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  • Java loading user-specified classes at runtime

    - by user349043
    I'm working on robot simulation in Java (a Swing application). I have an abstract class "Robot" from which different types of Robots are derived, e.g. public class StupidRobot extends Robot { int m_stupidness; int m_insanityLevel; ... } public class AngryRobot extends Robot { float m_aggression; ... } As you can see, each Robot subclass has a different set of parameters. What I would like to do is control the simulation setup in the initial UI. Choose the number and type of Robots, give it a name, fill in the parameters etc. This is one of those times where being such a dinosaur programmer, and new to Java, I wonder if there is some higher level stuff/thinking that could help me here. So here is what I've got: (1) User Interface Scrolling list of Robot types on the left. "Add " and "<< Remove" buttons in the middle. Default-named scrolling list of Robots on the right. "Set Parameters" button underneath. (So if you wanted an AngryRobot, you'd select AngryRobot on the left list, click "Add" and "AngryRobot1" would show up on the right.) When selecting a Robot on the right, click "Set Parameters..." button which would call yet another model dialog where you'd fill in the parameters. Different dialog called for each Robot type. (2) Data structures an implementation As an end-product I think a HashMap would be most convenient. The keys would be Robot types and the accompanying object would be all of the parameters. The initializer could just retrieve each item one and a time and instantiate. Here's what the data structures would look like: enum ROBOT_TYPE {STUPID, ANGRY, etc} public class RobotInitializer { public ROBOT_TYPE m_type; public string m_name; public int[] m_int_params; public float[] m_float_params; etc. The initializer's constructor would create the appropriate length parameter arrays based on the type: public RobotInitializer(ROBOT_TYPE type, int[] int_array, float[] float_array, etc){ switch (type){ case STUPID: m_int_params = new int[STUPID_INT_PARAM_LENGTH]; System.arraycopy(int_array,0,m_int_params,0,STUPID_INT_PARAM_LENGTH); etc. Once all the RobotInitializers are instantiated, they are added to the HashMap. Iterating through the HashMap, the simulation initializer takes items from the Hashmap and instantiates the appropriate Robots. Is this reasonable? If not, how can it be improved? Thanks

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  • Changing RGB color image to Grayscale image using Objective C

    - by user567167
    I was developing a application that changes color image to gray image. However, some how the picture comes out wrong. I dont know what is wrong with the code. maybe the parameter that i put in is wrong please help. UIImage *c = [UIImage imageNamed:@"downRed.png"]; CGImageRef cRef = CGImageRetain(c.CGImage); NSData* pixelData = (NSData*) CGDataProviderCopyData(CGImageGetDataProvider(cRef)); size_t w = CGImageGetWidth(cRef); size_t h = CGImageGetHeight(cRef); unsigned char* pixelBytes = (unsigned char *)[pixelData bytes]; unsigned char* greyPixelData = (unsigned char*) malloc(w*h); for (int y = 0; y < h; y++) { for(int x = 0; x < w; x++){ int iter = 4*(w*y+x); int red = pixe lBytes[iter]; int green = pixelBytes[iter+1]; int blue = pixelBytes[iter+2]; greyPixelData[w*y+x] = (unsigned char)(red*0.3 + green*0.59+ blue*0.11); int value = greyPixelData[w*y+x]; } } CFDataRef imgData = CFDataCreate(NULL, greyPixelData, w*h); CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData(imgData); size_t width = CGImageGetWidth(cRef); size_t height = CGImageGetHeight(cRef); size_t bitsPerComponent = 8; size_t bitsPerPixel = 8; size_t bytesPerRow = CGImageGetWidth(cRef); CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); CGBitmapInfo info = kCGImageAlphaNone; CGFloat *decode = NULL; BOOL shouldInteroplate = NO; CGColorRenderingIntent intent = kCGRenderingIntentDefault; CGDataProviderRelease(imgDataProvider); CGImageRef throughCGImage = CGImageCreate(width, height, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpace, info, imgDataProvider, decode, shouldInteroplate, intent); UIImage* newImage = [UIImage imageWithCGImage:throughCGImage]; CGImageRelease(throughCGImage); newImageView.image = newImage;

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  • Doing some stuff right before the user exits the page

    - by Mike
    I have seen some questions here regarding what I want to achieve and have based what I have so far on those answer. But there is a slight misbehavior that is still irritating me. What I have is sort of a recovery feature. Whenever you are typing text, the client sends a sync request to the server every 45 seconds. It does 2 things. First, it extends the lease the client has on the record (only one person may edit at one time) for another 60 seconds. Second, it sends the text typed so far to the server in case the server crashes, internet connection fails, etc. In that case, the next time the user enters our application, the user is notified that something has gone wrong and that some text was recovered. Think of Microsoft or OpenOffice recovery whenever they crash! Of course, if the user leaves the page willingly, the user does not need to be notified and as a result, the recovery is deleted. I do that final request via a beforeunload event. Everything went fine until I was asked to make a final adjustment... The same behavior you have here at stack overflow when you exit the editor... a confirm dialogue. This works so far, BUT, the confirm dialogue is shown twice. Here is the code. The event if (local.sync.autosave_textelement) { window.onbeforeunload = exitConfirm; } The function function exitConfirm() { var local = Core; if (confirm('blub?')) { local.sync.autosave_destroy = true; sync(false); return true; } else { return false; } }; Some problem irrelevant clarifications: Core is a global Object that contains a lot of variables that are used everywhere. sync makes an ajax request. The values are based on the values that the Core.sync object contains. The parameter determines if the call should be async (default) or sync. Edit 1 I did try to separate both things (recovery deletion and user confirmation that is) into beforeunload and unload. The problem there was that unload is a bit too late. The user gets informed that there is a recovery even though it is scheduled to be deleted. If you refresh the page 1 second later, the dialogue disappears as the file was deleted by then.

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  • How to use a LinkButton inside gridview to delete selected username in the code-behind file?

    - by jenifer
    I have a "UserDetail" table in my "JobPost.mdf". I have a "Gridview1" showing the column from "UserDetail" table,which has a primary key "UserName". This "UserName" is originally saved using Membership class function. Now I add a "Delete" linkbutton to the GridView1. This "Delete" is not autogenerate button,I dragged inside the column itemtemplate from ToolBox. The GridView1's columns now become "Delete_LinkButton"+"UserName"(within the UserDetail table)+"City"(within the UserDetail table)+"IsAdmin"(within the UserDetail table) What I need is that by clicking this "delete_linkButton",it will ONLY delete the entire User Entity on the same row (link by the corresponding "UserName") from the "UserDetail" table,as well as delete all information from the AspNetDB.mdf (User,Membership,UserInRole,etc). I would like to fireup a user confirm,but not mandatory. At least I am trying to make it functional in the correct way. for example: Command UserName City IsAdmin delete ken Los Angles TRUE delete jim Toronto FALSE When I click "delete" on the first row, I need all the record about "ken" inside the "UserDetail" table to be removed. Meanwhile, all the record about "ken" in the AspNetDB.mdf will be gone, including UserinRole table. I am new to asp.net, so I don't know how to pass the commandargument of the "Delete_LinkButton" to the code-behind file LinkButton1_Click(object sender, EventArgs e), because I need one extra parameter "UserName". My partial code is listed below: <asp:TemplateField> <ItemTemplate> <asp:LinkButton ID="Delete_LinkButton" runat="server" onclick="LinkButton1_Click1" CommandArgument='<%# Eval("UserName","{0}") %>'>LinkButton</asp:LinkButton> </ItemTemplate> </asp:TemplateField> protected void Delete_LinkButton_Click(object sender, EventArgs e) { ((LinkButton) GridView1.FindControl("Delete_LinkButton")).Attributes.Add("onclick", "'return confirm('Are you sure you want to delete {0} '" + UserName); Membership.DeleteUser(UserName); JobPostDataContext db = new JobPostDataContext(); var query = from u in db.UserDetails where u.UserName == UserName select u; for (var Item in query) { db.UserDetails.DeleteOnSubmit(Item); } db.SubmitChanges(); } Please do help! Thanks in advance.

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  • SAX parser does not resolve filename

    - by phantom-99w
    Another day, another strange error with SAX, Java, and friends. I need to iterate over a list of File objects and pass them to a SAX parser. However, the parser fails because of an IOException. However, the various File object methods confirm that the file does indeed exist. The output which I get: 11:53:57.838 [MainThread] DEBUG DefaultReactionFinder - C:\project\trunk\application\config\reactions\TestReactions.xml 11:53:57.841 [MainThread] ERROR DefaultReactionFinder - C:\project\trunk\application\config\reactions\null (The system cannot find the file specified) So the problem is obviously that null in the second line. I've tried nearly all variations of passing the file as a parameter to the parser, including as a String (both from getAbsolutePath() and entered by hand), as a URI and, even more weirdly, as a FileInputStream (for this I get the same error, except that the entire relative path gets reported as null, so C:\project\trunk\null). All that I can think of is that the SAXParserFactory is incorrectly configured. I have no idea what is wrong, though. Here is the code concerned: SAXParserFactory factory = SAXParserFactory.newInstance(); factory.setValidating(true); try { parser = factory.newSAXParser(); } catch (ParserConfigurationException e) { throw new InstantiationException("Error configuring an XML parser. Given error message: \"" + e.getMessage() + "\"."); } catch (SAXException e) { throw new InstantiationException("Error creating a SAX parser. Given error message: \"" + e.getMessage() + "\"."); } ... for (File f : fileLister.getFileList()) { logger.debug(f.getAbsolutePath()); try { parser.parse(f, new ReactionHandler(input)); //FileInputStream fs = new FileInputStream(f); //parser.parse(fs, new ReactionHandler(input)); //fs.close(); } catch (IOException e) { logger.error(e.getMessage()); throw new ReactionNotFoundException("An error occurred processing file \"" + f + "\"."); } ... } I have made no special provisions to provide a custom SAX parser implementation: I use the system default. Any help would be greatly appreciated!

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  • Implementing default constructors

    - by James
    Implement the default constructor, the constructors with one and two int parameters. The one-parameter constructor should initialize the first member of the pair, the second member of the pair is to be 0. Overload binary operator + to add the pairs as follows: (a, b) + (c, d) = (a + c, b + d); Overload the - analogously. Overload the * on pairs ant int as follows: (a, b) * c = (a * c, b * c). Write a program to test all the member functions and overloaded operators in your class definition. You will also need to write accessor (get) functions for each member. The definition of the class Pairs: class Pairs { public: Pairs(); Pairs(int first, int second); Pairs(int first); // other members and friends friend istream& operator>> (istream&, Pair&); friend ostream& operator<< (ostream&, const Pair&); private: int f; int s; }; Self-Test Exercise #17: istream& operator (istream& ins, Pair& second) { char ch; ins ch; // discard init '(' ins second.f; ins ch; // discard comma ',' ins second.s; ins ch; // discard final '(' return ins; } ostream& operator<< (ostream& outs, const Pair& second) { outs << '('; outs << second.f; outs << ", " ;// I followed the Author's suggestion here. outs << second.s; outs << ")"; return outs; }

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  • How can i maintain last cookie value in flex with jsp?

    - by praveen
    Hi All, my login form in flex when I login I have created a cookie in jsp like this name setValueCookie.jsp <%@ page language="java" import="java.util.* , javax.net.*" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-8859-1"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <% String username = request.getParameter("value"); System.out.println("Email got in cookieSet = " + username); if(username==null) username=""; Date now = new Date(); String timestamp = now.toString(); Cookie cookie = new Cookie("username",username); cookie.setMaxAge(365 * 24 * 60 * 60); response.addCookie(cookie); %> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>DashBoard-Cookie</title> </head> <body> </body> </html> now using Http service request parameter i am passing username 'Value' to this jsp. and i am reading cookie value from getValueCookie.jsp like this <% String cookieName = "username"; Cookie cookies [] = request.getCookies (); Cookie myCookie = null; String result; if (cookies != null) { for (int i = 0; i < cookies.length; i++) { if (cookies [i].getName().equals (cookieName)) { myCookie = cookies[i]; break; } } } %> <data> <status><%=myCookie.getValue().toString()%></status> </data> through the httpservice value i am getting but if i open a new window or any new tab cookie value is not getting how can i solve this? Thanks in advance.

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  • cflock do not throw timeout for same url called in same browser

    - by Pritesh Patel
    I am trying lock block on page test.cfm and below is code written on page. <cfscript> writeOutput("Before lock at #now()#"); lock name="threadlock" timeout="3" type="exclusive" { writeOutput("<br/>started at #now()#"); thread action="sleep" duration="10000"; writeOutput("<br/>ended at #now()#"); } writeOutput("<br/>After lock at #now()#"); </cfscript> assuming my url for page is http://localhost.local/test.cfm and running it on browser in two different tabs. I was expecting one of the url will throw timeout error after 3 second since another url lock it atleast for 10 seconds due to thread sleep. Surprisingly I do not get any timeout error rather second page call run after 10 seconds as first call finish execution. But I am appending some url parameter (e.g. http://localhost.local/test.cfm?q=1) will throw error. Also I am calling same url in different browser then one of the call will throw timeout issue. Is lock based on session and url? Update Here is output for two different cases: Case 1: TAB1 Url: http://localhost.local/test/test.cfm Before lock at {ts '2013-10-18 09:21:35'} started at {ts '2013-10-18 09:21:35'} ended at {ts '2013-10-18 09:21:45'} After lock at {ts '2013-10-18 09:21:45'} TAB2 Url: http://localhost.local/test/test.cfm Before lock at {ts '2013-10-18 09:21:45'} started at {ts '2013-10-18 09:21:45'} ended at {ts '2013-10-18 09:21:55'} After lock at {ts '2013-10-18 09:21:55'} Case 2: TAB1 Url: http://localhost.local/test/test.cfm Before lock at {ts '2013-10-18 09:27:18'} started at {ts '2013-10-18 09:27:18'} ended at {ts '2013-10-18 09:27:28'} After lock at {ts '2013-10-18 09:27:28'} TAB2 Url: http://localhost.local/test/test.cfm? (Added ? at the end) Before lock at {ts '2013-10-18 09:27:20'} A timeout occurred while attempting to lock threadlock. The error occurred in C:/inetpub/wwwroot/test/test.cfm: line 13 11 : 12 : <cfoutput>Before lock at #now()#</cfoutput> 13 : <cflock name="threadlock" timeout="3" type="exclusive"> 14 : <cfoutput><br/>started at #now()#</cfoutput> 15 : <cfthread action="sleep" duration="10000"/> ... Result for case 2 as expected. For case 1, strange thing I just noticed is tab 2 output "Before lock at {ts '2013-10-18 09:21:45'} indicates that whole request start after 10 seconds (means after the complete execution of first tab) when I have fired it in second URL just after 2 seconds of first tabs.

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  • getting Cannot identify image file when trying to create thumbnail in django

    - by Mo J. Mughrabi
    Am trying to create a thumbnail in django, am trying to build a custom class specifically to be used for generating thumbnails. As following from StringIO import StringIO from PIL import Image class Thumbnail(object): source = '' size = (50, 50) output = '' def __init__(self): pass @staticmethod def load(src): self = Thumbnail() self.source = src return self def generate(self, size=(50, 50)): if not isinstance(size, tuple): raise Exception('Thumbnail class: The size parameter must be an instance of a tuple.') self.size = size # resize properties box = self.size factor = 1 fit = True image = Image.open(self.source) # Convert to RGB if necessary if image.mode not in ('L', 'RGB'): image = image.convert('RGB') while image.size[0]/factor > 2*box[0] and image.size[1]*2/factor > 2*box[1]: factor *=2 if factor > 1: image.thumbnail((image.size[0]/factor, image.size[1]/factor), Image.NEAREST) #calculate the cropping box and get the cropped part if fit: x1 = y1 = 0 x2, y2 = image.size wRatio = 1.0 * x2/box[0] hRatio = 1.0 * y2/box[1] if hRatio > wRatio: y1 = int(y2/2-box[1]*wRatio/2) y2 = int(y2/2+box[1]*wRatio/2) else: x1 = int(x2/2-box[0]*hRatio/2) x2 = int(x2/2+box[0]*hRatio/2) image = image.crop((x1,y1,x2,y2)) #Resize the image with best quality algorithm ANTI-ALIAS image.thumbnail(box, Image.ANTIALIAS) # save image to memory temp_handle = StringIO() image.save(temp_handle, 'png') temp_handle.seek(0) self.output = temp_handle return self def get_output(self): return self.output.read() the purpose of the class is so i can use it inside different locations to generate thumbnails on the fly. The class works perfectly, I've tested it directly under a view.. I've implemented the thumbnail class inside the save method of the forms to resize the original images on saving. in my design, I have two fields for thumbnails. I was able to generate one thumbnail, if I try to generate two it crashes and I've been stuck for hours not sure whats the problem. Here is my model class Image(models.Model): article = models.ForeignKey(Article) title = models.CharField(max_length=100, null=True, blank=True) src = models.ImageField(upload_to='publication/image/') r128 = models.ImageField(upload_to='publication/image/128/', blank=True, null=True) r200 = models.ImageField(upload_to='publication/image/200/', blank=True, null=True) uploaded_at = models.DateTimeField(auto_now=True) Here is my forms class ImageForm(models.ModelForm): """ """ class Meta: model = Image fields = ('src',) def save(self, commit=True): instance = super(ImageForm, self).save(commit=True) file = Thumbnail.load(instance.src) instance.r128 = SimpleUploadedFile( instance.src.name, file.generate((128, 128)).get_output(), content_type='image/png' ) instance.r200 = SimpleUploadedFile( instance.src.name, file.generate((200, 200)).get_output(), content_type='image/png' ) if commit: instance.save() return instance the strange part is, when i remove the line which contains instance.r200 in the form save. It works fine, and it does the thumbnail and stores it successfully. Once I add the second thumbnail it fails.. Any ideas what am doing wrong here? Thanks Update: I tried earlier doing the following but I still got the same error class ImageForm(models.ModelForm): """ """ class Meta: model = Image fields = ('src',) def save(self, commit=True): instance = super(ImageForm, self).save(commit=True) instance.r128 = SimpleUploadedFile( instance.src.name, Thumbnail.load(instance.src).generate((128, 128)).get_output(), content_type='image/png' ) instance.r200 = SimpleUploadedFile( instance.src.name, Thumbnail.load(instance.src).generate((200, 200)).get_output(), content_type='image/png' ) if commit: instance.save() return instance

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  • Derived template override return type of member function C++

    - by Ruud v A
    I am writing matrix classes. Take a look at this definition: template <typename T, unsigned int dimension_x, unsigned int dimension_y> class generic_matrix { ... generic_matrix<T, dimension_x - 1, dimension_y - 1> minor(unsigned int x, unsigned int y) const { ... } ... } template <typename T, unsigned int dimension> class generic_square_matrix : public generic_matrix<T, dimension, dimension> { ... generic_square_matrix(const generic_matrix<T, dimension, dimension>& other) { ... } ... void foo(); } The generic_square_matrix class provides additional functions like matrix multiplication. Doing this is no problem: generic_square_matrix<T, 4> m = generic_matrix<T, 4, 4>(); It is possible to assign any square matrix to M, even though the type is not generic_square_matrix, due to the constructor. This is possible because the data does not change across children, only the supported functions. This is also possible: generic_square_matrix<T, 4> m = generic_square_matrix<T, 5>().minor(1,1); Same conversion applies here. But now comes the problem: generic_square_matrix<T, 4>().minor(1,1).foo(); //problem, foo is not in generic_matrix<T, 3, 3> To solve this I would like generic_square_matrix::minor to return a generic_square_matrix instead of a generic_matrix. The only possible way to do this, I think is to use template specialisation. But since a specialisation is basically treated like a separate class, I have to redefine all functions. I cannot call the function of the non-specialised class as you would do with a derived class, so I have to copy the entire function. This is not a very nice generic-programming solution, and a lot of work. C++ almost has a solution for my problem: a virtual function of a derived class, can return a pointer or reference to a different class than the base class returns, if this class is derived from the class that the base class returns. generic_square_matrix is derived from generic_matrix, but the function does not return a pointer nor reference, so this doesn't apply here. Is there a solution to this problem (possibly involving an entirely other structure; my only requirements are that the dimensions are a template parameter and that square matrices can have additional functionality). Thanks in advance, Ruud

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  • What web platform is right for me?

    - by egervari
    I've been looking at web frameworks like Rails, Grails, etc. I'm used to doing applications in Spring Framework with Hibernate... and I want something more productive. One of the things I realized is that while some of the things in Grails is sexy, there are some serious problems with it. Grails' controllers: 1) are implemented awfully. They don't seem to be able to extend from super classes at runtime. I tried this to add base actions and helper methods, and this seems to cause grails to blow up. 2) are based on an obsolete request parameters model (rather than form backing objects, which are much nicer). 3) are hard to test. Command objects are treated totally differently... and it's actually MUCH harder to write the test than it is to write the controller code. 4) Command objects operate totally differently. They are pre-validated and bound, which causes a lot of inconsistencies than basic parameter model. 5) Command objects are not reusable, and it's a pain in the rear to reuse most of the stuff from the domain classes, like constraints and fields. This is TRIVIAL to do in basic Spring. Why the hell was it not trivial to do in Grails? 6) The scaffolding that is generated is pure crap. It doesn't generalize inserts and updates... and it actually copy/pastes a pile of code in two views: create.gsp and edit.gsp. The views themselves are gargantuan piles of doggie do-do. This is further compounded by the fact that it uses low-level parameters and not objects. Integration tests are 30x slower than a Spring integration test. It is disgusting. Some mocking tests are so hard to write and aren't guaranteed to work when it's deployed, that I think it discourages fast, tdd test cycles. Most things seem to screw up grails while it's running, like adding a taglib, or anything really. The server restart problem wasn't solved at all. I'm starting to think going with Spring/Hibernate/Java is the only way to go. While there is a pretty big cost at startup, I know it'll eventually smooth out. It sucks I can't use a language like Scala... because idiomatically, it is so incompatible with Hibernate. This app is also not a run-of-the-mill UI over a database. It's got some of that, but it's not going to be a slouch. I am deathly scared of Grails now because of how crap it is in the Controller layer. Suggestions on what I can do?

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  • Issues accessing an object's array values - returns null or 0s

    - by PhatNinja
    The function below should return an array of objects with this structure: TopicFrequency = { name: "Chemistry", //This is dependent on topic data: [1,2,3,4,5,6,7,8,9,10,11,12] //This would be real data }; so when I do this: myData = this.getChartData("line"); it should return two objects: {name : "Chemistry", data : [1,2,3,4,51,12,0,0, 2,1,41, 31]} {name : "Math", data : [0,0,41,4,51,12,0,0, 2,1,41, 90]} so when I do console.log(myData); it's perfect, returns exactly this. However when I do console.log(myData[0].data) it returns all 0s, not the values. I'm not sure what this issues is known as, and my question is simple what is this problem known as? Here is the full function. Somethings were hardcoded and other variables (notable server and queryContent) removed. Those parts worked fine, it is only when manipulated/retreiving the returned array's values that I run into problems. Note this is async. so not sure if that is also part of the problem. getChartData: function (chartType) { var TopicsFrequencyArray = new Array(); timePairs = this.newIntervalSet("Month"); topicList = new Array("Chemistry", "Math");//Hard coded for now var queryCopy = { //sensitive information }; for (i = 0; i < topicList.length; i++) { var TopicFrequency = { name: null, data: this.newFilledArray(12, 0) }; j = 0; TopicFrequency.name = topicList[i]; while (j < timePairs.length) { queryCopy.filter = TopicFrequency.name; //additional queryCopy parameter changes made here var request = esri.request({ url: server, content: queryCopy, handleAs: "json", load: sucess, error: fail }); j = j + 1; function sucess(response, io) { var topicCountData = 0; query = esri.urlToObject(io.url); var dateString = query.query.fromDate.replace("%", " "); dateString = dateString.replace(/-/g, "/"); dateString = dateString.split("."); date = new Date(dateString[0]); dojo.forEach(response.features, function (feature) { if (feature.properties.count > 0) { topicCountData = feature.properties.count; } TopicFrequency.data[date.getMonth()] = topicCountData; }); } function fail(error) { j = j + 1; alert("There was an unspecified error with this request"); console.log(error); } } TopicsFrequencyArray.push(TopicFrequency); } },

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  • Trying to run multiple HTTP requests in parallel, but being limited by Windows (registry)

    - by Nailuj
    I'm developing an application (winforms C# .NET 4.0) where I access a lookup functionality from a 3rd party through a simple HTTP request. I call an url with a parameter, and in return I get a small string with the result of the lookup. Simple enough. The challenge is however, that I have to do lots of these lookups (a couple of thousands), and I would like to limit the time needed. Therefore I would like to run requests in parallel (say 10-20). I use a ThreadPool to do this, and the short version of my code looks like this: public void startAsyncLookup(Action<LookupResult> returnLookupResult) { this.returnLookupResult = returnLookupResult; foreach (string number in numbersToLookup) { ThreadPool.QueueUserWorkItem(lookupNumber, number); } } public void lookupNumber(Object threadContext) { string numberToLookup = (string)threadContext; string url = @"http://some.url.com/?number=" + numberToLookup; WebClient webClient = new WebClient(); Stream responseData = webClient.OpenRead(url); LookupResult lookupResult = parseLookupResult(responseData); returnLookupResult(lookupResult); } I fill up numbersToLookup (a List<String>) from another place, call startAsyncLookup and provide it with a call-back function returnLookupResult to return each result. This works, but I found that I'm not getting the throughput I want. Initially I thought it might be the 3rd party having a poor system on their end, but I excluded this by trying to run the same code from two different machines at the same time. Each of the two took as long as one did alone, so I could rule out that one. A colleague then tipped me that this might be a limitation in Windows. I googled a bit, and found amongst others this post saying that by default Windows limits the number of simultaneous request to the same web server to 4 for HTTP 1.0 and to 2 for HTTP 1.1 (for HTTP 1.1 this is actually according to the specification (RFC2068)). The same post referred to above also provided a way to increase these limits. By adding two registry values to [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings] (MaxConnectionsPerServer and MaxConnectionsPer1_0Server), I could control this myself. So, I tried this (sat both to 20), restarted my computer, and tried to run my program again. Sadly though, it didn't seem to help any. I also kept an eye on the Resource Monitor (see screen shot) while running my batch lookup, and I noticed that my application (the one with the title blacked out) still only was using two TCP connections. So, the question is, why isn't this working? Is the post I linked to using the wrong registry values? Is this perhaps not possible to "hack" in Windows any longer (I'm on Windows 7)? Any ideas would be highly appreciated :) And just in case anyone should wonder, I have also tried with different settings for MaxThreads on ThreadPool (everyting from 10 to 100), and this didn't seem to affect my throughput at all, so the problem shouldn't be there either.

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  • How does System.TraceListener prepend message with process name?

    - by btlog
    I have been looking at using System.Diagnostics.Trace for doing logging is a very basic app. Generally it does all I need it to do. The downside is that if I call Trace.TraceInformation("Some info"); The output is "SomeApp.Exe Information: 0: Some info". Initally this entertained me but no longer. I would like to just output "Some info" to console. So I thought writing a cusom TraceListener, rather than using the inbuilt ConsoleTraceListener, would solve the problem. I can see a specific format that I want all the text after the second colon. Here is my attempt to see if this would work. class LogTraceListener : TraceListener { public override void Write(string message) { int firstColon = message.IndexOf(":"); int secondColon = message.IndexOf(":", firstColon + 1); Console.Write(message); } public override void WriteLine(string message) { int firstColon = message.IndexOf(":"); int secondColon = message.IndexOf(":", firstColon + 1); Console.WriteLine(message); } } If I output the value of firstColon it is always -1. If I put a break point the message is always just "Some info". Where does all the other information come from? So I had a look at the call stack at the point just before Console.WriteLine was called. The method that called my WriteLine method is: System.dll!System.Diagnostics.TraceListener.TraceEvent(System.Diagnostics.TraceEventCache eventCache, string source, System.Diagnostics.TraceEventType eventType, int id, string message) + 0x33 bytes When I use Reflector to look at this message it all seems pretty straight forward. I can't see any code that changes the value of the string after I have sent it to Console.WriteLine. The only method that could posibly change the underlying string value is a call to UnsafeNativeMethods.EventWriteString which has a parameter that is a pointer to the message. Does anyone understand what is going on here and whether I can change the output to be just my message with out the additional fluff. It seems like evil magic that I can pass a string "Some info" to Console.WriteLine (or any other method for that matter) and the string that output is different.

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  • Best approach for using Scanner Objects in Java?

    - by devjeetroy
    Although I'm more of a C++/ASM guy, I have to work with java as a part of my undergrad course at college. Our teacher taught us input using Scanner(System.in), and told us that if multiple functions are were taking user input, it would be advisable that a single Scanner object is passed around so as to reduce chances of the input stream getting screwed up. Now using this approach has gotten me into a situation where I'm trying to use a Scanner.nextLine(), and this statement does not wait for user input. It just moves on to the following statement. I figured there may be some residual cr/lf or other characters in the Scanner that might not have been retrieved are causing the problem. Here is the code. while(lineScanner.hasNext()) { if(isPlaceHolder(temp = lineScanner.next())) { temp = temp.replace("<",""); temp = temp.replace(">", ""); System.out.print("Enter "+aOrA(temp.charAt(0)) +" " +temp + " : "); temp = consoleInput.nextLine(); } outputFileStream.print(temp + " "); } All of the code is inside a function which receives a Scanner object consoleInput. Ok, so what happens when i run it is that when the program enters the if() the first time, It carries out theSystem.out.print, does not wait for user input, and moves on to the second time that it enters the 'if' block. This time, it takes the input and the rest of the program operates normally. What is even more surprising is that when i check the output file created by the program, it is perfect, just as i want to be. Almost as if the first time input using the scanner is correct. I have solved this problem by creating a new system.in Scanner in the function itself, instead of receiving the Scanner object as a parameter. But I am still very curious to know what the hell is happening and why it couldn't be solved using a simple Scanner.reset(). Would it be better to just simply create a Scanner Object for each function? Thanks, Devjeet PS. Although I know how to take input using fileinputstreams and the like, we are not supposed to use it with the homework.

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  • Delphi / MySql : Problems escpaing strings

    - by mawg
    N00b here, having problems escaping strings. I used the QuotedStr() function - shouldn't that be enough. Unfortunately, the string that I am trying to quote is rather messy, but I will post it here in case anyone wants to paste it into WinMerge or KDiff3, etc. I am trying to store an entire Delphi form into the database, rather than into a .DFM file. It has only one field, a TEdit edit box. The debugger shows the form as text as 'object Form1: TScriptForm'#$D#$A' Left = 0'#$D#$A' Top = 0'#$D#$A' Align = alClient'#$D#$A' BorderStyle = bsNone'#$D#$A' ClientHeight = 517'#$D#$A' ClientWidth = 993'#$D#$A' Color = clBtnFace'#$D#$A' Font.Charset = DEFAULT_CHARSET'#$D#$A' Font.Color = clWindowText'#$D#$A' Font.Height = -11'#$D#$A' Font.Name = 'MS Sans Serif''#$D#$A' Font.Style = []'#$D#$A' OldCreateOrder = False'#$D#$A' SaveProps.Strings = ('#$D#$A' 'Visible=False')'#$D#$A' PixelsPerInch = 96'#$D#$A' TextHeight = 13'#$D#$A' object Edit1: TEdit'#$D#$A' Left = 192'#$D#$A' Top = 64'#$D#$A' Width = 121'#$D#$A' Height = 21'#$D#$A' TabOrder = 8'#$D#$A' end'#$D#$A'end'#$D#$A before calling QuotedStr() and ''object Form1: TScriptForm'#$D#$A' Left = 0'#$D#$A' Top = 0'#$D#$A' Align = alClient'#$D#$A' BorderStyle = bsNone'#$D#$A' ClientHeight = 517'#$D#$A' ClientWidth = 993'#$D#$A' Color = clBtnFace'#$D#$A' Font.Charset = DEFAULT_CHARSET'#$D#$A' Font.Color = clWindowText'#$D#$A' Font.Height = -11'#$D#$A' Font.Name = ''MS Sans Serif'''#$D#$A' Font.Style = []'#$D#$A' OldCreateOrder = False'#$D#$A' SaveProps.Strings = ('#$D#$A' ''Visible=False'')'#$D#$A' PixelsPerInch = 96'#$D#$A' TextHeight = 13'#$D#$A' object Edit1: TEdit'#$D#$A' Left = 192'#$D#$A' Top = 64'#$D#$A' Width = 121'#$D#$A' Height = 21'#$D#$A' TabOrder = 8'#$D#$A' end'#$D#$A'end'#$D#$A''' afterwards. The strange thing is that my complete command 'INSERT INTO designerFormDfm(designerFormDfmText) VALUES ("'object Form1: TScriptForm'#$D#$A' Left = 0'#$D#$A' Top = 0'#$D#$A' Align = alClient'#$D#$A' BorderStyle = bsNone'#$D#$A' ClientHeight = 517'#$D#$A' ClientWidth = 993'#$D#$A' Color = clBtnFace'#$D#$A' Font.Charset = DEFAULT_CHARSET'#$D#$A' Font.Color = clWindowText'#$D#$A' Font.Height = -11'#$D#$A' Font.Name = ''MS Sans Serif'''#$D#$A' Font.Style = []'#$D#$A' OldCreateOrder = False'#$D#$A' SaveProps.Strings = ('#$D#$A' ''Visible=False'')'#$D#$A' PixelsPerInch = 96'#$D#$A' TextHeight = 13'#$D#$A' object Edit1: TEdit'#$D#$A' Left = 192'#$D#$A' Top = 64'#$D#$A' Width = 121'#$D#$A' Height = 21'#$D#$A' TabOrder = 8'#$D#$A' end'#$D#$A'end'#$D#$A''");' executes in a MySql console, but not from Delphi, where I pass that command as parameter command to a function which ADOCommand.CommandText := command; ADOCommand.CommandType := cmdText; ADOCommand.Execute(); I can only assume that I am having problems escpaing sequences which contain single quotes (and QuotedStr() doesn't seem to escape backslahes(?!)) What am I doing that is obviously, glaringly wrong?

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  • Where are the function literals c++?

    - by academicRobot
    First of all, maybe literals is not the right term for this concept, but its the closest I could think of (not literals in the sense of functions as first class citizens). The idea is that when you make a conventional function call, it compiles to something like this: callq <immediate address> But if you make a function call using a function pointer, it compiles to something like this: mov <memory location>,%rax callq *%rax Which is all well and good. However, what if I'm writing a template library that requires a callback of some sort with a specified argument list and the user of the library is expected to know what function they want to call at compile time? Then I would like to write my template to accept a function literal as a template parameter. So, similar to template <int int_literal> struct my_template {...};` I'd like to write template <func_literal_t func_literal> struct my_template {...}; and have calls to func_literal within my_template compile to callq <immediate address>. Is there a facility in C++ for this, or a work around to achieve the same effect? If not, why not (e.g. some cataclysmic side effects)? How about C++0x or another language? Solutions that are not portable are fine. Solutions that include the use of member function pointers would be ideal. I'm not particularly interested in being told "You are a <socially unacceptable term for a person of low IQ>, just use function pointers/functors." This is a curiosity based question, and it seems that it might be useful in some (albeit limited) applications. It seems like this should be possible since function names are just placeholders for a (relative) memory address, so why not allow more liberal use (e.g. aliasing) of this placeholder. p.s. I use function pointers and functions objects all the the time and they are great. But this post got me thinking about the don't pay for what you don't use principle in relation to function calls, and it seems like forcing the use of function pointers or similar facility when the function is known at compile time is a violation of this principle, though a small one.

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  • How to infer the type of a derived class in base class?

    - by enzi
    I want to create a method that allows me to change arbitrary properties of classes that derive from my base class, the result should look like this: SetPropertyValue("size.height", 50); – where size is a property of my derived class and height is a property of size. I'm almost done with my implementation but there's one final obstacle that I want to solve before moving on, to describe this I will first have to explain my implementation a bit: Properties that can be modified are decorated with an attribute There's a method in my base class that searches for all derived classes and their decorated properties For each property I generate a "property modifier", a class that contains 2 delegates: one to set and one to get the value of the property. Property Modifiers are stored in a dictionary, with the name of the property as key In my base class, there is another dictionary that contains all property-modifier-dictionaries, with the Type of the respective class as key. What the SetPropertyValue method does is this: Get the correct property-modifier-dictionary, using the concrete type of the derived class (<- yet to solve) Get the property modifier of the property to change (e.g. of the property size) Use the get or set delegate to modify the property's value Some example code to clarify further: private static Dictionary<RuntimeTypeHandle, object> EditableTypes; //property-modifier-dictionary protected void SetPropertyValue<T>(EditablePropertyMap<T> map, string property, object value) { var property = map[property]; // get the property modifier property.Set((T)this, value); // use the set delegate (encapsulated in a method) } In the above code, T is the Type of the actual (derived) class. I need this type for the get/set delegates. The problem is how to get the EditablePropertyMap<T> when I don't know what T is. My current (ugly) solution is to pass the map in an overriden virtual method in the derived class: public override void SetPropertyValue(string property, object value) { base.SetPropertyValue((EditablePropertyMap<ExampleType>)EditableTypes[typeof(ExampleType)], property, value); } What this does is: get the correct dictionary containing the property modifiers of this class using the class's type, cast it to the appropiate type and pass it to the SetPropertyValue method. I want to get rid of the SetPropertyValue method in my derived class (since there are a lot of derived classes), but don't know yet how to accomplish that. I cannot just make a virtual GetEditablePropertyMap<T> method because I cannot infer a concrete type for T then. I also cannot acces my dictionary directly with a type and retrieve an EditablePropertyMap<T> from it because I cannot cast to it from object in the base class, since again I do not know T. I found some neat tricks to infere types (e.g. by adding a dummy T parameter), but cannot apply them to my specific problem. I'd highly appreciate any suggestions you may have for me.

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  • How to use jaxb_commons plugins from maven

    - by user243155
    I'm trying to use a jaxb plugin to insert a interface into a choice element generating the classes from maven. The problem is that I can't seem to figure out how to do so from maven, the repository isn't clear from the documentation and the only example (bellow) doesn't work, it seems to ignore the plugin (maven reports no error about not finding it) or the plugin doesn't have all the adds-ons currently listed in the project documentation: <plugin> <groupId>org.jvnet.jaxb2.maven2</groupId> <artifactId>maven-jaxb2-plugin</artifactId> <version>0.6.1</version> <executions> <execution> <goals> <goal>generate</goal> </goals> </execution> </executions> <configuration> <generatePackage>br.com.wonder.nfe.xml</generatePackage> <args> <arg>-Xifins</arg> </args> <plugins> <plugin> <groupId>org.jvnet.jaxb2_commons</groupId> <artifactId>basic</artifactId> <version>0.4.1.5</version> </plugin> </plugins> </configuration> </plugin> I have these in the root pom: <pluginRepositories> <pluginRepository> <id>maven2-repository.dev.java.net</id> <url>http://download.java.net/maven/2</url> </pluginRepository> <pluginRepository> <id>maven-repository.dev.java.net</id> <name>Java.net Maven 1 Repository (legacy)</name> <url>http://download.java.net/maven/1</url> <layout>legacy</layout> </pluginRepository> </pluginRepositories> Running that gives: Error while setting CmdLine options '[-Xifins, -episode, /home/administrador/JavaApp/wnfe3/wnfe-ejb/target/generated-sources/xjc/META-INF/sun-jaxb.episode]'! Embedded error: unrecognized parameter -Xifins

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  • How come Java doesn't accept my LinkedList in a Generic, but accepts its own?

    - by master chief
    For a class assignment, we can't use any of the languages bultin types, so I'm stuck with my own list. Anyway, here's the situation: public class CrazyStructure <T extends Comparable<? super T>> { MyLinkedList<MyTree<T>> trees; //error: type parameter MyTree is not within its bound } However: public class CrazyStructure <T extends Comparable<? super T>> { LinkedList<MyTree<T>> trees; } Works. MyTree impleements the Comparable interface, but MyLinkedList doesn't. However, Java's LinkedList doesn't implement it either, according to this. So what's the problem and how do I fix it? MyLinkedList: public class MyLinkedList<T extends Comparable<? super T>> { private class Node<T> { private Node<T> next; private T data; protected Node(); protected Node(final T value); } Node<T> firstNode; public MyLinkedList(); public MyLinkedList(T value); //calls node1.value.compareTo(node2.value) private int compareElements(final Node<T> node1, final Node<T> node2); public void insert(T value); public void remove(T value); } MyTree: public class LeftistTree<T extends Comparable<? super T>> implements Comparable { private class Node<T> { private Node<T> left, right; private T data; private int dist; protected Node(); protected Node(final T value); } private Node<T> root; public LeftistTree(); public LeftistTree(final T value); public Node getRoot(); //calls node1.value.compareTo(node2.value) private int compareElements(final Node node1, final Node node2); private Node<T> merge(Node node1, Node node2); public void insert(final T value); public T extractMin(); public int compareTo(final Object param); }

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  • This code appears to achieve the return of a null reference in C++

    - by Chuck
    Hi folks, My C++ knowledge is somewhat piecemeal. I was reworking some code at work. I changed a function to return a reference to a type. Inside, I look up an object based on an identifier passed in, then return a reference to the object if found. Of course I ran into the issue of what to return if I don't find the object, and in looking around the web, many people claim that returning a "null reference" in C++ is impossible. Based on this advice, I tried the trick of returning a success/fail boolean, and making the object reference an out parameter. However, I ran into the roadblock of needing to initialize the references I would pass as actual parameters, and of course there is no way to do this. I retreated to the usual approach of just returning a pointer. I asked a colleague about it. He uses the following trick quite often, which is accepted by both a recent version of the Sun compiler and by gcc: MyType& someFunc(int id) { // successful case here: // ... // fail case: return *static_cast<MyType*>(0); } // Use: ... MyType& mt = somefunc(myIdNum); if (&mt) // test for "null reference" { // whatever } ... I have been maintaining this code base for a while, but I find that I don't have as much time to look up the small details about the language as I would like. I've been digging through my reference book but the answer to this one eludes me. Now, I had a C++ course a few years ago, and therein we emphasized that in C++ everything is types, so I try to keep that in mind when thinking things through. Deconstructing the expression: "*static_cast(0);", it indeed seems to me that we take a literal zero, cast it to a pointer to MyType (which makes it a null pointer), and then apply the dereferencing operator in the context of assigning to a reference type (the return type), which should give me a reference to the same object pointed to by the pointer. This sure looks like returning a null reference to me. Any advice in explaining why this works (or why it shouldn't) would be greatly appreciated. Thanks, Chuck

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  • php functions within functions.

    - by Adamski
    Hi all, ihave created a simple project to help me get to grips with php and mysql, but have run into a minor issue, i have a working solution but would like to understand why i cannot run this code successfully this way, ill explain: i have a function, function fetch_all_movies(){ global $connection; $query = 'select distinct * FROM `'.TABLE_MOVIE.'` ORDER BY movieName ASC'; $stmt = mysqli_prepare($connection,$query); mysqli_execute($stmt); mysqli_stmt_bind_result($stmt,$id,$name,$genre,$date,$year); while(mysqli_stmt_fetch($stmt)){ $editUrl = "index.php?a=editMovie&movieId=".$id.""; $delUrl = "index.php?a=delMovie&movieId=".$id.""; echo "<tr><td>".$id."</td><td>".$name."</td><td>".$date."</td><td>".get_actors($id)."</td><td><a href=\"".$editUrl."\">Edit</a> | <a href=\"".$delUrl."\">Delete</a></td></tr>"; } } this fetches all the movies in my db, then i wish to get the count of actors for each film, so i pass in the get_actors($id) function which gets the movie id and then gives me the count of how many actors are realted to a film. here is the function for that: function get_actors($movieId){ global $connection; $query = 'SELECT DISTINCT COUNT(*) FROM `'.TABLE_ACTORS.'` WHERE movieId = "'.$movieId.'"'; $result = mysqli_query($connection,$query); $row = mysqli_fetch_array($result); return $row[0]; } the functions both work perfect when called separately, i just would like to understand when i pass the function inside a function i get this warning: Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in /Applications/MAMP/htdocs/movie_db/includes/functions.inc.php on line 287 could anyone help me understand why? many thanks.

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  • Passing custom info to mongrel_rails start

    - by whaka
    One thing I really don't understand is how I can pass custom start-up options to a mongrel instance. I see that a common approach is the use environment variables, but in my environment this is not going to work because my rails application serves many different clients. Much code is shared between clients, but there are also many differences which I implement by subclassing controllers and views to overload or extend existing features or introduce new ones. To make this all work, I simply add the paths to client specific modules the module load path ($:). In order to start the application for a particular client, I could now use an environment variable like say, TARGET=AMAZONE. Unfortunately, on some systems I'm running multiple mongrel clusters, each cluster serving a different client. Some of these systems run under Windows and to start mongrel I installed mongrel_services. Clearly, this makes my environment variable unsuitable. Passing this extra bit of data to the application is proving to be a real challenge. For a start, mongrel_rails service_install will reject any [custom] command line parameters that aren't documented. I'm not too concerned as installing the services using the install program is trivial. However, even if I manage to install mongrel_services such that when run it passes the custom command line option --target to mongrel_rails start, I get an error because mongrel_rails doesn't recognize the switch. So here were the things I looked at: Pass an extra parameter: mongrel_rails start --target XYZ ... use a config file and add target:XYZ, then do: mongrel_rails start -C x:\myapp\myconfig.yml modify the file: Ruby\lib\ruby\gems\1.8\gems\mongrel-1.1.5-x86-mswin32-60\lib\mongrel\command.rb Perhaps I can use the --script option, but all docs that I found on it were for Unix 1 and 2 simply don't work. I played with 4 but never managed it to do anything. So I had no choice but to go with 3. While it is relatively simple, I hate changing ruby library code. Particularly disappointing is that 2 doesn't work. I mean what is so unreasonable about adding other [custom] options in the config file? Actually I think this is a fundamental piece that is missing in rails. Somehow, the application should be able to register and access command line arguments it expects. If anybody has a good idea how to do this more elegantly using the current infrastructure, I have a chocolate fish to give away!!!

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  • Java exercise - display table with 2d array

    - by TheHacker66
    I'm struggling to finish a java exercise, it involves using 2d arrays to dinamically create and display a table based on a command line parameter. Example: java table 5 +-+-+-+-+-+ |1|2|3|4|5| +-+-+-+-+-+ |2|3|4|5|1| +-+-+-+-+-+ |3|4|5|1|2| +-+-+-+-+-+ |4|5|1|2|3| +-+-+-+-+-+ |5|1|2|3|4| +-+-+-+-+-+ What i have done so far: public static void main(String[] args) { int num = Integer.parseInt(args[0]); String[][] table = new String[num*2+1][num]; int[] numbers = new int[num]; int temp = 0; for(int i=0; i<numbers.length; i++) numbers[i] = i+1; // wrong for(int i=0; i<table.length; i++){ for(int j=0; j<num;j++){ if(i%2!=0){ temp=numbers[0]; for(int k=1; k<numbers.length; k++){ numbers[k-1]=numbers[k]; } numbers[numbers.length-1]=temp; for(int l=0; l<numbers.length; l++){ table[i][j] = "|"+numbers[l]; } } else table[i][j] = "+-"; } } for(int i=0; i<table.length; i++){ for(int j=0; j<num; j++) System.out.print(table[i][j]); if(i%2==0) System.out.print("+"); else System.out.print("|"); System.out.println();} } This doesn't work, since it prints 1|2|3|4 in every row, which isn't what i need. I found the issue, and it's because the first for loop changes the array order more times than needed and basically it returns as it was at the beginning. I know that probably there's a way to achieve this by writing more code, but i always tend to nest as much as possible to "optimize" the code while i write it, so that's why i tried solving this exercise by using less variables and loops as possible. Thanks in advance for your help!

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  • Is order of parameters for database Command object really important?

    - by nawfal
    I was debugging a database operation code and I found that proper UPDATE was never happening though the code never failed as such. This is the code: condb.Open(); OleDbCommand dbcom = new OleDbCommand("UPDATE Word SET word=?,sentence=?,mp3=? WHERE id=? AND exercise_id=?", condb); dbcom.Parameters.AddWithValue("id", wd.ID); dbcom.Parameters.AddWithValue("exercise_id", wd.ExID); dbcom.Parameters.AddWithValue("word", wd.Name); dbcom.Parameters.AddWithValue("sentence", wd.Sentence); dbcom.Parameters.AddWithValue("mp3", wd.Mp3); But after some tweaking this worked: condb.Open(); OleDbCommand dbcom = new OleDbCommand("UPDATE Word SET word=?,sentence=?,mp3=? WHERE id=? AND exercise_id=?", condb); dbcom.Parameters.AddWithValue("word", wd.Name); dbcom.Parameters.AddWithValue("sentence", wd.Sentence); dbcom.Parameters.AddWithValue("mp3", wd.Mp3); dbcom.Parameters.AddWithValue("id", wd.ID); dbcom.Parameters.AddWithValue("exercise_id", wd.ExID); Why is it so important that the parameters in WHERE clause has to be given the last in case of OleDb connection? Having worked with MySQL previously, I could (and usually do) write parameters of WHERE clause first because that's more logical to me. Is parameter order important when querying database in general? Some performance concern or something? Is there a specific order to be maintained in case of other databases like DB2, Sqlite etc? Update: I got rid of ? and included proper names with and without @. The order is really important. In both cases only when WHERE clause parameters was mentioned last, actual update happened. To make matter worse, in complex queries, its hard to know ourselves which order is Access expecting, and in all situations where order is changed, the query doesnt do its intended duty with no warning/error!!

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