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  • Garbage Collection in Java

    - by simion
    On the slides I am revising from it says the following: Live objects can be identified either by maintaining a count of the number of references to each object, or by tracing chains of references from the roots. Reference counting is expensive – it needs action every time a reference changes and it doesn’t spot cyclical structures, but it can reclaim space incrementally. Tracing involves identifying live objects only when you need to reclaim space – moving the cost from general access to the time at which the GC runs, typically only when you are out of memory. I understand the principles of why reference counting is expensive but do not understand what "doesn’t spot cyclical structures, but it can reclaim space incrementally." means. Could anyone help me out a little bit please? Thanks

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  • Java/Swing: Problem with key listener

    - by Mike
    I have a search dialog with a JTextField that's being used as a search box. When the user types something, it searches the DB, shows the result in a JTable and selects the first item in it. If the first result is what they were looking for, I want to let them quickly accept the dialog, by pressing Enter (while the JTextField is focused). So I added a KeyListener to the JTextField and it's working OK. Now the problem: The user opens can open the dialog by pressing Enter when a "Search" button on the dialog's parent frame is focused. The dialog is displayed and the JTextField gets the keyReleased event (from the Enter key that displayed it), so it shows up and closes. If the user holds Enter down, then the JTextField receives the keyPressed, keyTyped and keyReleased events. How can I fix without resorting to ugly workarounds? Platform is Windows 7 x64, btw. Test NetBeans project here: http://dl.dropbox.com/u/6354360/KeyListenerTest.zip Thanks.

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  • Need a hand understanding this Java code please :-)

    - by Brian
    Hi all, Just wondering if anyone would be able to take a look at this code for implementing the quicksort algorithm and answer me a few questions, please :-) public class Run { /*************************************************************************** * Quicksort code from Sedgewick 7.1, 7.2. **************************************************************************/ public static void quicksort(double[] a) { //shuffle(a); // to guard against worst-case quicksort(a, 0, a.length - 1, 0); } static void quicksort(final double[] a, final int left, final int right, final int tdepth) { if (right <= left) return; final int i = partition(a, left, right); if ((tdepth < 4) && ((i - left) > 1000)) { final Thread t = new Thread() { public void run() { quicksort(a, left, i - 1, tdepth + 1); } }; t.start(); quicksort(a, i + 1, right, tdepth + 1); try { t.join(); } catch (InterruptedException e) { throw new RuntimeException("Cancelled", e); } } else { quicksort(a, left, i - 1, tdepth); quicksort(a, i + 1, right, tdepth); } } // partition a[left] to a[right], assumes left < right private static int partition(double[] a, int left, int right) { int i = left - 1; int j = right; while (true) { while (less(a[++i], a[right])) // find item on left to swap ; // a[right] acts as sentinel while (less(a[right], a[--j])) // find item on right to swap if (j == left) break; // don't go out-of-bounds if (i >= j) break; // check if pointers cross exch(a, i, j); // swap two elements into place } exch(a, i, right); // swap with partition element return i; } // is x < y ? private static boolean less(double x, double y) { return (x < y); } // exchange a[i] and a[j] private static void exch(double[] a, int i, int j) { double swap = a[i]; a[i] = a[j]; a[j] = swap; } // shuffle the array a[] private static void shuffle(double[] a) { int N = a.length; for (int i = 0; i < N; i++) { int r = i + (int) (Math.random() * (N - i)); // between i and N-1 exch(a, i, r); } } // test client public static void main(String[] args) { int N = 5000000; // Integer.parseInt(args[0]); // generate N random real numbers between 0 and 1 long start = System.currentTimeMillis(); double[] a = new double[N]; for (int i = 0; i < N; i++) a[i] = Math.random(); long stop = System.currentTimeMillis(); double elapsed = (stop - start) / 1000.0; System.out.println("Generating input: " + elapsed + " seconds"); // sort them start = System.currentTimeMillis(); quicksort(a); stop = System.currentTimeMillis(); elapsed = (stop - start) / 1000.0; System.out.println("Quicksort: " + elapsed + " seconds"); } } My questions are: What is the purpose of the variable tdepth? Is this considered a "proper" implementation of a parallel quicksort? I ask becuase it doesn't use implements Runnable or extends Thread... If it doesn't already, is it possible to modify this code to use multiple threads? By passing in the number of threads you want to use as a parameter, for example...? Many thanks, Brian

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  • Java Switch Incompatible Types Boolean Int

    - by ikurtz
    i have the following class: public class NewGameContract { public boolean HomeNewGame = false; public boolean AwayNewGame = false; public boolean GameContract(){ if (HomeNewGame && AwayNewGame){ return true; } else { return false; } } } when i try to use it like so: if (networkConnection){ connect4GameModel.newGameContract.HomeNewGame = true; boolean status = connect4GameModel.newGameContract.GameContract(); switch (status){ case true: break; case false: break; } return; } i am getting the error: incompatible types found: boolean required: int on the following switch (status) code. what am i doing wrong please?

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  • Java: Difference between PrintStream and PrintWriter

    - by Martijn Courteaux
    Hi, What is the difference between PrintStream and PrintWriter? They have much methods in common. I always mix up this classes because of that reason. And I think we can use them for exactly the same. But there has to be a difference. Otherwise there was only one class. I first searched on StackOverflow, but not yet this question. Thanks

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  • EhCache default cache in java

    - by user349302
    Hello I have this configuration for ehCache: <ehcache> <defaultCache name="defaut" maxElementsInMemory="5" eternal="false" timeToIdleSeconds="20" timeToLiveSeconds="20" overflowToDisk="false" diskPersistent="false" memoryStoreEvictionPolicy="LRU" /> </ehcache> How can I get access to default cache of EhCache? CacheManager.getInstance().getCache("default") - returns null thank you

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  • List all files from a directory recursively with Java

    - by Hultner
    Okay I got this function who prints the name of all files in a directory recursively problem is that it's very slow and it gets the stuff from a network device and with my current code it has to access the device time after time. What I would want is to first load all the files from the directory recursively and then after that go through all files with the regex to filter out all the files I don't want. Unless anyone got a better suggestion. I've never before done anything like this. public static printFnames(String sDir){  File[] faFiles = new File(sDir).listFiles();  for(File file: faFiles){ if(file.getName().matches("^(.*?)")){   System.out.println(file.getAbsolutePath()); }   if(file.isDirectory()){     printFnames(file.getAbsolutePath());   }  } } This is just a test later on I'm not going to use the code like this, instead I'm going to add the path and modification date of every file which matches an advanced regex to an array.

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  • Java Web App: Passing form parameters across multiple pages

    - by digiarnie
    Hi, what is the best practice or best way of passing form parameters from page to page in a flow? If I have a flow where a user enters data in a form and hits next and repeats this process until they get to an approval page, what ways could I approach this problem to make the retention of data as simple as possible over the flow? I guess you could put all the information as you go in the session but could you get into memory issues if a lot of people are using your app and going through the flow at the same time?

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  • Setting the height of a row in a JTable in java

    - by Douglas Grealis
    I have been searching for a solution to be able to increase the height of a row in a JTable. I have been using the setRowHeight(int int) method which compiles and runs OK, but no row[s] have been increased. When I use the getRowHeight(int) method of the row I set the height to, it does print out the size I increased the row to, so I'm not sure what is wrong. The code below is a rough illustration how I am trying to solve it. My class extends JFrame. String[] columnNames = {"Column 1", "Column 2", "Column 1 3"}; JTable table = new JTable(new DefaultTableModel(columnNames, people.size())); DefaultTableModel model = (DefaultTableModel) table.getModel(); int count =1; for(Person p: people) { model.insertRow(count,(new Object[]{count, p.getName(), p.getAge()+"", p.getNationality})); count++; } table.setRowHeight(1, 15);//Try set height to 15 (I've tried higher) Can anyone tell me where I am going wrong? I am trying to increase the height of row 1 to 15 pixels?

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  • PLEASE HELP JAVA/SQL question

    - by fred-ghosn
    Hello everyone, well I'm new here and I really need some help.. I want to create a table and this table's name will be inserted from a textfield. However when I run the query it's giving me an error, any help on this one? Ill paste the code here: public boolean CreateTable() { TableNumber=jTextField4.getText(); try { String password = null; String s = "CREATE TABLE '"+TableNumber+'" (Item char(50),Price char(50))"; ConnectionForOrders(); stmt = conn.createStatement(); stmt.executeUpdate(s); boolean f=false; ConnectionForOrdersclose();

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  • Java Thread - Memory consistency errors

    - by Yatendra Goel
    I was reading a Sun's tutorial on Concurrency. But I couldn't understand exactly what memory consistency errors are? I googled about that but didn't find any helpful tutorial or article about that. I know that this question is a subjective one, so you can provide me links to articles on the above topic. It would be great if you explain it with a simple example.

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  • Java document parsing over internet using POST

    - by Travis
    I've looked all around and decided to make my own library for accessing the EVE API. Requests are sent to a server address such as /account/Characters.xml.aspx. Characters.xml.aspx requires two item be submitted in POST and then it returns an XML file. So far I have this but it does not work, probably becuase I am using GET instead of POST: //Get the API data DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); String url = "http://api.eveonline.com/account/Characters.xml.aspx?userID="+ userID+"?apiKey="+key; Document doc = builder.parse(url); How would I go about being able to parst an XML file that is generated by submitting variables in POST?

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  • Generate a collection of changed lines between two revisions of a file using Java

    - by mchr
    I am writing an eclipse plugin which needs to be able to determine which lines of a file have changed compared to a different version of the same file. Is there an existing class or library which I can use for this task? The closest I have found is org.eclipse.compare.internal.merge.DocumentMerger. This can be used to find the information I need but is in an internal package so is not suitable for me to use. I could copy/paste the source of this class and adapt it to my requirements. However, I am hoping there is an existing library to handle textual comparisons.

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  • How to profile object creation in Java?

    - by gooli
    The system I work with is creating a whole lot of objects and garbage collecting them all the time which results in a very steeply jagged graph of heap consumption. I would like to know which objects are being generated to tune the code, but I can't figure out a way to dump the heap at the moment the garbage collection starts. When I tried to initiate dumpHeap via JConsole manually at random times, I always got results after GC finished its run, and didn't get any useful data. Any notes on how to track down excessive temporary object creation are welcome.

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  • Java: Tracking a user login session - Session EJBs vs HTTPSession

    - by bguiz
    If I want to keep track of a conversational state with each client using my web application, which is the better alternative - a Session Bean or a HTTP Session - to use? Using HTTP Session: //request is a variable of the class javax.servlet.http.HttpServletRequest //UserState is a POJO HttpSession session = request.getSession(true); UserState state = (UserState)(session.getAttribute("UserState")); if (state == null) { //create default value .. } String uid = state.getUID(); //now do things with the user id Using Session EJB: In the implementation of ServletContextListener registered as a Web Application Listener in WEB-INF/web.xml: //UserState NOT a POJO this this time, it is //the interface of the UserStateBean Stateful Session EJB @EJB private UserState userStateBean; public void contextInitialized(ServletContextEvent sce) { ServletContext servletContext = sce.getServletContext(); servletContext.setAttribute("UserState", userStateBean); ... In a JSP: public void jspInit() { UserState state = (UserState)(getServletContext().getAttribute("UserState")); ... } Elsewhere in the body of the same JSP: String uid = state.getUID(); //now do things with the user id It seems to me that the they are almost the same, with the main difference being that the UserState instance is being transported in the HttpRequest.HttpSession in the former, and in a ServletContext in the case of the latter. Which of the two methods is more robust, and why?

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  • java alternative for phpMyAdmin

    - by rcourtna
    I find myself working in an environment where all I have access to is Tomcat + MySQL. No Apache, no PHP. I'm looking for a web interface to MySQL that will run under Tomcat (can't be a desktop interface, as the mysql port is not accessible). I'm tried jMyAdmin and javaMyAdmin. I can't get either to work, and both lack documentation and community support. Can anyone make a recommendation please?

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  • ontology with java(jena)

    - by Udayanga
    I'm doing some project which is based on ontology.I want to identify semantic of the text that has entered by user. Is there any possible way to fulfill my task dealing with ontology through jena?

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  • Java application failing on special characters.

    - by Scottm
    An application I am working on reads information from files to populate a database. Some of the characters in the files are non-English, for example accented French characters. The application is working fine in Windows but on our Solaris machine it is failing to recognise the special characters and is throwing an exception. For example when it encounters the accented e in "Gérer" it says :- Encountered: "\u0161" (353), after : "\'G\u00c3\u00a9rer les mod\u00c3" (an exception which is thrown from our application) I suspect that in order to stop this from happening I need to change the file.encoding property of the JVM. I tried to do this via System.setProperty() but it has not stopped the error from occurring. Are there any suggestions for what I could do? I was thinking about setting the basic locale of the solaris platform in /etc/default/init to be UTF-8. Does anyone think this might help? Any thoughts are much appreciated.

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  • how can i acess a variable outside of an if statement in java

    - by themanepalli
    i have defined a variable inside an if statement and I am trying to access it outside of that if statement now. now the error is saying that it cannot find the symbol which is because its being defined as an intance variable, is there a way i can change it so i can access it outside the variable? heres the code if((e.getSource()==userOrder2)&& (orderType==1)) { String buyO= userOrder2.getText(); int buyOrder= Integer.parseInt(buyO); //variable im trying to access } // trying to use buyOrder in a different if statement if(orderType==1 && (stockPrice <= buyOrder)) { orderResult.setText("The Stock" + (stockName2.getText()) + "was bought at" + stockPrice); }

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  • How to pass checkbox array to Java from jsp

    - by eddy
    Hi, I'd like to know if there's any way to send data to the server for the selected rows using the checkboxes I've put on those rows? I mean , how can I send only the data of those selected rows to the server? Here's the html code I use: <table> <thead> <tr class="tableheader"> <td width="10%"></td> <td width="30%">Vehicle</td> <td width="40%">Driver</td> <td width="10%">Mileage</td> </tr> </thead> <tbody> <c:forEach items="${list}" var="item"> <tr> <td align="center"> <input type="checkbox" name="selectedItems" value="c:out value="${item.numberPlate}"/>"/> </td> <td align="left"><c:out value="${item.numberPlate}"/></td> <td align="left"><c:out value="${item.driver.fullName}" /></td> <td align="left"><input type="text" name="mileage" value="" /></td> </tr> </c:forEach> </tbody> </table> I really hope you can give some guidance on this. Thanks in beforehand.

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  • Changing Encoding while Xml.parse() with SaxFeedParser Java

    - by zOro
    Hi , I am trying to load hebrew rss using the fllow : Xml.parse(_InputStream, Xml.Encoding.ISO_8859_1 , root.getContentHandler()); taken from ibm site : link text I would like to use other Encoding like "ISO8859_8" rather than : Xml.Encoding.ISO_8859_1, Xml.Encoding.US_ASCII, Xml.Encoding.UTF_16, Xml.Encoding.UTF_8 Thanks a lot!

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