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  • How would you code a washing machine?

    - by Dan
    Imagine I have a class that represents a simple washing machine. It can perform following operations in the following order: turn on - wash - centrifuge - turn off. I see two basic alternatives: A) I can have a class WashingMachine with methods turnOn(), wash(int minutes), centrifuge(int revs), turnOff(). The problem with this is that the interface says nothing about the correct order of operations. I can at best throw InvalidOprationException if the client tries to centrifuge before machine was turned on. B) I can let the class itself take care of correct transitions and have the single method nextOperation(). The problem with this on the other hand, is that the semantics is poor. Client will not know what will happen when he calls the nextOperation(). Imagine you implement the centrifuge button’s click event so it calls nextOperation(). User presses the centrifuge button after machine was turned on and ups! machine starts to wash. I will probably need a few properties on my class to parameterize operations, or maybe a separate Program class with washLength and centrifugeRevs fields, but that is not really the problem. Which alternative is better? Or maybe there are some other, better alternatives that I missed to describe?

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  • How to configure log4j with a properties file

    - by Dan
    How do I get log4j to pick up a properties file. I'm writing a Java desktop app which I want to use log4j. In my main method if have this: PropertyConfigurator.configure("log4j.properties"); The log4j.properties file sits in the same directory when I open the Jar. Yet I get this error: log4j:ERROR Could not read configuration file [log4j.properties]. java.io.FileNotFoundException: log4j.properties (The system cannot find the file specified) What am I doing wrong?

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  • Writing to a java socket channel which should be closed does not generate an exception

    - by Dan Serfaty
    Hi all, We have a java server that keeps a socket channel open with an Android client in order to provide push capabilities to our client application. However, after putting the Android in airplane mode, which I expected would sever the connection, the server can still write to the SocketChannel object associated with that Android client and no error is thrown. Calling SocketChannel.isConnected() before writing to it returns true. What are we missing? Is the handling of sockets different with mobile devices? Thanks in advance for your help.

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  • Hierarchy / Flyweight / Instancing Problem in Python

    - by Dan
    Here is the problem I am trying to solve, (I have simplified the actual problem, but this should give you all the relevant information). I have a hierarchy like so: 1.A 1.B 1.C 2.A 3.D 4.B 5.F (This is hard to illustrate - each number is the parent, each letter is the child). Creating an instance of the 'letter' objects is expensive (IO, database costs, etc), so should only be done once. The hierarchy needs to be easy to navigate. Children in the hierarchy need to have just one parent. Modifying the contents of the letter objects should be possible directly from the objects in the hierarchy. There needs to be a central store containing all of the 'letter' objects (and only those in the hierarchy). 'letter' and 'number' objects need to be possible to create from a constructor (such as Letter(**kwargs) ). It is perfectably acceptable to expect that when a letter changes from the hierarchy, all other letters will respect the same change. Hope this isn't too abstract to illustrate the problem. What would be the best way of solving this? (Then I'll post my solution) Here's an example script: one = Number('one') a = Letter('a') one.addChild(a) two = Number('two') a = Letter('a') two.addChild(a) for child in one: child.method1() for child in two: print '%s' % child.method2()

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  • In MS SQL Server, is there a way to "atomically" increment a column being used as a counter?

    - by Dan P
    Assuming a Read Committed Snapshot transaction isolation setting, is the following statement "atomic" in the sense that you won't ever "lose" a concurrent increment? update mytable set counter = counter + 1 I would assume that in the general case, where this update statement is part of a larger transaction, that it wouldn't be. For example, I think this scenario is possible: update the counter within transaction #1 do some other stuff in transaction #1 update the counter with transaction #2 commit transaction #2 commit transaction #1 In this situation, wouldn't the counter end up only being incremented by 1? Does it make a difference if that is the only statement in a transaction? How does a site like stackoverflow handle this for its question view counter? Or is the possibility of "losing" some increments just considered acceptable?

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  • How to apply coding methodologies and practices to non-coding work?

    - by Dan
    I can talk for hours about best-practice, source control, change management, feature tracking, development cycles and the lot, but most of what I've learnt or read seems to apply to nuts-and-bolts programming of compiled applications. You know, ASCII files that gets turned into 1s and 0s. How does one apply the same discipline and wisdom to working in environments that are point-and-click, config-centric. I'm thinking of CMSs and specifically, my current 9 to 5, SharePoint. Traditional practices of source control, dev-staging-production seem to break down since we're not working with code, and the live environment changes with user input. So to sum up a rather lengthy question, what works in a no-code environment?

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  • Checking for empty arrays: count vs empty

    - by Dan McG
    This question on 'How to tell if a PHP array is empty' had me thinking of this question Is there a reason that count should be used instead of empty when determining if an array is empty or not? My personal thought would be if the 2 are equivalent for the case of empty arrays you should use empty because it gives a boolean answer to a boolean question. From the question linked above, it seems that count($var) == 0 is the popular method. To me, while technically correct, makes no sense. E.g. Q: $var, are you empty? A: 7. Hmmm... Is there a reason I should use count == 0 instead or just a matter of personal taste? As pointed out by others in comments for a now deleted answer, count will have performance impacts for large arrays because it will have to count all elements, whereas empty can stop as soon as it knows it isn't empty. So, if they give the same results in this case, but count is potentially inefficient, why would we ever use count($var) == 0?

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  • How do I pass a DBNull value to a parameterized SELECT statement?

    - by Dan
    I have a SQL statement in C# (.NET Framework 4 running against SQL Server 2k8) that looks like this: SELECT [Column1] FROM [Table1] WHERE [Column2] = @Column2 The above query works fine with the following ADO.NET code: DbParameter parm = Factory.CreateDbParameter(); parm.Value = "SomeValue"; parm.ParameterName = "@Column2"; //etc... This query returns zero rows, though, if I assign DBNull.Value to the DbParameter's Value member even if there are null values in Column2. If I change the query to accommodate the null test specifically: SELECT [Column1] FROM [Table1] WHERE [Column2] IS @Column2 I get an "Incorrect syntax near '@Column2'" exception at runtime. Is there no way that I can use null or DBNull as a parameter in the WHERE clause of a SELECT statement?

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  • Focus behavior in Applet-Javascript interaction

    - by Dan
    I have a web page with an applet that opens a popup window and also makes Javascript calls. When that Javascript call results in a focus() call on an HTML input, that causes the browser window to push itself in front of the applet window. But only on certain browsers, namely MSIE. On Firefox the applet window remains on top. How can I keep that behavior consistent in MSIE? Note that using the old Microsoft VM for Java also achieves the desired (applet window in front) result. HTML code: <html> <head> <script type="text/javascript"> function focusMe() { document.getElementById('mytext').focus(); } </script> </head> <body> <applet id="myapplet" mayscript code="Popup.class" ></applet> <form> <input type="text" id="mytext"> <input type="button" onclick="document.getElementById('myapplet').showPopup()" value="click"> </form> </body> </html> Java code: public class Popup extends Applet { Frame frame; public void start() { frame = new Frame("Test Frame"); frame.setLayout(new BorderLayout()); Button button = new Button("Push Me"); frame.add("Center", button); button.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e) { frame.setVisible(false); } }); frame.pack(); } public void showPopup() { frame.setVisible(true); JSObject.getWindow(this).eval("focusMe()"); } }

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  • .NET JAXB equivalent?

    - by Dan
    Is there an equivalent library for JAXB in .NET? I am trying to convert an XML I get to a .NET class. I have the XSD, but not sure how to convert the XML received into a concrete Class? I used the XSD tool to generate a class from the schema, but what I want to to convert the XML I receive on the fly to a object that I can work with in code. I've seen the thread here that deals with this, but my query is - I want the object created to contain the data that I receive in the XML (i.e. the field values must be populated).

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  • Can a database function be called in the predicate of a llblgen query?

    - by Dan Appleyard
    I want to use a table-valued database function in the where clause of a query I am building using LLBLGen Pro 2.6 (self-servicing). SELECT * FROM [dbo].[Users] WHERE [dbo].[Users].[UserID] IN ( SELECT UserID FROM [dbo].[GetScopedUsers] (@ScopedUserID) ) I am looking into the FieldCompareSetPredicate class, but can't for the life of me figure out what the exact signature would be. Any help would be greatly appreciated.

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  • Python - List of Lists Slicing Behavior

    - by Dan Dobint
    When I define a list and try to change a single item like this: list_of_lists = [['a', 'a', 'a'], ['a', 'a', 'a'], ['a', 'a', 'a']] list_of_lists[1][1] = 'b' for row in list_of_lists: print row It works as intended. But when I try to use list comprehension to create the list: row = ['a' for range in xrange(3)] list_of_lists = [row for range in xrange(3)] list_of_lists[1][1] = 'b' for row in list_of_lists: print row It results in an entire column of items in the list being changed. Why is this? How can I achieve the desired effect with list comprehension?

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  • Non Document Centric SharePoint Workflow

    - by Dan Revell
    SharePoint workflows are document centric in that the base thing the workflow runs on has to be a thing; be it a document or just a list item. The workflow itself is task based, so stuff a user has to do. Now I can put any sort of code in these tasks that I want to and even put complex InfoPath forms in for the user to perform the task. This has been fine on all my previous workflows. But what if I want the tasks to be actual official forms themselves. The item that the workflow runs on is just some abstract concept like an event. An example could be an accident has happened. There isn't an accident form, but a whole set of forms that need to be completed by different people. Task forms aren't really a nice way to go, because it locks all the forms into the task list. You can only access the forms by not deleting the tasks when complete and going to the workflow summery and following the task links to the InfoPath forms or going straight to the tasks list and doing a filter on particular "accidents". These are official documents so ideally there would be a library for each type of document and the workflow would orchestrate the completion of the right forms. It would mean each task would have to create a new blank form and then link the user to that form. The user would go complete the form but then have to go back to the task form and click yes I've completed it until the workflow could progress. Well this is short of the workflow monitoring the forms library form for some completion trigger. But then it all gets messy with the user experience from clicking the link in the task email, to open the Infopath task form, to clicking the link in the subsequent Infopath library form and then return through these forms on completion. It just gets messy trying to retrofit this non document centric sort of workflow into SharePoint. I would really appreciate any input on what might be the best way to do this. Store the forms as task forms Store the forms as library forms and create/link from the task forms Store the forms as different infopath views, and use a forms library. The workflow would trigger variables that progress the view the infopath form shows. Using the same form template for both task forms and a forms library and when a task form is complete, copy the xml into the forms library to have a official record outside of the workflow. Thanks

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  • Is this a correct Interlocked synchronization design?

    - by Dan Bryant
    I have a system that takes Samples. I have multiple client threads in the application that are interested in these Samples, but the actual process of taking a Sample can only occur in one context. It's fast enough that it's okay for it to block the calling process until Sampling is done, but slow enough that I don't want multiple threads piling up requests. I came up with this design (stripped down to minimal details): public class Sample { private static Sample _lastSample; private static int _isSampling; public static Sample TakeSample(AutomationManager automation) { //Only start sampling if not already sampling in some other context if (Interlocked.CompareExchange(ref _isSampling, 0, 1) == 0) { try { Sample sample = new Sample(); sample.PerformSampling(automation); _lastSample = sample; } finally { //We're done sampling _isSampling = 0; } } return _lastSample; } private void PerformSampling(AutomationManager automation) { //Lots of stuff going on that shouldn't be run in more than one context at the same time } } Is this safe for use in the scenario I described?

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  • How to return all aspnet_compiler errors (not just those in first directory)

    - by Dan Atkinson
    Hi there! Is there a way to get the aspnet_compiler to go through all views and return all errors, rather than just the errors in the current view directory? For example, lets say I have a project that has a bunch of folders... Views Folder1 Folder2 Folder3 Folder4 Two of them (Folder2 and Folder3) have errors. aspnet_compiler will run, and only return the errors it comes across in Folder2. It won't return those in Folder3 at the same time. Once I fix the errors in Folder2 and run it again, it'll then pick up the ones in the Folder3. I fix those. And then have to run the tool again, and again until it's all fixed. This is getting annoying!! For reference, here's the command I use: C:\Windows\Microsoft.NET\Framework\v2.0.50727\aspnet_compiler -v / -p "C:\path\to\project" Thanks in advance!

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  • Question about design (inheritance, polymorphism)

    - by Dan
    Hi, I have a question about a problem I'm struggling with. Hope you can bear with me. Imagine I have an Object class representing the base class of a hierarchy of physical objects. Later I inherit from it to create an Object1D, Object2D and Object3D classes. Each of these derived classes will have some specific methods and attributes. For example, the 3d object might have functionality to download a 3d model to be used by a renderer. So I'd have something like this: class Object {}; class Object1D : public Object { Point mPos; }; class Object2D : public Object { ... }; class Object3D : public Object { Model mModel; }; Now I'd have a separate class called Renderer, which simply takes an Object as argument and well, renders it :-) In a similar way, I'd like to support different kinds of renderers. For instance, I could have a default one that every object could rely on, and then provide other specific renderers for some kind of objects: class Renderer {}; // Default one class Renderer3D : public Renderer {}; And here comes my problem. A renderer class needs to get an Object as an argument, for example in the constructor in order to retrieve whatever data it needs to render the object. So far so good. But a Renderer3D would need to get an Object3D argument, in order to get not only the basic attributes but also the specific attributes of a 3d object. Constructors would look like this: CRenderer(Object& object); CRenderer3D(Object3D& object); Now how do I specify this in a generic way? Or better yet, is there a better way to design this? I know I could rely on RTTI or similar but I'd like to avoid this if possible as I feel there is probably a better way to deal with this. Thanks in advance!

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  • Best way to implement keywords for image upload gallery

    - by Dan Berlyoung
    I'm starting to spec out an image gallery type system similar to Facebook's. Members of the site will be able to create image galleries and upload images for others to view. Images will have keywords the the uploader can specify. Here's the question, what's the best way to model this? With image and keyword tables linked vi a HABTM relation? Or a single image table with the keywords saved as comma delimited values in a text field in the image record? Then search them using a LIKE or FULL TEXT index function? I want to be able to pull up all images containing a given keyword as well as generate a keyword cloud. I'm leaning toward the HABTM setup but I wanted to see what everyone else though. Thanks!!

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