked( Class<E> exceptionClass, Throwable t) throws E, Error, RuntimeException { Rethrow.unchecked(t); if (exceptionClass.isInstance(t)) throw exceptionClass.cast(t); } } Typical usage: public void doStuff() throws SomeException { initializeStuff(); try { doSomeWork(); } catch (Throwable t) { undoInitialize(); Rethrow.instanceOrUnchecked(SomeException.class, t); // We shouldn't get past the above line as only unchecked or // SomeException exceptions are thrown in the try block, but // we don't want to risk swallowing an error, so: throw new SomeException("Unexpected exception", t); } private void doSomeWork() throws SomeException { ... } } It's a bit wordy, catching Throwable is usually frowned upon, I'm not really happy at using reflection just to rethrow an exception, and I always feel a bit uneasy writing "this will not happen" comments, but in practice it works well (or seems to, at least). What I wonder is: Do I have any flaws in my rethrow helper methods? Some corner cases I've missed? (I know that the Throwable may have been caused by something so severe that my undoInitialize will fail, but that's OK.) Has someone already invented this? I looked at Commons Lang's ExceptionUtils but that does other things. Edit: finally is not the droid I'm looking for. I'm only interested to do stuff when an exception is thrown. Yes, I know catching Throwable is a big no-no, but I think it's the lesser evil here compared to having three catch clauses (for Error, RuntimeException and SomeException, respectively) with identical code. Note that I'm not trying to suppress any errors - the idea is that any exceptions thrown in the try block will continue to bubble up through the call stack as soon as I've rewinded a few things.

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• JAX-WS wsgen and collections of collections: wsgen broken?

  - by ayang

  I've been playing around with "bottom-up" JAX-WS and have come across something odd when running wsgen. If I have a service class that does something like: @WebService public class Foo { public ArrayList<Bar> getBarList(String baz) { ... } } then running wsgen gets me a FooService_schema1.xsd that has something like this: <xs:complexType name="getBarListResponse"> <xs:sequence> <xs:element name="return" type="tns:bar" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> which seems reasonable. However, if I want a collection of collections like: public BarCollection getBarCollection(String baz) { ... } // BarCollection is just a container for an ArrayList<Bar> then the generated schema ends up with stuff like: <xs:complexType name="barCollection"> <xs:sequence/> </xs:complexType> <xs:complexType name="getBookCollectionsResponse"> <xs:sequence> <xs:element name="return" type="tns:barCollection" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> An empty sequence is not what I had in mind at all. My original approach was to go with: public ArrayList<ArrayList<Bar>> getBarLists(String baz) { ... } but that ends up with a big chain of complexTypes that just wind up with an empty sequence at the end as well: <xs:complexType name="getBarListsResponse"> <xs:sequence> <xs:element name="return" type="tns:arrayList" minOccurs="0" maxOccurs="unbounded"/> </xs:sequence> </xs:complexType> <xs:complexType name="arrayList"> <xs:complexContent> <xs:extension base="tns:abstractList"> <xs:sequence/> </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="abstractList" abstract="true"> <xs:complexContent> <xs:extension base="tns:abstractCollection"> <xs:sequence/> </xs:extension> </xs:complexContent> </xs:complexType> <xs:complexType name="abstractCollection" abstract="true"> <xs:sequence/> </xs:complexType> Am I missing something or is this a known hole in wsgen? JAXB? Andy

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• trace this java method

  - by Bader

  public static int ABC(int x, int y) { if(y==0) return(0); else return(x + ABC(x,y-1)); } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(ABC(5,3)); }

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• operator+ overload returning object causing memory leaks, C++

  - by lampshade

  The problem i think is with returing an object when i overload the + operator. I tried returning a reference to the object, but doing so does not fix the memory leak. I can comment out the two statements: dObj = dObj + dObj2; and cObj = cObj + cObj2; to free the program of memory leaks. Somehow, the problem is with returning an object after overloading the + operator. #include <iostream> #include <vld.h> using namespace std; class Animal { public : Animal() {}; virtual void eat() = 0 {}; virtual void walk() = 0 {}; }; class Dog : public Animal { public : Dog(const char * name, const char * gender, int age); Dog() : name(NULL), gender(NULL), age(0) {}; virtual ~Dog(); Dog operator+(const Dog &dObj); private : char * name; char * gender; int age; }; class MyClass { public : MyClass() : action(NULL) {}; void setInstance(Animal &newInstance); void doSomething(); private : Animal * action; }; Dog::Dog(const char * name, const char * gender, int age) : // allocating here, for data passed in ctor name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Dog::~Dog() { delete name; delete gender; age = 0; } Dog Dog::operator+(const Dog &dObj) { Dog d; d.age = age + dObj.age; return d; } void MyClass::setInstance(Animal &newInstance) { action = &newInstance; } void MyClass::doSomething() { action->walk(); action->eat(); } int main() { MyClass mObj; Dog dObj("Scruffy", "Male", 4); // passing data into ctor Dog dObj2("Scooby", "Male", 6); mObj.setInstance(dObj); // set the instance specific to the object. mObj.doSomething(); // something happens based on which object is passed in dObj = dObj + dObj2; // invoke the operator+ return 0; }

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