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  • Java: thread-safe RandomAccessFile

    - by Folkert van Heusden
    Hi, After some serious googleing I found out that the RandomAccessFile-class is not thread-safe. Now I could use one semaphore to lock all reads and writes but I don't think that performs very well. In theory it should be possible to do multiple reads and one write at a time. How can I do this in Java? Is it possible at all? Thanks!

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  • Why wont my while loop take new input (c++)

    - by Van
    I've written a program to get a string input from a user and parse it into tokens and move a robot according to the input. My problem is trying to issue more than one command. The code looks like: void Navigator::manualDrive() { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; while(true) { Navigator::parseInstruction(uinput); } } /* parseInstruction(char *c) -- parses cstring instructions received * and moves robot accordingly */ void Navigator::parseInstruction(char * c) { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, bufSize); token=strtok(uinput, delim); if(strcmp("forward", token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); Navigator::travel(inches); } if(strcmp("back",token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); double value = fabs(0.0735 * fabs(inches) - 0.0550); myRobot.backward(1/*speed*/, value/*time*/); } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("left",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnLeft(1/*speed*/, value/*time*/); } } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("right",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnRight(1/*speed*/, value/*time*/); } } if(strcmp("stop",token) == 0) { myRobot.motors(0,0); } } In the function manualDrive I have a while loop calling the function parseInstruction infinitely. The program outputs "Enter your directions below: " When I give the program instructions it executes them, and then it outputs "enter your directions below: " again and when I input my directions again it does not execute them and outputs "Enter your directions below: " instead. I'm sure this is a very simple fix I'm just very new to c++. So if you could please help me out and tell me why the program only takes the first set of directions. thanks

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  • A* algorithm works OK, but not perfectly. What's wrong?

    - by Bart van Heukelom
    This is my grid of nodes: I'm moving an object around on it using the A* pathfinding algorithm. It generally works OK, but it sometimes acts wrongly: When moving from 3 to 1, it correctly goes via 2. When going from 1 to 3 however, it goes via 4. When moving between 3 and 5, it goes via 4 in either direction instead of the shorter way via 6 What can be wrong? Here's my code (AS3): public static function getPath(from:Point, to:Point, grid:NodeGrid):PointLine { // get target node var target:NodeGridNode = grid.getClosestNodeObj(to.x, to.y); var backtrace:Map = new Map(); var openList:LinkedSet = new LinkedSet(); var closedList:LinkedSet = new LinkedSet(); // begin with first node openList.add(grid.getClosestNodeObj(from.x, from.y)); // start A* var curNode:NodeGridNode; while (openList.size != 0) { // pick a new current node if (openList.size == 1) { curNode = NodeGridNode(openList.first); } else { // find cheapest node in open list var minScore:Number = Number.MAX_VALUE; var minNext:NodeGridNode; openList.iterate(function(next:NodeGridNode, i:int):int { var score:Number = curNode.distanceTo(next) + next.distanceTo(target); if (score < minScore) { minScore = score; minNext = next; return LinkedSet.BREAK; } return 0; }); curNode = minNext; } // have not reached if (curNode == target) break; else { // move to closed openList.remove(curNode); closedList.add(curNode); // put connected nodes on open list for each (var adjNode:NodeGridNode in curNode.connects) { if (!openList.contains(adjNode) && !closedList.contains(adjNode)) { openList.add(adjNode); backtrace.put(adjNode, curNode); } } } } // make path var pathPoints:Vector.<Point> = new Vector.<Point>(); pathPoints.push(to); while(curNode != null) { pathPoints.unshift(curNode.location); curNode = backtrace.read(curNode); } pathPoints.unshift(from); return new PointLine(pathPoints); } NodeGridNode::distanceTo() public function distanceTo(o:NodeGridNode):Number { var dx:Number = location.x - o.location.x; var dy:Number = location.y - o.location.y; return Math.sqrt(dx*dx + dy*dy); }

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  • Components don't show in custom JPanel/JComponent

    - by Bart van Heukelom
    I've created a custom swing component. I can see it (the grid from the paint method is drawn), but the buttons that are added (verified by println) aren't shown. What am I doing wrong? Background information: I'm trying to build a tree of visible objects like the Flash/AS3 display list. public class MapPanel extends JComponent { // or extends JPanel, same effect private static final long serialVersionUID = 4844990579260312742L; public MapPanel(ShapeMap map) { setBackground(Color.LIGHT_GRAY); setPreferredSize(new Dimension(1000,1000)); setLayout(null); for (Layer l : map.getLayers()) { // LayerView layerView = new LayerView(l); // add(layerView); System.out.println(l); JButton test = new JButton(l.getName()); add(test); validate(); } } @Override protected void paintComponent(Graphics g) { // necessary? super.paintComponent(g); // background g.setColor(getBackground()); g.fillRect(0, 0, getWidth(), getHeight()); // grid g.setColor(Color.GRAY); for (double x = 0; x < getWidth(); x += 10) { g.drawLine((int)x, 0, (int)x, getHeight()); } for (double y = 0; y < getHeight(); y += 10) { g.drawLine(0, (int)y, getWidth(), (int)y); } } }

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  • How to write a custom (odd) authentication plugins for Wordpress, Joomla and MediaWiki

    - by Bart van Heukelom
    On our network (a group of related websites - not a LAN) we have a common authentication system which works like this: On a network site ("consumer") the user clicks on a login link This redirects the user to a login page on our auth system ("RAS"). Upon successful login the user is directed back to the consumer site. Extra data is passed in the query string. This extra data does not include any information about the user yet. The consumer site's backend contacts RAS to get the information about the logged in user. So as you can see, the consumer site knows nothing about the authentication method. It doesn't know if it's by username/password, fingerprint, smartcard, or winning a game of poker. This is the main problem I'm encountering when trying to find out how I could write custom authentication plugins for these packages, acting as consumer sites: Wordpress Joomla MediaWiki For example Joomla offers a pretty simple auth plugin system, but it depends on a username/password entered on the Joomla site. Any hints on where to start?

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  • Simply display RSS feed in/on aspx page

    - by Louis van Tonder
    Maybe I am being a n00b here, but for the life of me, I cant find a simple drop in type solution for displaying an rss feed inside an aspx page? I am looking for a simple solution, as when Firefox gets pointed to an rss feed, it just plainly displays it, no thrills, no fuss. I don't want to get into the xml and format it extensively. I just want a basic feed, will style it with font and a:styles. Thats it. Any ideas? EDIT: I am attempting to show a worpress "feed" inside an aspx page...

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  • The ultimate .NET file and directory utility library?

    - by Serge van den Oever
    I find myself writing file and directory utility functions all the time, and I was wondering if there is good file and directory library that already implements a more extensive set than available by default in System.IO. The kind of functions I'm looking for is things like: public static void GetTemporaryDirectory() { string tempDirectory = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName()); Directory.CreateDirectory(tempDirectory); return tempDirectory; } public static void CreateEmptyFile(string filename) { File.Create(filename).Dispose(); } public static void CreateEmptyFile(string path, string filename) { File.Create(Path.Combine(path, filename)).Dispose(); } public static void CreateDirectory(string path) { Directory.CreateDirectory(path); } public static void CreateDirectory(string path, string childpath) { Directory.CreateDirectory(Path.Combine(path, childpath)); }

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  • Attributes in XML subtree that belong to the parent

    - by Bart van Heukelom
    Say I have this XML <doc:document> <objects> <circle radius="10" doc:colour="red" /> <circle radius="20" doc:colour="blue" /> </objects> </doc:document> And this is how it is parsed (pseudo code): // class DocumentParser public Document parse(Element edoc) { doc = new Document(); doc.objects = ObjectsParser.parse(edoc.getChild("objects")); for ( ...?... ) { doc.objectColours.put(object, colour); } return doc; } ObjectsParser is responsible for parsing the objects bit, but is not and should not be aware of the existence of documents. However, in Document colours are associated with objects by use of a Map. What kind of pattern would you recommend to give the colour settings back to DocumentParser.parse from ObjectsParser.parse so it can associate it with the objects they belong to in a map? The alternative would be something like this: <doc:document> <objects> <circle id="1938" radius="10" /> <circle id="6398" radius="20" /> </objects> <doc:objectViewSettings> <doc:objectViewSetting object="1938" colour="red" /> <doc:objectViewSetting object="6398" colour="blue" /> </doc:objectViewSettings> </doc:document> Ugly!

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  • Entity Framework 5 Enum Naming

    - by Tyrel Van Niekerk
    I am using EF 5 with migrations and code first. It all works rather nicely, but there are some issues/questions I would like to resolve. Let's start with a simple example. Lets say I have a User table and a user type table. The user type table is an enum/lookup table in my app. So the user table has a UserTypeId column and a foreign key ref etc to UserType. In my poco, I have a property called UserType which has the enum type. To add the initial values to the UserType table (or add/change values later) and to create the table in the initial migrator etc. I need a UserType table poco to represent the actual table in the database and to use in the map files. I mapped the UserType property in the User poco to UserTypeId in the UserType poco. So now I have a poco for code first/migrations/context mapping etc and I have an enum. Can't have the same name for both, so do I have a poco called UserType and something else for the enum or have the poco for UserType be UserTypeTable or something? More importantly however, am I missing some key element in how code first works? I tried the example above, ran Add-Migration and it does not add the lookup table for the enum.

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  • Incompatible classes when loading SWF

    - by Bart van Heukelom
    I have two ActionScript 3 projects, game(.swf) and minigame(.swf). At runtime the main game loads the minigame via Loader. I also have a shared library (SWC) of event classes, included by both, which minigame will need to dispatch and game will need to listen to. First: Is this possible this way? Second: What will happen if I compile the minigame, then change the event classes so they're incompatible, then compile the main game. Will Flash crash when trying to load the minigame SWF? (I hope so) Third: And what will happen if I change the event classes, but in a way that preserves interface-level compatibility?

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  • Iterator blocks and inheritance.

    - by Dave Van den Eynde
    Given a base class with the following interface: public class Base { public virtual IEnumerable<string> GetListOfStuff() { yield return "First"; yield return "Second"; yield return "Third"; } } I want to make a derived class that overrides the method, and adds its own stuff, like so: public class Derived : Base { public override IEnumerable<string> GetListOfStuff() { foreach (string s in base.GetListOfStuff()) { yield return s; } yield return "Fourth"; yield return "Fifth"; } } However, I'm greeted with a warning that "access to a member through a base keyword from an iterator cannot be verified". What's the accepted solution to this problem then?

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  • Why wont my while loop wont take new input (c++)

    - by Van
    I've written a program to get a string input from a user and parse it into tokens and move a robot according to the input. My problem is trying to issue more than one command. The code looks like: void Navigator::manualDrive() { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; while(true) { Navigator::parseInstruction(uinput); } } /* parseInstruction(char *c) -- parses cstring instructions received * and moves robot accordingly */ void Navigator::parseInstruction(char * c) { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, bufSize); token=strtok(uinput, delim); if(strcmp("forward", token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); Navigator::travel(inches); } if(strcmp("back",token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); double value = fabs(0.0735 * fabs(inches) - 0.0550); myRobot.backward(1/*speed*/, value/*time*/); } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("left",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnLeft(1/*speed*/, value/*time*/); } } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("right",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnRight(1/*speed*/, value/*time*/); } } if(strcmp("stop",token) == 0) { myRobot.motors(0,0); } } In the function manualDrive I have a while loop calling the function parseInstruction infinitely. The program outputs "Enter your directions below: " When I give the program instructions it executes them, and then it outputs "enter your directions below: " again and when I input my directions again it does not execute them and outputs "Enter your directions below: " instead. I'm sure this is a very simple fix I'm just very new to c++. So if you could please help me out and tell me why the program only takes the first set of directions. thanks

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  • Java respawn process

    - by Bart van Heukelom
    I'm making an editor-like program. If the user chooses File-Open in the main window I want to start a new copy of the editor process with the chosen filename as an argument. However, for that I need to know what command was used to start the first process: java -jar myapp.jar blabalsomearguments // --- need this information Open File (fileUrl) exec("java -jar myapp.jar blabalsomearguments fileUrl"); I'm not looking for an in-process solution, I've already implemented that. I'd like to have the benefits that seperate processes bring.

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  • Maven 2: How to package current project version in a WAR file?

    - by Tom van Zummeren
    I am using Maven 2 to build my Java project and I am looking for a way to present the current version number of the pom.xml to the user (using a Servlet or JSP for example). As far as I can see, the best way would be that Maven packages the version number as a text file into the WAR. This allows me to read the version from that file and present it the way I want. Does anyone know of a plugin that can do something like that for me? Maybe the WAR plugin can be configured to do so? Or maybe using some other approach all together?

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  • Building a system that allows users to see a video only once

    - by Bart van Heukelom
    My client wants to distribute a video to some people, specifically car dealers, but he doesn't want the video to end up on Youtube or something like that. Therefore he wants the recipients of the video to be able to see it only once. My idea to implement this is: Generate a unique key per viewer Send each viewer a link to a page with a Flash based video player, with their key in the URL Have Flash get the video from the server. On the server the key is checked and the file sent (using php's readfile or something equivalent). Then the key is invalidated. I was thinking this wouldn't take more than a day to build. I know that if you want somebody to be able to play something, you implicitly give them the power to record it as well, but the client just wants me to make it as hard as possible. Do you think this is secure enough for the intended audience? Anything else I can do to add some security without exceeding the development time of 1 day? I'm also interested in ready made solutions, if they exist.

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  • Regular Expression .net flavor

    - by user1440109
    Dont ask how this works but currently it does ("^\|(.?)\|*$")....kinda. This removes all extra pipes...part one....I have searched all over no anwser yet. I am using VB2011 beta...asp web form......vb coding though! I want to capture special character pipe (|) which is used to seperate words...i.e. car|truck|van|cycle problem is users lead with, trail with, use multiple, and use spaces before and after...i.e. |||car||truck | van || cycle. another example: george bush|micheal jordon|bill gates|steve jobs <-- this would be correct but when I do remove space it takes correct space out. so I want to get rid of whitespace leading, trailing, any space before | and space after | and only allow one pipe (|)....in between alphanumeric of course.

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  • jframe adding own design jinternal frame error

    - by Van Minh
    I designed a title bar color on my JInternal frame. Then I took attempt to add it to my JFrame, but I cannot. Here is the code of my title bar: public class MyIFtitleBar extends BasicInternalFrameTitlePane { public MyIFtitleBar(JInternalFrame jif) { super(jif); } protected void paintTitleBackground(Graphics g){ g.setColor(Color.pink); g.fillRect(0, 0, getWidth(), getHeight()); } } Here is my JInternal frame. I tried running it in its psvm method, that worked! public class FitnessProg_Frame extends javax.swing.JInternalFrame { public FitnessProg_Frame() { initComponents(); this.setUI(new BasicInternalFrameUI(this){ @Override protected JComponent createNorthPane(JInternalFrame jif) { return new MyIFtitleBar(jif); } }); } @SuppressWarnings("unchecked") private void initComponents() { setBackground(new java.awt.Color(255, 255, 255)); setBorder(new javax.swing.border.MatteBorder(null)); setTitle("Fitness Progarm"); setPreferredSize(new java.awt.Dimension(507, 304)); pack(); } } But when I add it to my JFrame I get an error: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException Here is my JFrame code: public class NewJFrame extends javax.swing.JFrame { public NewJFrame() { initComponents(); FitnessProg_Frame ff = new FitnessProg_Frame(); ff.setVisible(true); mydes.add(ff); // this line made errors } @SuppressWarnings("unchecked") private void initComponents() { mydes = new javax.swing.JDesktopPane(); setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); javax.swing.GroupLayout mydesLayout = new javax.swing.GroupLayout(mydes); mydes.setLayout(mydesLayout); mydesLayout.setHorizontalGroup( mydesLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGap(0, 400, Short.MAX_VALUE) ); mydesLayout.setVerticalGroup( mydesLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) .addGap(0, 300, Short.MAX_VALUE) ); getContentPane().add(mydes, java.awt.BorderLayout.CENTER); pack(); } public static void main(String args[]) { try { for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) { if ("Nimbus".equals(info.getName())) { javax.swing.UIManager.setLookAndFeel(info.getClassName()); break; } } } catch (ClassNotFoundException ex) { java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (InstantiationException ex) { java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (IllegalAccessException ex) { java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } catch (javax.swing.UnsupportedLookAndFeelException ex) { java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex); } java.awt.EventQueue.invokeLater(new Runnable() { public void run() { new NewJFrame().setVisible(true); } }); } private javax.swing.JDesktopPane mydes; }

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  • Make Java parent class not part of the interface

    - by Bart van Heukelom
    (This is a hypothetical question for discussion, I have no actual problem). Say that I'm making an implementation of SortedSet by extending LinkedHashMap: class LinkedHashSortedMapThing extends LinkedHashMap implements SortedSet { ... } Now programmers who use this class may do LinkedHashMap x = new LinkedHashSortedMapThing(); But what if I consider the extending of LinkedHashMap an implementation detail, and do not want it to be a part of the class' contract? If people use the line above, I can no longer freely change this detail without worrying about breaking existing code. Is there any way to prevent this sort of thing, other than favouring composition over inheritance (which is not always possible due to private/protected members)?

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  • Why does /**[newline] not always insert the Javadoc template including @param and @return in Eclipse

    - by Bas van den Broek
    I'm documenting code in Eclipse and have been using the /** followed by Enter alot to insert the Javadoc template. However this does not always work for some reason, it will create the template for writing comments but it won't automatically insert the @param and @return text. If I copy the exact same method to another class it will insert the full template. It would be a big help if anyone could tell me why it won't do this in some situations.

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