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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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  • Why does a sub-class class of a class have to be static in order to initialize the sub-class in the

    - by Alex
    So, the question is more or less as I wrote. I understand that it's probably not clear at all so I'll give an example. I have class Tree and in it there is the class Node, and the empty constructor of Tree is written: public class RBTree { private RBNode head; public RBTree(RBNode head,RBTree leftT,RBTree rightT){ this.head=head; this.head.leftT.head.father = head; this.head.rightT.head.father = head; } public RBTree(RBNode head){ this(head,new RBTree(),new RBTree()); } public RBTree(){ this(new RBNode(),null,null); } public class RBNode{ private int value; private boolean isBlack; private RBNode father; private RBTree leftT; private RBTree rightT; } } Eclipse gives me the error: "No enclosing instance of type RBTree is available due to some intermediate constructor invocation" for the "new RBTree()" in the empty constructor. However, if I change the RBNode to be a static class, there is no problem. So why is it working when the class is static. BTW, I found an easy solution for the cunstructor: public RBTree(){ this.head = new RBNode(); } So, I have no idea what is the problem in the first piece of code.

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  • How to add a jar build by a project to the project in eclipse?

    - by Xetius
    I have a project which as part of the build process creates an XMLBeans jar file (stbSchemas.jar) which I want to include and reference in this project. Is this the best way to go about this (Single project) or should I have a child project which is built from the parent project? I am building this using Maven2 inside Eclipse. Is there a better way to do this so that I can maintain the integrity of the projects and stability of the builds.

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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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  • Server Emulator Design Pattern

    - by adisembiring
    I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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  • Shortcut for adding to List in a HashMap

    - by Damo
    I often have a need to take a list of objects and group them into a Map based on a value contained in the object. Eg. take a list of Users and group by Country. My code for this usually looks like: Map<String, List<User>> usersByCountry = new HashMap<String, List<User>>(); for(User user : listOfUsers) { if(usersByCountry.containsKey(user.getCountry())) { //Add to existing list usersByCountry.get(user.getCountry()).add(user); } else { //Create new list List<User> users = new ArrayList<User>(1); users.add(user); usersByCountry.put(user.getCountry(), users); } } However I can't help thinking that this is awkward and some guru has a better approach. The closest I can see so far is the MultiMap from Google Collections. Are there any standard approaches? Thanks!

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  • [iText] Inserting Image onCloseDocument

    - by David
    I'm trying to insert an image in the footer of my document using iText's onCloseDocument event. I have the following code: public void onCloseDocument(PdfWriter writer, Document document) { PdfContentByte pdfByte = writer.getDirectContent(); try { // logo is a non-null global variable Image theImage = new Jpeg(logo); pdfByte.addImage(theImage, 400.0f, 0.0f, 0.0f, 400.0f, 0.0f, 0.0f); } catch (Exception e) { e.printStackTrace(); } } The code throws no exceptions, but it also fails to insert the image. This identical code is used onOpenDocument to insert the same logo. The only difference between the two methods are the coordinates in pdfByte.addImage. However, I've tried quite a few different coordinations in onCloseDocument and none of them appear anywhere in my document. Is there any troubleshooting technique for detecting content which is displayed off-page in a PDF? If not, can anyone see the problem with my onCloseDocument method? Edit: As a followup, it seems that onDocumentClose puts its content on page document.length() + 1 (according to its API). However, I don't know how to change the page number back to document.length() and place my logo on the last page.

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  • Workaround for richfaces combobox hotkey bug

    - by John
    Hi, Does anyone know a workaround for the bug https://jira.jboss.org/jira/browse/RF-8076 ? Just to clarify things, we have a form with multiple inputs, one of them being a combobox with auto complete features. We've setup a hotkey via <rich:hotKey key="return" ... /> It works great everywhere except in the combobox, and I would really like to get it working on the combobox as well. The behaviour I want when the ENTER key is pressed inside the combobox is: If the combobox context was modified by auto complete then do nothing Else action the event on ENTER key pressed We're running on seam/richfaces. I'm open to any workaround, but simplicity is much sought for. Thanks!

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Anyone know exactly which JMS messages will be redelivered in CLIENT_ACKNOWLEDGE mode if the client

    - by user360612
    The spec says "Acknowledging a consumed message automatically acknowledges the receipt of all messages that have been delivered by its session" - but what I need to know is what it means by 'delivered'. For example, if I call consumer.receive() 6 times, and then call .acknowledge on the 3rd message - is it (a) just the first 3 messages that are ack'd, or (b) all 6? I'm really hoping it's option a, i.e. messages after the one you called acknowledge on WILL be redelivered, otherwise it's hard to see how you could prevent message lost in the event of my receiver process crashing before I've had a chance to persist and acknowledge the messages. But the spec is worded such that it's not clear. I get the impression the authors of the JMS spec considered broker failure, but didn't spend too long thinking about how to protect against client failure :o( Anyway, I've been able to test with SonicMQ and found that it implements (a), i.e. messages 'received' later than the message you call .ack on DO get redelivered in the event of a crash, but I'd love to know how other people read the standard, and if anyone knows how any other providers have implemented CLIENT_ACKNOWLEDGE? (i.e. what the 'de facto' standard is) Thanks Ben

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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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  • 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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  • 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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