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Do the 'up to date' guarantees provided by final field in Java's memory model extend to indirect ref

- by mattbh

The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?

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LINQ to SQL: NOTing a prebuilt expression

- by ck

I'm building a library of functions for one of my core L2S classes, all of which return a bool to allow checking for certain situations. Example: Expression<Func<Account, bool>> IsSomethingX = a => a.AccountSupplementary != null && a.AccountSupplementary.SomethingXFlag != null && a.AccountSupplementary.SomethingXFlag.Value; Now to query where this is not true, I CAN'T do this: var myAccounts= context.Accounts .Where(!IsSomethingX); // does not compile However, using the syntax from the PredicateBuilder class, I've come up with this: public static IQueryable<T> WhereNot<T>(this IQueryable<T> items, Expression<Func<T, bool>> expr1) { var invokedExpr = Expression.Invoke(expr1, expr1.Parameters.Cast<Expression>()); return items.Where(Expression.Lambda<Func<T, bool>> (Expression.Not(invokedExpr), expr1.Parameters)); } var myAccounts= context.Accounts .WhereNot(IsSomethingX); // does compile which actually produces the correct SQL. Does this look like a good solution, and is there anything I need to be aware of that might cause me problems in future?

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Full and Partial Matching of Sets

- by jeffrey

I have several sets of the same type [Y, M, D] and am trying to write a function to search these sets and return an array of the available sets that fit my parameters. ReturnedSets = return_matches(Y,M,D); I want the three parameters of the function return_matches to be optional. Which means any combination of values can be used to return the sets. For example, one could write - return_matches(13,null,2); - and the function would look for all sets that contain [13, anyValue, 2]; I'm writing this in PHP, to allow users to manage dated files on my website, but I'd like to be able to use this function again for other uses. Thanks! edit: (This, or variations of this, is all I can come up with so far... There is something extra that I don't understand, because this function ends up / would not work to return sets that contain y and d, but leaving m arbitrary. if(y == s[0]){ if(m == s[1]){ if(d == s[2]){ print "day match"; } } else {print "month match";} } else {print "year match";} } else {print "no match";}

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Is there a case for parameterising using Abstract classes rather than Interfaces?

- by Chris

I'm currently developing a component based API that is heavily stateful. The top level components implement around a dozen interfaces each. The stock top-level components therefore sit ontop of a stack of Abstract implementations which in turn contain multiple mixin implementations and implement multiple mixin interfaces. So far, so good (I hope). The problem is that the base functionality is extremely complex to implement (1,000s of lines in 5 layers of base classes) and therefore I do not wish for component writers to implement the interfaces themselves but rather to extend my base classes (where all the boiler plate code is already written). If the API therefore accepts interfaces rather than references to the Abstract implementation that I wish for component writers to extends, then I have a risk that the implementer will not perform the validation that is both required and assumed by other areas of code. Therefore, my question is, is it sometimes valid to paramerise API methods using an abstract implementation reference rather than a reference to the interface(s) that it implements? Do you have an example of a well-designed API that uses this technique or am I trying to talk myself into bad-practice?

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Query Parameter Value Is Null When Enum Item 0 is Cast to Int32

- by Timothy

When I use the first item in a zero-based Enum cast to Int32 as a query parameter, the parameter value is null. I've worked around it by simply setting the first item to a value of 1, but I was wondering though what's really going on here? This one has me scratching my head. Why does the parameter regarded the value as null, instead of 0? Enum LogEventType : int { SignIn, SignInFailure, SignOut, ... } private static DataTable QueryEventLogSession(DateTime start, DateTime stop) { DataTable entries = new DataTable(); using (FbConnection conn = new FbConnection(DSN)) { using (FbDataAdapter adapter = new FbDataAdapter( "SELECT event_type, event_timestamp, event_details FROM event_log " + "WHERE event_timestamp BETWEEN @start AND @stop " + "AND event_type IN (@signIn, @signInFailure, @signOut) " + "ORDER BY event_timestamp ASC", conn)) { adapter.SelectCommand.Parameters.AddRange(new Object[] { new FbParameter("@start", start), new FbParameter("@stop", stop), new FbParameter("@signIn", (Int32)LogEventType.SignIn), new FbParameter("@signInFailure", (Int32)LogEventType.SignInFailure), new FbParameter("@signOut", (Int32)LogEventType.SignOut)}); Trace.WriteLine(adapter.SelectCommand.CommandText); foreach (FbParameter p in adapter.SelectCommand.Parameters) { Trace.WriteLine(p.Value.ToString()); } adapter.Fill(entries); } } return entries; }

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Adding a column to a model at runtime (without additional tables) in rails

- by Marek

I'm trying to give admins of my web application the ability to add some new fields to a model. The model is called Artwork and i would like to add, for instante, a test_column column at runtime. I'm just teting, so i added a simple link to do it, it will be of course parametric. I managed to do it through migrations: def test_migration_create Artwork.add_column :test_column, :integer flash[:notice] = "Added Column test_column to artworks" redirect_to :action => 'index' end def test_migration_delete Artwork.remove_column :test_column flash[:notice] = "Removed column test_column from artworks" redirect_to :action => 'index' end It works, the column gets added/ removed to/from the databse without issues. I'm using active_scaffold at the moment, so i get the test_column field in the form without adding anything. When i submit a create or an update, however, the test_column does not get updated and stay empty. Inspecting the parameters, i can see: Parameters: {"commit"=>"Update", "authenticity_token"=>"37Bo5pT2jeoXtyY1HgkEdIhglhz8iQL0i3XAx7vu9H4=", "id"=>"62", "record"=>{"number"=>"test_artwork", "author"=>"", "title"=>"Opera di Test", "test_column"=>"TEEST", "year"=>"", "description"=>""}} the test_column parameter is passed correctly. So why active record keeps ignoring it? I tried to restart the server too without success. I'm using ruby 1.8.7, rails 2.3.5, and mongrel with an sqlite3 database. Thanks

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C# WinForms populating TreeView from List<myObj>

- by user743354

I have this structure of classes: public class L3Message { public int Number { get; set; } public string MessageName { get; set; } public string Device { get; set; } public string Time { get; set; } public string ScramblingCode { get; set; } public List<Parameter> Parameters { get; set; } public L3Message() { Parameters = new List<Parameter>(); } } public class Parameter { public int numOfWhitespaces { get; set; } public string ParameterName { get; set; } public string ParameterValue { get; set; } public Parameter Parent { get; set; } public List<Parameter> SubParameters { get; set; } public Parameter() { SubParameters = new List<Parameter>(); } } So, as return type from one of my Methods I have List of L3Messages (List < L3Message ), and I need to map that to TreeView in WinForms (populate TreeView from that List). If possible, I would like to that in separate thread. How can I achieve that?

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What is a good "Error Checking" Pattern (Java)?

- by Jack

I'll explain what I mean by input error checking. Say you have a function doSomething(x). If the function completes successfully doSomething does something and returns nothing. However, if there are errors I'd like to be notified. That is what I mean by error checking. I'm looking for, in general, the best way to check for errors. I've thought of the following solutions, each with a potential problem. Flag error checking. If doSomething(x) completes successfully return null. Otherwise, it returns a boolean or an error string. Problem: Side effects. Throwing an exception. Throw an exception if doSomething(x) encounters an error. Problem: If you are performing error checking for parameters only, throwing an IllegalArgumentExceptionseems inappropriate. Validating input prior to function call. If the error checking is only meant for the parameters of the function, then you can call a validator function before calling the doSomething(x) function. Problem: What if a client of the class forgets to call the validator function before calling doSomething(x)? I often encounter this problem and any help or a point in the right direction would be much appreciated.

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MVC route doesn't work

- by bill

Hi All, I have a bunch of Views in a default folder that represent single "static" pages. Everything works as advertised except i tried adding a new page yesterday.. using the exact same routing syntax and cannot for the life of me get it to work. here's is an example of a working route: routes.MapRoute( "OurProgram", // Route name "Our_Program", // URL with parameters new { controller = "Default", action = "OurProgram" } ); The filename is OurProgram and hitting http:// localhost/Our_Program/ opens the correct view which resides in the Views/Default folder. So i added another view into this folder: Views/Default/BuyNow.aspx and added the route: routes.MapRoute( "BuyNow", // Route name "Buy_Now", // URL with parameters new { controller = "Default", action = "BuyNow" } ); And this doesn't open. I have tried the "route debugger http://haacked.com/archive/2008/03/13/url-routing-debugger.aspx" and it correctly identifies the route. I am at a lose. I have tried re-creating the view.. I am using MVC.Net 2.0 and VS 10. Any help is appreciated!

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How to preserve the state of JavaScript closure?

- by Uccio

I am working on a migration platform to migrate web applications from a device to another. I am extending it to add the support for preserving JavaScript state. My main task is to create a file representing the current state of the executing application, to transmit it to another device and to reload the state in the destination device. The basic solution I adopted is to navigate the window object and to save all its descendant properties using JSON as base format for exportation and extending it to implement some features: preserving object reference, even if cyclic (dojox.json.ref library) support for timers Date non-numericproperties of arrays reference to DOM elements The most important task I need to solve now is exportation of closures. At this moment I didn't know how to implement this feature. I read about the internal EcmaScript property [[scope]] containing the scope chain of a function, a list-like object composed by all the nested activation context of the function. Unfortunately it is not accessible by JavaScript. Anyone know if there is a way to directly access the [[scope]] property? Or another way to preserve the state of a closure?

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wget not completely processing the http call

- by user578458

Here is a wget command that executes a HTML / PHP stack report suite that is hosted by a third party - we don't have control over the PHP or HTML page wget --no-check-certificate --http-user=/myacc --http-password=mypass -O /tmp/myoutput.csv "https://myserver.mydomain.com/mymodule.php?myrepcode=9999&action=exportcsv&admin=myappuserid&password=myappuserpass&startdate=2011-01-16&enddate=2011-01-16&reportby=mypreferredview" All the elements are working perfectly: --http-user / --http-pass as offered by a browsers standard popup for username and password prompt -O /tmp/myoutput.csv - the output file of interest https://myserver.mydomain.com/mymodule.php?myrepcode=9999&action=exportcsv&admin=myappuserid&password=myappuserpass&startdate=2011-01-16&enddate=2011-01-16&reportby=mypreferredview" The file generated on the fly by the parameters myrepcode=9999 - a reference to the report in question action=exportcsv internally written in the function admin=myappuserid the third party operats SSL to access the site - then internal username and password stored in a database to access the functions of the site) password=myappuserpass startdate=2011-01-16 this and end data are parameters specific to the report 9999 enddate=2011-01-16 reportby=mypreferredview This is an option in the report that facilitates different levels of detail or aggregation The problem is that the reportby parameter is a radio button selection in a list of 5 selections (sure I enough the default is highest level of aggregation , I want the last one which is the most detailed) Here is a sample of the HTML page code for the options of reportby View by The Default My Least Preferred My Second Least Preferred My Third Least Preferred My Preferred No matter which of the reportby items I select in the wget statement - thedefault is always executed. Questions 1) Has anyone come across this notation in HTML (id=inputname[inputelement]) I spoke to a senior web developer and he has never seen this notation for inputs (id=inputname[inputelement]) - and w3schools do not appear familiar with this either based on an extensive search 2) Can a wget command select a none default radio item when executing the command ? This probably will be initially received with a "Use CURL" response- however the wget approach works very well in the limited environment I am operating in - particularly as I need to download 10000 of these such items. Thanks ahead of response

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SQL Server find and replace in TEXT field

- by incubushead

I have a database in SQL Server 2005 that was brought up from SQL Server 2000 and is still using TEXT type fields instead of varchar(max). I need to find and replace a string of characters in the text field but all of the examples of how to do this that I have found don't seem like they would work for me. It seems the UPDATETEXT command requires that the two parameters "insert_offset" and "delete_length" be set explicitly but the string i am searching for could show up in the text at any point or even at several points in the same cell. My understanding of these two parameters is that the string im searching for will always be in the same place, so that insert_offset is the number of spaces into the text that the UPDATETEXT command will start replacing text. Example: Need to find: <u> and Replace it with: <u> Text field example: *Everyone in the room was <b><u>tired</u>.</b><br>Then they woke <b><u>up</u>. Can anyone help me out with this? THANKS!

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DCI: How to implement Context with Dependency Injection?

- by ciscoheat

Most examples of a DCI Context are implemented as a Command pattern. When using Dependency Injection though, it's useful to have the dependencies injected in the constructor and send the parameters into the executing method. Compare the Command pattern class: public class SomeContext { private readonly SomeRole _someRole; private readonly IRepository<User> _userRepository; // Everything goes into the constructor for a true encapsuled command. public SomeContext(SomeRole someRole, IRepository<User> userRepository) { _someRole = someRole; _userRepository = userRepository; } public void Execute() { _someRole.DoStuff(_userRepository); } } With the Dependency injected class: public class SomeContext { private readonly IRepository<User> _userRepository; // Only what can be injected using the DI provider. public SomeContext(IRepository<User> userRepository) { _userRepository = userRepository; } // Parameters from the executing method public void Execute(SomeRole someRole) { someRole.DoStuff(_userRepository); } } The last one seems a bit nicer, but I've never seen it implemented like this so I'm curious if there are any things to consider.

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VB.NET CInt(Long) behaving differently in 32- and 64-bit environments

- by LocoDelAssembly

Hello everybody, this is my first message here. Today I had a problem converting a Long (Int64) to an Integer (Int32). The problem is that my code was always working in 32-bit environments, but when I try THE SAME executable in a 64-bit computer it crashes with a System.OverflowException exception. I've prepared this test code in VS2008 in a new project with default settings: Module Module1 Sub Main() Dim alpha As Long = -1 Dim delta As Integer Try delta = CInt(alpha And UInteger.MaxValue) Console.WriteLine("CINT OK") delta = Convert.ToInt32(alpha And UInteger.MaxValue) Console.WriteLine("Convert.ToInt32 OK") Catch ex As Exception Console.WriteLine(ex.GetType().ToString()) Finally Console.ReadLine() End Try End Sub End Module On my 32-bit setups (Windows XP SP3 32-bit and Windows 7 32-bit) it prints "CINT OK", but in the 64-bit computer (Windows 7 64-bit) that I've tested THE SAME executable it prints the exception name only. Is this behavior documented? I tried to find a reference but failed miserably. For reference I leave the MSIL code too: .method public static void Main() cil managed { .entrypoint .custom instance void [mscorlib]System.STAThreadAttribute::.ctor() = ( 01 00 00 00 ) // Code size 88 (0x58) .maxstack 2 .locals init ([0] int64 alpha, [1] int32 delta, [2] class [mscorlib]System.Exception ex) IL_0000: nop IL_0001: ldc.i4.m1 IL_0002: conv.i8 IL_0003: stloc.0 IL_0004: nop .try { .try { IL_0005: ldloc.0 IL_0006: ldc.i4.m1 IL_0007: conv.u8 IL_0008: and IL_0009: conv.ovf.i4 IL_000a: stloc.1 IL_000b: ldstr "CINT OK" IL_0010: call void [mscorlib]System.Console::WriteLine(string) IL_0015: nop IL_0016: ldloc.0 IL_0017: ldc.i4.m1 IL_0018: conv.u8 IL_0019: and IL_001a: call int32 [mscorlib]System.Convert::ToInt32(int64) IL_001f: stloc.1 IL_0020: ldstr "Convert.ToInt32 OK" IL_0025: call void [mscorlib]System.Console::WriteLine(string) IL_002a: nop IL_002b: leave.s IL_0055 } // end .try catch [mscorlib]System.Exception { IL_002d: dup IL_002e: call void [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.ProjectData::SetProjectError(class [mscorlib]System.Exception) IL_0033: stloc.2 IL_0034: nop IL_0035: ldloc.2 IL_0036: callvirt instance class [mscorlib]System.Type [mscorlib]System.Exception::GetType() IL_003b: callvirt instance string [mscorlib]System.Type::ToString() IL_0040: call void [mscorlib]System.Console::WriteLine(string) IL_0045: nop IL_0046: call void [Microsoft.VisualBasic]Microsoft.VisualBasic.CompilerServices.ProjectData::ClearProjectError() IL_004b: leave.s IL_0055 } // end handler } // end .try finally { IL_004d: nop IL_004e: call string [mscorlib]System.Console::ReadLine() IL_0053: pop IL_0054: endfinally } // end handler IL_0055: nop IL_0056: nop IL_0057: ret } // end of method Module1::Main I suspect that the instruction that is behaving differently is either conv.ovf.i4 or the ldc.i4.m1/conv.u8 pair. If you know what is going on here please let me know Thanks

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how to pass value to controller??

- by rajesh

When I try to pass url value to controller action, action is not getting the required value. I'm sending the value like this: function value(url,id) { alert(url); document.getElementById('rating').innerHTML=id; var params = 'artist='+id; alert(params); // var newurl='http://localhost/songs_full/public/eslresult/ratesong/userid/1/id/27'; var myAjax = new Ajax.Request(newurl,{method: 'post',parameters:params,onComplete: loadResponse}); //var myAjax = new Ajax.Request(url,{method:'POST',parameters:params,onComplete: load}); //alert(myAjax); } function load(http) { alert('success'); } and in the controller I have: public function ratesongAction() { $user=$_POST['rating']; echo $user; $post= $this->getRequest()->getPost(); //echo $post; $ratesongid= $this->_getParam('id'); } But still not getting the result. I am using zend framework.

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Firefox "intelligently" and silently fixes incorrect file references in CSS and Scripts at runtime.

- by bobsoap

Well this is a really weird issue, I really didn't find anything on this elsewhere so I thought I'd address it here. Say I have an "image.jpg" and accidentally reference it in the CSS like so: url(imag.jpg) Note the missing "e". Now for me, Firefox is so incredibly clever that it will still find the correct image, but NOT SPIT OUT A WARNING. So I assume that everything is ok. But later, when I test the page in any other browser, all of a sudden the image doesn't display (and rightly so). That's because Firefox thought it was a good idea to correct my error without telling me. This becomes more critical with scripts. Firefox will also auto-correct a typo in a reference. I just wasted a whole hour scratching my head and trying to debug an ajax function in Webkit - turns out, I just had a typo where I included the file. Why on earth does Firefox do this without telling, and where the heck can I turn this off? This has first occured somewhere around FF 3.0 and still persists in 3.6.3. /rant an thank fo any inpu ;)

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C++ Conceptual problem with (Pointer) Pointers

- by Ptr

I have a structure usually containing a pointer to an int. However, in some special cases, it is necessary that this int pointer points to another pointer which then points to an int. Wow: I mentioned the word pointer 5 times so far! Is this even possible? I thought about it that way: Instead of using a second int pointer, which is most likely not possible as my main int pointer can only point to an int and not to another int pointer, I could make it a reference like this: int intA = 1; int intB = 2; int& intC = intB; int* myPointers[ 123 ]; myPointers[ 0 ] = &intA; myPointers[ 1 ] = &intB; myPointers[ 3 ] = &intC; So the above would do what I want: The reference to intB (intC) behaves quite like I want it to (If it gets changed it also changes intB) The problem: I can't change references once they are set, right? Or is there a way? Everything in short: How do I get a value to work with * (pointers) and ** (pointers to pointers)?

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Is there a maximum number of input controls that can be used on an HTML form?

- by Rich

I have an ambitious requirement for an asp.net 2.0 web page that contains a table (gridview), and each row in the grid contains 6 select (dropdown) controls for data entry. The number of rows that will be displayed is dependent upon the user's search parameters, which are specified in another area of the page. Unfortunately, with the default (and even basic) search parameters specified, the grid could contain several hundred rows. I've noticed that the browser, in this case IE8, starts behaving rather erratically once I reach a large number of rows -- no documented evidence for the number of rows where this begins to be a problem. For example, trying to view the source of the page results in a message from IE stating that there was a problem with the page that forced the browser to reload it, and I never get the source. Obviously the page loads and renders rather slowly also. I know that my solution is probably going to involve paging the gridview such that it only displays 20 or so rows per page, and I'll have to write code to handle the saving of changes in the dropdown values when the user changes pages. I can probably turn off viewstate on the gridview also. However, the question I really want to pose is this -- has anyone seen a documented rule indicating the maximum number of input controls that an HTML browser form is supposed to be able to contain? I could not find anything on the Internet after doing a search, and I suspect the answer may be whatever the browser can handle based on the machine configuration it is running on. Any rules of thumb you use? Thanks for any suggestions. Rich

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mvc design in a card game

- by Hong

I'm trying to make a card game. some classes I have are: CardModel, CardView; DeckModel, DeckView. The deck model has a list of card model, According to MVC, if I want to send a card to a deck, I can add the card model to the deck model, and the card view will be added to the deck view by a event handler. So I have a addCard(CardModel m) in the DeckModel class, but if I want to send a event to add the card view of that model to the deck view, I only know let the model has a reference to view. So the question is: If the card model and deck model have to have a reference to their view classes to do it? If not, how to do it better? Update, the code: public class DeckModel { private ArrayList<CardModel> cards; private ArrayList<EventHandler> actionEventHandlerList; public void addCard(CardModel card){ cards.add(card); //processEvent(event x); //must I pass a event that contain card view here? } CardModel getCards(int index){ return cards.get(index); } public synchronized void addEventHandler(EventHandler l){ if(actionEventHandlerList == null) actionEventHandlerList = new ArrayList<EventHandler>(); if(!actionEventHandlerList.contains(l)) actionEventHandlerList.add(l); } public synchronized void removeEventHandler(EventHandler l){ if(actionEventHandlerList!= null && actionEventHandlerList.contains(l)) actionEventHandlerList.remove(l); } private void processEvent(Event e){ ArrayList list; synchronized(this){ if(actionEventHandlerList!= null) list = (ArrayList)actionEventHandlerList.clone(); else return; } for(int i=0; i<actionEventHandlerList.size(); ++i){ actionEventHandlerList.get(i).handle(e); } } }

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Magic Method __set() on a Instanciated Object

- by streetparade

Ok i have a problem, sorry if i cant explaint it clear but the code speaks for its self. i have a class which generates objects from a given class name; Say we say the class is Modules: public function name($name) { $this->includeModule($name); try { $module = new ReflectionClass($name); $instance = $module->isInstantiable() ? $module->newInstance() : "Err"; $this->addDelegate($instance); } catch(Exception $e) { Modules::Name("Logger")->log($e->getMessage()); } return $this; } The AddDelegate Method: protected function addDelegate($delegate) { $this->aDelegates[] = $delegate; } The __call Method public function __call($methodName, $parameters) { $delegated = false; foreach ($this->aDelegates as $delegate) { if(class_exists(get_class($delegate))) { if(method_exists($delegate,$methodName)) { $method = new ReflectionMethod(get_class($delegate), $methodName); $function = array($delegate, $methodName); return call_user_func_array($function, $parameters); } } } The __get Method public function __get($property) { foreach($this->aDelegates as $delegate) { if ($delegate->$property !== false) { return $delegate->$property; } } } All this works fine expect the function __set public function __set($property,$value) { //print_r($this->aDelegates); foreach($this->aDelegates as $k=>$delegate) { //print_r($k); //print_r($delegate); if (property_exists($delegate, $property)) { $delegate->$property = $value; } } //$this->addDelegate($delegate); print_r($this->aDelegates); } class tester { public function __set($name,$value) { self::$module->name(self::$name)->__set($name,$value); } } Module::test("logger")->log("test"); // this logs, it works echo Module::test("logger")->path; //prints /home/bla/test/ this is also correct But i cant set any value to class log like this Module::tester("logger")->path ="/home/bla/test/log/"; The path property of class logger is public so its not a problem of protected or private property access. How can i solve this issue? I hope i could explain my problem clear.

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C++, inject additional data in a method

- by justik

I am adding the new modul in some large library. All methods here are implemented as static. Let mi briefly describe the simplified model: typedef std::vector<double> TData; double test ( const TData &arg ) { return arg ( 0 ) * sin ( arg ( 1 ) + ...;} double ( * p_test ) ( const TData> &arg) = &test; class A { public: static T f1 (TData &input) { .... //some computations B::f2 (p_test); } }; Inside f1() some computations are perfomed and a static method B::f2 is called. The f2 method is implemented by another author and represents some simulation algorithm (example here is siplified). class B { public: static double f2 (double ( * p_test ) ( const TData &arg ) ) { //difficult algorithm working p_test many times double res = p_test(arg); } }; The f2 method has a pointer to some weight function (here p_test). But in my case some additional parameters computed in f1 for test() methods are required double test ( const TData &arg, const TData &arg2, char *arg3.... ) { } How to inject these parameters into test() (and so to f2) to avoid changing the source code of the f2 methods (that is not trivial), redesign of the library and without dirty hacks :-) ? The most simple step is to override f2 static double f2 (double ( * p_test ) ( const TData &arg ), const TData &arg2, char *arg3.... ) But what to do later? Consider, that methods are static, so there will be problems with objects. Thanks for your help.

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What is the meaning of @ModelAttribute annotation at method argument level?

- by beemaster

Spring 3 reference teaches us: When you place it on a method parameter, @ModelAttribute maps a model attribute to the specific, annotated method parameter I don't understand this magic spell, because i sure that model object's alias (key value if using ModelMap as return type) passed to the View after executing of the request handler method. Therefore when request handler method executes the model object's name can't be mapped to the method parameter. To solve this contradiction i went to stackoverflow and found this detailed example. The author of example said: // The "personAttribute" model has been passed to the controller from the JSP It seems, he is charmed by Spring reference... To dispel the charms i deployed his sample app in my environment and cruelly cut @ModelAttribute annotation from method MainController.saveEdit. As result the application works without any changes! So i conclude: the @ModelAttribute annotation is not needed to pass web form's field values to the argument's fields. Then i stuck to the question: what is the mean of @ModelAttribute annotation? If the only mean is to set alias for model object in View, then why this way better than explicitly adding of object to ModelMap?

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IS operator behaving a bit strangely

- by flockofcode

1) According to my book, IS operator can check whether expression E (E is type) can be converted to the target type only if E is either a reference conversion, boxing or unboxing. Since in the following example IS doesn’t check for either of the three types of conversion, the code shouldn’t work, but it does: int i=100; if (i is long) //returns true, indicating that conversion is possible l = i; 2) a) B b; A a = new A(); if (a is B) b = (B)a; int i = b.l; class A { public int l = 100; } class B:A { } The above code always causes compile time error “Use of unassigned variable”. If condition a is B evaluates to false, then b won’t be assigned a value, but if condition is true, then it will. And thus by allowing such a code compiler would have no way of knowing whether the usage of b in code following the if statement is valid or not ( due to not knowing whether a is b evaluates to true or false) , but why should it know that? Intsead why couldn’t runtime handle this? b) But if instead we’re dealing with non reference types, then compiler doesn’t complain, even though the code is identical.Why? int i = 100; long l; if (i is long) l = i; thank you

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Does ReleaseStringUTF do more than free memory?

- by Bayou Bob

Consider the following C code segments. Segment 1: char * getSomeString(JNIEnv *env, jstring jstr) { char * retString; retString = (*env)->GetStringUTFChars(env, jstr, NULL); return retString; } void useSomeString(JNIEnv *env, jobject jobj, char *mName) { jclass cl = (*env)->GetObjectClass(env, jobj); jmethodId mId = (*env)->GetMethodID(env, cl, mName, "()Ljava/lang/String;"); jstring jstr = (*env)->CallObjectMethod(env, obj, id, NULL); char * myString = getSomeString(env, jstr); /* ... use myString without modifing it */ free(myString); } Because myString is freed in useSomeString, I do not think I am creating a memory leak; however, I am not sure. The JNI spec specifically requires the use of ReleaseStringUTFChars. Since I am getting a C style 'char *' pointer from GetStringUTFChars, I believe the memory reference exists on the C stack and not in the JAVA heap so it is not in danger of being Garbage Collected; however, I am not sure. I know that changing getSomeString as follows would be safer (and probably preferable). Segment 2: char * getSomeString(JNIEnv *env, jstring jstr) { char * retString; char * intermedString; intermedString = (*env)->GetStringUTFChars(env, jstr, NULL); retString = strdup(intermedString); (*env)->ReleaseStringUTFChars(env, jstr, intermedString); return retString; } Because of our 'process' I need to build an argument on why getSomeString in Segment 2 is preferable to Segment 1. Is anyone aware of any documentation or references which detail the behavior of GetStringUTFChars and ReleaseStringUTFChars in relation to where memory is allocated or what (if any) additional bookkeeping is done (i.e. local Reference Pointer to the Java Heap being created, etc). What are the specific consequences of ignoring that bookkeeping. Thanks in advance.

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Does std::vector change its address? How to avoid

- by kunigami

Since vector elements are stored contiguously, I guess it may not have the same address after some push_back's , because the initial allocated space could not suffice. I'm working on a code where I need a reference to an element in a vector, like: int main(){ vector<int> v; v.push_back(1); int *ptr = &v[0]; for(int i=2; i<100; i++) v.push_back(i); cout << *ptr << endl; //? return 0; } But it's not necessarily true that ptr contains a reference to v[0], right? How would be a good way to guarantee it? My first idea would be to use a vector of pointers and dynamic allocation. I'm wondering if there's an easier way to do that? PS.: Actually I'm using a vector of a class instead of int, but I think the issues are the same.

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