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• Comparing objects and inheritance

  - by ereOn

  Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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• Hibernate many-to-one - bad usage?

  - by DaveA

  Just trying out Hibernate (with Annotations) and I'm having problems with my mappings. I have two entity classes, AudioCD and Artist. @Entity public class AudioCD implements CatalogItem { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; private String title; @ManyToOne(cascade = { CascadeType.ALL }, optional = false) private Artist artist; .... } @Entity @Table(uniqueConstraints = { @UniqueConstraint(columnNames = { "name" }) }) public class Artist { @Id @GeneratedValue(strategy = GenerationType.AUTO) private int id; @Column(nullable = false) private String name; ..... } I get AudioCD objects from an external source. When I try to persist the AudioCD the Artist gets persisted as well, just like I want to happen. If I try persisting another different CD, but Artist already exists I get errors due to constraint violations. I want Hibernate to recognise that the Artist already exists and shouldn't be inserted again. Can this be done via annotations? Or do I have to manage the persistence of the AudioCD and Artist seperately?

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• Expose webservice directly to webclients or keep a thin server-side script layer in between?

  - by max

  Hi, I'm developing a REST webservice (Java, Jersey). The people I'm doing this for want to directly access the webservice via Javascript. Some instinct tells me this is not a good idea, but I cannot really explain that instinct. My natural approach would have been to have the webservice do the real logic and database access, but also have some (relatively thin) server-side script layer (e.g. in PHP). Clients would talk to the PHP layer which in turn would talk to the webservice. (The webservice would be pretty local to the apache/PHP server and implicitly trust calls from the script layer. The script layer would take care of session management.) (Btw, I am not talking about just hiding the webservice behind an Apache which simply redirects calls.) But as I find myself at a lack of words/arguments to explain my instinct, I wonder whether my instinct is right - note that while I have been developing all kinds of software in all kinds of languages and frameworks for like 17 years, this is the first time I develop a webservice. So my question is basically: what are your opinions? Are there any standard setups? Is my instinct totally wrong? Or partially? ;P Many thanks, Max PS: I might add a few bits of information about the planned usage of the whole application: will be accessed by different kinds of users, partly general public, partly privileged thus, all major OS/browser combinations can be expected as clients however, writing the client is not my responsibility will potentially have very high load/traffic logic of webservice will later be massively expanded for another product which is basically a superset of the functionality of the current project there is a significant likelihood that at some point an API should be exposed which can be used by 3rd party developers - obviously, with some restrictions at some point, the public view of the product should become accessible via smartphones, too (in other words, maybe a customized version of the site to adapt to the smaller display and different input methods)

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• Fast find object by string property

  - by Andrew Kalashnikov

  Hello, colleagues. I've got task to fast find object by its string property. Object: class DicDomain { public virtual string Id{ get; set; } public virtual string Name { get; set; } } For storing my object I use List[T] dictionary where T is DicDomain for now . I've got 5-10 such lists, which contain about 500-20000 at each one. Task is find objects by its Name. I use next code now: List<T> entities = dictionary.FindAll(s => s.Name.Equals(word, StringComparison.OrdinalIgnoreCase)); I've got some questions: Is my search speed optimal. I think now. Data structure. It List good for this task. What about hashtable,sorted... Method Find. May be i should use string intern?? I haven't much exp at these tasks. Can u give me good advice for increase perfomance. Thanks

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• How do I place widgets above and below a listview?

  - by Jay Askren

  I have a list view and want to put stuff both above(on the y axis) and below(y axis) it including images, text views, and a row of buttons. Below is a simplified version of what I am creating. Unfortunately the list covers(i.e. above on the z axis) the header so the header text is not visible instead of being underneath (on the y axis) <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="wrap_content" android:layout_height="wrap_content"> <TextView android:id="@+id/footer" android:text="footer" android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_alignParentBottom="true" /> <ListView android:id="@+id/list_view" android:layout_height="fill_parent" android:layout_width="fill_parent" android:layout_above="@id/footer" android:background="#ff9999ff"/> <TextView android:id="@+id/header" android:text="header" android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_alignParentTop="true" android:layout_above="@id/list_view" android:baselineAlignBottom="false" /> </RelativeLayout> Here is the corresponding Activity class: public class SampleListActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.list_activity); } }

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• Why doesn't String's hashCode() cache 0?

  - by polygenelubricants

  I noticed in the Java 6 source code for String that hashCode only caches values other than 0. The difference in performance is exhibited by the following snippet: public class Main{ static void test(String s) { long start = System.currentTimeMillis(); for (int i = 0; i < 10000000; i++) { s.hashCode(); } System.out.format("Took %d ms.%n", System.currentTimeMillis() - start); } public static void main(String[] args) { String z = "Allocator redistricts; strict allocator redistricts strictly."; test(z); test(z.toUpperCase()); } } Running this in ideone.com gives the following output: Took 1470 ms. Took 58 ms. So my questions are: Why doesn't String's hashCode() cache 0? What is the probability that a Java string hashes to 0? What's the best way to avoid the performance penalty of recomputing the hash value every time for strings that hash to 0? Is this the best-practice way of caching values? (i.e. cache all except one?) For your amusement, each line here is a string that hash to 0: pollinating sandboxes amusement & hemophilias schoolworks = perversive electrolysissweeteners.net constitutionalunstableness.net grinnerslaphappier.org BLEACHINGFEMININELY.NET WWW.BUMRACEGOERS.ORG WWW.RACCOONPRUDENTIALS.NET Microcomputers: the unredeemed lollipop... Incentively, my dear, I don't tessellate a derangement. A person who never yodelled an apology, never preened vocalizing transsexuals.

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• Which pattern to use for logging? Dependency Injection or Service Locator?

  - by andlju

  Consider this scenario. I have some business logic that now and then will be required to write to a log. interface ILogger { void Log(string stuff); } interface IDependency { string GetInfo(); } class MyBusinessObject { private IDependency _dependency; public MyBusinessObject(IDependency dependency) { _dependency = dependency; } public string DoSomething(string input) { // Process input var info = _dependency.GetInfo(); var intermediateResult = PerformInterestingStuff(input, info); if (intermediateResult== "SomethingWeNeedToLog") { // How do I get to the ILogger-interface? } var result = PerformSomethingElse(intermediateResult); return result; } } How would you get the ILogger interface? I see two main possibilities; Pass it using Dependency Injection on the constructor. Get it via a singleton Service Locator. Which method would you prefer, and why? Or is there an even better pattern? Update: Note that I don't need to log ALL method calls. I only want to log a few (rare) events that may or may not occur within my method.

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• Using boost::iterator_adaptor

  - by Neil G

  I wrote a sparse vector class (see #1, #2.) I would like to provide two kinds of iterators: The first set, the regular iterators, can point any element, whether set or unset. If they are read from, they return either the set value or value_type(), if they are written to, they create the element and return the lvalue reference. Thus, they are: Random Access Traversal Iterator and Readable and Writable Iterator The second set, the sparse iterators, iterate over only the set elements. Since they don't need to lazily create elements that are written to, they are: Random Access Traversal Iterator and Readable and Writable and Lvalue Iterator I also need const versions of both, which are not writable. I can fill in the blanks, but not sure how to use boost::iterator_adaptor to start out. Here's what I have so far: class iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::?????? // CategoryOrTraversal > class sparse_iterator : public boost::iterator_adaptor< iterator // Derived , value_type* // Base , boost::use_default // Value , boost::random_access_traversal_tag? // CategoryOrTraversal >

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• Can I transform this asynchronous java network API into a monadic representation (or something else

  - by AlecZorab

  I've been given a java api for connecting to and communicating over a proprietary bus using a callback based style. I'm currently implementing a proof-of-concept application in scala, and I'm trying to work out how I might produce a slightly more idiomatic scala interface. A typical (simplified) application might look something like this in Java: DataType type = new DataType(); BusConnector con = new BusConnector(); con.waitForData(type.getClass()).addListener(new IListener<DataType>() { public void onEvent(DataType t) { //some stuff happens in here, and then we need some more data con.waitForData(anotherType.getClass()).addListener(new IListener<anotherType>() { public void onEvent(anotherType t) { //we do more stuff in here, and so on } }); } }); //now we've got the behaviours set up we call con.start(); In scala I can obviously define an implicit conversion from (T = Unit) into an IListener, which certainly makes things a bit simpler to read: implicit def func2Ilistener[T](f: (T => Unit)) : IListener[T] = new IListener[T]{ def onEvent(t:T) = f } val con = new BusConnector con.waitForData(DataType.getClass).addListener( (d:DataType) => { //some stuff, then another wait for stuff con.waitForData(OtherType.getClass).addListener( (o:OtherType) => { //etc }) }) Looking at this reminded me of both scalaz promises and f# async workflows. My question is this: Can I convert this into either a for comprehension or something similarly idiomatic (I feel like this should map to actors reasonably well too) Ideally I'd like to see something like: for( d <- con.waitForData(DataType.getClass); val _ = doSomethingWith(d); o <- con.waitForData(OtherType.getClass) //etc )

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• ASP.net MVC Linq-To-SQL Extended Class Field Binding

  - by user336858

  Hi there, The short version of this question is "Is there a way to get automatic View Object binding for fields defined in a partial class for a Linq-To-SQL generated class?" Apologies if it's been asked before. Example Suppose I have a typical MVC setup with the tables: Posts {PostID, ...} Categories {CategoryID, ...} A post can have more than one category, and a category can identify more than one post. Thus suppose further that I need an extra table: PostCategories {PostID, CategoryID, ...} This handles the many-to-many relationship between posts and categories. As far as I know, there's no way to do this in Linq-to-SQL right now so I have to shoehorn it in by adding a partial Postclass to the project to add that functionality. Something like: public partial class Post { public IEnumerable<Category> Categories{ get { ... } set { ... } } } So here's my question: If a user is accessing my MVC application front-end and begins editing a Post object, they might enter an invalid category. When the server recognizes the invalid input, the usual practice is to return the faulty object to the original view for re-editing along with some error messages. The fields in the edit page are re-populated with the provided values. However I don't know how to get this mechanism to work with the properties I created with the partial class as shown above. Any terminology, links, or tips you can provide would be tremendously helpful!

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• Why doesn't this CompiledQuery give a performance improvement?

  - by Grammarian

  I am trying to speed up an often used query. Using a CompiledQuery seemed to be the answer. But when I tried the compiled version, there was no difference in performance between the compiled and non-compiled versions. Can someone please tell me why using Queries.FindTradeByTradeTagCompiled is not faster than using Queries.FindTradeByTradeTag? static class Queries { // Pre-compiled query, as per http://msdn.microsoft.com/en-us/library/bb896297 private static readonly Func<MyEntities, int, IQueryable<Trade>> mCompiledFindTradeQuery = CompiledQuery.Compile<MyEntities, int, IQueryable<Trade>>( (entities, tag) => from trade in entities.TradeSet where trade.trade_tag == tag select trade); public static Trade FindTradeByTradeTagCompiled(MyEntities entities, int tag) { IQueryable<Trade> tradeQuery = mCompiledFindTradeQuery(entities, tag); return tradeQuery.FirstOrDefault(); } public static Trade FindTradeByTradeTag(MyEntities entities, int tag) { IQueryable<Trade> tradeQuery = from trade in entities.TradeSet where trade.trade_tag == tag select trade; return tradeQuery.FirstOrDefault(); } }

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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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• server controls complex properties with sub collections.

  - by Richard Friend

  Okay i have a custom server control that has some autocomplete settings, i have this as follows and it works fine. /// <summary> /// Auto complete settings /// </summary> [System.ComponentModel.DesignerSerializationVisibility (System.ComponentModel.DesignerSerializationVisibility.Content), PersistenceMode(PersistenceMode.InnerProperty), Category("Data"), Description("Auto complete settings"), NotifyParentProperty(true)] public AutoCompleteLookupSettings AutoComplete { private set; get; } I also have a ParameterCollection that is really related to the auto complete settings, currently this collection resides off the control itself like so : /// <summary> /// Parameters for any data lookups /// </summary> [System.ComponentModel.DesignerSerializationVisibility(System.ComponentModel.DesignerSerializationVisibility.Content), PersistenceMode(PersistenceMode.InnerProperty)] public ParameterCollection Parameters { get; set; } What i would like to do is move the parameter collection inside of the AutoCompleteSettings as it really relates to my autocomplete, i have tried this but to no avail.. I would like to move from <cc1:TextField ID="TextField1" runat='server'> <AutoComplete MethodName="GetTest" TextField="Item1" TypeName ="AppFrameWork.Utils" /> <Parameters> <asp:ControlParameter ControlID="txtTest" PropertyName="Text" Name="test" /> </Parameters> </cc1:TextField> To <cc1:TextField ID="TextField1" runat='server'> <AutoComplete MethodName="GetTest" TextField="Item1" TypeName ="AppFrameWork.Utils" > <Parameters> <asp:ControlParameter ControlID="txtTest" PropertyName="Text" Name="test" /> </Parameters> </AutoComplete> </cc1:TextField>

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• My java program seems to be skipping over the try{}, executing the catch{} and then throwing a NullPointerException. What should I do?

  - by Matt Bolopue

  I am writing a program that calculates the number of words, syllables, and sentences in any given text file. I don't need help finding those numbers, however my program (which currently should only find the number of words in the text file) will not import the text file even when I type in the name of the file correctly. The text file is in the same folder as the source code. Instead it tells me every time that what I typed in has the wrong file extension (see my catch{}) and then proceeds to throw a null pointer. I am at a loss for what could be causing it. Any suggestions? import java.io.*; import java.util.*; public class Reading_Lvl_Calc { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int words = 0; String fileName; Scanner scan; Scanner keyread = new Scanner(System.in); System.out.println("Please enter a file name (or QUIT to exit)"); fileName = keyread.nextLine(); File doc = new File(fileName); //while(scan.equals(null)){ try { scan = new Scanner(doc); } catch(Exception e) { if(fileName.substring(fileName.indexOf(".")) != ".txt") System.out.println("I'm sorry, the file \"" + fileName + "\" has an invalid file extension."); else System.out.println("I am sorry, the file \"" + fileName + " \" cannot be found.\n The file must be in the same directory as this program"); scan = null; } // } while(scan.hasNext()){ words++; scan.next(); } System.out.println(words); } }

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• If statement String trouble

  - by Jeremy Stone

  I'm trying to create a program which takes user input of two words and determines whether or not these words are the same. import java.util.Scanner; public class L7E3 { public static void main(String[] args) { Scanner keyboard = new Scanner(System. in ); String word1, word2; System.out.println("Please enter a word: "); word1 = keyboard.nextLine(); System.out.println("Please enter a word: "); word2 = keyboard.nextLine(); if (word1 == word2) { System.out.println("The words are " + word1 + " and " + word2 + ". These words are the same."); } else { System.out.println("The words are " + word1 + " and " + word2 + ". These words are not the same."); } } } I figured that word1==word2 would have worked to determine whether the two strings were equal, I'm using JGrasp and it goes directly to my else option regardless of input. Am I doing something wrong with strings?

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• Could I return a FileStream as a generic interface to a file?

  - by Eric

  I'm writing a class interface that needs to return references to binary files. Typically I would provide a reference to a file as a file path. However, I'm considering storing some of the files (such as a small thumbnail) in a database directly rather then on a file system. In this case I don't want to add the extra step of reading the thumbnail out of the database onto the disc and then returning a path to the file for my program to read. I'd want to stream the image directly out of the database into my program and avoid writing anything to the disc unless the user explicit wants to save something. Would having my interface return a FileStreamor even a Imagemake sense? Then it would be up to the implementing class to determine if the source of the FileStream or Image is a file on a disc or binary data in a database. public interface MyInterface { string Thumbnail {get;} string Attachment {get;} } vs public interface MyInterface { Image Thumbnail {get;} FileStream Attachment {get;} }

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• ASP.net MVC3 howto edit sql database

  - by user1662380

  MovieStoreEntities MovieDb = new MovieStoreEntities(); public ActionResult Edit(int id) { //var EditMovie1 = MovieDb AddMovieModel EditMovie = (from M in MovieDb.Movies from C in MovieDb.Categories where M.CategoryId == C.Id where M.Id == id select new AddMovieModel { Name = M.Name, Director = M.Director, Country = M.Country, categorie = C.CategoryName, Category = M.CategoryId }).FirstOrDefault(); //AddMovieModel EditMovie1 = MovieDb.Movies.Where(m => m.Id == id).Select(m => new AddMovieModel {m.Id }).First(); List<CategoryModel> categories = MovieDb.Categories .Select(category => new CategoryModel { Category = category.CategoryName, id = category.Id }) .ToList(); ViewBag.Category = new SelectList(categories, "Id", "Category"); return View(EditMovie); } // // POST: /Default1/Edit/5 [HttpPost] public ActionResult Edit(AddMovieModel Model2) { List<CategoryModel> categories = MovieDb.Categories .Select(category => new CategoryModel { Category = category.CategoryName, id = category.Id }) .ToList(); ViewBag.Category = new SelectList(categories, "Id", "Category"); if (ModelState.IsValid) { //MovieStoreEntities model = new MovieStoreEntities(); MovieDb.SaveChanges(); return View("Thanks2", Model2); } else return View(); } This is the Code that I have wrote to edit Movie details and update database in the sql server. This dont have any compile errors, But It didnt update sql server database.

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• Android: How to declare global variables?

  - by niko

  Hi, I am creating an application which requires login. I created the main and the login activity. In the main activity onCreate method I added the following condition: public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ... loadSettings(); if(strSessionString == null) { login(); } ... } The onActivityResult method which is executed when the login form terminates looks like this: @Override public void onActivityResult(int requestCode, int resultCode, Intent data) { super.onActivityResult(requestCode, resultCode, data); switch(requestCode) { case(SHOW_SUBACTICITY_LOGIN): { if(resultCode == Activity.RESULT_OK) { strSessionString = data.getStringExtra(Login.SESSIONSTRING); connectionAvailable = true; strUsername = data.getStringExtra(Login.USERNAME); } } } The problem is the login form sometimes appears twice (the login() method is called twice) and also when the phone keyboard slides the login form appears again and I guess the problem is the variable strSessionString. Does anyone know how to set the variable global in order to avoid login form appearing after the user already successfully authenticates? Thanks!

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• Getting a type for a template instantiation?

  - by ebo

  I have the following situation: I have a object of type MyClass, which has a method to cast itself to it's base class. The class includes a typedef for it's base class and a method to do the downcast. template <class T, class B> class BaseClass; template <class T> class NoAccess; template <class T> class MyClass : public BaseClass<T, NoAccess<T> > { private: typedef BaseClass<T, NoAccess<T> > base; public: base &to_base(); }; I need to pass the result of a base call to a functor Operator: template <class Y> class Operator { Operator(Y &x); }; Operator<???> op(myobject.to_base()); Is there a easy way to fill the ??? provided that I do not want to use NoAccess?

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• Fast serialization/deserialization of structs

  - by user256890

  I have huge amont of geographic data represented in simple object structure consisting only structs. All of my fields are of value type. public struct Child { readonly float X; readonly float Y; readonly int myField; } public struct Parent { readonly int id; readonly int field1; readonly int field2; readonly Child[] children; } The data is chunked up nicely to small portions of Parent[]-s. Each array contains a few thousands Parent instances. I have way too much data to keep all in memory, so I need to swap these chunks to disk back and forth. (One file would result approx. 2-300KB). What would be the most efficient way of serializing/deserializing the Parent[] to a byte[] for dumpint to disk and reading back? Concerning speed, I am particularly interested in fast deserialization, write speed is not that critical. Would simple BinarySerializer good enough? Or should I hack around with StructLayout (see accepted answer)? I am not sure if that would work with array field of Parent.children. UPDATE: Response to comments - Yes, the objects are immutable (code updated) and indeed the children field is not value type. 300KB sounds not much but I have zillions of files like that, so speed does matter.

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• Custom bean instantiation logic in Spring MVC

  - by Michal Bachman

  I have a Spring MVC application trying to use a rich domain model, with the following mapping in the Controller class: @RequestMapping(value = "/entity", method = RequestMethod.POST) public String create(@Valid Entity entity, BindingResult result, ModelMap modelMap) { if (entity== null) throw new IllegalArgumentException("An entity is required"); if (result.hasErrors()) { modelMap.addAttribute("entity", entity); return "entity/create"; } entity.persist(); return "redirect:/entity/" + entity.getId(); } Before this method gets executed, Spring uses BeanUtils to instantiate a new Entity and populate its fields. It uses this: ... ReflectionUtils.makeAccessible(ctor); return ctor.newInstance(args); Here's the problem: My entities are Spring managed beans. The reason for this is to inject DAOs on them. Instead of calling new, I use EntityFactory.createEntity(). When they're retrieved from the database, I have an interceptor that overrides the public Object instantiate(String entityName, EntityMode entityMode, Serializable id) method and hooks the factories into that. So the last piece of the puzzle missing here is how to force Spring to use the factory rather than its own BeanUtils reflective approach? Any suggestions for a clean solution? Thanks very much in advance.

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• c# creating a database query METHOD

  - by Sinaesthetic

  I'm not sure if im delluded but what I would like to do is create a method that will return the results of a query, so that i can reuse the connection code. As i understand it, a query returns an object but how do i pass that object back? I want to send the query into the method as a string argument, and have it return the results so that I can use them. Here's what i have which was a stab in the dark, it obviously doesn't work. This example is me trying to populate a listbox with the results of a query; the sheet name is Employees and the field/column is name. The error i get is "Complex DataBinding accepts as a data source either an IList or an IListSource.". any ideas? public Form1() { InitializeComponent(); openFileDialog1.ShowDialog(); openedFile = openFileDialog1.FileName; lbxEmployeeNames.DataSource = Query("Select [name] FROM [Employees$]"); } public object Query(string sql) { System.Data.OleDb.OleDbConnection MyConnection; System.Data.OleDb.OleDbCommand myCommand = new System.Data.OleDb.OleDbCommand(); string connectionPath; //build connection string connectionPath = "provider=Microsoft.Jet.OLEDB.4.0;Data Source='" + openedFile + "';Extended Properties=Excel 8.0;"; MyConnection = new System.Data.OleDb.OleDbConnection(connectionPath); MyConnection.Open(); myCommand.Connection = MyConnection; myCommand.CommandText = sql; return myCommand.ExecuteNonQuery(); }

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• How to avoid concurrent execution of a time-consuming task without blocking?

  - by Diego V

  I want to efficiently avoid concurrent execution of a time-consuming task in a heavily multi-threaded environment without making threads wait for a lock when another thread is already running the task. Instead, in that scenario, I want them to gracefully fail (i.e. skip its attempt to execute the task) as fast as possible. To illustrate the idea considerer this unsafe (has race condition!) code: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing running = true; try { runExpensiveTask(); } finally { running = false; } } I though about using a variation of Double-Checked Locking (consider that running is a primitive 32-bit field, hence atomic, it could work fine even for Java below 5 without the need of volatile). It could look like this: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing synchronized (ThisClass.class) { if (running) return; running = true; try { runExpensiveTask(); } finally { running = false; } } } Maybe I should also use a local copy of the field as well (not sure now, please tell me). But then I realized that anyway I will end with an inner synchronization block, that still could hold a thread with the right timing at monitor entrance until the original executor leaves the critical section (I know the odds usually are minimal but in this case we are thinking in several threads competing for this long-running resource). So, could you think in a better approach?

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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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• Is there an alias for 'this' in TypeScript?

  - by Todd

  I've attempted to write a class in TypeScript that has a method defined which acts as an event handler callback to a jQuery event. class Editor { textarea: JQuery; constructor(public id: string) { this.textarea = $(id); this.textarea.focusin(onFocusIn); } onFocusIn(e: JQueryEventObject) { var height = this.textarea.css('height'); // <-- This is not good. } } Within the onFocusIn event handler, TypeScript sees 'this' as being the 'this' of the class. However, jQuery overrides the this reference and sets it to the DOM object associated with the event. One alternative is to define a lambda within the constructor as the event handler, in which case TypeScript creates a sort of closure with a hidden _this alias. class Editor { textarea: JQuery; constructor(public id: string) { this.textarea = $(id); this.textarea.focusin((e) => { var height = this.textarea.css('height'); // <-- This is good. }); } } My question is, is there another way to access the this reference within the method-based event handler using TypeScript, to overcome this jQuery behavior?

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