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  • Gracefully avoiding NullPointerException in Java

    - by Yuval A
    Consider this line: if (object.getAttribute("someAttr").equals("true")) { // .... Obviously this line is a potential bug, the attribute might be null and we will get a NullPointerException. So we need to refactor it to one of two choices: First option: if ("true".equals(object.getAttribute("someAttr"))) { // .... Second option: String attr = object.getAttribute("someAttr"); if (attr != null) { if (attr.equals("true")) { // .... The first option is awkward to read but more concise, while the second one is clear in intent, but verbose. Which option do you prefer in terms of readability?

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  • How to call superconstructor in a neat way

    - by sandis
    So here is my code: public MyClass (int y) { super(y,x,x); //some code } My problem is that in this case i want to generate a 'x' and sent to the super constructor. However the call to the superconstructor must be the first line in this constructor. Of course I could do something like this: int x; { x = generateX(); } But this feels ugly, and then the code will run no matter what constructor I use, which feels not so nice. Right now I am consider encapsulating my whole object in another object that only calculates x and then starts this object. Is this the best approach?

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  • Activator.CreateInstance with type name as string and including parameters

    - by Kelly
    I am working in .Net 3.5, looking at all the various constructors for Activator.CreateInstance. I want to create an instance of a class, calling a particular constructor. I do not have the class type, only its name. I have the following, which works, but actually winds up calling the parameterless constructor first, then the one I want. This is not a terribly big deal, but the parameterless constructor calls a rather busy base constructor, and the constructor I want to call does, too. In other words, given a type, calling CreateInstance with parameters is easy (only the last two lines below), but given only a type name, is there a better way than this? ObjectHandle oh = Activator.CreateInstance( "MyDllName", "MyNS." + "MyClassName" ); object o = oh.Unwrap( ); object newObj = Activator.CreateInstance( o.GetType( ), new object[] { param1 } ); return ( IMyDesiredObject )newObject; Thanks!

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  • Interesting AS3 hash situation. Is it really using strict equality as the documentation says?

    - by Triynko
    AS3 Code: import flash.utils.Dictionary; var num1:Number = Number.NaN; var num2:Number = Math.sqrt(-1); var dic:Dictionary = new Dictionary( true ); trace(num1); //NaN trace(num2); //NaN dic[num1] = "A"; trace( num1 == num2 ); //false trace( num1 === num2 ); //false trace( dic[num1] ); //A trace( dic[num2] ); //A Concerning the key comparison method... "The Dictionary class lets you create a dynamic collection of properties, which uses strict equality (===) for key comparison. When an object is used as a key, the object's identity is used to look up the object, and not the value returned from calling toString() on it." If Dictionary uses strict equality, as the documentation states, then how is it that num1 === num2 is false, and yet dic[num1] resolves to the same hash slot as dic[num2]?

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  • Adding Colours (Colors) Together like Paint (Blue + Yellow = Green, etc)

    - by glenstorey
    I'm making an iOS game using cocos2d libraries. Lets say you have two objects that have two separate colours - defined in RGB as Blue: 0,0,255 Yellow: 255,255,0 I want to add blue and yellow to make green. To over complicate things, let's say that the Blue object is bigger than the Yellow object (for the sake of argument let's say that the ratio is 2:1), I'm adding twice as much blue as yellow - how to I calculate this new (light green) colour correctly. I understand LAB * Color Space is useful for this sort of 'natural colour' kind of thing, but I'm not sure how to use it - especially in the context of a cocos2d object which (AFAIK) is limited to using RGB in its colour schemes. I'd really appreciate practical help on how to implement this. Thanks heaps!

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  • nginx and awstats and 404's

    - by user66700
    I'm running awstats server stats log from another machine, nginx.conf: http://pastebin.com/buKAdfdd cgi-bin.conf: http://pastebin.com/qbbJ1rwK But I'm getting 404 when I visit http://domain2.com/awstats/awstats.domain.com.html (and the 23 files are there..) in /var/www/awstats/ I was following this, but not sure how to resolve the 404's http://www.goitworld.com/analysis-access-logs-of-nginx-by-awstats/

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  • Export with VB to Excel and update file

    - by Filipe Costa
    Hello. This is the code that i have to export data to Excel. Dim oExcel As Object Dim oBook As Object Dim oSheet As Object oExcel = CreateObject("Excel.Application") oBook = oExcel.Workbooks.Add oSheet = oBook.Worksheets(1) oSheet.Range("A1").Value = "ID" oSheet.Range("B1").Value = " Nome" oSheet.Range("A1:B1").Font.Bold = True oSheet.Range("A2").Value = CStr(Request("ID")) oSheet.Range("B2").Value = "John" oBook.SaveAs("C:\Book1.xlsx") oExcel.Quit() I can create and save the excel file, but i can't update the contents. How can i do it? Thanks.

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  • Why does jQuery do this in its constructor function implementation?

    - by mattcodes
    If we look at the latest jQuery source at http://code.jquery.com/jquery-latest.js we see the following: var jQuery = function( selector, context ) { // The jQuery object is actually just the init constructor 'enhanced' return new jQuery.fn.init( selector, context ); } My understanding of the new keyword in Javascript is essentially JavaScript passes the function an empty object {} and the function sets stuff on it via this.blah. Also from my understanding new differs from .call/.apply etc.. in that the return object also has the prototype set to that of the function. So the return value should have a prototype that the same as jQuery.prototype.init.prototype (or jQuery.fn.init.prototype). However from what I see its prototype is set to jQuery.prototype thus all the commands available to work on the set. Why is this? What am I missing in my understanding?

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  • Looking for Programming Language that allows you to change true and false.

    - by Maushu
    For my curiosity sake I'm looking for a dynamic object oriented language that allows you to change true to false and vice versa. Something like this: true = false, false = true; This should also affect any conditional statements, therefore 42 == 42 should return False. Basically, with this premise, nothing in the language would be safe from the programmer. Is there any language like this?

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  • Temporarily disabled NSArrayController filterPredicate, or consult ManagedObjectContext?

    - by ndg
    I have an NSArrayController which is bound to a class in my Managed Object Context. During runtime the NSArrayController can have a number of different filter predicates applied. At certain intervals, I want to iterate through my NSArrayController's contents regardless of the filter predicate applied to it. To do this, I set the filterPredicate to nil and then reinstate it after having iterated through my array. This seems to work, but I'm wondering if it's best practice? Should I instead be polling my Managed Object Context manually? NSPredicate *predicate = nil; predicate = [myArrayController filterPredicate]; [myArrayController setFilterPredicate:nil]; for(MyManagedObject *object in [myArrayController arrangedObjects]) { // ... } [myArrayController setFilterPredicate:predicate];

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  • Raise an event when Property Changed using Reflection

    - by Dante
    I am working in C# and I have an object which I can only access using Reflection (for some personal reasons). So, when I need to set some value to one of its properties I do as below: System.Reflection.PropertyInfo property = this.Parent.GetType().GetProperty("SomeProperty"); object someValue = new object(); // Just for example property.SetValue(this.Parent, someValue, null); And, to get its value I use the method GetValue. My question is: Is there a way to fire an event when the property changes using Reflection? Thank you in advance.

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  • When a template is rendered in template tag code, MEDIA_URL is not in context

    - by culebrón
    I want to use a template for 2 template tags. In the template, I used {{ MEDIA_URL }} and discovered that MEDIA_URL is not in context as expected. Had to use get_config and pass it manually. Why is the setting not in context, how else can I put it there, or maybe there's a better way that a template tag? (include, etc?) from django.template import Library from apps.annoying.functions import get_config from django.template.loader import render_to_string register = Library() @register.simple_tag def next_in_gallery(photo, gallery): next = photo.get_next_in_gallery(gallery) return make_arrow('right', next) @register.simple_tag def previous_in_gallery(photo, gallery): prev = photo.get_previous_in_gallery(gallery) return make_arrow('left', prev) def make_arrow(direction, object): return render_to_string('myapp/arrow.html', {'direction': direction, 'object': object, 'MEDIA_URL': get_config('MEDIA_URL', '')})

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  • K/APL style programming in C++?

    - by anon
    I'm writing code in C++, but I really like K/APL's array-oriented style. Does anyone know of a good set of operator overloading tricks / macros / ... to allow some K/APL -style programming in C++? Thanks!

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  • CSS Multi-Column Forms in HTML/ASP.NET

    - by Caveatrob
    I've researched for hours and still haven't found a robust, non-absolute-positioning solution for displaying multiple-column forms and values without using TABLE tags. Can someone point me to a resource specifically oriented towards reproducing table-based, multiple-column forms (like name and address forms) in CSS to standards? Most of the forms I see only have a single column with field/value.

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  • C++ program runs slow in VS2008

    - by Nima
    I have a program written in C++, that opens a binary file(test.bin), reads it object by object, and puts each object into a new file (it opens the new file, writes into it(append), and closes it). I use fopen/fclose, fread and fwrite. test.bin contains 20,000 objects. This program runs under linux with g++ in 1 sec but in VS2008 in debug/release mode in 1min! There are reasons why I don't do them in batches or don't keep them in memory or any other kind of optimizations. I just wonder why it is that much slow under windows. Thanks,

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  • How to create real-life robots?

    - by Click Upvote
    Even before I learnt programming I've been fascinated with how robots could work. Now I know how the underlying programming instructions would be written, but what I don't understand is how those intructions are followed by the robot. For example, if I wrote this code: object=Robot.ScanSurroundings(300,400); if (Objects.isEatable(object)) { Robot.moveLeftArm(300,400); Robot.pickObject(object); } How would this program be followed by the CPU in a way that would make the robot do the physical action of looking to the left, moving his arm, and such? Is it done primarily in binary language/ASM? Lastly, where would i go if I wanted to learn how to create a robot?

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  • System.Threading.Timer example to run and display seconds until you click a button

    - by Roy
    Hi, I am having some issues creating an asp.net page using C# When you first click a button it starts the display of seconds via a label control. When you click the button again the seconds stop. Currently my code behind looks like this: System.Threading.Timer Timer; bool endProcess = false; int i = 0; protected void Page_Load(object sender, EventArgs e) { Timer = new System.Threading.Timer(TimerCallback, null, 10, 10); } private void TimerCallback(object state) { Label1.Text = i.ToString(); i++; if (endProcess == true) { Timer.Dispose(); return; } } public void Button1_Click(object sender, System.EventArgs e) { endProcess = true; }

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  • How to filter entities by their parents in ManyToOne side in Google App Engine

    - by palto
    I use Google App Engine. When I try to do a JPA query like this: "SELECT p FROM Participant p WHERE p.party.id = :partyKey AND p.name=:participantName" I get the following error Caused by: org.datanucleus.store.appengine.FatalNucleusUserException: SELECT FROM Participant p WHERE p.party.id = :partyKey AND p.name=:participantName: Can only reference properties of a sub-object if the sub-object is embedded. I gave the key of the Party object as a parameter to the "partyKey" named parameter. The model is like this: Party has multiple Participants. I want to query a participant based on the party and the name of the participant. I just can't figure out how to filter using the party. What options do I have?

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  • Hibernate: getting a record but it's being updated in the database?

    - by jack
    For some reason Hibernate seems to be keeping my session open and updating the object without me explicitely invoking a save/update/saveorupdate. I guess the session is staying open and it's beeing marked as dirty. However this is not the desired behaviour, so what's the cleanest way to fix this? The issue seems to occur because I store a phone number without formatting in the database but the getter of the object returns a formatted telephone number. My flow: go to a jsp = controller = service = dao DAO getter function if(userId != 0) { return (User)dbFactory.get(User.class, userId); } return null; The service just passes it to the controller and the controller puts te User object in the request scope. I display it on my JSP page using EL.

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  • How to exclude results with get_object_or_404?

    - by googletorp
    In Django you can use the exclude to create SQL similar to not equal. An example could be. Model.objects.exclude(status='deleted') Now this works great and exclude is very flexible. Since I'm a bit lazy, I would like to get that functionality when using get_object_or_404, but I haven't found a way to do this, since you cannot use exclude on get_object_or_404. What I want is to do something like this: model = get_object_or_404(pk=id, status__exclude='deleted') But unfortunately this doesn't work as there isn't an exclude query filter or similar. The best I've come up with so far is doing something like this: object = get_object_or_404(pk=id) if object.status == 'deleted': return HttpResponseNotfound('text') Doing something like that, really defeats the point of using get_object_or_404, since it no longer is a handy one-liner. Alternatively I could do: object = get_object_or_404(pk=id, status__in=['list', 'of', 'items']) But that wouldn't be very maintainable, as I would need to keep the list up to date. I'm wondering if I'm missing some trick or feature in django to use get_object_or_404 to get the desired result?

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  • NullReferenceException makes me want to shoot myself

    - by rockinthesixstring
    Ok, so once upon a time, my code worked. Since then I did some refactoring (basic stuff so I thought) but now I'm getting a null reference exception, and I can't bloody well figure out why. Here's where it starts. note, this is the logout method, but all of my ActivityLogs sections are throwing this error Function LogOut(ByVal go As String) As ActionResult ActivityLogService.AddActivity(AuthenticationHelper.RetrieveAuthUser.ID, _ IActivityLogService.LogType.UserLogout, _ HttpContext.Request.UserHostAddress) ActivityLogService.SubmitChanges() ''# more stuff happens after this End Function The service is pretty straight forward (notice the ERROR THROWN HERE) Public Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String) Implements IActivityLogService.AddActivity Dim _activity As ActivityLog = New ActivityLog With {.Activity = activity, .UserID = userid, .UserIP = ip.IPAddressToNumber, .ActivityDate = DateTime.UtcNow} ActivityLogRepository.Create(_activity) ''#ERROR THROWN HERE End Sub And the Interface that the Service uses looks like this Public Interface IActivityLogService Sub AddActivity(ByVal userid As Integer, ByVal activity As Integer, ByVal ip As String) Function GetUsersLastActivity(ByVal UserID As Integer) As ActivityLog Sub SubmitChanges() ''' <summary> ''' The type of activity done by the user ''' </summary> ''' <remarks>Each int refers to an activity. ''' There can be no duplicates or modifications ''' after this application goes live</remarks> Enum LogType As Integer ''' <summary> ''' A new session started ''' </summary> SessionStarted = 1 ''' <summary> ''' A new user is Added/Created ''' </summary> UserAdded = 2 ''' <summary> ''' User has updated their profile ''' </summary> UserUpdated = 3 ''' <summary> ''' User has logged into they system ''' </summary> UserLogin = 4 ''' <summary> ''' User has logged out of the system ''' </summary> UserLogout = 5 ''' <summary> ''' A new event has been added ''' </summary> EventAdded = 6 ''' <summary> ''' An event has been updated ''' </summary> EventUpdated = 7 ''' <summary> ''' An event has been deleted ''' </summary> EventDeleted = 8 ''' <summary> ''' An event has received a Up/Down vote ''' </summary> EventVoted = 9 ''' <summary> ''' An event has been closed ''' </summary> EventCloseVoted = 10 ''' <summary> ''' A comment has been added to an event ''' </summary> CommentAdded = 11 ''' <summary> ''' A comment has been updated ''' </summary> CommentUpdated = 12 ''' <summary> ''' A comment has been deleted ''' </summary> CommentDeleted = 13 ''' <summary> ''' An event or comment has been reported as spam ''' </summary> SpamReported = 14 End Enum End Interface And the repository is equally straight forward Public Sub Create(ByVal activity As ActivityLog) Implements IActivityLogRepository.Create dc.ActivityLogs.InsertOnSubmit(activity) End Sub The stack trace is as follows [NullReferenceException: Object reference not set to an instance of an object.] MyApp.Core.Domain.ActivityLogService.AddActivity(Int32 userid, Int32 activity, String ip) in E:\Projects\MyApp\MyApp.Core\Domain\Services\ActivityLogService.vb:49 MyApp.Core.Controllers.UsersController.Authenticate(String go) in E:\Projects\MyApp\MyApp.Core\Controllers\UsersController.vb:258 lambda_method(Closure , ControllerBase , Object[] ) +163 System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +51 System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary2 parameters) +409 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) +52 System.Web.Mvc.<c_DisplayClass15.b_12() +127 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func1 continuation) +436 System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +61 System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList1 filters, ActionDescriptor actionDescriptor, IDictionary2 parameters) +305 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +830 System.Web.Mvc.Controller.ExecuteCore() +136 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +232 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +39 System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +68 System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +44 System.Web.Mvc.Async.<>c__DisplayClass81.b__7(IAsyncResult ) +42 System.Web.Mvc.Async.WrappedAsyncResult`1.End() +141 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +54 System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 System.Web.Mvc.<c_DisplayClasse.b_d() +61 System.Web.Mvc.SecurityUtil.b_0(Action f) +31 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +56 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +110 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +690 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +194 here's an image of the error when attached to the debugger. And here's an image of the DB schema in question Can anyone shed some light on what I might be missing here?

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  • Transparent QGLWidget on top of QGraphicsView

    - by maciej.gryka
    I'm using QGraphicsView to show a 2D image and also have a separate QGLWidget window to display some 3D object. I'm dynamically changing the image displayed in `QGraphicsView' based on the rotation of the 3D object. I would like to render a semi-transparent 3D object on top of the 2D image, something like Maya 2009 used to do (notice the cube in the upper right corner of the viewport): Is it possible to do this with my current widgets? If not, how could it be done? One option I can think of would be to render everything in QGLWidget and display the 2D image as a texture on a background plane, but that seems slightly painful.

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