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  • C#: An object reference is required for the non-static field, method, or Property

    - by Omin
    I feel bad for asking this when there are so many questions that are related but I was not able to find/understand the answer I am looking for. // 2. Develop a program to convert currency X to currency Y and visa versa. using System; class Problem2 { static void Main (string[] args) { while (true) { Console.WriteLine ("1. Currency Conversion from CAD to Won"); Console.WriteLine ("2. Currency Conversion from Won to Cad"); Console.Write ("Choose from the Following: (1 or 2)? "); int option = int.Parse( Console.ReadLine() ); //double x; if (option == 1) { Console.WriteLine ("Type in the amount you would like to Convert CAD to Won: "); //double y =double.Parse( Console.ReadLine()); //Console.WriteLine( cadToWon( y ) ); Console.WriteLine( cadToWon( double.Parse( Console.ReadLine() ) )); } if (option == 2) { Console.WriteLine ("Type in the amount you would like to Convert Won to CAD: "); Console.WriteLine( wonToCad (double.Parse( Console.ReadLine()))); } } } double cadToWon( double x ) { return x * 1113.26; } double wonToCad( double x) { return x / 1113.26; } } This give me the Error messgae "An object reference is required for the non-static field, method, or property 'Problem2..." I know that I'll be able to run the program if I add static infront of the methods but I'm wondering why I need it (I think it's because Main is static?) and what do I need to change in order to use these methods without adding static to them? Thank you

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  • creating an object within a function of a program

    - by user1066524
    could someone please tell me what I need to do in order to create an object in a function. I will try to explain by making up some sort of example... Let's say I have a program named TimeScheduler.cpp that implements the class Schedule.h (and I have the implementation in a separate file Schedule.cpp where we define the methods). In the declaration file we have declared two constructors Schedule(); //the default and Schedule(int, int, int);//accepts three arguments to get to the point--let's say in the main program file TimeScheduler.cpp we created our own functions in this program apart from the functions inherited from the class Schedule. so we have our prototypes listed at the top. /*prototypes*/ void makeSomeTime(); etc..... we have main(){ //etc etc... } we then define these program functions void makeSomeTime(){ //process } let's say that inside the function makeSomeTime(), we would like to create an array of Schedule objects like this Schedule ob[]={ summer(5,14, 49), fall(9,25,50) }; what do I have to do to the function makeSomeTime() in order for it to allow me to create this array of objects. The reason I ask is currently i'm having difficulty with my own program in that it WILL allow me to create this array of objects in main()....but NOT in a function like I just gave an example of. The strange thing is it will allow me to create a dynamic array of objects in the function..... like Schedule *ob = new Schedule[n+1]; ob[2]= Schedule(x,y,z); Why would it let me assign to a non-dynamic array in main(), but not let me do that in the function?

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  • Object Reference with TimeSpan/DateTime

    - by user1732039
    When creating an appointment i want to send an email out to the patient with details like Time, Date etc. I know the email service i have created works (i have tested it by hardcoding strings into the method with the problem. The Problem is that i am getting Object reference issues with converting the Time and Date to a string. It does create the appointment data in the database correctly (time and date). User_Doctor thisDoc = user_DoctorComboBox.SelectedItem as User_Doctor; User_Patient thisPatient = appointment_Patient_autoComplete.SelectedItem as User_Patient; Appointment App = AppointmentSlots.SelectedItem as Appointment; DateTime date = (DateTime)datePickerAppointment.SelectedDate; TimeSpan timeslot = App.Time; //For Emailing Patients string fullname = thisPatient.PatientName + " " + thisPatient.PatientSurname; string mestime = timeslot.ToString("HH:mm"); string mesdate = date.ToString("MM/dd/yyyy"); string email = thisPatient.aspnet_Users.aspnet_Membership.LoweredEmail; EmailServiceClient em = new EmailServiceClient(); em.createMessageAsync(email, "Upcomming Appointment", fullname, mestime, mesdate, thisDoc.aspnet_Users.UserName, true); The problem occures with the strings mestime and mesdate, as well as with getting the email of the user from the database (again this exists in the db, as a nvar)

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  • Object reference not set to an instance of an object- Linked List Example

    - by Zoro Roronoa
    I am seeing following errors : Object reference not set to an instance of an object! Check to determinate if the object is null before calling the method! I'am new with C#,and I made a program for Sorted Linked Lists. Here is the code where the error comes! public void Insert(double data) { Link newLink = new Link(data); Link current = first; Link previous = null; if (first == null) { first = newLink; } else { while (data > current.DData && current != null) { previous = current; current = current.Next; } previous.Next = newLink; newLink.Next = current; } } It says that the current referenc is null while (data current.DData && current != null), but I assigned it current = first; Please Help ! The rest is the complete code of the Program! class Link { double dData; Link next=null; public Link Next { get { return next; } set { next = value; } } public double DData { get { return dData; } set { dData = value; } } public Link(double dData) { this.dData = dData; } public void DisplayLink() { Console.WriteLine("Link : "+ dData); } } class SortedList { Link first; public SortedList() { first = null; } public bool IsEmpty() { return (this.first == null); } public void Insert(double data) { Link newLink = new Link(data); Link current = first; Link previous = null; if (first == null) { first = newLink; } else { while (data > current.DData && current != null) { previous = current; current = current.Next; } previous.Next = newLink; newLink.Next = current; } } public Link Remove() { Link temp = first; first = first.Next; return temp; } public void DisplayList() { Link current; current = first; Console.WriteLine("Display the List!"); while (current != null) { current.DisplayLink(); current = current.Next; } } } class SortedListApp { public void TestSortedList() { SortedList newList = new SortedList(); newList.Insert(20); newList.Insert(22); newList.Insert(100); newList.Insert(1000); newList.Insert(15); newList.Insert(11); newList.DisplayList(); newList.Remove(); newList.DisplayList(); } }

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  • load Javascript object from file

    - by megapool020
    Hi there, I asked a question in this thread Stackoverflow, and it works perfect. So tnx to all the users who gave me a reply. But now I have a other question. I would like to have the object in a seperate file, so I only need to update the file in stead of the JS file (otherwise it will be very big). I'm using JQUERY. I now looks like this (with all the info in the JS file). IBANInfo is used to fill a selectbox var IBANInfo = { "ccAL":{ countryCode:"AL", countryName:"Albani&euml;", IBANlength:"28", bankFormCode:"0 8n 0 ", accountNum:"0 16 0 " }, "ccAD":{ countryCode:"AD", countryName:"Andorra", IBANlength:"24", bankFormCode:"0 4n 4n", accountNum:"0 12 0 " }, "ccBE":{ countryCode:"BE", countryName:"Belgi&euml;", IBANlength:"16", bankFormCode:"0 3n 0 ", accountNum:"0 7n 2n" } }; //---- then this function is used to build the selectList function createSelect(){ var selectList = ''; var key; selectList += "<option value=''>Kies een land</option>\n"; for (key in IBANInfo) { if (IBANInfo.hasOwnProperty(key)) { var countryInfo = IBANInfo[key]; selectList += "<option value='"+countryInfo.countryCode+"'>"+countryInfo.countryName+"</option>\n"; } } $('#selectBox').html(selectList); } I thought I could do it like this, but I get the message undefined in my selectbox. var IBANInfo = $.get('include/countryCodes.txt'); // also tried var IBANInfo = $.getJSON('include/countryCodes.txt'); //---- then this function is used to build the selectList function createSelect(){ var selectList = ''; var key; selectList += "<option value=''>Kies een land</option>\n"; for (key in IBANInfo) { if (IBANInfo.hasOwnProperty(key)) { var countryInfo = IBANInfo[key]; selectList += "<option value='"+countryInfo.countryCode+"'>"+countryInfo.countryName+"</option>\n"; } } $('#selectBox').html(selectList); } /* the countryCodes.txt file is like this: { "ccAL":{ countryCode:"AL", countryName:"Albani&euml;", IBANlength:"28", bankFormCode:"0 8n 0 ", accountNum:"0 16 0 " }, "ccAD":{ countryCode:"AD", countryName:"Andorra", IBANlength:"24", bankFormCode:"0 4n 4n", accountNum:"0 12 0 " }, "ccBE":{ countryCode:"BE", countryName:"Belgi&euml;", IBANlength:"16", bankFormCode:"0 3n 0 ", accountNum:"0 7n 2n" } } */ What am I doing wrong. Tnx in advance

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  • Jquery Var Returned As object

    - by alex
    I'm trying to pass a variable from one function to another, but the var elmId is being returned as an object and giving an error. When we click on any of the generated divs we should be able to change the size of the div by choosing a width / height value from the drop down menus. I'm trying to pass the clicked div id which is elmId to function displayVals but it is not working. If we replace "#"+elmId in the function displayVals with the actual id of the first div created with is "#divid1" then it works. Why is the value of var elmId not being passed to displayVals <link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.7/themes/base/jquery-ui.css" type="text/css" media="all" /> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js" type="text/javascript"></script> <script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.7/jquery-ui.min.js" type="text/javascript"></script> <style> .aaa{width:100px; height:100px; background-color:#ccc;} button{width:100px; height:20px;} </style> <button class="idiv">div</button> <select id="width"> <option>100px</option> <option>200px</option> <option>300px</option> </select> <select id="height"> <option>100px</option> <option>200px</option> <option>300px</option> </select> <p></p> <script type="text/javascript"> var divId = 1; $("button").click(function(){ var elm = $('<div id=divid' + divId + ' class=aaa></div>'); elm.appendTo('p'); divId++; }); $("p").click(function(e){ var elmType = $(e.target)[0].nodeName, elmId = $(e.target)[0].id; return displayVals(elmId); }); function displayVals(elmId) { var iwidth = $("#width").val(); var iheight = $("#height").val(); $("#"+elmId).css({width:iwidth, height:iheight}); console.log(elmId); } $("select").change(displayVals); displayVals(); </script>

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  • Android - Saving an object in onSaveInstanceState?

    - by Donal Rafferty
    I have created a small XML parsing application for Android that displays information in a listview and then allows a user to click on the list view and a dialog with further info will pop up. The problem is that when the screen orientation is changed when a dialog screen is open I get a null pointer error. The null pointer occurs on the following line: if(setting.getAddForPublicUserNames() == 1){ This line is part of my dialogPrepare method: @Override public void onPrepareDialog(int id, Dialog dialog) { switch(id) { case (SETTINGS_DIALOG) : afpunText = ""; if(setting.getAddForPublicUserNames() == 1){ afpunText = "Yes"; } else{ afpunText = "No"; } String Text = "Login Settings: " + "\n" + "Password: " + setting.getPassword() + "\n" + "Server: " + setting.getServerAddress() + "\n" + "Register: " + setting.getRegistrarAddress() + "\n" + "Realm: " + setting.getRealm() + "\n" + "Public UserNames: " + afpunText + "\n" + "Preference Settings: " + "\n" + "Request VDN: " + setting.getRequestVDN() + "\n" + "Handover Settings: " + "\n" + "Enable Handover: " + setting.getEnableHandover() + "\n" + "Hand Over Number: " + setting.getHandoverNum() + "\n"; AlertDialog settingsDialog = (AlertDialog)dialog; settingsDialog.setTitle("Auth ID: " + setting.getUserName()); tv = (TextView)settingsDialog.findViewById(R.id.detailsTextView); if (tv != null) tv.setText(Text); break; } } So the error is that my variable setting is null after the screen orientation changes. I have tried to use the onSaveInstance state methods to fix that as follows: @Override public void onSaveInstanceState(Bundle savedInstanceState) { for(int i = 0; i < settings.size(); i++){ savedInstanceState.putString("Username"+i, settings.get(i).getUserName()); savedInstanceState.putString("Password"+i, settings.get(i).getPassword()); savedInstanceState.putString("Server"+i, settings.get(i).getServerAddress()); savedInstanceState.putString("Registrar"+i, settings.get(i).getRegistrarAddress()); savedInstanceState.putString("Realm"+i, settings.get(i).getRealm()); savedInstanceState.putInt("PUserNames"+i, settings.get(i).getAddForPublicUserNames()); savedInstanceState.putString("RequestVDN"+i, settings.get(i).getRequestVDN()); savedInstanceState.putString("EnableHandOver"+i, settings.get(i).getEnableHandover()); savedInstanceState.putString("HandOverNum"+i, settings.get(i).getHandoverNum()); } super.onSaveInstanceState(savedInstanceState); } and @Override public void onRestoreInstanceState(Bundle savedInstanceState) { super.onRestoreInstanceState(savedInstanceState); //Check to see if this is required // Restore UI state from the savedInstanceState. // This bundle has also been passed to onCreate. for(int i = 0; i<settings.size(); i++){ settings.get(i).setUserName(savedInstanceState.getString("Username"+i)); settings.get(i).setPassword(savedInstanceState.getString("Password"+i)) ; settings.get(i).setServerAddress(savedInstanceState.getString("Server"+i)); settings.get(i).setRegistrarAddress(savedInstanceState.getString("Registrar"+i)); settings.get(i).setRealm(savedInstanceState.getString("Realm"+i)); settings.get(i).setAddForPublicUserNames(savedInstanceState.getInt("PUserNames"+i)); settings.get(i).setRequestVDN(savedInstanceState.getString("RequestVDN"+i)); settings.get(i).setEnableHandover(savedInstanceState.getString("EnableHandOver"+i)); settings.get(i).setHandoverNum(savedInstanceState.getString("HandOverNum"+i)); } } However the error still remains, I think I have to save the selected setting from what was selected from the ListView? But how do I save a setting object in onSavedInstance?

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  • AutoMapper How To Map Object A To Object B Differently Depending On Context

    - by IanT8
    Calling all AutoMapper gurus! I'd like to be able to map object A to object B differently depending on context at runtime. In particular, I'd like to ignore certain properties in one mapping case, and have all properties mapped in another case. What I'm experiencing is that Mapper.CreateMap can be called successfully in the different mapping cases however, once CreateMap is called, the map for a particular pair of types is set and is not subsequently changed by succeeding CreateMap calls which might describe the mapping differently. I found a blog post which advocates Mapper.Reset() to get round the problem, however, the static nature of the Mapper class means that it is only a matter of time before a collision and crash occur. Is there a way to do this? What I think I need is to call Mapper.CreateMap once per appdomain, and later, be able to call Mapper.Map with hints about which properties should be included / excluded. Right now, I'm thinking about changing the source code by writing a non-static mapping class that holds the mapping config instance based. Poor performance, but thread safe. What are my options. What can be done? Automapper seems so promising.

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  • Disposing underlying object from finalizer in an immutable object

    - by Juan Luis Soldi
    I'm trying to wrap around Awesomium and make it look to the rest of my code as close as possible to NET's WebBrowser since this is for an existing application that already uses the WebBrowser. In this library, there is a class called JSObject which represents a javascript object. You can get one of this, for instance, by calling the ExecuteJavascriptWithResult method of the WebView class. If you'd call it like myWebView.ExecuteJavascriptWithResult("document", string.Empty).ToObject(), then you'd get a JSObject that represents the document. I'm writing an immutable class (it's only field is a readonly JSObject object) called JSObjectWrap that wraps around JSObject which I want to use as base class for other classes that would emulate .NET classes such as HtmlElement and HtmlDocument. Now, these classes don't implement Dispose, but JSObject does. What I first thought was to call the underlying JSObject's Dispose method in my JSObjectWrap's finalizer (instead of having JSObjectWrap implement Dispose) so that the rest of my code can stay the way it is (instead of having to add using's everywhere and make sure every JSObjectWrap is being properly disposed). But I just realized if more than two JSObjectWrap's have the same underlying JSObject and one of them gets finalized this will mess up the other JSObjectWrap. So now I'm thinking maybe I should keep a static Dictionary of JSObjects and keep count of how many of each of them are being referenced by a JSObjectWrap but this sounds messy and I think could cause major performance issues. Since this sounds to me like a common pattern I wonder if anyone else has a better idea.

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  • Calling Object Methods in Code

    - by Mister R2
    I'm a bit new to PHP, and I'm more experienced with strongly-typed languages such as JAVA, C# or C++.I'm currently writing a web tool in PHP, and I am having an issue trying to do what I want. The simple idea of what I want to do in code is run through some emails I used PHP-IMAP to get. I then create email objects (a class I defined), and put them in an array. Later on the code, however, I cycle through those emails to display them. However, as you might have guessed I'd have an issue with, I try to use an Email Class object method in that later loop -- and I'm pretty sure PHP doesn't know that the variables in the array happen to be Email Class objects! I wrote a toString method, and I want to call it in the loop. While I don't need to do this for the final version of this tool, I would like to find out what I'm missing. This is the class and the loop where I'm calling the method: include 'imap_email_interface.php'; class ImapEmail implements imap_email_interface { // Email data var $msgno; var $to; var $from; var $subject; var $body; var $attachment; // Email behavior /* PHP 4 ~ legacy constructor */ public function ImapEmail($message_number) { $this->__construct(); $this->msgno = $message_number; } /* PHP 5 Constructor */ public function __construct($message_number) { $this->msgno = $message_number; } public function send($send_to) { // Not Yet Needed! Seriously! } public function setHeaderDirectly($TO, $FROM, $SUBJECT) { $this->to = $TO; $this->from = $FROM; $this->subject = $SUBJECT; } public function setHeaderIndirectly($HEADER) { if (isset($HEADER->to[0]->personal)) $this->to = '"'.$HEADER->to[0]->personal.'", '.$HEADER->to[0]->mailbox.'@'.$HEADER->to[0]->host; else $this->to = $HEADER->to[0]->mailbox.'@'.$HEADER->to[0]->host; $this->from = '"'.$HEADER->from[0]->personal.'", '.$HEADER->from[0]->mailbox.'@'.$HEADER->from[0]->host; $this->subject = $HEADER->subject; } public function setBody($BODY) { $this->body = $BODY; } public function setAttachment($ATTCH) { $this->attachment = $ATTCH; } public function toString() { $str = '[TO]: ' . $this->to . '<br />' . '[FROM]: ' . $this->from . '<br />' . '[SUBJECT]: ' . $this->subject . '<br />'; $str .= '[Attachment]: '.$this->attachment.'<br />'; return $str; } } ?> The Loop: foreach ($orderFileEmails as $x) { $x->toString(); echo '<br /><br />'; } Any ideas?

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  • jQuery/Javascript Cookies and variable returning with value [object Object]

    - by user1706661
    I am attempting to set a cookie to a site using jQuery, ONLY if the user came from a specific site. In this case, lets use -http://referrersite.com- as the site they must come from for the cookie to be created as an example. The cookie value is being stored in a variable and everything up to this point is working fine. There is a conditional statement checking whether the user came from the referred site, if the cookie exists already and if the cookie doesn't exist and the user did not come from the referred site. If the user came from the referred site the cookie is created and stored in a variable. If the cookie already exists, it is then stored in a variable. If the cookie does not exist and the user did not come from the referred site I am assigning the variable a static string of characters - this is where the issue lies. When the variable is alerted from the non referred site and no existing cookie, it returns: [object Object], not the static string of characters. The code I am using is below: $(document).ready(function() { var referrer = document.referrer; if(referrer == "http://referrersite.com") { $.cookie("code","123456", { expires: 90, path: '/' }); cookieContainer = $.cookie("code"); alert(cookieContainer); } else if($.cookie("code")) { cookieContainer = $.cookie("code"); alert(cookieContainer); } else if($.cookie("code") == null && referrer != "http://referrersite.com") { cookieContainer = "67890"; alert(cookieContainer); } }); Please let me know if there is something I am missing as the code to me looks like it should work. Thanks!

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  • How to design a scalable notification system?

    - by Trent
    I need to write a notification system manager. Here is my requirements: I need to be able to send a Notification on different platforms, which may be totally different (for exemple, I need to be able to send either an SMS or an E-mail). Sometimes the notification may be the same for all recipients for a given platform, but sometimes it may be a notification per recipients (or several) per platform. Each notification can contain platform specific payload (for exemple an MMS can contains a sound or an image). The system need to be scalable, I need to be able to send a very large amount of notification without crashing either the application or the server. It is a two step process, first a customer may type a message and choose a platform to send to, and the notification(s) should be created to be processed either real-time either later. Then the system needs to send the notification to the platform provider. For now, I end up with some though but I don't know how scalable it will be or if it is a good design. I've though of the following objects (in a pseudo language): a generic Notification object: class Notification { String $message; Payload $payload; Collection<Recipient> $recipients; } The problem with the following objects is what if I've 1.000.000 recipients ? Even if the Recipient object is very small, it'll take too much memory. I could also create one Notification per recipient, but some platform providers requires me to send it in batch, meaning I need to define one Notification with several Recipients. Each created notification could be stored in a persistent storage like a DB or Redis. Would it be a good it to aggregate this later to make sure it is scalable? On the second step, I need to process this notification. But how could I distinguish the notification to the right platform provider? Should I use an object like MMSNotification extending an abstract Notification? or something like Notification.setType('MMS')? To allow to process a lot of notification at the same time, I think a messaging queue system like RabbitMQ may be the right tool. Is it? It would allow me to queue a lot of notification and have several worker to pop notification and process them. But what if I need to batch the recipients as seen above? Then I imagine a NotificationProcessor object for which I could I add NotificationHandler each NotificationHandler would be in charge to connect the platform provider and perform notification. I can also use an EventManager to allow pluggable behavior. Any feedbacks or ideas? Thanks for giving your time. Note: I'm used to work in PHP and it is likely the language of my choice.

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  • Stop a rotating object at a specified angle?

    - by Krummelz
    I'm working in JavaScript with HTML5 and the canvas. I have an object which is rotating at a certain speed, and I need the object's rotation to slow down gradually and the front of the object to stop at a specified angle. (I'm using radians, not degrees.) I have a variable to keep track of the angle which the object is facing, as it rotates. How would I go about getting the object to come to rest, facing the direction I want it to?

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  • SQLAuthority News – Download Whitepaper – Choosing a Tabular or Multidimensional Modeling Experience in SQL Server 2012 Analysis Services

    - by pinaldave
    Data modeling is the most important task for any BI professional. Matter of the fact, the biggest challenge is to organizing disparate data into an analytic model that effectively and efficiently supports the reporting and analysis. SQL Server 2012 introduces BI Semantic Model (BISM), a single model that can support a broad range of reporting and analysis while blending two Analysis Services modeling experiences behind the scenes. Multidimensional modeling – enables BI professionals to create sophisticated multidimensional cubes using traditional online analytical processing (OLAP). Tabular modeling – provides self-service data modeling capabilities to business and data analysts. As data modeling is evolving and business needs are growing new technologies and tools are emerging to help end users to make the necessary adjustment to the reporting and analysis needs. This white paper is will provide practical guidance to help you decide which SQL Server 2012 Analysis Services modeling experience – tabular or multidimensional. Do let me know what do is your opinion as a comment. In simple word – I would like to know when will you use Tabular modeling and when Multidimensional modeling? Download Choosing a Tabular or Multidimensional Modeling Experience in SQL Server 2012 Analysis Services Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Business Intelligence, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, SQL White Papers, T SQL, Technology

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  • What are the disadvantages of self-encapsulation?

    - by Dave Jarvis
    Background Tony Hoare's billion dollar mistake was the invention of null. Subsequently, a lot of code has become riddled with null pointer exceptions (segfaults) when software developers try to use (dereference) uninitialized variables. In 1989, Wirfs-Brock and Wikerson wrote: Direct references to variables severely limit the ability of programmers to re?ne existing classes. The programming conventions described here structure the use of variables to promote reusable designs. We encourage users of all object-oriented languages to follow these conventions. Additionally, we strongly urge designers of object-oriented languages to consider the effects of unrestricted variable references on reusability. Problem A lot of software, especially in Java, but likely in C# and C++, often uses the following pattern: public class SomeClass { private String someAttribute; public SomeClass() { this.someAttribute = "Some Value"; } public void someMethod() { if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { return this.someAttribute; } } Sometimes a band-aid solution is used by checking for null throughout the code base: public void someMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Value" ) ) { // do something... } } public void anotherMethod() { assert this.someAttribute != null; if( this.someAttribute.equals( "Some Default Value" ) ) { // do something... } } The band-aid does not always avoid the null pointer problem: a race condition exists. The race condition is mitigated using: public void anotherMethod() { String someAttribute = this.someAttribute; assert someAttribute != null; if( someAttribute.equals( "Some Default Value" ) ) { // do something... } } Yet that requires two statements (assignment to local copy and check for null) every time a class-scoped variable is used to ensure it is valid. Self-Encapsulation Ken Auer's Reusability Through Self-Encapsulation (Pattern Languages of Program Design, Addison Wesley, New York, pp. 505-516, 1994) advocated self-encapsulation combined with lazy initialization. The result, in Java, would resemble: public class SomeClass { private String someAttribute; public SomeClass() { setAttribute( "Some Value" ); } public void someMethod() { if( getAttribute().equals( "Some Value" ) ) { // do something... } } public void setAttribute( String s ) { this.someAttribute = s; } public String getAttribute() { String someAttribute = this.someAttribute; if( someAttribute == null ) { setAttribute( createDefaultValue() ); } return someAttribute; } protected String createDefaultValue() { return "Some Default Value"; } } All duplicate checks for null are superfluous: getAttribute() ensures the value is never null at a single location within the containing class. Efficiency arguments should be fairly moot -- modern compilers and virtual machines can inline the code when possible. As long as variables are never referenced directly, this also allows for proper application of the Open-Closed Principle. Question What are the disadvantages of self-encapsulation, if any? (Ideally, I would like to see references to studies that contrast the robustness of similarly complex systems that use and don't use self-encapsulation, as this strikes me as a fairly straightforward testable hypothesis.)

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  • Odd "Object reference not set to an instance of an object" involving xWinForms

    - by Kyle
    Hey, I've been trying to get the xWinForms 3.0 library (a library with forms support in xna) working with my C# XNA Game project but I keep getting the same problem. I add the reference to my project, put in the using statement, declare a formCollection variable and then I try to initialize it. whenever I run the project I get stopped on this line: formCollection = new FormCollection(this.Window, Services, ref graphics); it gives me the error: " System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="Microsoft.Xna.Framework" StackTrace: at Microsoft.Xna.Framework.Graphics.VertexShader..ctor(GraphicsDevice graphicsDevice, Byte[] shaderCode) at Microsoft.Xna.Framework.Graphics.SpriteBatch.ConstructPlatformData() at Microsoft.Xna.Framework.Graphics.SpriteBatch..ctor(GraphicsDevice graphicsDevice) at xWinFormsLib.FormCollection..ctor(GameWindow window, IServiceProvider services, GraphicsDeviceManager& graphics) at GameSolution.Game2.LoadContent() in C:\Users\Owner\Documents\School\Year 3\Winter\Soen 390\TeamWTF_3\SourceCode\GameSolution\GameSolution\Game2.cs:line 45 at Microsoft.Xna.Framework.Game.Initialize() at GameSolution.Game2.Initialize() in C:\Users\Owner\Documents\School\Year 3\Winter\Soen 390\TeamWTF_3\SourceCode\GameSolution\GameSolution\Game2.cs:line 37 at Microsoft.Xna.Framework.Game.Run() at GameSolution.Program.Main(String[] args) in C:\Users\Owner\Documents\School\Year 3\Winter\Soen 390\TeamWTF_3\SourceCode\GameSolution\GameSolution\Program.cs:line 14 InnerException: " In a project I downloaded that used the xWinForms, I put the following code in and it compiled and ran no error. but when I put it in my project I get the error. Am I making some stupid mistake about including dlls or something? I've been at this for hours and I can't seem to find anything that would cause this. using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; using Microsoft.Xna.Framework.Net; using Microsoft.Xna.Framework.Storage; using xWinFormsLib; namespace GameSolution { public class Game2 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; SpriteBatch spriteBatch; FormCollection formCollection; public Game2() { graphics = new GraphicsDeviceManager(this); Content.RootDirectory = "Content"; } protected override void Initialize() { // TODO: Add your initialization logic here base.Initialize(); } protected override void LoadContent() { // Create a new SpriteBatch, which can be used to draw textures. spriteBatch = new SpriteBatch(GraphicsDevice); formCollection = new FormCollection(this.Window, Services, ref graphics); } protected override void Update(GameTime gameTime) { base.Update(gameTime); } protected override void Draw(GameTime gameTime) { base.Draw(gameTime); } } } Any help would be greatly appreciated ._.

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  • Need to cast to an object without knowing what type the object is

    - by jle
    I am trying to dynamically load my authentication server type based on a setting. I am hung up on how to cast to a type when I don't know the type. Type t = Type.GetType(WebConfigurationManager.AppSettings.Get("AuthenticationSvcImpl")); IAuthenticationService authCli = Activator.CreateInstance(t); return authCli.AuthenticateUser(login); I know there is Convert.ChangeType(), but that just converts to an object...

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  • Javascript: how to access anonymous object within object?

    - by Caballero
    I have a string generated by php's json_encode() that looks like this: [ { "key1":"value1", "key2":"value2", "key3":"value3" }, { "key1":"value1", "key2":"value2", "key3":"value3" } ] I use Javascript function to convert the string to Javascript object: var jsonObj=JSON.parse(string); How do I access the data inside since the inner objects have no names? I tried something like: alert(jsonObj.firstChild.key1); It gives me "undefined". Why is that so?

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  • Write a network simulator for fun

    - by Jono
    I want to write my own network simulator, for fun and for personal challenge. I hope to learn both new programming techniques, and a little bit more about networking. Previous object-oriented attempts ended very quickly, but I've recently downloaded and played with Microsoft's Axum (a new version was released today) and their Concurrency and Co-ordination Runtime. As I come from a very OO dominant background, I had never heard of Actor-oriented programming before; now it seems I've had my head in the sand until Scala and F# brought the paradigm to me. My questions are: a) is actor-oriented programming a better choice than object-oriented programming for this task, and if so b) where is a good place to start learning actor-oriented design?

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  • Static code analysis for new language. Where to start?

    - by tinny
    I just been given a new assignment which looks like its going to be an interesting challenge. The customer is wanting a code style checking tool to be developed for their internal (soon to be open sourced) programming language which runs on the JVM. The language syntax is very Java like. The customer basically wants me to produce something like checkstyle. So my question is this, how would you approach this problem? Given a clean slate what recommendations would you make to the customer? I think I have 3 options Write something from scratch. Id prefer not to do this as it seems like this sort of code analysis tool problem has been solved so many times that there must be a more "framework" or "platform" orientated approach. Fork an existing code style checking tool and modify the parsing to fit with this new language etc etc Extend or plug into an existing static code analysis tool. (maybe write a plugin for Yasca?) Maybe you would like to share your experiences in this area? Thanks for reading

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  • Understanding UML composition better

    - by Prog
    The technical difference between Composition and Aggregation in UML (and sometimes in programming too) is that with Composition, the lifetime of the objects composing the composite (e.g. an engine and a steering wheel in a car) is dependent on the composite object. While with Aggregation, the lifetime of the objects making up the composite is independent of the composite. However I'm not sure about something related to composition in UML. Say ClassA is composed of an object of ClassB: class ClassA{ ClassB bInstance; public ClassA(){ bInstance = new ClassB(); } } This is an example of composition, because bInstance is dependent on the lifetime of it's enclosing object. However, regarding UML notation - I'm not sure if I would notate the relationship between ClassA and ClassB with a filled diamond (composition) or a white diamond (aggregation). This is because while the lifetime of some ClassB instances is dependent of ClassA instances - there could be ClassB instances anywhere else in the program - not only within ClassA instances. The question is: if ClassA objects are composed of ClassB objects - but other ClassB objects are free to be used anywhere else in the program: Should the relationship between ClassA and ClassB be notated as aggregation or as composition?

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  • null pointers vs. Null Object Pattern

    - by GlenH7
    Attribution: This grew out of a related P.SE question My background is in C / C++, but I have worked a fair amount in Java and am currently coding C#. Because of my C background, checking passed and returned pointers is second-hand, but I acknowledge it biases my point of view. I recently saw mention of the Null Object Pattern where the idea is than an object is always returned. Normal case returns the expected, populated object and the error case returns empty object instead of a null pointer. The premise being that the calling function will always have some sort of object to access and therefore avoid null access memory violations. So what are the pros / cons of a null check versus using the Null Object Pattern? I can see cleaner calling code with the NOP, but I can also see where it would create hidden failures that don't otherwise get raised. I would rather have my application fail hard (aka an exception) while I'm developing it than have a silent mistake escape into the wild. Can't the Null Object Pattern have similar problems as not performing a null check? Many of the objects I have worked with hold objects or containers of their own. It seems like I would have to have a special case to guarantee all of the main object's containers had empty objects of their own. Seems like this could get ugly with multiple layers of nesting.

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  • Formal definition for term "pure OO language"?

    - by Yauhen Yakimovich
    I can't think of a better place among SO siblings to pose such a question. Originally I wanted to ask "Is python a pure OO language?" but considering troubles and some sort of discomfort people experience while trying to define the term I decided to start with obtaining a clear definition for the term itself. It would be rather fair to start with correspondence by Dr. Alan Kay, who has coined the term (note the inspiration in biological analogy to cells or other living objects). There are following ways to approach the task: Give a comparative analysis by listing programming languages that exhibits certain properties unique and sufficient to define the term (although Smalltalk and Java are passing examples but IMO this way seems neither really complete or nor fruitful) Give a formal definition (or close to it, e.g. in more academic or mathematical style). Give a philosophical definition that would totally rely on semantical context of concrete language or a priori programming experience (there must be some chance of successful explanation by the community). My current version: "If a certain programing (formal) language that can (grammatically) differentiate between operations and operands as well as infer about the type of each operand whether this type is an object (in sense of OOP) or not then we call such a language an OO-language as long as there is at least one type in this language which is an object. Finally, if all types of the language are also objects we define such language to be pure OO-language." Would appreciate any possible improvement of it. As you can see I just made the definition dependent on the term "object" (often fully referenced as class of objects).

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  • About shared (static) Members and its behavior

    - by Allende
    I just realized that I can access shared members from instances of classes (probably this is not correct, but compile and run), and also learn/discover that, I can modify shared members, then create a new instance and access the new value of the shared member. My question is, what happens to the shared members, when it comes back to the "default" value (class declaration), how dangerous is it do this ? is it totally bad ? is it valid in some cases ?. If you want to test my point here is the code (console project vb.net) that I used to test shared members, as you can see/compile/run, the shared member "x" of the class "Hello" has default value string "Default", but at runtime it changes it, and after creating a new object of that class, this object has the new value of the shared member. Module Module1 Public Class hello Public Shared x As String = "Default" Public Sub New() End Sub End Class Sub Main() Console.WriteLine("hello.x=" & hello.x) Dim obj As New hello() Console.WriteLine("obj.x=" & obj.x) obj.x = "Default shared memeber, modified in object" Console.WriteLine("obj.x=" & obj.x) hello.x = "Defaul shared member, modified in class" Console.WriteLine("hello.x=" & hello.x) Dim obj2 As New hello() Console.WriteLine("obj2.x=" & obj2.x) Console.ReadLine() End Sub End Module UPDATE: First at all, thanks to everyone, each answer give feedback, I suppose, by respect I should choose one as "the answer", I don't want to be offensive to anyone, so please don't take it so bad if I didn't choose you answer.

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