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• Displaying a collection of objects in a .Net grid on a smartphone without data binding.

  - by Xav

  I know there's No DataGridView in the CF, but I've got a collection of in-memory objects that I want to display in a grid on a phone. Options I have thought of: Stick all the objects into a SQL-CE database and use a bound datagrid. This'll mean pulling my classes apart and separating the data from the functionality, which may or may not be a bad thing, but seems a little overkill. Write my own dataset and binding code so that I can bind my collection of objects to a bound datagrid. No idea how practical or possible this is, but seems like it's either do-able or impossible and I'm hoping someone here knows which! Find a third-party unbound grid control. The only one I've seen mentioned is OpenNetCF, which I'm downloading as I type. Are there others? Are any of them any good? Do something very nasty with dynamically loading labels and textboxes into a scrolling region on the form. REALLY don't want to go there. I'm not much experienced with data-bound controls other than occasionally making use of the very vanilla functionality in WinForms or ASP.Net, and that quite a long time ago, so if any of the above are silly, please be gentle. Thanks Xav

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• Ant path/pathelement not expanding properties correctly

  - by Jonas Byström

  My property gwt.sdk expands just fine everywhere else, but not inside a path/pathelement: <target name="setup.gwtenv"> <property environment="env"/> <condition property="gwt.sdk" value="${env.GWT_SDK}"> <isset property="env.GWT_SDK" /> </condition> <property name="gwt.sdk" value="/usr/local/gwt" /> <!-- Default value. --> </target> <path id="project.class.path"> <pathelement location="${gwt.sdk}/gwt-user.jar"/> </path> <target name="libs" depends="setup.gwtenv" description="Copy libs to WEB-INF/lib"> </target> <target name="javac" depends="libs" description="Compile java source"> <javac srcdir="src" includes="**" encoding="utf-8" destdir="war/WEB-INF/classes" source="1.5" target="1.5" nowarn="true" debug="true" debuglevel="lines,vars,source"> <classpath refid="project.class.path"/> </javac> </target> For instance, placing an echo of ${gwt.sdk} just above works, but not inside "project.class.path". Is it a bug, or do I have to do something that I'm not? Edit: I tried moving the property out from target setup.gwtenv into "global space", that helped circumvent the problem.

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• Compare Properties automatically

  - by juergen d

  I want to get the names of all properties that changed for matching objects. I have these (simplified) classes: public enum PersonType { Student, Professor, Employee } class Person { public string Name { get; set; } public PersonType Type { get; set; } } class Student : Person { public string MatriculationNumber { get; set; } } class Subject { public string Name { get; set; } public int WeeklyHours { get; set; } } class Professor : Person { public List<Subject> Subjects { get; set; } } Now I want to get the objects where the Property values differ: List<Person> oldPersonList = ... List<Person> newPersonList = ... List<Difference> = GetDifferences(oldPersonList, newPersonList); public List<Difference> GetDifferences(List<Person> oldP, List<Person> newP) { //how to check the properties without casting and checking //for each type and individual property?? //can this be done with Reflection even in Lists?? } In the end I would like to have a list of Differences like this: class Difference { public List<string> ChangedProperties { get; set; } public Person NewPerson { get; set; } public Person OldPerson { get; set; } } The ChangedProperties should contain the name of the changed properties.

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• Why are we getting a WCF "Framing error" on some machines but not others

  - by Ian Ringrose

  We have just found we are getting “framing errors” (as reported by the WCF logs) when running our system on some customer test machine. It all works ok on our development machines. We have an abstract base class, with KnownType attributes for all its sub classes. One of it’s subclass is missing it’s DataContract attribute. However it all worked on our test machine! On the customers test machine, we got “framing error” showing up the WCF logs, this is not the error message I have seen in the past when missing a DataContract attribute, or a KnownType attribute. I wish to get to the bottom of this, as we can no longer have confidence in our ability to test the system before giving it to the customer until we can make our machines behave the some as the customer’s machines. Code that try to show what I am talking about, (not the real code) [DataContract()] [KnownType(typeof(SubClass1))] [KnownType(typeof(SubClass2))] // other subclasses with data members public abstract class Base { [DataMember] public int LotsMoreItemsThenThisInRealLife; } /// <summary> /// This works on some machines (not not others) when passed to Contract::DoIt, /// note the missing [DataContract()] /// </summary> public class SubClass1 : Base { // has no data members } /// <summary> /// This works in all cases when passed to Contract::DoIt /// </summary> [DataContract()] public class SubClass2 : Base { // has no data members } public interface IContract { void DoIt(Base[] items); } public static class MyProgram { public static IContract ConntectToServerOverWCF() { // lots of code ... return null; } public static void Startup() { IContract server = ConntectToServerOverWCF(); // this works all of the time server.DoIt(new Base[]{new SubClass2(){LotsMoreItemsThenThisInRealLife=2}}); // this works "in develperment" e.g. on our machines, but not on the customer's test machines! server.DoIt(new Base[] { new SubClass1() { LotsMoreItemsThenThisInRealLife = 2 } }); } }

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• Floats being pushed down in IE8 but not IE7 or Firefox

  - by BReno

  The page in question is here: http://supportdogs.digitalportals.net/PhotoGallery/16-Events You can see in IE8 that the content is being pushed down under the sidebar. If you view it in IE8 compatibility mode, it doesn't happen, nor does it happen in Firefox. If you browse to a different page in IE8 the issue does not persist. The basic layout is <div class="contentContainer"> <div class="left"></div> <div class="right"></div> </div> The css for those three classes is here #contentContainer { background: transparent url('../images/bodyBG.png') repeat-y center top; clear: both; padding: 0px 30px 0px 30px; margin-top: 83px; width: 935px; } #contentContainer .left { float: left; margin-top: 60px; padding-left: 5px; width: 195px; } #contentContainer .right { float: right; margin: -55px 0px 20px 0px; min-height: 620px; width: 700px; } Anyone have any idea what could be causing this?

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• Building an 'Activation Key' Generator in JAVA

  - by jax

  I want to develop a Key generator for my phone applications. Currently I am using an external service to do the job but I am a little concerned that the service might go offline one day hence I will be in a bit of a pickle. How authentication works now. Public key stored on the phone. When the user requests a key the 'phone ID' is sent to the "Key Generation Service" and the encrypted key key is returned and stored inside a license file. On the phone I can check if the key is for the current phone by using a method getPhoneId() which I can check with the the current phone and grant or not grant access to features. I like this and it works well, however, I want to create my own "Key Generation Service" from my own website. Requirements: Public and Private Key Encryption:(Bouncy Castle) Written in JAVA Must support getApplicationId() (so that many applications can use the same key generator) and getPhoneId() (to get the phone id out of the encrypted license file) I want to be able to send the ApplicationId and PhoneId to the service for license key generation. Can someone give me some pointers on how to accomplish this? I have dabbled around with some java encryption but am definitely no expert and can't find anything that will help me. A list of the Java classes I would need to instantiate would be helpful.

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• Refactoring an ASP.NET 2.0 app to be more "modern"

  - by Wayne M

  This is a hypothetical scenario. Let's say you've just been hired at a company with a small development team. The company uses an internal CRM/ERP type system written in .NET 2.0 to manage all of it's day to day things (let's simplify and say customer accounts and records). The app was written a couple of years ago when .NET 2.0 was just out and uses the following architectural designs: Webforms Data layer is a thin wrapper around SqlCommand that calls stored procedures Rudimentary DTO-style business objects that are populated via the sprocs A "business logic" layer that acts as a gateway between the webform and database (i.e. code behind calls that layer) Let's say that as there are more changes and requirements added to the application, you start to feel that the old architecture is showing its age, and changes are increasingly more difficult to make. How would you go about introducing refactoring steps to A) Modernize the app (i.e. proper separation of concerns) and B) Make sure that the app can readily adapt to change in the organization? IMO the changes would involve: Introduce an ORM like Linq to Sql and get rid of the sprocs for CRUD Assuming that you can't just throw out Webforms, introduce the M-V-P pattern to the forms Make sure the gateway classes conform to SRP and the other SOLID principles. Change the logic that is re-used to be web service methods instead of having to reuse code What are your thoughts? Again this is a totally hypothetical scenario that many of us have faced in the past, or may end up facing.

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• WPF - Extend ListView with checkable AND selectable ListViewItems

  - by Marks

  Hi there. I already read many examples on extending ListViews with checkboxes bound with IsSelected. But I want something more. I want a seperation between the checked and selected state, so i get a ListBox that has a single selected item, but can have multiple checked items. Unfortunately ListViewItem does not have a property for checked and I dont see a possibility to get the ListView to work with a custom CheckableListViewItem. Of course i could use a List of objects with a checked property as ItemSource, but I dont think thats a good way to go. Checked or not is a matter of the list or item-container, not of the object listed in it. Beside that I dont want all my classes like user, role, group to have counterparts like checkableUser, checkableRole and checkableGroup. The behaviour i want can be easyly accomblished for the UI with a <DataTemplate x:Key="CheckBoxCell"> <StackPanel Orientation="Horizontal"> <CheckBox /> </StackPanel> </DataTemplate> and a <GridViewColumn CellTemplate="{StaticResource CheckBoxCell}" Width="30"/> But without a binding on the checkbox i cant check if it is checked or not. Is there any way to accomplish something like that? The perfect solution for me would be to have listView1.SelectedItem, listView1.CheckedItems and maybe a listView1.UncheckedItems and of course listView1.CheckItem and listView1.UncheckItem. Thanks for any help.

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• Linq to xml, retreaving generic interface-based list

  - by Rita

  I have an xml document that looks like this <Elements> <Element> <DisplayName /> <Type /> </Element> </Elements> I have an interface, interface IElement { string DisplayName {get;} } and a couple of derived classes: public class AElement: IElement public class BElement: IElement What I want to do, is to write the most efficient query to iterate through the xml and create a list of IElement, containing AElement or BElement, based on the 'Type' property in the xml. So far I have this: IEnumerable<AElement> elements = from xmlElement in XElement.Load(path).Elements("Element") where xmlElement.Element("type").Value == "AElement" select new AElement(xmlElement.Element("DisplayName").Value); return elements.Cast<IElement>().ToList(); But this is only for AElement, is there a way to add BElement in the same query, and also make it generic IEnumerable? Or would I have to run this query once for each derived type?

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• Preserving timestamps on Clojure .clj files when building shaded jar via Maven Shade Plugin

  - by Dereference

  When using the maven-shade-plugin to package our jar artifact that contained a few Clojure libs and some Java. We were using AOT compilation for our Clojure code. When we loaded the jar, it was having very slow load times. AOT compilation is supposed to help this quite a bit, but that wasn't what we were seeing. We noticed in java jar -verbose output that there was a lot of JVM__DEFINE_CLASS calls happening when Clojure classes were being loaded. This didn't make sense, since more of our Clojure code was AOT compiled to .class files. Turns out the maven-shade-plugin creates all new files, with new timestamps in the final artifact Clojure uses the timestamp information on a .clj file vs. a .class file, to determine if the file needs to be recompiled. The maven-shade-plugin was causing the .clj file and it's associated .class file to have the same timestamp, so Clojure always chose to dynamically recompile the source. The only workaround that we have been able to figure out, at this point, is to write a script that would re-open the shaded jar and bump the .clj file timestamps back to some time in the past, so that they wouldn't be equal to the timestamps of their associated .class files. Does anyone know of a better approach?

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• Will a Ph. D. in Computer Science help?

  - by Francisco Garcia

  I am close to my 30s and still learning about programming and software engineering. Like most people who like their profession I truly believe that I should aim to improve and keep updated. One of the things I do is reading technical papers from professional publications (IEEE and ACM) but I admit there are very good bloggers out there too. Lately I started to think (should I say realize?) that Ph. D people actually are expected to expand constantly their knowledge, but little is expected from lower classes once they know enough This made me think that maybe having a Ph. D will help to have more... respect? but I also believe that I am already getting old for that. Futhermore I see many master and doctor programs that does not seem to add any value over hard experience and self learning. I belive that a degree in computer science, althought not necessary, can lay out a good base for programming work. However: What can a Ph. D. degree give you that you cannot learn on your own? (if you are not into something VERY specific and want to work in a non academic environment)

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• JPA entitylisteners and @embeddable

  - by seanizer

  I have a class hierarchy of JPA entities that all inherit from a BaseEntity class: @MappedSuperclass @EntityListeners( { ValidatorListener.class }) public abstract class BaseEntity implements Serializable { // other stuff } I want all entities that implement a given interface to be validated automatically on persist and/or update. Here's what I've got. My ValidatorListener: public class ValidatorListener { private enum Type { PERSIST, UPDATE } @PrePersist public void checkPersist(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.PERSIST); } } @PreUpdate public void checkUpdate(final Object entity) { if (entity instanceof Validateable) { this.check((Validateable) entity, Type.UPDATE); } } private void check(final Validateable entity, final Type persist) { switch (persist) { case PERSIST: if (entity instanceof Persist) { ((Persist) entity).persist(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; case UPDATE: if (entity instanceof Update) { ((Update) entity).update(); } if (entity instanceof PersistOrUpdate) { ((PersistOrUpdate) entity).persistOrUpdate(); } break; default: break; } } } and here's my Validateable interface that it checks against (the outer interface is just a marker, the inner contain the methods): public interface Validateable { interface Persist extends Validateable { void persist(); } interface PersistOrUpdate extends Validateable { void persistOrUpdate(); } interface Update extends Validateable { void update(); } } All of this works, however I would like to extend this behavior to Embeddable classes. I know two solutions: call the validation method of the embeddable object manually from the entity validation method: public void persistOrUpdate(){ // validate my own properties first // then manually validate the embeddable property: myEmbeddable.persistOrUpdate(); // this works but I'd like something that I don't have to call manually } use reflection, checking all properties to see if their type is of one of their interface types. This would work, but it's not pretty. Is there a more elegant solution?

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• using spring, hibernate and scala, is there a better way to load test data than dbunit?

  - by egervari

  Here are some things I really dislike about dbunit: 1) You cannot specify the exact ordering the inserts because dbunit likes to group your inserts by table name, and not by the order you define them in the XML file. This is a problem when you have records depending on other records in other tables, so you have to disable foreign key constraints during your tests... which actually sucks because these foreign key constraints will get fired in production while your tests won't be aware of them! 2) They seem hellbent on forcing you to use an xml namespace to define your xml... and I honestly can't be bothered to do this. I like the data.xml without any namespace. It works. But they are so hellbent on deprecating it. 3) Creating different xml files is hard on a per test basis, so it actually encourages creating data for your entire app. Unfortunately, this process is a little bloated too once the data grows in size and things get inter tangled. There has got to be a better way to split up your test data into chunks without having to copy/paste a lot of the test data across all of your tests. 4) Keeping track of id references in a big xml file is just impossible. If you have 130 domain classes, it just gets bewildering. This model simply does not scale. Is there something less bloated and better in the Spring/Hibernate space? db unit has worn out its welcome and I'm really looking for something better.

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• UML diagrams that are actually pretty?

  - by Borek

  I'm looking for a diagramming software that would produce good looking output. It doesn't need to support everything (or even much) from UML, is doesn't need to have code engineering functions or anything, it just needs to produce visually interesting output. Here is a couple of samples of products that I consider ugly / not good enough: Visio with default UML stencils (didn't find better looking ones), Enterprise Architect, Dia, ArgoUML and many other "professional" UML tools. A couple of visually compelling tools that I considered (but found issues with): Visual Studio class diagrams - just for .NET classes but the output is miles better than what UML tools typically produce NClass - similar to VS's class diagrams but I could not find the "pretty", blue skin anywhere yuml.me - very nice but lacking some advanced layout options. I have to say that I find their style almost ideal for high-level diagrams - they look sketchy which is good. Balsamiq - I think Joel used this for hginit.com and I liked it. However, it's not suited for creating software diagrams so I can imagine it would be quite a lot of work MS Word has actually quite a good graphics engine but I'd rather leave this as a choice of the last resort I'd be grateful for any good tips.

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• Convert SVG to PDF

  - by Adrian Smith

  How would one go about converting a SVG file to a PDF programatically? (I need to alter the SVG in certain respects before generating the PDF so simply pre-converting it using a tool won't be sufficient.) Ideally using Java but Perl or PHP would be fine too. Obviously I am basically considering Apache FOP and Batik with Java. However no matter how long I search I cannot find a simple introduction on how to do it. Things like SVGConverter have descriptions like "Defines the interface for classes that are able to convert part or all of a GraphicContext", but I don't really know what that means. I have this feeling there must be an API to do this quite simply, provided by FOP or Batik, but I'm just not able to find it at the moment (or perhaps it really doesn't exist.) In terms of the supported SVG features I need, the file has some paths which are filled with some linear gradients. Ideally if I could pass the SVG in as a DOM Document that would be ideal; then I would load my template SVG file, change it as specified by the user, and then generate the PDF.

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• Java - problems iterating through an ArrayList

  - by cc0

  Ok so I have an ArrayList (arrBok), which is full of book objects (the code is in Norwegian, so pay no attention to that please). I want to make a public method which iterates through all the objects in the arraylist. When I execute the code, it just seems to run in an infinite loop, not producing any return values. Here is the relevant (I hope, because there are a couple of other classes involved) part of the code; public String listAll() { itr = arrBok.iterator(); while (itr.hasNext()) { i++; } return "lol"; } This code does nothing useful, but I just want to see if it can iterate through it successfully. What I have tried so far; Tested if the bokArr (arraylist) is empty, which it's not. It has 4 objects inside of it. Return the toString() method of the itr, with the following result; java.util.AbstractList$Itr@173a10f // <-- not sure if this would be relevant to anything return itr.next().toString(); <-- // which seems to return the first object in the array, does that make sense?

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• How can I use a compound condition in a join in Linq?

  - by Gary McGill

  Let's say I have a Customer table which has a PrimaryContactId field and a SecondaryContactId field. Both of these are foreign keys that reference the Contact table. For any given customer, either one or two contacts may be stored. In other words, PrimaryContactId can never be NULL, but SecondaryContactId can be NULL. If I drop my Customer and Contact tables onto the "Linq to SQL Classes" design surface, the class builder will spot the two FK relationships from the Customer table to the Contact table, and so the generated Customer class will have a Contact field and a Contact1 field (which I can rename to PrimaryContact and SecondaryContact to avoid confusion). Now suppose that I want to get details of all the contacts for a given set of customers. If there was always exactly one contact then I could write something like: from customer in customers join contact in contacts on customer.PrimaryContactId equals contact.id select ... ...which would be translated into something like: SELECT ... FROM Customer INNER JOIN Contact ON Customer.FirstSalesPersonId = Contact.id But, because I want to join on both the contact fields, I want the SQL to look something like: SELECT ... FROM Customer INNER JOIN Contact ON Customer.FirstSalesPersonId = Contact.id OR Customer.SecondSalesPersonId = Contact.id How can I write a Linq expression to do that?

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• Jersey, JAXB and getting an objectextending an abstract class as a parameter

  - by krajol

  I want to get an object as a parameter of a POST request. I got an abstract superclass that is called Promotion and subclasses Product and Percent. Here's how I try to get a request: @POST @Consumes(MediaType.APPLICATION_XML) @Produces(MediaType.APPLICATION_XML) @Path("promotion/") public Promotion createPromotion(Promotion promotion) { Product p = (Product) promotion; System.out.println(p.getPriceAfter()); return promotion; } and here's how I use JAXB in classes' definitions: @XmlRootElement(name="promotion") @XmlSeeAlso({Product.class,Percent.class}) public abstract class Promotion { //body } @XmlRootElement(name="promotion") public class Product extends Promotion { //body } @XmlRootElement(name="promotion") public class Percent extends Promotion { //body } So the problem now is when I send a POST request with a body like this: <promotion> <priceBefore>34.5</priceBefore> <marked>false</marked> <distance>44</distance> </promotion> and I try to cast it to Product (as in this case, fields 'marked' and 'distance' are from Promotion class and 'priceBefore' is from Product class) I get an Exception: java.lang.ClassCastException: Percent cannot be cast to Product. It seems like Percent is chosen as a 'default' subclass. Why is that and how can I get an object that is a Product?

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• Storing values in the DataValueField and DataTextField of a dropdownlist using a linq query

  - by user1318369

  I have a website for dance academy where Users can register and add/drop dance classes. In the web page to drop a particular dance, for a particular user, the dropdown displays her registered dances. Now I want to delete one of the dances from the list. So I'll remove the row from the table and also from the dropdownlist. The problem is that everytime the item with the lowest ID (index) is getting deleted, no matter which one the user selects. I think I am storing the DataTextField and DataValueField for the dropdown incorrectly. The code is: private void PopulateDanceDropDown() { // Retrieve the username MembershipUser currentUser = Membership.GetUser(); var username = currentUser.UserName; // Retrive the userid of the curren user var dancerIdFromDB = from d in context.DANCER where d.UserName == username select d.UserId; Guid dancerId = new Guid(); var first = dancerIdFromDB.FirstOrDefault(); if (first != null) { dancerId = first; } dances.DataSource = (from dd in context.DANCER_AND_DANCE where dd.UserId == dancerId select new { Text = dd.DanceName, Value = dd.DanceId }).ToList(); dances.DataTextField = "Text"; dances.DataValueField = "Value"; dances.DataBind(); } protected void dropthedance(object o, EventArgs e) { String strDataValueField = dances.SelectedItem.Value; int danceIDFromDropDown = Convert.ToInt32(strDataValueField); var dancer_dance = from dd in context.DANCER_AND_DANCE where dd.DanceId == danceIDFromDropDown select dd; foreach (var dndd in dancer_dance) { context.DANCER_AND_DANCE.DeleteOnSubmit(dndd); } try { context.SubmitChanges(); } catch (Exception ex) { Console.WriteLine(ex); } } The problem is in the line: String strDataValueField = dances.SelectedItem.Value; The strDataValueField is always getting the minimum id from the list of dance item ids in the dropdown (which happens by default). I want this to hold the id of the dance selected by the user.

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• Not all symbols of an DLL-exported class is exported (VS9)

  - by mandrake

  I'm building a DLL from a group of static libraries and I'm having a problem where only parts of classes are exported. What I'm doing is declaring all symbols I want to export with a preprocessor definition like: #if defined(MYPROJ_BUILD_DLL) //Build as a DLL # define MY_API __declspec(dllexport) #elif defined(MYPROJ_USE_DLL) //Use as a DLL # define MY_API __declspec(dllimport) #else //Build or use as a static lib # define MY_API #endif For example: class MY_API Foo{ ... } I then build static library with MYPROJ_BUILD_DLL & MYPROJ_USE_DLL undefined causing a static library to be built. In another build I create a DLL from these static libraries. So I define MYPROJ_BUILD_DLL causing all symbols I want to export to be attributed with __declspec(dllexport) (this is done by including all static library headers in the DLL-project source file). Ok, so now to the problem. When I use this new DLL I get unresolved externals because not all symbols of a class is exported. For example in a class like this: class MY_API Foo{ public: Foo(char const* ); int bar(); private: Foo( char const*, char const* ); }; Only Foo::Foo( char const*, char const*); and int Foo::bar(); is exported. How can that be? I can understand if the entire class was missing, due to e.g. I forgot to include the header in the DLL-build. But it's only partial missing. Also, say if Foo::Foo( char const*) was not implemented; then the DLL build would have unresolved external errors. But the build is fine (I also double checked for declarations without implementation). Note: The combined size of the static libraries I'm combining is in the region of 30MB, and the resulting DLL is 1.2MB. I'm using Visual Studio 9.0 (2008) to build everything. And Depends to check for exported symbols.

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• How should I return different types in a method based on the value of a string in Java?

  - by Siracuse

  I'm new to Java and I have come to having the following problem: I have created several classes which all implement the interface "Parser". I have a JavaParser, PythonParser, CParser and finally a TextParser. I'm trying to write a method so it will take either a File or a String (representing a filename) and return the appropriate parser given the extension of the file. Here is some psuedo-code of what I'm basically attempting to do: public Parser getParser(String filename) { String extension = filename.substring(filename.lastIndexOf(".")); switch(extension) { case "py": return new PythonParser(); case "java": return new JavaParser(); case "c": return new CParser(); default: return new TextParser(); } } In general, is this the right way to handle this situation? Also, how should I handle the fact that Java doesn't allow switching on strings? Should I use the .hashcode() value of the strings? I feel like there is some design pattern or something for handling this but it eludes me. Is this how you would do it?

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• Concurrency problem with arrays (Java)

  - by Johannes

  For an algorithm I'm working on I tried to develop a blacklisting mechanism that can blacklist arrays in a specific way: If "1, 2, 3" is blacklisted "1, 2, 3, 4, 5" is also considered blacklisted. I'm quite happy with the solution I've come up with so far. But there seem to be some serious problems when I access a blacklist from multiple threads. The method "contains" (see code below) sometimes returns true, even if an array is not blacklisted. This problem does not occur if I only use one thread, so it most likely is a concurrency problem. I've tried adding some synchronization, but it didn't change anything. I also tried some slightly different implementations using java.util.concurrent classes. Any ideas on how to fix this? public class Blacklist { private static final int ARRAY_GROWTH = 10; private final Node root = new Node(); private static class Node{ private volatile Node[] childNodes = new Node[ARRAY_GROWTH]; private volatile boolean blacklisted = false; public void blacklist(){ this.blacklisted = true; this.childNodes = null; } } public void add(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return; else if(currentNode.childNodes.length <= edge) { currentNode.childNodes = Arrays.copyOf(currentNode.childNodes, edge + ARRAY_GROWTH); } if(currentNode.childNodes[edge] == null) { currentNode.childNodes[edge] = new Node(); } currentNode = currentNode.childNodes[edge]; } currentNode.blacklist(); } } public boolean contains(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return true; else if(currentNode.childNodes.length <= edge || currentNode.childNodes[edge] == null) return false; currentNode = currentNode.childNodes[edge]; } return currentNode.blacklisted; } } }

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• C# wrapper for objects

  - by Haggai

  I'm looking for a way to create a generic wrapper for any object. The wrapper object will behave just like the class it wraps, but will be able to have more properties, variable, methods etc., for e.g. object counting, caching etc. Say the wrapper class be called Wrapper, and the class to be wrapped be called Square and has the constructor Square(double edge_len) and the properties/methods EdgeLength and Area, I would like to use it as follows: Wrapper<Square> mySquare = new Wrapper<Square>(2.5); /* or */ new Square(2.5); Console.Write("Edge {0} -> Area {1}", mySquare.EdgeLength, mySquare.Area); Obviously I can create such a wrapper class for each class I want to wrap, but I'm looking for a general solution, i.e. Wrapper<T> which can handle both primitive and compound types (although in my current situation I would be happy with just wrapping my own classes). Suggestions? Thanks.

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• How can I abstract out the core functionality of several Rails applications?

  - by hornairs

  I'd like to develop a number of non-trivial Rails applications which all implement a core set of functionality but each have certain particular customizations, extensions, and aesthetic differences. How can I pull the core functionality (models, controllers, helpers, support classes, tests) common to all these systems out in such a way that updating the core will benefit every application based upon it? I've seen Rails Engines but they seem to be too detached, almost too abstracted to be built upon. I can seem them being useful for adding one component to an existing app, for example bolting on a blog engine to your existing e-commerce site. Since engines seem to be mostly self contained, it seems difficult and inconvenient to override their functionality and views while keeping DRY. I've also considered abstracting the code into a gem, but this seems a little odd. Do I make the gem depend on the Rails gems, and the define models & controllers inside it, and then subclass them in my various applications? Or do I define many modules inside the gem that I include in the different spots inside my various applications? How do I test the gem and then test the set of customizations and overridden functionality on top of it? I'm also concerned with how I'll develop the gem and the Rails apps in tandem, can I vendor a git repository of the gem into the app and push from that so I don't have to build a new gem every iteration? Also, are there private gem hosts/can I set my own gem source up? Also, any general suggestions for this kind of undertaking? Abstraction paradigms to adhere to? Required reading? Comments from the wise who have done this before? Thanks!

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• What to call factory-like (java) methods used with immutable objects

  - by StaxMan

  When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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