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  • How to solve this Java type safety warning? (Struts2)

    - by Nicolas Raoul
    Map session = ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map should be parameterized. Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: Unchecked cast from Map to Map. The getSession method belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful. I guess all Struts2 users in the world faced the same problem... is there an elegant solution?

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  • What can you do and not do with java annotations?

    - by swampsjohn
    The typical use-case is for simple things like @Override, but clearly you can do a lot more with them. If you push the limits of them, you get things like Project Lombok, though my understanding is that that's a huge abuse of annotations. What exactly can you do? What sort of things can you do at compile-time and run-time with annotations? What can you not do?

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  • How do I close a file after catching an IOException in java?

    - by DimDom
    All, I am trying to ensure that a file I have open with BufferedReader is closed when I catch an IOException, but it appears as if my BufferedReader object is out of scope in the catch block. public static ArrayList readFiletoArrayList(String fileName, ArrayList fileArrayList) { fileArrayList.removeAll(fileArrayList); try { //open the file for reading BufferedReader fileIn = new BufferedReader(new FileReader(fileName)); // add line by line to array list, until end of file is reached // when buffered reader returns null (todo). while(true){ fileArrayList.add(fileIn.readLine()); } }catch(IOException e){ fileArrayList.removeAll(fileArrayList); fileIn.close(); return fileArrayList; //returned empty. Dealt with in calling code. } } Netbeans complains that it "cannot find symbol fileIn" in the catch block, but I want to ensure that in the case of an IOException that the Reader gets closed. How can I do that without the ugliness of a second try/catch construct around the first? Any tips or pointers as to best practise in this situation is appreciated,

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  • How to sort data in a table data structure in Java?

    - by rgksugan
    I need to sort data based on the third column of the table data structure. I tried based on the answers for the following question. But my sorting does not work. Please help me in this. Here goes my code. Object[] data = new Object[y]; rst.beforeFirst(); while (rst.next()) { int p_id = Integer.parseInt(rst.getString(1)); String sw2 = "select sum(quantity) from tbl_order_detail where product_id=" + p_id; rst1 = stmt1.executeQuery(sw2); rst1.next(); String sw3 = "select max(order_date) from tbl_order where tbl_order.`Order_ID` in (select tbl_order_detail.`Order_ID` from tbl_order_detail where product_id=" + p_id + ")"; rst2 = stmt2.executeQuery(sw3); rst2.next(); data[i] = new Object[]{new String(rst.getString(2)), new String(rst.getString(3)), new Integer(rst1.getString(1)), new String(rst2.getString(1))}; i++; } ColumnComparator cc = new ColumnComparator(2); Arrays.sort(data, cc); if (i == 0) { table.addCell(""); table.addCell(""); table.addCell(""); table.addCell(""); } else { for (int j = 0; j < y; j++) { Object[] theRow = (Object[]) data[j]; table.addCell((String) theRow[0]); table.addCell((String) theRow[1]); table.addCell((String) theRow[2]); table.addCell((String) theRow[3]); }

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  • How is this statement making sense? (Sun's naming convention for Java variables)

    - by polygenelubricants
    I've been quoting this segment from Sun's document for the past few days, and only now do I stop and think about what it's saying, and I can't make sense out of it. Please keep in mind that English is not my first language. Naming conventions Variables: Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. How is this making sense? Isn't this saying that class names are in mixed case with a lowercase first letter? Like I should name it class myClass? And class constants are also in mixed case with a lowercase first letter? Like I should name it Integer.maxValue? And is it really saying anything about how variables themselves should be named? Am I not parsing this properly or is this actually a blatant error?

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  • Can i create different observables and different corresponding observers in java?

    - by mithun1538
    Hello everyone, Currently, I have one observable and many observers. What i need is different observables, and depending on the observable, different observers. How do I achieve this? ( For understanding, assume I have different apples - say apple1 apple2... I have observer_1 observing apple1, observer_2 observing apple2, observer_3 observing apple 2 and so on..). I tried creating different objects of the Observable class, but since observers are observing the same class of observable, I don't know how to access a particular instance of the Observable. I have included the following servlet code that contains Observer and Observable classes: public class CustomerServlet extends HttpServlet { public String getNextMessage() { // Create a message sink to wait for a new message from the // message source. return new MessageSink().getNextMessage(source); } @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); String recMSG = getNextMessage(); dout.writeObject(recMSG); dout.flush(); } public void broadcastMessage(String message) { // Send the message to all the HTTP-connected clients by giving the // message to the message source source.sendMessage(message); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try { ObjectInputStream din= new ObjectInputStream(request.getInputStream()); String message = (String)din.readObject(); ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream()); dout.writeObject("1"); dout.flush(); if (message != null) { broadcastMessage(message); } // Set the status code to indicate there will be no response response.setStatus(response.SC_NO_CONTENT); } catch (Exception e) { e.printStackTrace(); } } @Override public String getServletInfo() { return "Short description"; }// </editor-fold> MessageSource source = new MessageSource(); } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSource extends Observable { public void sendMessage(String message) { setChanged(); notifyObservers(message); } } class MessageSink implements Observer { String message = null; // set by update() and read by getNextMessage() // Called by the message source when it gets a new message synchronized public void update(Observable o, Object arg) { // Get the new message message = (String)arg; // Wake up our waiting thread notify(); } // Gets the next message sent out from the message source synchronized public String getNextMessage(MessageSource source) { // Tell source we want to be told about new messages source.addObserver(this); // Wait until our update() method receives a message while (message == null) { try { wait(); } catch (Exception e) { System.out.println("Exception has occured! ERR ERR ERR"); } } // Tell source to stop telling us about new messages source.deleteObserver(this); // Now return the message we received // But first set the message instance variable to null // so update() and getNextMessage() can be called again. String messageCopy = message; message = null; return messageCopy; } }

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  • Java: How to I change the color of a specific line or row of string in a Text area?

    - by Kevin
    Hi all, the one way I could change the color is by setForground(). However when there are multiple lines of code it makes everything green or black. Is there another method or any way of solving this problem? Thanks! int key = evt.getKeyCode(); if (key == KeyEvent.VK_ENTER) { String tb1EnterdValue = tb1.getText().toString(); if((tb1EnterdValue.equals("yes")) ) { TextArea1.setForeground(Color.green); else { TextArea1.setForeground(Color.lightGray); } this.TextArea1.append(">"+tb1EnterdValue+newline); this.tb1.setText("");

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  • What's the easiest way to add Java servlets to a WAMP configured machine?

    - by Rhubarb
    I have WAMP installed on my local machine and am looking to serve up charts using jFree's Eastwood charting, which requires me to use servlets. So basically I will insert images with src tags that have URLs pointing to my servlet on the same machine. What's the easiest way to enable servlets on the same machine? Do I need to install a servlet server on a different port? Or is there a way to integrate it into WAMP?

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  • How to display an icon on JOptionPane.showInputDialog() in Java?

    - by Lion
    The following segment of code shows JOptionPane.showInputDialog() method. It works fine but I need to display a custom icon on it. I currently left it null as shown below. String operatingSystem = System.getProperty("os.name"); Object o[] = {"Turn Off", "Restart", "Stand By", "Log Off"}; Frame frame = new Frame(operatingSystem); Object selectedValue = JOptionPane.showInputDialog(frame, "What would you like to do with the system?", "Select a task", JOptionPane.INFORMATION_MESSAGE, null, o, o[0]); //<---- Here it is. How can an icon be displayed on it replacing null?

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  • Analysing objects generated by a Java application in between GCs.

    - by elec
    Is there a tool which could be used to analyse the objects being created between two separate garbage collection run (= number of objects created and their type) ? Heapdumps dont really work here as they perform a GC when they're invoked (or at least that's what I observed everytime so far), and I want to see which objects are collected by the GC, not which objects are left after the GC run, if that makes sense. ...or is it possible somehow to inspect the nature and size of objects being collected by the garbage collector ?

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  • Java me : Can we retrieve bluetooth address of connected device from an open slave connection ?

    - by Rohit
    Here is a typical sequence of events that occur : Host device opens a service ( Host device accepts and opens all incoming connections) A remote device connects to host device. Now, we have a slave connection open at host device. At host device, I want to know the bluetooth address of remote device. I can always pass it as data from remote to host device, but can I extract it from connection object somehow without any data transfer? Thanks in advance...

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  • How to get the line number an xml element is on via the Java w3c dom api

    - by Benju
    Is there a way to lookup the line number that a given element is at in an xml file via the w3c dom api? My use case for this is that we have 30,000+ maps in kml/xml format. I wrote a unit test that iterates over each file found on the hard drive (about 17GB worth) and tests that it is parseable by our application. When it fails I throw an exception that contains the element instance that was considered "invalid". In order for our mapping department (nobody here knows how to program) to easily track down the typo we would like to log the line number of the element that caused the exception. Can anybody suggest a way to do this? Please note we are using the W3C dom api included in the Android 1.6 SDK.

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  • Auto-size zoom on Google Maps in java? (depending android screen resolution)

    - by poeschlorn
    Hey guys, i've got 2 GeoPoints given to show them on the map with markers... so far so good... how can I get the optimum zoom level for the MapController in order to focus the middle of both points, but also have them on the map. The whole thing should work at different screen resolutions. Sorry for asking that silly question, I know thats not very difficult, but at the moment my head is boiling :/

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  • Java Swing rendering bug on Windows 7 look-and-feel?

    - by John B.
    The knob on vertical JSlider's on my Windows 7 machine (with native look-and-feel) is really, really tiny in both directions. Not just skinny but short as well. Can anyone confirm this? Should I report it? If so, where? Thanks! Here is the code for the sample program (in the screen shot): import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JSlider; import javax.swing.SwingConstants; import javax.swing.UIManager; public class SliderTest { public static void main( String[] args ) { // Set the look and feel to that of the system try { UIManager.setLookAndFeel( UIManager.getSystemLookAndFeelClassName() ); } catch ( Exception e ) { System.err.println( e ); } // Launch the GUI from the event dispatch thread javax.swing.SwingUtilities.invokeLater( new Runnable() { public void run () { JFrame window = new JFrame(); window.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); JPanel contentPane = new JPanel(); contentPane.add( new JSlider(SwingConstants.HORIZONTAL) ); contentPane.add( new JSlider(SwingConstants.VERTICAL) ); window.setContentPane( contentPane ); window.pack(); window.setLocationRelativeTo( null ); // Center window window.setVisible( true ); } }); } }

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  • [app-engine-java-groovy] One-to-Many relationship. Select objects from datastore.

    - by Olexandr
    Hi. I've omitted some code(package declarations, imports, other fields) for shortness. I have here simple One-to-Many relation. It worked fine till this moment. @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true") class Restaurant implements Serializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) Key id @Persistent(mappedBy = "restaurant") List<RestaurantAddress> addresses = new ArrayList<RestaurantAddress>() } //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= @PersistenceCapable(identityType = IdentityType.APPLICATION, detachable="true") class RestaurantAddress implements Serializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) Key id @Persistent Restaurant restaurant } Now i need to get(select) all the Restaurants from DB: def getRestaurantsToExport(final String dst, final int count) { String field = restaurantExportFields[dst] return transactionExecute() { PersistenceManager pm -> Query q = pm.newQuery(Restaurant.class) q.filter = "$field == null" q.setRange(0, count) return q.execute() } } But there are on problem - query gives me 12 restaurants(as in DB) but every Restaurant has 0 Address but in Datastore every Restaurant has minimum 2 addresses. Have anyone the same problem or knows the solution ?

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  • Java: Allowing the child thread to kill itself on InterruptedException?

    - by Zombies
    I am using a ThreadPool via ExecutorService. By calling shutDownNow() it interrupts all running threads in the pool. When this happens I want these threads to give up their resources (socket and db connections) and simply die, but without continuing to run anymore logic, eg: inserting anything into the DB. What is the simplest way to achieve this? Bellow is some sample code: public void threadTest() { Thread t = new Thread(new Runnable() { public void run() { try { Thread.sleep(999999); } catch (InterruptedException e) { //invoke thread suicide logic here } } }); t.start(); t.interrupt(); try { Thread.sleep(4000); } catch (InterruptedException e) { } }

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  • How to access java collection, just like the table in the database, having indexes and LINQ-like que

    - by Shaman
    This task occurs from time to time in my projects. I need to handle a collection of some complex elements, having different attributes, such as login, password_hash, role, etc. And, I need to be able to query that collection, just like I query a table in the database, having only partial data. For example: get all users, with role "user". Or check, if there's a user with login "root" and role "superuser". Removing items, based on same data is also needed. The first attempt I've tried is to use Google collections, Apache collections, and lambdaj. All of them have very similar preicate mechanism, but with a great disadvantage: it is based on iteration, one by one, over the collection of items, which is not good, for often used collections, containing big amounts of data. Could you please suggest me some solution? Thanks.

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