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  • Sending arbitrarily long string over Java TCP socket

    - by bibismcbryde
    I have an Android app that communicates over a TCP socket with a server I wrote. The method I'm using now to read and write output works fine for smaller strings (up to 60kB) but I get an exception thrown when the string is much longer than that. Here is the relevant part of what I have for the server and client: Server: DataInputStream dis = null; DataOutputStream dos = null; try { dis = new DataInputStream(server.getInputStream()); dos = new DataOutputStream(server.getOutputStream()); String input = ""; input = dis.readUTF(); handle_input info = new handle_input(input, id); String xml = info.handle(); dos.writeUTF(xml); server.close(); } Client: Socket socket = null; DataOutputStream dos = null; DataInputStream dis = null; Boolean result; try { socket = new Socket(ip, port); dos = new DataOutputStream(socket.getOutputStream()); dis = new DataInputStream(socket.getInputStream()); dos.writeUTF(the_text); String in = ""; while (in.equals("")) { in += dis.readUTF(); } } How can I modify it to deal with potentially enormous Strings? I've been looking around and can't seem to find a clear answer. Thanks.

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  • C# property exactly the same, defined in two places

    - by Sarah Vessels
    I have the following classes: Defect - represents a type of data that can be found in a database FilterQuery - provides a way of querying the database by setting simple Boolean filters Both Defect and FilterQuery implement the same interface: IDefectProperties. This interface specifies particular fields that are in the database. Different classes have methods that return lists of Defect instances. With FilterQuery, you specify some filters for the particular properties implemented as part of IDefectProperties, and then you run the query and get back a list of Defect instances. My problem is that I end up implementing some properties exactly the same in FilterQuery and Defect. The two are inherently different classes, they just share some of the same properties. For example: public DateTime SubmitDateAsDate { get { return DateTime.Parse(SubmitDate); } set { SubmitDate = value.ToString(); } } This is a property required by IDefectProperties that depends on a different property, SubmitDate, which returns a string instead of a DateTime. Now SubmitDate is implemented differently in Defect and FilterQuery, but SubmitDateAsDate is exactly the same. Is there a way that I can define SubmitDateAsDate in only place, but both Defect and FilterQuery provide it as a property? FilterQuery and Defect already inherit from two different classes, and it wouldn't make sense for them to share an ancestor anyway, I think. I am open to suggestions as to my design here as well.

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  • 2 bucks for !! java basic question

    - by Max
    How can I get a specific value from an object? I'm trying to get a value of an instance for eg. ListOfPpl newListOfPpl = new ListOfPpl(id, name, age); Object item = newListOfPpl; How can I get a value of name from an Object item?? Even if it is easy or does not interest you can anyone help me?? Edited: I was trying to build a binary tree contains the node of ListOfPpl, and need to sort it in the lexicographic. Here's my code for insertion on the node. Any clue?? public void insert(Object item){ Node current = root; Node follow = null; if(!isEmpty()){ root = new Node(item, null, null); return; }boolean left = false, right = false; while(current != null){ follow = current; left = false; right = false; //I need to compare and sort it if(item.compareTo(current.getFighter()) < 0){ current = current.getLeft(); left = true; }else { current = current.getRight(); right = true; } }if(left) follow.setLeft(new Node(item, null, null)); else follow.setRight(new Node(item, null, null)); }

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  • Printing distinct integers in an array

    - by ???
    I'm trying to write a small program that prints out distinct numbers in an array. For example if a user enters 1,1,3,5,7,4,3 the program will only print out 1,3,5,7,4. I'm getting an error on the else if line in the function checkDuplicate. Here's my code so far: import javax.swing.JOptionPane; public static void main(String[] args) { int[] array = new int[10]; for (int i=0; i<array.length;i++) { array[i] = Integer.parseInt(JOptionPane.showInputDialog("Please enter" + "an integer:")); } checkDuplicate (array); } public static int checkDuplicate(int array []) { for (int i = 0; i < array.length; i++) { boolean found = false; for (int j = 0; j < i; j++) if (array[i] == array[j]) { found = true; break; } if (!found) System.out.println(array[i]); } return 1; } }

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  • MVC and binding to List of Checkboxes

    - by Josh
    Here is my problem. I have a list of models that are displayed to the user. On the left is a checkbox for each model to indicate that the user wants to choose this model (in this case, we're building products a user can add to their shopping cart). The model has no concept of being chosen...it strictly has information about the product in question. I've talked with a few other developers after having gone through and the best I could come up with is getting the formcollection and string parsing the key values to determine whether the checkbox is checked or not. This doesn't seem ideal. I was thinking there would be something more strongly bound, but I can't figure out a way to do it. I tried creating another model that had a boolean property to represent being checked and a property of the model and passing a list of that model type to the view and creating a ActionResult on the controller that accepts a list of the new model / checked property, but it comes back null. Am I just thinking too much like web forms and should just continue on with parsing checkbox values? Here's what I've done for wrapping the models inside a collection: public class SelectableCollection[T] : IList[T] {} public class SelectableTrack{ public bool IsChecked{get;set;} public bool CurrentTrack{get;set;} } For the view, I inherit from ViewPage[SelectableCollection[SelectableTrack]] For the controller, I have this as the ActionResult: [HttpPost] public ActionResult SelectTracks(SelectableCollection sc) { return new EmptyResult(); } But when I break inside the ActionResult, the collection is null. Any reason why it isn't coming through?

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  • Should I use a class in this: Reading a XML file using lxml.

    - by PulpFiction
    Hi everyone. This question is in continuation to my previous question, in which I asked about passing around an ElementTree. I need to read the XML files only and to solve this, I decided to create a global ElementTree and then parse it wherever required. My question is: Is this an acceptable practice? I heard global variables are bad. If I don't make it global, I was suggested to make a class. But do I really need to create a class? What benefits would I have from that approach. Note that I would be handling only one ElementTree instance per run, the operations are read-only. If I don't use a class, how and where do I declare that ElementTree so that it available globally? (Note that I would be importing this module) Please answer this question in the respect that I am a beginner to development, and at this stage I can't figure out whether to use a class or just go with the functional style programming approach.

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  • Multisite Enabling a Table

    - by Joe Fitzgibbons
    I am creating a table (table A) that will have a number of columns(of course) and there will be another table (table B) that holds metadata associated to rows in table A. I am working with a multi site implementation that has one database for the whole shabang. Rows in table A could belong to any number of sites but must belong to at least one. The problem I have is I am not sure what the best practice is for defining what site each row in table A belongs to. I want performance and scalability. There is no finite number of sites going forward. Rows in table A could belong to any number of sites in the future. Right now there are only 3. My initial thoughts are to have a primary site ID in Table A and then metadata in table B will have rows defining additional sites as needed. Another thought is to have a column in Table A for each site and it is a boolean as to wether it belongs to that site. Lastly I have thought about having another table to map rows in Table A to each site. What is the best way to associate rows in a table with any number of sites with performance and scalability in mind?

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  • what are good ways to implement search and search results using ajax?

    - by Amr ElGarhy
    i have some text box in a page and in the same page there will be a table 'grid' like for holding the search result. When the user start editing and of the textbox above, the search must start by sending all textboxs values to the server 'ajax', and get back with the results to fill the below grid. Notes: This grid should support paging, sorting by clicking on headers and it will contains some controls beside the results such as checkboxs for boolean values and links for opening details in another page. I know many ways to do this some of them are: 1- updatepanel around all of these controls and thats it "fast dirty solution" 2- send the search criteria using ajax request using JQuery post function for example and get back the JSON result, and using a template will draw the grid "clean but will take time to finish and will be harder to edit later". 3- .... My question is: What do you think will be the best choice to implement this scenario? because i face this scenario too much, and want to know which implementation will be better regarding performance, optimization, and time to finish. I just want to know your thoughts about this issue.

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  • task_current redundant field

    - by user341940
    Hi, I'm writing a kernel module that reads from a /proc file. When someone writes into the /proc file the reader will read it, but if it reads again while there is no "new" write, it should be blocked. In order to remember if we already read, i need to keep a map of the latest buffer that process read. To avoid that, I was told that there might be some redundant field inside the current- (task_struct struct) that i can use to my benefits in order to save some states on the current process. How can I find such fields ? and how can i avoid them being overwritten ? I read somewhere that i can use the offset field inside the struct in order to save my information there and i need to block lseek operations so that field will stay untouched. How can I do so ? and where is that offset field, i can't find it inside the task_Struct. Thanks and I need to save for each process some information in order to map it against other information. I can write a ma

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  • Two forms but only 1 jsp file

    - by joshft91
    Here's what I've got going on. I have one .jsp file. However, I have two forms with multiple inputs inside those forms. What is the best way to detect that one form was submitted but not the other? Here's an example: I have this form: <form name = "login" action="index.jsp" method="get"> Username: <input id="username" name="username" type="text"/><br/> Password: <input id="password" name="password" type="password"/> <input type="submit" Value="Login" ></input> </form> If that button is clicked, I'd like to run this code: String username = request.getParameter("username"); String password = request.getParameter("password"); if((username!= null && !username.trim().equals("")) && (password != null && !username.trim().equals(""))) { DBentry DBentry=new DBentry(); boolean flag = DBentry.isTaken(username); if(flag) {%><script type="text/javascript">alert("Login Successful!");</script><% } else { %><script type="text/javascript">alert("Unrecognized username. Please register!");</script><% } } else { %><script type="text/javascript">alert("Please enter both a username and password!");</script><% } Further down I would have something exactly like it but submitting a different form. Thanks!

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  • What is a truly empty std::vector in C++?

    - by RyanG
    I've got a two vectors in class A that contain other class objects B and C. I know exactly how many elements these vectors are supposed to hold at maximum. In the initializer list of class A's constructor, I initialize these vectors to their max sizes (constants). If I understand this correctly, I now have a vector of objects of class B that have been initialized using their default constructor. Right? When I wrote this code, I thought this was the only way to deal with things. However, I've since learned about std::vector.reserve() and I'd like to achieve something different. I'd like to allocate memory for these vectors to grow as large as possible because adding to them is controlled by user-input, so I don't want frequent resizings. However, I iterate through this vector many, many times per second and I only currently work on objects I've flagged as "active". To have to check a boolean member of class B/C on ever iteration is silly. I don't want these objects to even BE there for my iterators to see when I run through this list. Is reserving the max space ahead of time and using push_back to add a new object to the vector a solution to this?

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  • Kill process started with System.Diagnostic.Process.Start("FileName")

    - by PedroC88
    Hello; I am trying to create an app that will perform actions on specific times (much like the Windows Task Scheduler). I am currently using Process.Start() to lunch the file (or exe) required by the task. I am initiating a process by calling a file (an .mp3) and the process starts WMP (since it is the default application), so far so good. Now I wan't to kill that process. I know that it is normal behavior for the Process.Start(string, string) to return nothing (null in C#) in this case. So I am asking how can i close WMP when I called it through Process.Start(string, string)?? Edit: Please note that I am not opening WMP directly with Process.Start() and this is the line with which I run the process: VB: Me._procs.Add(Process.Start(Me._procInfo)) C#: this._procs.Add(Process.Start(this._procInfo)) _procInfo is a ProcessStartInfo instance. _procInfo.FileName is "C:\route\myFile.mp3". That is why WMP opens. In any case, all of the Start() methods, except for the instance-one which returns a boolean, return nothing (null in C#), because WMP is not the process that was directly created (please note that WMP is run and the song does play).

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  • Why extremely occasionally will one of bof/eof be true for a new non-empty recordset

    - by jjb
    set recordsetname = databasename.openrecordset(SQLString) if recordsetname.bof <> true and recordsetname.eof <> true then 'do something end if 2 questions : the above test can evaluate to false incorrectly but only extremely rarely (I've had one lurking in my code and it failed today, I believe for the first time in 5 years of daily use-that's how I found it). Why very occasionally will one of bof/eof be true for a non-empty recordset. It seems so rare that I wonder why it occurs at all. Is this a foolproof replacement: if recordsetname.bof <> true or recordsetname.eof <> true then Edit to add details of code : Customers have orders, each order begins with a BeginOrder item and end with an EndOrder item and in between are the items in the order. The SQL is: ' ids are autoincrement long integers ' SQLString = "select * from Orders where type = OrderBegin or type = OrderEnd" Dim OrderOpen as Boolean OrderOpen = False Set rs = db.Openrecordset(SQLString) If rs.bof <> True And rs.eof <> True Then myrec.movelast If rs.fields("type").value = BeginOrder Then OrderOpen = True End If End If If OrderOpen F False Then 'code here to add new BeginOrder Item to Orders table ' End If ShowOrderHistory 'displays the customer's Order history ' In this case which looks this this BeginOrder Item a Item b ... Item n EndOrder BeginOrder Item a Item b ... Item n EndOrder BeginOrder Item a item b ... Item m BeginOrder <----should not be there as previous order still open

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  • Share variable across site ASP.NET

    - by Anders
    I have a class isSearching with a single boolean property in a 'functions' file in my webapp. On my search page, I have a variable oSearchHandler declared as a Public Shared variable. How can I access the contents of oSearchHandler on other pages in my webapp? Code with Session.... 'search.aspx Public Function oSearchString(ByVal oTextBoxName As String) As String For Each oKey As String In Request.Form.AllKeys If oKey.Contains(oTextBoxName) Then Session.Add("searching", True) Session.Add("search-term", Request.Form(oKey)) Return Request.Form(oKey) End If Next Return "" End Function 'theMaster.master <% If Session("searching") Then %><ul style="float: right;"> <li> <div class="gsSearch"> <asp:TextBox ID="searchbox" runat="server"></asp:TextBox> </div> </li> <li> <div class="gsSearch"> <asp:Button ID="searchbutton" runat="server" Text="search" UseSubmitBehavior="true" PostBackUrl="search.aspx" CssClass="searchBtn" /> </div> </li> </ul> <% End If %> I think that the session will work just fine.

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  • C function prototype: void f(). Is it recommended?

    - by ycalleecharan
    Hi, I'm learning C and I saw in a book that a function prototype has the form void f() and in the function declaration or in the calling function, the f function takes arguments. Thus In the function declaration we have something like void f(long double y[], long double A) and in the calling function is f(y, A). The function is doing operations on the array y i.e. when the function is called, some elements in the array y are changing. A is just a constant numerical value that doesn't change. I have two questions: If defining the function prototype at the top in the program as void f() a good practice? Or is it better to put it as void f(long double y[], long double A) as in the function declaration? The called function f is changing elements in the array y. Is void the right return type? The program is working fine as such with the void as described. Or should I change all my "voids" to "long double". I'm working with long double as I need as much precision as possible though on my machine both double and long double gives me 15 precision digits. Thanks a lot

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  • PHP function: find argument's variable name, and function calls line number

    - by Majid
    I want to do something like this for simplifying logging operations. Any idea what I should put in for ?[1]? and ?[2]?? function log_var($var) { $line = ?[1]?; $var_name = ?[2]?; $line--; $filepath = 'log-' . date('Y-m-d'). '.txt'; $message = "$line, $var_name = $var\n"; $fp = fopen($filepath, "a"); fwrite($fp, $message); fclose($fp); @chmod($filepath, 0666); return TRUE; } This how I'd use the function in code (numbers are assumed to be line numbers in actual code): 23 $a = 'hello'; 24 log_var($a); 25 $b = 'bye'; 26 log_var($b); And this is what I want to be written to the log file: 23, a = hello 25, b = bye

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  • How to add a checkbox for each row in Rails 3.2 index page?

    - by user938363
    We would like to add a checkbox to each row on Rails index page to flag for the row. This checkbox is not part of the object (no checkbox boolean in database). When the index page shows, a user can check the box to trigger an event for the row in following process: #objects/checkbox_index.html.erb <table> <tr> <th>CheckBox</th> <th>Object Name</th> <th>Object ID</th> </tr> <%= @objects.each do |obj| %> <tr> <td><%= checkbox %></td> <td><%= obj.name %></td> <td><%= obj.id %></td> </tr> <% end %> </table> In controller, the process will be like this: @objects.each do |obj| some_event if obj.checked end There are a couple of questions we don't quite understand: 1. How to declare an array checkbox variable on the form and link it to each row of obj? We have been using `attr_accessor` to declare var for a form. 2. How to retrieve each row on checkbox_index form and pass them back to controller? We are using simple_form for new/edit. Can anyone point me towards any good examples of this sort of behavior, or suggest what we should be thinking about? Many Thanks.

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  • Using Gtk.TreeDragSource.drag_data_get()

    - by knutsondc
    I have a simple Gtk.TreeView with a Gtk.ListStore with four columns as the model. I want to be able to drag and drop rows within the TreeView and track row insertions, changes and deletions as they happen so I can implement undo/redo to drag and drop operations. I'm using PyGObject 3 and Python 3.2. I thought that using methods under the Gtk.TreeDragSource and Gtk.TreeDragDest interfaces would suit my needs perfectly, with Gtk.TreeDragSource.drag_data_get() in my drag_data_get handler and Gtk.TreeDragDest.drag_data_received() or Gtk.tree_get_row_drag_data() in my drag_data_received handler. Basically, what I've tried looks something like this: def drag_data_received(self, treeview, context, x, y, selection, info, time): treeselection = tv.get_selection() model, my_iter = treeselection.get_selected() path = model.get_path(my_iter) result = Gtk.TreeDragSource.drag_data_get(path, selection) def drag_data_received(self, tv, context, x, y, selection, info, time): result, model, row = Gtk.tree_get_row_drag_data(selection) my_iter = model.get_iter(row) data = [model.get_value(my_iter, i) for i in range(model.get_n_columns())] drop_info = tv.get_dest_row_at_pos(x, y) if drop_info: path, position = drop_info my_iter = model.get_iter(path) if (position == Gtk.TreeViewDropPosition.BEFORE or position == Gtk.TreeViewDropPosition.INTO_OR_BEFORE): model.insert_before(my_iter, [data]) else: model.insert_after(my_iter, [data]) else: model.append([data]) if context.get_actions() == Gdk.DragAction.MOVE|Gdk.DragAction.DEFAULT: context.finish(True, True, time) return This fails spectacularly - when Python hits the call to Gtk.TreeDragSource.drag_data_get(), Python crashes and my program window swiftly disappears. I don't even get to the drag_data_received handler. Can anyone point me to some example code showing how these methods using the TreeDragSource and TreeDragDest interfaces work? Any help much appreciated!

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  • how to start activity of the positive button?

    - by Wisnuardi
    when I click an item in maps, it will appears positive button that reads "Route to". Question, how do I start activity from that positive button? I also use like this, dialog.setPositiveButton("Tampilkan Rute", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int Button) { Intent i = new Intent(this, Rute.class); startActivity(i); } }); to startactivity into Rute class but it always say "remove argument to match intent()" then I don't know what to do. here is my code @Override protected boolean onTap(int index) { OverlayItem item = items.get(0); AlertDialog.Builder dialog = new AlertDialog.Builder(mContext); dialog.setTitle(item.getTitle()); dialog.setMessage(item.getSnippet()); dialog.setPositiveButton("Tampilkan Rute", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int Button) { Intent i = new Intent(this, Rute.class); startActivity(i); } }); dialog.setNegativeButton("Kembali", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int Button) { dialog.cancel(); } }); dialog.show(); return true; } Any suggestions will be greatly appreciated. Thank's i'm sorry if my english is bad :(

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  • self-destructing objects in php5?

    - by user151841
    I am working on a class in php that is basically an interface to a database row. I wanted to create a delete() method that would 1. delete the database row and 2. destroy the instance of itself so that further attempts to manipulate the row via the object would throw warnings. Doing some googling, it seems that, in php5, it's not possible for an object to unset itself. http://bugs.php.net/bug.php?id=36971 In fact they discuss the very situation I was wanting to do :( So how should I proceed? I could make boolean flag as a class property, for whether the row still exists, and have each operation check that flag and throw an error if the row has been deleted. This maintains the oo structure of code, so I would have $objDbRow->delete(); But then I have to put checks at the beginning of each method. Or, I could implement a __destruct method that deletes the row. But that would seem counter-intuitive to me; if I saw in code unset($objDbRow); All I would suspect that's happening is that the object is being discarded, not that a row is being deleted. So that to me would seem like bad practice.

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  • dm_exec_query_stats returning stale data?

    - by VoiceOfUnreason
    I've been testing my app on a SQL Server 2005 database, and am trying to establish a preliminary picture of the query performance using sys.dm_exec_query_stats. Problem: there's a particular query that I'm interested in, because total_elapsed_time and last_elapsed_time are both large numbers. When I tickle my app to invoke that query (this runs successfully), then refresh my view of the stats, I find that 1) execution_count has incremented (expected) 2) last_execution_time has updated to now (expected) 3) last_elapsed_time is still a large value (not expected - I anticipated a new value) 4) total_elapsed_time is unchanged (contradiction?) If last_elapsed_time refers to the execution that happened @ last_execution_time, then the total_elapsed_time should have increased? This documentation: http://msdn.microsoft.com/en-us/library/ms189741(SQL.90).aspx tells me that last_execution_time is the last time the plan was executed, and last_elapsed_time comes from the "most recently executed plan", but doesn't tell me why those might be different. The query itself is uncomplicated (SELECT/WHERE/ORDER BY - parameters appearing in the where clause, but no clever operations), the table has maybe 25 rows in it right now. Questions: 1) What's the real relationship between execution_count, last_execution_time, and last_elapsed_time? 2) Where is the documentation of this relationship (manual, third party book, blog, bug ticket, stone tablets...) ?

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  • Just a small help about switch's use

    - by Laurent Fournier
    If an answer on this already exist, my apologies i've not found on this question... is this statement correct if i want presice actions on integers from -2 to 0, and for those between 1 and 6 apply the same methods with only my integer who'll change ? Like this: public void setCaseGUI(Point pt, int i, boolean b){ plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setSelected(b); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setIcon(null); switch(i) { case -2: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText("F"); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(Color.red); break; case -1: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText("B"); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(Color.red); break; case 0: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText(""); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(null); break; case 1: case 2: case 3: case 4: case 5: case 6: case 7: case 8: plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setText(String.valueOf(i)); plateau.cellule[(int)pt.getAbs()][(int)pt.getOrd()].setForeground(null); break; default: System.out.println("Erreur de changement d'état/case !"); } } Please don't be too harsh on me i've started to learn dev only a few month ago

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  • php mysql_fetch_array() error

    - by user1877823
    I am getting this error while i am trying to delete a record the query is working but this line remains on the page. i want to echo "Deleted" written in the while should show up but the while loop is not working, i have tried and searched alot nothing helps! mysql_fetch_array() expects parameter 1 to be resource, boolean given in delete.php on line 27 delete.php <html> <body> <form method="post"> Id : <input type="text" name="id"> Name : <input type="text" name="name"> Description : <input type="text" name="des"> <input type="submit" value="delete" name="delete"> </form> <?php include("connect.php"); $id = $_POST['id']; $name = $_POST['name']; $des = $_POST['des']; $result = mysql_query("DELETE FROM fact WHERE id='$id'") or die(mysql_error()); while($row = mysql_fetch_array($result)) { echo "Deleted"; } mysql_close($con); ?> </body> </html> connect.php <?php $con = mysql_connect("localhost","root",""); if (!$con) { die('Could not connect: ' . mysql_error()); } mysql_select_db("Dataentry", $con); ?> How should i make the while loop work..

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  • How do I code a tree of objects in Haskell with pointers to parent and children?

    - by axilmar
    I've got the following problem: I have a tree of objects of different classes where an action in the child class invalidates the parent. In imperative languages, it is trivial to do. For example, in Java: public class A { private List<B> m_children = new LinkedList<B>(); private boolean m_valid = true; public void invalidate() { m_valid = false; } public void addChild(B child) { m_children.add(child); child.m_parent = this; } } public class B { public A m_parent = null; private int m_data = 0; public void setData(int data) { m_data = 0; m_parent.invalidate(); } } public class Main { public static void main(String[] args) { A a = new A(); B b = new B(); b.setData(0); //invalidates A } } How do I do the above in Haskell? I cannot wrap my mind around this, since once I construct an object in Haskell, it cannot be changed. I would be much obliged if the relevant Haskell code is posted.

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  • Trouble understanding the semantics of volatile in Java

    - by HungryTux
    I've been reading up about the use of volatile variables in Java. I understand that they ensure instant visibility of their latest updates to all the threads running in the system on different cores/processors. However no atomicity of the operations that caused these updates is ensured. I see the following literature being used frequently A write to a volatile field happens-before every read of that same field . This is where I am a little confused. Here's a snippet of code which should help me better explain my query. volatile int x = 0; volatile int y = 0; Thread-0: | Thread-1: | if (x==1) { | if (y==1) { return false; | return false; } else { | } else { y=1; | x=1; return true; | return true; } | } Since x & y are both volatile, we have the following happens-before edges between the write of y in Thread-0 and read of y in Thread-1 between the write of x in Thread-1 and read of x in Thread-0 Does this imply that, at any point of time, only one of the threads can be in its 'else' block(since a write would happen before the read)? It may well be possible that Thread-0 starts, loads x, finds it value as 0 and right before it is about to write y in the else-block, there's a context switch to Thread-1 which loads y finds it value as 0 and thus enters the else-block too. Does volatile guard against such context switches (seems very unlikely)?

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