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  • Efficient synchronization of querying an array of resources

    - by Erel Segal Halevi
    There is a list of N resources, each of them can be queried by at most a single thread at a time. There are serveral threads that need to do the same thing at approximately the same time: query each of the resources (each thread has a different query), in arbitrary order, and collect the responses. If each thread loops over the resources in the same order, from 0 to N-1, then they will probably have to wait for each other, which is not efficient. I thought of letting the threads loop over the resources in a random permutation, but this seems too complex and also not so efficient, for example, for 2 resources and 2 threads, in half the cases they will choose the same order and wait for each other. Is there a simple and more efficient way to solve this?

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  • Are there any guarantees in JLS about order of execution static initialization blocks?

    - by Roman
    I wonder if it's reliable to use a construction like: private static final Map<String, String> engMessages; private static final Map<String, String> rusMessages; static { engMessages = new HashMap<String, String> () {{ put ("msgname", "value"); }}; rusMessages = new HashMap<String, String> () {{ put ("msgname", "????????"); }}; } private static Map<String, String> msgSource; static { msgSource = engMessages; } public static String msg (String msgName) { return msgSource.get (msgName); } Is there a possibility that I'll get NullPointerException because msgSource initialization block will be executed before the block which initializes engMessages? (about why don't I do msgSource initialization at the end of upper init. block: just the matter of taste; I'll do so if the described construction is unreliable)

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  • Help in J2ME for creating image and parse it

    - by HAMED
    Can anyone tell me how i can parse a png image into many png images in J2ME??? for examole:I just wnat to have a source image 150*150 pixel and parse it to 10 image with 15*15 pixel. I write an elemantary code that have exeption. This is my code: public class HelloMIDlet extends MIDlet implements CommandListener { private boolean midletPaused = false; private Command exitCommand; private Form form; private StringItem stringItem; Image im , im2; Form form1 = null; public HelloMIDlet() { try { // create source image im = Image.createImage("/image1.JPG"); int height = im.getHeight() ; int width = im.getWidth() ; int x = 0 ; int y = 0 ; while ( y < height ){ while ( x < width ){ // create 15*15 pixel of source image im2 = im.createImage(im, x, y, 15, 15, Sprite.TRANS_NONE) ; x += 15 ; } y += 15 ; x = 0 ; } } catch (IOException ex) { ex.printStackTrace(); } } please help me to make it right....It's emergency! Thanks a lot guys...

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  • Tower of Hanoi, stop sliding

    - by ArtWorkAD
    Hi, I developed a solution for the Tower of Hanoi problem: public static void bewege(int h, char quelle, char ablage, char ziel) { if(h > 0){ bewege(h - 1, quelle, ziel, ablage); System.out.println("Move "+ h +" from " + quelle + " to " + ziel); bewege(h - 1, ablage, quelle, ziel); } } It works fine. Now i want to limit the number of slides and throw an exception if a certain limit is reached. I tried it with a counter but it does not work: class HanoiNK{ public static void main(String args[]){ Integer n = Integer.parseInt(args[0]); Integer k = Integer.parseInt(args[1]); try{ bewege(k, n, 'A', 'B', 'C'); }catch(Exception e){ System.out.println(e); } } public static void bewege(int c, int h, char quelle, char ablage, char ziel) throws Exception{ if(h > 0){ if(counter != 0){ bewege(c, h - 1, quelle, ziel, ablage); c--; System.out.println("Move "+ h +" from " + quelle + " to " + ziel); bewege(c, h - 1, ablage, quelle, ziel); c--; }else{ throw new Exception("stop sliding"); } } } } The exception is never thrown. Any ideas?

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  • How can I change GWT's widget CSS values?

    - by Xorty
    Basically, I like default theme widgets. However, I need to change font size on DecoratedStackPanel widget. I think it should be possible with something like this: decoratedStackPanel.getElement().getStyle().setProperty("fontSize", "12pt"); However, "fontSize" is not valid name for property and I didn't find way how to get all element's properties. Therefore, I don't know correct property name. Any ideas? Please, don't post about inheriting widget or writing custom CSS. I like default one but the font size. This should be possible afaik.

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  • Accessing global variable in multithreaded Tomcat server

    - by jwegan
    I have a singleton object that I construct like thus: private static volatile KeyMapper mapper = null; public static KeyMapper getMapper() { if(mapper == null) { synchronized(Utils.class) { if(mapper == null) { mapper = new LocalMemoryMapper(); } } } return mapper; } The class KeyMapper is basically a synchronized wrapper to HashMap with only two functions, one to add a mapping and one to remove a mapping. When running in Tomcat 6.24 on my 32bit Windows machine everything works fine. However when running on a 64 bit Linux machine (CentOS 5.4 with OpenJDK 1.6.0-b09) I add one mapping and print out the size of the HashMap used by KeyMapper to verify the mapping got added (i.e. verify size = 1). Then I try to retrieve the mapping with another request and I keep getting null and when I checked the size of the HashMap it was 0. I'm confident the mapping isn't accidentally being removed since I've commented out all calls to remove (and I don't use clear or any other mutators, just get and put). The requests are going through Tomcat 6.24 (configured to use 200 threads with a minimum of 4 threads) and I passed -Xnoclassgc to the jvm to ensure the class isn't inadvertently getting garbage collected (jvm is also running in -server mode). I also added a finalize method to KeyMapper to print to stderr if it ever gets garbage collected to verify that it wasn't being garbage collected. I'm at my wits end and I can't figure out why one minute the entry in HashMap is there and the next it isn't :(

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  • How can I make a family of singletons?

    - by Jay
    I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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  • jaxb entity print out as xml

    - by Cristian Boariu
    Hi, I have a class, let's say User adnotated with @XmlRootElement, with some properties (name, surname etc). I use this class for REST operations, as application/xml. The client will POST User class so i want to keep the values in the log. Is there any method in jax-ws to prints out this object as xml? For instance: log.info("Customers sent a USER"+user.whichMethod()); Customer sent a User <user> <name>cristi</name> <surname>kevin</surname> </user> Thanks.

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  • display a confirmation popup on button click based on condition

    - by Raaz
    I have a p:commandButton on click of which I need to add a few values to a list. In my managed bean, I'm validating the value that has to be added, and if it validates to false, I have to display a confirmation popup. This is my code - <p:commandButton id="add" value="Add" type="submit" action="#{bean.doAdd}" ajax="false" update=":List"/> And in the bean, on click of the "Add" button, public String doAdd() throws Exception { if(response != null) { if(keyList.contains(response)) { if(!responseList.contains(response)) { responseList.add(response); } } else { //Have to display confirmation popup. } response = ""; } return response; } I'm using jsf 2.0 and primefaces 3.0. Can someone please tell me how to display the popup from the bean?

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  • JDO in Google App Engine: order of keys in unowned one-to-many relationship

    - by Kel
    I'm implementing web application with JDO in Google App Engine. According to documentation, in owned one-to-many relationships, order of elements in "owner" object collection is determined either by automatically created index field, or by information given in explicit ordering clause. For example: @PersistenceCapable public class Person { // ... @Order(extensions = @Extension(vendorName="datanucleus", key="list-ordering", value="country asc, city asc")) private List<ContactInfo> contacts = new List<ContactInfo>(); In unowned relationships, "owner" object contains collection of keys of "nested" objects, for example: @PersistenceCapable public class Author { // ... @Persistent private List<Key> books; Is order of keys preserved, if I use List<Key> collection in "owner" object for storing keys of "nested" elements? I could not find answer neither in JDO relationships article, nor in Data Classes article :(

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  • Why are only some of my attributes shown in the response xml of jaxws?

    - by Andreas
    I created a jaxws webservice, but it returns only some of the attributes of my objects in the response xml. E.g. public class MyObject { private String attribute1; private String attribute2; //getter and setter } But the returned XML only contains <soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ns2:getVariantsResponse xmlns:ns2="mynamespace"> <myObject> <attribute1>stringcontent</attribute1> </myObject> ....

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  • Why do InterruptedExceptions clear a thread's interrupted status?

    - by Hanno Fietz
    If a thread is interrupted while inside Object.wait() or Thread.join(), it throws an InterruptedException, which resets the thread's interrupted status. I. e., if I have a loop like this inside a Runnable.run(): while (!this._workerThread.isInterrupted()) { // do something try { synchronized (this) { this.wait(this._waitPeriod); } } catch (InterruptedException e) { if (!this._isStopping()) { this._handleFault(e); } } } the thread will continue to run after calling interrupt(). This means I have to explicitly break out of the loop by checking for my own stop flag in the loop condition, rethrow the exception, or add a break. Now, this is not exactly a problem, since this behaviour is well documented and doesn't prevent me from doing anything the way I want. However, I don't seem to understand the concept behind it: Why is a thread not considered interrupted anymore once the exception has been thrown? A similar behaviour also occurs if you get the interrupted status with interrupted() instead of isInterrupted(), then, too, the thread will only appear interrupted once. Am I doing something unusual here? For example, is it more common to catch the InterruptedException outside the loop? (Even though I'm not exactly a beginner, I tagged this "beginner", because it seems like a very basic question to me, looking at it.)

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  • Debugging stack data not assigned to a named variable

    - by gibbss
    Is there a way to view stack elements like un-assigned return values or exceptions that not assigned to a local variable? (e.g. throw new ...) For example, suppose I have code along the lines of: public String foo(InputStream in) throws IOException { NastyObj obj = null; try { obj = new NastyObj(in); return (obj.read()); } finally { if (obj != null) obj.close(); } } Is there any way to view the return or exception value without stepping to a higher level frame where it is assigned? This is particularly relevant with exceptions because you often have to step back up through a number of frames to find an actual handler. I usually use the Eclipse debugging environment, but any answer is appreciated. Also, if this cannot be done, can you explain why? (JVM, JPDA limitation?)

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  • Using Apache Velocity with StringBuilders/CharSequences

    - by mindas
    We are using Apache Velocity for dynamic templates. At the moment Velocity has following methods for evaluation/replacing: public static boolean evaluate(Context context, Writer writer, String logTag, Reader reader) public static boolean evaluate(Context context, Writer out, String logTag, String instring) We use these methods by providing StringWriter to write evaluation results. Our incoming data is coming in StringBuilder format so we use StringBuilder.toString and feed it as instring. The problem is that our templates are fairly large (can be megabytes, tens of Ms on rare cases), replacements occur very frequently and each replacement operation triples the amount of required memory (incoming data + StringBuilder.toString() which creates a new copy + outgoing data). I was wondering if there is a way to improve this. E.g. if I could find a way to provide a Reader and Writer on top of same StringBuilder instance that only uses extra memory for in/out differences, would that be a good approach? Has anybody done anything similar and could share any source for such a class? Or maybe there any better solutions to given problem?

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  • Add 'expand' button to JTree node that has no children?

    - by thedude19
    I'd like to add the 'expand' button to my JTree's nodes to indicate that they are expandable. The catch is that they have no children until the user clicks on them (due to processing that happens in the background). Is there any way I can set a node as a parent or having children without it actually having children? Thanks

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  • non-servlet JSP

    - by h2g2java
    I realise there are EL and near EL frameworks like StringTemplate, JUEL, Velocity, etc. However, I am not asking for list of alternatives to JSTL/EL. I came across a package more than a year ago, someone who wrote a util that emulates the functionality of JSP for non-servlet env, i.e., JSP composition which does not need a "servlet container" to function. I ignored it and now I think it would be helpful to me and I need help to recall what it is. My actual motivation is similar to what StringTemplate, JUEL, Velocity would offer to help me compose SQL blocks, HTML blocks but I am thinking that JSPs are precompiled into bytecode and JSPs are more run-time efficient since run-time parsing is done no more than once. So actually, recommendation for alternatives would be acceptable as long as the templates are precompiled into bytecode. But I still prefer the JSP emulator.

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  • Relation many-to-many with attributes : how ?

    - by mada
    Hi, Excuse me for my poor english in advance as it is not my mother tongue. Like in this example: http://www.xylax.net/hibernate/manytomany.html But i have in the table foo-bar 2 attributes which are not part of the primary or foreign keys.: one boolean(A) & one string(B). I know how to map it without attributes but not in this case. I have not found an answer in the documentation. I need to know please how to map it & what kind of collection i have to declare in my class Foo. Thanks in advance for your answer. I really appreciate the time given by you.

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  • Get rid of jfreechart chartpanel unnecessary space

    - by ryvantage
    I am trying to get a JFreeChart ChartPanel to remove unwanted extra space between the edge of the panel and the graph itself. To best illustrate, here's a SSCCE (with JFreeChart installed): public static void main(String[] args) { JPanel panel = new JPanel(new GridBagLayout()); GridBagConstraints gbc = new GridBagConstraints(); gbc.fill = GridBagConstraints.BOTH; gbc.gridwidth = 1; gbc.gridheight = 1; gbc.weightx = 1; gbc.weighty = 1; gbc.gridy = 1; gbc.gridx = 1; panel.add(createChart("Sales", Chart_Type.DOLLARS, 100000, 115000), gbc); gbc.gridx = 2; panel.add(createChart("Quotes", Chart_Type.DOLLARS, 250000, 240000), gbc); gbc.gridx = 3; panel.add(createChart("Profits", Chart_Type.PERCENTAGE, 40.00, 38.00), gbc); JFrame frame = new JFrame(); frame.add(panel); frame.setSize(800, 300); frame.setLocationRelativeTo(null); frame.setVisible(true); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } private static ChartPanel createChart(String title, Chart_Type type, double goal, double actual) { double maxValue = goal * 2; double yellowToGreenNum = goal; double redToYellowNum = goal * .75; DefaultValueDataset dataset = new DefaultValueDataset(actual); JFreeChart jfreechart = createChart(dataset, Math.max(actual, maxValue), redToYellowNum, yellowToGreenNum, title, type); ChartPanel chartPanel = new ChartPanel(jfreechart); chartPanel.setBorder(new LineBorder(Color.red)); return chartPanel; } private static JFreeChart createChart(ValueDataset valuedataset, Number maxValue, Number redToYellowNum, Number yellowToGreenNum, String title, Chart_Type type) { MeterPlot meterplot = new MeterPlot(valuedataset); meterplot.setRange(new Range(0.0D, maxValue.doubleValue())); meterplot.addInterval(new MeterInterval(" Goal Not Met ", new Range(0.0D, redToYellowNum.doubleValue()), Color.lightGray, new BasicStroke(2.0F), new Color(255, 0, 0, 128))); meterplot.addInterval(new MeterInterval(" Goal Almost Met ", new Range(redToYellowNum.doubleValue(), yellowToGreenNum.doubleValue()), Color.lightGray, new BasicStroke(2.0F), new Color(255, 255, 0, 64))); meterplot.addInterval(new MeterInterval(" Goal Met ", new Range(yellowToGreenNum.doubleValue(), maxValue.doubleValue()), Color.lightGray, new BasicStroke(2.0F), new Color(0, 255, 0, 64))); meterplot.setNeedlePaint(Color.darkGray); meterplot.setDialBackgroundPaint(Color.white); meterplot.setDialOutlinePaint(Color.gray); meterplot.setDialShape(DialShape.CHORD); meterplot.setMeterAngle(260); meterplot.setTickLabelsVisible(false); meterplot.setTickSize(maxValue.doubleValue() / 20); meterplot.setTickPaint(Color.lightGray); meterplot.setValuePaint(Color.black); meterplot.setValueFont(new Font("Dialog", Font.BOLD, 0)); meterplot.setUnits(""); if(type == Chart_Type.DOLLARS) meterplot.setTickLabelFormat(NumberFormat.getCurrencyInstance()); else if(type == Chart_Type.PERCENTAGE) meterplot.setTickLabelFormat(NumberFormat.getPercentInstance()); JFreeChart jfreechart = new JFreeChart(title, JFreeChart.DEFAULT_TITLE_FONT, meterplot, false); return jfreechart; } enum Chart_Type { DOLLARS, PERCENTAGE } If you resize the frame, you can see that you cannot make the edge of the graph go to the edge of the panel (the panels are outlined in red). Especially on the bottom - there is always a gap between the bottom the graph and the bottom of the panel. Is there a way to make the graph fill the entire area? Is there a way to at least guarantee that it is touching one edge of the panel (i.e., it is touching the top and bottom or the left and right) ??

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  • Entities equals(), hashCode() and toString(). How to correctly implement them?

    - by spike07
    I'm implementing equals(), hashCode() and toString() of my entities using all the available fields in the bean. I'm getting some Lazy init Exception on the frontend when I try to compare the equality or when I print the obj state. That's because some list in the entity can be lazy initialized. I'm wondering what's the correct way to for implementing equals() and toString() on an entity object.

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  • writing large excel spreadsheets

    - by pstanton
    has anybody found a library that works well with large spreadsheets? I've tried apache's POI but it fails miserably working with large files - both reading and writing. It uses massive amounts of memory leaving you needing a supercomputer to parse or create a 20+mb spreadsheet. Surely there is a more memory efficient way and someone has written it?!

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  • create zip files with arabic characters

    - by fatiDev
    i have the following situation i have to modify an existing files and return a zip containing this modified files , i'm in web application context what i done up to now is : ///////////////// modifying the existing file with poi librairy FileInputStream inpoi = new FileInputStream("file_path"); POIFSFileSystem fs = new POIFSFileSystem(inpoi); HWPFDocument doc = new HWPFDocument(fs); Range r = doc.getRange(); r.replaceText("<nomPrenom>","test"); byte[] b = doc.getDataStream(); //////////////////////// create the zip file and copy the modified files into it ZipOutputStream out = new ZipOutputStream(new FileOutputStream("my.zip")); out.putNextEntry(new ZipEntry("file")); for (int j = 0; j < b.length; j++) { out.write(b[j]); } the created zipped file can't be read correctly with word given that the original file is wrotten in arabic

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