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• Convert pre-IEEE-574 C++ floating-point numbers to/from C#

  - by Richard Kucia

  Before .Net, before math coprocessors, before IEEE-574, Microsoft defined a bit pattern for floating-point numbers. Old versions of the C++ compiler happily used that definition. I am writing a C# app that needs to read/write such floating-point numbers in a file. How can I do the conversions between the 2 bit formats? I need conversion methods in both directions. This app is going to run in a PocketPC/WinCE environment. Changing the structure of the file is out-of-scope for this project. Is there a C++ compiler option that instructs it to use the old FP format? That would be ideal. I could then exchange data between the C# code and C++ code by using a null-terminated text string, and the C++ methods would be simple wrappers around sprintf and atof functions. At the very least, I'm hoping someone can reply with the bit definitions for the old FP format, so I can put together a low-level bit manipulation algorithm if necessary. Thanks.

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• PHPUnit: Testing if a protected method was called

  - by Luiz Damim

  I´m trying to test if a protected method is called in a public interface. <?php abstract class SomeClassAbstract { abstract public foo(); public function doStuff() { $this->_protectedMethod(); } protected function _protectedMethod(); { // implementation is irrelevant } } <?php class MyTest extends PHPUnit_Framework_TestCase { public function testCalled() { $mock = $this->getMockForAbstractClass('SomeClass'); $mock->expects($this->once()) ->method('_protectedMethod'); $mock->doStuff(); } } I know it is called correctly, but PHPUnit says its never called. The same happens when I test the other way, when a method is never called: <?php abstract class AnotherClassAbstract { abstract public foo(); public function doAnotherStuff() { $this->_loadCache(); } protected function _loadCache(); { // implementation is irrelevant } } <?php class MyTest extends PHPUnit_Framework_TestCase { public function testCalled() { $mock = $this->getMockForAbstractClass('AnotherClass'); $mock->expects($this->once()) ->method('_loadCache'); $mock->doAnotherStuff(); } } The method is called but PHPUnit says that it is not. What I´m doing wrong? Edit I wasn´t declaring my methods with double colons, it was just for denoting that it was a public method (interface). Updated to full class/methods declarations. Edit 2 I should have said that I´m testing some method implementations in an abstract class (edited the code to reflect this). Since I can not instantiate the class, how can I test this? I´m thinking in creating an SomeClassSimple extending SomeClassAbstract and testing this one instead. Is it the right approach?

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• How to handle update events on a ASP.NET GridView?

  - by Bogdan M

  Hello, This may sound silly, but I need to find out how to handle an Update event from a GridView. First of all, I have a DataSet, where there is a typed DataTable with a typed TableAdapter, based on a "select all query", with auto-generated Insert, Update, and Delete methods. Then, in my aspx page, I have an ObjectDataSource related to my typed TableAdapter on Select, Insert, Update and Delete methods. Finnally, I have a GridView bound to this ObjectDataSource, with default Edit, Update and Cancel links. How should I implement the edit functionality? Should I have something like this? protected void GridView_RowEditing(object sender, GridViewEditEventArgs e) { using(MyTableAdapter ta = new MyTableAdapter()) { ta.Update(...); TypedDataTable dt = ta.GetRecords(); this.GridView.DataSource = dt; this.GridView.DataBind(); } } In this scenario, I have the feeling that I update some changes to the DB, then I retrive and bind all the data, and not only the modified parts. Is there any way to update only the DataSet, and this to update on his turn the DataBase and the GridView? I do not want to retrive all the data after a CRUD operations is performed, I just want to retrive the changes made. Thanks. PS: I'm using .NET 3.5 and VS 2008 with SP1.

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• using compareTo in Binary Search Tree program

  - by Scott Rogener

  I've been working on this program for a few days now and I've implemented a few of the primary methods in my BinarySearchTree class such as insert and delete. Insert seemed to be working fine, but once I try to delete I kept getting errors. So after playing around with the code I wanted to test my compareTo methods. I created two new nodes and tried to compare them and I get this error: Exception in thread "main" java.lang.ClassCastException: TreeNode cannot be cast to java.lang.Integer at java.lang.Integer.compareTo(Unknown Source) at TreeNode.compareTo(TreeNode.java:16) at BinarySearchTree.myComparision(BinarySearchTree.java:177) at main.main(main.java:14) Here is my class for creating the nodes: public class TreeNode<T> implements Comparable { protected TreeNode<T> left, right; protected Object element; public TreeNode(Object obj) { element=obj; left=null; right=null; } public int compareTo(Object node) { return ((Comparable) this.element).compareTo(node); } } Am I doing the compareTo method all wrong? I would like to create trees that can handle integers and strings (seperatly of course)

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• JUnit confusion: use 'extend Testcase' or '@Test' ?

  - by Rabarberski

  I've found the proper use (or at least the documentation) of JUnit very confusing. This question serves both as a future reference and as a real question. If I've understood correctly, there are two main approaches to create and run a JUnit test: Approach A: create a class that extends TestCase, and start test methods with the word test. When running the class as a JUnit Test (in Eclipse), all methods starting with the word test are automatically run. import junit.framework.TestCase; public class DummyTestA extends TestCase { public void testSum() { int a = 5; int b = 10; int result = a + b; assertEquals(15, result); } } Approach B: create a 'normal' class and prepend a @Test annotation to the method. Note that you do NOT have to start the method with the word test. import org.junit.*; import static org.junit.Assert.*; public class DummyTestB { @Test public void Sum() { int a = 5; int b = 10; int result = a + b; assertEquals(15, result); } } Mixing the two seems not to be a good idea, see e.g. this stackoverflow question: Now, my questions(s): What is the preferred approach, or when would you use one instead of the other? Approach B allows for testing for exceptions by extending the @Test annotation like in @Test(expected = ArithmeticException.class). But how do you test for exceptions when using approach A? When using approach A, you can group a number of test classes in a test suite. TestSuite suite = new TestSuite("All tests");<br/> suite.addTestSuite(DummyTestA.class); suite.addTestSuite(DummyTestAbis.class);` But this can't be used with approach B (since each testclass should subclass TestCase). What is the proper way to group tests for approach B?

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• C# reference collection for storing reference types

  - by ivo s

  I like to implement a collection (something like List<T>) which would hold all my objects that I have created in the entire life span of my application as if its an array of pointers in C++. The idea is that when my process starts I can use a central factory to create all objects and then periodically validate/invalidate their state. Basically I want to make sure that my process only deals with valid instances and I don't re-fetch information I already fetched from the database. So all my objects will basically be in one place - my collection. A cool thing I can do with this is avoid database calls to get data from the database if I already got it (even if I updated it after retrieval its still up-to-date if of course some other process didn't update it but that a different concern). I don't want to be calling new Customer("James Thomas"); again if I initted James Thomas already sometime in the past. Currently I will end up with multiple copies of the same object across the appdomain - some out of sync other in sync and even though I deal with this using timestamp field on the MSSQL server I'd like to keep only one copy per customer in my appdomain (if possible process would be better). I can't use regular collections like List or ArrayList for example because I cannot pass parameters by their real local reference to the their existing Add() methods where I'm creating them using ref so that's not to good I think. So how can this be implemented/can it be implemented at all ? A 'linked list' type of class with all methods working with ref & out params is what I'm thinking now but it may get ugly pretty quickly. Is there another way to implement such collection like RefList<T>.Add(ref T obj)? So bottom line is: I don't want re-create an object if I've already created it before during the entire application life unless I decide to re-create it explicitly (maybe its out-of-date or something so I have to fetch it again from the db). Is there alternatives maybe ?

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• Intellisense on custom types in Iron Python

  - by Anish Patel

  Hi everybody, I'm just starting to play around with IronPython and am having a hard time using it with custom types created in C#. I can get IronPython to load in assemblies from C# classes, but I'm struggling without the help of intellisense. If I have a class in C# as defined below, how can I make it so that IronPython will be able to see the methods/properties that are available in it? public class Person { public string Name { get; set; } public int Age{ get; set; } public double Weight{ get; set; } public double Height { get; set; } public double CalculateBMI() { return Weight/Math.Pow(Height, 2); } } In Iron python I'd instance a Person object as follows: newPerson = Person() newPerson.Name = 'John' newPerson.Age = 25 newPerson.Weight = 75 newPerson.Height = 1.70 newPerson.CalculateBMI() The thing that is annoying me is that I want to be able to say newPerson = Person() And then be able to see all the methods and properties associated with the person object whenever I type: newPerson. Anyone have any ideas if this can be done?

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• how do I get eclipse to use a different compiler version for Java?

  - by codeman73

  It seems like this should be a simple task, with the options in the Preferences menu for different JREs and the ability to set different compiler and build paths per project. However, it also seems to simply not work. For example, I have my JAVA_HOME set to a jre for Java 1.6. It's still not clear to me how Eclipse uses this, but it appears to be defaulting to this and not taking the project overrides. I have also installed Java 1.5, and added a JRE for this in eclipse in the Java-Installed JREs section. In my project, I've set the compiler compliance level to 1.5. In the build path for the project, I've added the System Library for the Java 1.5 JRE. However, I'm getting compile errors for a class that implements PreparedStatement for not implementing abstract methods that only exist in Java 1.6 PreparedStatement. Specifically, the methods setAsciiStream(int, InputStream, long) and setAsciiStream(int, InputStream) Strangely enough, it worked when we were compiling it against Java 1.4, which it was originally written for. We added the JREs for Java 1.4 and referenced that system library in the project, and set the project's compiler level to 1.4, and it works fine. But when I do the same changes to try to point to Java 1.5, it instead uses 1.6. Any ideas why?

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• Returning true or error message in Ruby

  - by seaneshbaugh

  I'm wondering if writing functions like this is considered good or bad form. def test(x) if x == 1 return true else return "Error: x is not equal to one." end end And then to use it we do something like this: result = test(1) if result != true puts result end result = test(2) if result != true puts result end Which just displays the error message for the second call to test. I'm considering doing this because in a rails project I'm working on inside my controller code I make calls to a model's instance methods and if something goes wrong I want the model to return the error message to the controller and the controller takes that error message and puts it in the flash and redirects. Kinda like this def create @item = Item.new(params[:item]) if [email protected]? result = @item.save_image(params[:attachment][:file]) if result != true flash[:notice] = result redirect_to(new_item_url) and return end #and so on... That way I'm not constructing the error messages in the controller, merely passing them along, because I really don't want the controller to be concerned with what the save_image method itself does just whether or not it worked. It makes sense to me, but I'm curious as to whether or not this is considered a good or bad way of writing methods. Keep in mind I'm asking this in the most general sense pertaining mostly to ruby, it just happens that I'm doing this in a rails project, the actual logic of the controller really isn't my concern.

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• Refactor throwing not null exception if using a method that has a dependency on a certain contructor

  - by N00b

  In the method below the second constructor accepts a ForumThread object which the IncrementViewCount() method uses. There is a dependency between the method and that particular constructor. Without extracting into a new private method the null check in IncrementViewCount() and LockForumThread() (plus other methods not shown) is there some simpler re-factoring I can do or the implementation of a better design practice for this method to guard against the use of the wrong constructor with these dependent methods? Thank you for any suggestions in advance. private readonly IThread _forumLogic; private readonly ForumThread _ft; public ThreadLogic(IThread forumLogic) : this(forumLogic, null) { } public ThreadLogic(IThread forumLogic, ForumThread ft) { _forumLogic = forumLogic; _ft = ft; } public void Create(ForumThread ft) { _forumLogic.SaveThread(ft); } public void IncrementViewCount() { if (_ft == null) throw new NoNullAllowedException("_ft ForumThread is null; this must be set in the constructor"); lock (_ft) { _ft.ViewCount = _ft.ViewCount + 1; _forumLogic.SaveThread(_ft); } } public void LockForumThread() { if (_ft == null) throw new NoNullAllowedException("_ft ForumThread is null; this must be set in the constructor"); _ft.ThreadLocked = true; _forumLogic.SaveThread(_ft); }

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• oData/ADO.NET Data Services using LINQ-to-SQL with a decryption layer

  - by Program.X

  I have written an application using LINQ-to-SQL that submits a web form into a database. I absact the LINQ-to-SQL away using a Repository pattern. This repository has the basic methods: Get(), Save(), etc. As a development of the project, I needed to encrypt certain fields in the form. This was trivial, as I just added the encryption calls to the Get(), Save() methods in the Repository. Now, I want to put an oData layer over it, to allow RESTful extraction from MS Excel 2010 (when it comes out). I have this working, after a few stumbles on useless error messages, etc. However, obviously, those encrypted fields are still encrypted. My repository pattern would have decrypted these for me. As far as I know, I have to directly bind my oData service to the LINQ-to-SQL context for the schema, etc. to work - unless I enter a whole world of pain (any URLs appreciated). Is there a way I can insert my encryption/decryption layer into the request so decryption is done "on the fly"? I looked at the OnStartProcessingRequest() overload of DataService but this doesn't seem that useful.

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• Performance Difference between HttpContext user and Thread user

  - by atrueresistance

  I am wondering what the difference between HttpContext.Current.User.Identity.Name.ToString.ToLower and Thread.CurrentPrincipal.Identity.Name.ToString.ToLower. Both methods grab the username in my asp.net 3.5 web service. I decided to figure out if there was any difference in performance using a little program. Running from full Stop to Start Debugging in every run. Dim st As DateTime = DateAndTime.Now Try 'user = HttpContext.Current.User.Identity.Name.ToString.ToLower user = Thread.CurrentPrincipal.Identity.Name.ToString.ToLower Dim dif As TimeSpan = Now.Subtract(st) Dim break As String = "nothing" Catch ex As Exception user = "Undefined" End Try I set a breakpoint on break to read the value of dif. The results were the same for both methods. dif.Milliseconds 0 Integer dif.Ticks 0 Long Using a longer duration, loop 5,000 times results in these figures. Thread Method run 1 dif.Milliseconds 125 Integer dif.Ticks 1250000 Long run 2 dif.Milliseconds 0 Integer dif.Ticks 0 Long run 3 dif.Milliseconds 0 Integer dif.Ticks 0 Long HttpContext Method run 1 dif.Milliseconds 15 Integer dif.Ticks 156250 Long run 2 dif.Milliseconds 156 Integer dif.Ticks 1562500 Long run 3 dif.Milliseconds 0 Integer dif.Ticks 0 Long So I guess what is more prefered, or more compliant with webservice standards? If there is some type of a performance advantage, I can't really tell. Which one scales to larger environments easier?

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• UITouch Events and Table Views

  - by Andy

  I'm working on a navigation-based iPhone-only app that serves two main purposes: One, to present data in a hierarchical view, allowing users to drill down and eventually edit said data, and, two, to all users to perform a default action when the table view cell is tapped. I now need to offer a small set of options tied to the same data; however, both the didSelectRowAtIndexPath: and accessoryButtonTappedForRowAtIndexPath: methods are obviously taken. So, my options seem to be to implement a double-tap method, wherein the small list of additional options would be presented after (you guessed it) a double-tap on said table row; or, preferably, a tap-and-hold method. From what I can tell, tap-and-hold seems like the way to go in SDK 4.0 - which does me no good right this red-hot minute. I decided to go with the double-tap option, but I'm having a little trouble. First and foremost, the touchesBegan:withEvent: method does not seem to be getting called at all; a breakpoint placed within the method is never called while the application runs, and the table view responds exactly as it did before I inserted the method (which is to say, it performs the default action): - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *aTouch = [touches anyObject]; if (aTouch.tapCount == 2) { [NSObject cancelPreviousPerformRequestsWithTarget:self]; } } Second, I don't really need to handle a single-tap - the didSelectRowAtIndexPath: method can handle the single-tap just fine. The double-tap is the funky one I want to handle. I suspect the answer is going to contain the phrase, "You can't have the table view handle the single-tap and the touchesBegan: method handle the double-tap. The touch handling methods have to handle all of them." I would really appreciate some guidance from some of you who've dealt with this issue. Thanks in advance.

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• Java map with values limited by key's type parameter

  - by Ashley Mercer

  Is there a way in Java to have a map where the type parameter of a value is tied to the type parameter of a key? What I want to write is something like the following: public class Foo { // This declaration won't compile - what should it be? private static Map<Class<T>, T> defaultValues; // These two methods are just fine public static <T> void setDefaultValue(Class<T> clazz, T value) { defaultValues.put(clazz, value); } public static <T> T getDefaultValue(Class<T> clazz) { return defaultValues.get(clazz); } } That is, I can store any default value against a Class object, provided the value's type matches that of the Class object. I don't see why this shouldn't be allowed since I can ensure when setting/getting values that the types are correct. EDIT: Thanks to cletus for his answer. I don't actually need the type parameters on the map itself since I can ensure consistency in the methods which get/set values, even if it means using some slightly ugly casts.

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• Different EF Property DataType than Storage Layer Possible?

  - by dj_kyron

  Hi, I am putting together a WCF Data Service for PatientEntities using Entity Framework. My solution needs to address these requirements: Property DateOfBirth of entity Patient is stored in SQL Server as string. It would be ideal if the entity class did not also use the "string" type but rather a DateTime type. (I would expect this to be possible since we're abstracting away from the storage layer). Where could a conversion mechanism be put in place that would convert to and from DateTime/string so that the entity and SQL Server are in sync?. I cannot change the storage layer's structure, so I have to work around it. WCF Data Services (Read-only, so no need for saving changes) need to be used since clients will be able to use LINQ expressions to consume the service. They can generate results based on any given query scenario they need and not be constrained by a single method such as GetPatient(int ID). I've tried to use DTOs, but run into problem of mapping the ObjectContext to a DTO, I don't think that is theoretically possible...or too complicated if it is. I've tried to use Self Tracking Entities but they require the metadata from the .edmx file if I'm correct, and this isn't allowing a different property data type. I also want to add customizations to my Entity getter methods so that a property "MRN" of type "string" needs to have .Replace("MR~", string.Empty) performed before it is returned. I can add this to the getter methods but the problem with that is Entity Framework will overwrite that next time it refreshes the entity classes. Is there a permanent place I can put these? Should I use POCO instead? How would that work with WCF Data Services? Where would the service grab the metadata?

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• OO vs Simplicity when it comes to user interaction

  - by Oetzi

  Firstly, sorry if this question is rather vague but it's something I'd really like an answer to. As a project over summer while I have some downtime from Uni I am going to build a monopoly game. This question is more about the general idea of the problem however, rather than the specific task I'm trying to carry out. I decided to build this with a bottom up approach, creating just movement around a forty space board and then moving on to interaction with spaces. I realised that I was quite unsure of the best way of proceeding with this and I am torn between two design ideas: Giving every space its own object, all sub-classes of a Space object so the interaction can be defined by the space object itself. I could do this by implementing different land() methods for each type of space. Only giving the Properties and Utilities (as each property has unique features) objects and creating methods for dealing with the buying/renting etc in the main class of the program (or Board as I'm calling it). Spaces like go and super tax could be implemented by a small set of conditionals checking to see if player is on a special space. Option 1 is obviously the OO (and I feel the correct) way of doing things but I'd like to only have to handle user interaction from the programs main class. In other words, I don't want the space objects to be interacting with the player. Why? Errr. A lot of the coding I've done thus far has had this simplicity but I'm not sure if this is a pipe dream or not for larger projects. Should I really be handling user interaction in an entirely separate class? As you can see I am quite confused about this situation. Is there some way round this? And, does anyone have any advice on practical OO design that could help in general?

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• c# delegate and abstract class

  - by BeraCim

  Hi all: I currently have 2 concrete methods in 2 abstract classes. One class contains the current method, while the other contains the legacy method. E.g. // Class #1 public abstract class ClassCurrent<T> : BaseClass<T> where T : BaseNode, new() { public List<T> GetAllRootNodes(int i) { //some code } } // Class #2 public abstract class MyClassLegacy<T> : BaseClass<T> where T : BaseNode, new() { public List<T> GetAllLeafNodes(int j) { //some code } } I want the corresponding method to run in their relative scenarios in the app. I'm planning to write a delegate to handle this. The idea is that I can just call the delegate and write logic in it to handle which method to call depending on which class/project it is called from (at least thats what I think delegates are for and how they are used). However, I have some questions on that topic (after some googling): 1) Is it possible to have a delegate that knows the 2 (or more) methods that reside in different classes? 2) Is it possible to make a delegate that spawns off abstract classes (like from the above code)? (My guess is a no, since delegates create concrete implementation of the passed-in classes) 3) I tried to write a delegate for the above code. But I'm being technically challenged: public delegate List GetAllNodesDelegate(int k); GetAllNodesDelegate del = new GetAllNodesDelegate(ClassCurrent.GetAllRootNodes); I got the following error: An object reference is required for the non-static field, method, property ClassCurrent<BaseNode>.GetAllRootNodes(int) I might have misunderstood something... but if I have to manually declare a delegate at the calling class, AND to pass in the function manually as above, then I'm starting to question whether delegate is a good way to handle my problem. Thanks.

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• How to get a Class literal from a generically specific Class

  - by h2g2java

  There are methods like these which require Class literals as argument. Collection<EmpInfo> emps = SomeSqlUtil.select( EmpInfo.class, "select * from emps"); or GWT.create(Razmataz.class); The problem presents itself when I need to supply generic specific classes like EmpInfo<String> Razmataz<Integer> The following would be wrong syntax Collection<EmpInfo<String>> emps = SomeSqlUtil.select( EmpInfo<String>.class, "select * from emps"); or GWT.create(Razmataz<Integer>.class); Because you cannot do syntax like Razmataz<Integer>.class So, how would I be able to squeeze a class literal out of EmpInfo<String> Razmataz<Integer> so that I could feed them as arguments to methods requiring Class literals? Further info Okay, I confess that I am asking this primarily for GWT. I have a pair of GWT RPC interface Razmataz. (FYI, GWT RPC interface has to be defined in server-client pairs). I plan to use the same interface pair for communicating whether it be String, Integer, Boolean, etc. GWT.create(Razmataz) for Razmataz<T> complains that, since I did not specify T, GWT compiler treated it as Object. Then GWT compiler would not accept Object class. It needs to be more specific than being an Object. So, it seems there is no way for me to tell GWT.create what T is because a Class literal is a runtime concept while generics is a compile time concept, Right?

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• C# ASP.NET Binding Controls via Generic Method

  - by OverTech

  I have a few web applications that I maintain and I find myself very often writing the same block of code over and over again to bind a GridView to a data source. I'm trying to create a Generic method to handle data binding but I'm having trouble getting it to work with Repeaters and DataLists. Here is the Generic method I have so far: public void BindControl<T>(T control, SqlCommand sql) where T : System.Web.UI.WebControls.BaseDataBoundControl { cmd = sql; cn.Open(); SqlDataReader dr = cmd.ExecuteReader(); if (dr.HasRows) { control.DataSource = dr; control.DataBind(); } dr.Close(); cn.Close(); } That way I can just define my CommandText then make a call to "BindControls(myGridView, cmd)" instead of retyping this same basic block of code every time I need to bind a grid. The problem is, this doesn't work with Repeaters or DataLists. Each of these controls inherit their respective "DataSource" and "DataBind" methods from different classes. Someone on another forum suggested that I implement an interface, but I'm not sure how to make that work either. The GridView, Datalist and Repeater get their respective "DataBind" methods from BaseDataBoundControl, BaseDataList, and Repeater classes. How would I go about creating a single interface to tie them all together? Or am I better off just using 3 overloads for this method? Dave

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• Private Java class properties mysteriously reset between method calls....

  - by Michael Jones

  I have a very odd problem. A class property is mysteriously reset between method calls. The following code is executed so the constructor is called, then the parseConfiguration method is called. Finally, processData is called. The parseConfiguration method sets the "recursive" property to "true". However, as soon as it enters "processData", "recursive" becomes "false". This problem isn't isolated to a single class -- I have several examples of this in my code. How can this possibly be happening? I've tried initialising properties when they're declared outside any methods, I've tried initialising them in constructors... nothing works. The only complication I can think of here is that this class is invoked by an object that runs in a thread -- but here is one instance per thread, so surely no chance that threads are interfering. I've tried setting both methods to "synchronized", but this still happens. Please help! /** * This class or its superclasses are NOT threaded and don't extend Thread */ public class DirectoryAcquirer extends Manipulator { /** * @var Whether to recursively scan directories */ private boolean recursive = false; /** * Constructor */ public DirectoryAcquirer() { } /** * Constructor that initialises the configuration * * @param config * @throws InvalidConfigurationException */ public DirectoryAcquirer(HierarchicalConfiguration config) throws InvalidConfigurationException { super(config); } @Override protected void parseConfiguration() throws InvalidConfigurationException { // set whether to recurse into directories or not if (this.config.containsKey("recursive")) { // this.recursive gets set to "true" here this.recursive = this.config.getBoolean("recursive"); } } @Override public EntityCollection processData(EntityCollection data) { // here this.recursive is "false" this.logger.debug("processData: Entered method"); } }

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• How do I create efficient instance variable mutators in Matlab?

  - by Trent B

  Previously, I implemented mutators as follows, however it ran spectacularly slowly on a recursive OO algorithm I'm working on, and I suspected it may have been because I was duplicating objects on every function call... is this correct? %% Example Only obj2 = tripleAllPoints(obj1) obj.pts = obj.pts * 3; obj2 = obj1 end I then tried implementing mutators without using the output object... however, it appears that in MATLAB i can't do this - the changes won't "stick" because of a scope issue? %% Example Only tripleAllPoints(obj1) obj1.pts = obj1.pts * 3; end For application purposes, an extremely simplified version of my code (which uses OO and recursion) is below. classdef myslice properties pts % array of pts nROW % number of rows nDIM % number of dimensions subs % sub-slices end % end properties methods function calcSubs(obj) obj.subs = cell(1,obj.nROW); for i=1:obj.nROW obj.subs{i} = myslice; obj.subs{i}.pts = obj.pts(1:i,2:end); end end function vol = calcVol(obj) if obj.nROW == 1 obj.volume = prod(obj.pts); else obj.volume = 0; calcSubs(obj); for i=1:obj.nROW obj.volume = obj.volume + calcVol(obj.subs{i}); end end end end % end methods end % end classdef

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• Accessing running task scheduled with java.util.Timer

  - by jbatista

  I'm working on a Java project where I have created a class that looks like this (abridged version): public class Daemon { private static Timer[] timerarray=null; private static Daemon instance=null; protected Daemon() { ArrayList<Timer> timers = new ArrayList<Timer>(); Timer t = new Timer("My application"); t.schedule(new Worker(), 10000,30000); timers.add(t); //... timerarray = timers.toArray(new Timer[]{}); } public static Daemon getInstance() { if(instance==null) instance=new Daemon(); return instance; } public SomeClass getSomeValueFromWorker() { return theValue; } ///////////////////////////////////////////// private class Worker extends TimerTask { public Worker() {} public void run() { // do some work } public SomeReturnClass someMethod(SomeType someParameter) { // return something; } } ///////////////////////////////////////////// } I start this class, e.g. by invoking daemon.getInstance();. However, I'd like to have some way to access the running task objects' methods (for example, for monitoring the objects' state). The Java class java.util.Timer does not seem to provide the means to access the running object, it just schedules the object instance extending TimerTask. Are there ways to access the "running" object instanciated within a Timer? Do I have to subclass the Timer class with the appropriate methods to somehow access the instance (this "feels" strange, somehow)? I suppose someone might have done this before ... where can I find examples of this "procedure"? Thank you in advance for your feedback.

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• Choosing a method for a webservice

  - by Wrikken

  I'm asked to set up a new webservice which should be easily usable in whatever language (php, .NET, Java, etc.) possible. Of course rolling my own can be done, accepting different content-types (xml / x-www-form-urlencoded (normal post) / json / etc.), but an existing method or mechanism would of course be prefered, cutting down time spent on development for the consumers of the service. The webservice does accept modifications / sets (it is not only simply data retrieval), but those will most likely be quite a lot less then gets (we estimate about 2.5% sets, 97.5 gets). The term webservice here indicates the protocol should go over HTTP, not being able to implement it totally client sided (javascript in the end-users browser etc.), as it needs specific user authentication. Both gets and sets are pretty light on the parameter count (usually 1 to 4). Methods like REST (which I'd prefer for only gets), XML-RPC & SOAP (might be a bit overkill, but has the advantage of explicitly defined methods and returns) are the usual suspects. What in your opinion / experience is the most widely 'spoken' and most easily implementable protocol in different languages (seen from the consumers' viewpoint) which could fullfill this need?

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• Why does adding Crossover to my Genetic Algorithm give me worse results?

  - by MahlerFive

  I have implemented a Genetic Algorithm to solve the Traveling Salesman Problem (TSP). When I use only mutation, I find better solutions than when I add in crossover. I know that normal crossover methods do not work for TSP, so I implemented both the Ordered Crossover and the PMX Crossover methods, and both suffer from bad results. Here are the other parameters I'm using: Mutation: Single Swap Mutation or Inverted Subsequence Mutation (as described by Tiendil here) with mutation rates tested between 1% and 25%. Selection: Roulette Wheel Selection Fitness function: 1 / distance of tour Population size: Tested 100, 200, 500, I also run the GA 5 times so that I have a variety of starting populations. Stop Condition: 2500 generations With the same dataset of 26 points, I usually get results of about 500-600 distance using purely mutation with high mutation rates. When adding crossover my results are usually in the 800 distance range. The other confusing thing is that I have also implemented a very simple Hill-Climbing algorithm to solve the problem and when I run that 1000 times (faster than running the GA 5 times) I get results around 410-450 distance, and I would expect to get better results using a GA. Any ideas as to why my GA performing worse when I add crossover? And why is it performing much worse than a simple Hill-Climb algorithm which should get stuck on local maxima as it has no way of exploring once it finds a local max?

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• general learning methodology

  - by momo

  just wanted to hear on the different general learning paths people embark on when learning a new language/framework. the one i currently use, which is how i learned bash and am currently learning python, is: instant hacking tutorial (very short tutorial introducing the basic syntax, variable declaration, loops, data types, etc. and how they are generally used) in depth tutorial with good programming style and slightly topic-specific (e.g. Mark Pilgrim's Dive into Python), important topics for me personally are regex methods, file IO, and ways the different data types are utilized best (i wrote a very primitive bayesian spam filter using python's dictionaries to keep track of word occurrences) spaced-repition of syntax or short recipes (i use anki, with questions like 'create dictionary with filename and filesize metadata, human-readable' or simpler ones like 'match 0 - 3 occurences of the letter M in a string', or 'return/create an iterator from two sequences') the use of spaced-repitition has been invaluable, and i credit it with the ease that i can recall/create python algorithms. however, i've recently started looking into django, and i've found that spaced-repitition, at least in my case, doesn't work very well for learning a framework, it works best with short code recipes (either that or i should start looking into more basic django framework tutorials). the problem i'm encountering is that since framework programming is not only algorithms, but actually learning the API, which can be quite complex since you have to learn all the methods, modules, the places where they are stored, and the sequence of which things have to be done. for ex. in django to start a project that deals with polls (from the django tutorial), one has to create the project, edit the settings.py file, create the polls app, edit the models.py file (which requires knowing the classes that are present in the module models), edit the urls.py file, etc. i found that my spaced-repition method didn't work very well for this type of learning, so i wanted to ask you guys what method(s) you use for learning the different frameworks/APIs.

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