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  • Java. Writing a matrix in a file using column information. ( matrix transposition )

    - by Dmitry
    Hello, everybody! I have a file in which a matrix is stored. This file has a RandomAccessFile type. This matrix is stored by columns. I mean that in an i-th row of this matrix an i-th column (of a real matrix) is stored. There is an example: i-th row: 1 2 3 4 (in the file). That means that the real matrix has an i-th column: (1 2 3 4)(is transposed). I need to save this matrix in a natural way (by rows) in a new file, which I will then open with FileReader and display with TextArea. Do you know, how to do that? If so, please help =)

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  • Is this use of PreparedStatements in a Thread in JAVA correct?

    - by Gormcito
    I'm still an undergrad just working part time and so I'm always trying to be aware of better ways to do things. Recently I had to write a program for work where the main thread of the program would spawn "task" threads (for each db "task" record) which would perform some operations and then update the record to say that it has finished. Therefore I needed a database connection object and PreparedStatement objects in or available to the ThreadedTask objects. This is roughly what I ended up writing, is creating a PreparedStatement object per thread a waste? I thought static PreparedStatments could create race conditions... Thread A stmt.setInt(); Thread B stmt.setInt(); Thread A stmt.execute(); Thread B stmt.execute(); A´s version never gets execed.. Is this thread safe? Is creating and destroying PreparedStatement objects that are always the same not a huge waste? public class ThreadedTask implements runnable { private final PreparedStatement taskCompleteStmt; public ThreadedTask() { //... taskCompleteStmt = Main.db.prepareStatement(...); } public run() { //... taskCompleteStmt.executeUpdate(); } } public class Main { public static final db = DriverManager.getConnection(...); }

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  • What features do you expect from a Java (Rich) Client Framework?

    - by Peter Walser
    I'm intending to design (and provide a reference implementation for) a new Swing Rich Client Framework. My job and personal experience covers many project-specific Swing client frameworks as well as the Eclipse RCP, and every one of them had some original and clever concepts, but also drawbacks and rigid realizations. My plan is to incorporate the best of those concepts and features into a new framework whose core is very open and extendable. For my must-have-features list, I'm counting on your input and hope you can share some concept pearls & diamonds you've encountered in other frameworks, or features you always wanted to have or have in a better way. The framework is intended for very simple to very complex and sophisticated projects for clients that need full i18n for richt clients that execute some or all of the non-presentation logic on the server to be very lightweight to be easy to learn and use Thanks in advance for sharing your insights :)

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  • Java access the caller variable, is it possible? how?

    - by lacas
    i have a class main { Class1 class1=new Class1(); class1.function1(); } class Class1 { int abc=1; ArrayList<Class2> class2s=new ArrayList<Class2>(); int function1() { class2s.add(new Class2(asd)); abc=555; } } class Class2 { int functionx() { Log.e("abc?", ""+PARENT???.abc); } } How can I get the caller Class's variable, say abc?

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  • How should I map an abstract class with simple xml in Java?

    - by spderosso
    Hi, I want to achieve the following xml using simple xml framework (http://simple.sourceforge.net/): <events> <course-added date="01/01/2010"> ... </course-added> <course-removed date="01/02/2010"> .... </course-removed> <student-enrolled date="01/02/2010"> ... </student-enrolled> </events> I have the following (but it doesn't achieve the desired xml): @Root(name="events") class XMLEvents { @ElementList(inline=true) ArrayList<XMLEvent> events = Lists.newArrayList(); ... } abstract class XMLEvent { @Attribute(name="date") String dateOfEventFormatted; ... } And different type of XMLNodes that have different information (but are all different types of events) @Root(name="course-added") class XMLCourseAdded extends XMLEvent{ @Element(name="course") XMLCourseLongFormat course; .... } @Root(name="course-removed") class XMLCourseRemoved extends XMLEvent { @Element(name="course-id") String courseId; ... } How should I do the mapping or what should I change in order to be able to achieve de desired xml? Thanks!

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  • Selenium : Handling Loading screens obscuring the web elements. (Java)

    - by Sheldon Cooper
    I'm writing an automated test case for a web page. Here's my scenario. I have to click and type on various web elements in an html form. But, sometimes while typing on a text field, an ajax loading image appears , fogging all elements i want to interact with. So, I'm using web-driver wait before clicking on the actual elements like below, WebdriverWait innerwait=new WebDriverWait(driver,30); innerwait.until(ExpectedConditions.elementToBeClickable(By.xpath(fieldID))); driver.findelement(By.xpath(fieldID)).click(); But the wait function returns the element even if it is fogged by another image and is not clickable. But the click() throws an exception as Element is not clickable at point (586.5, 278). Other element would receive the click: <div>Loading image</div> Do I have to check every time if the loading image appeared before interacting with any elements?.(I can't predict when the loading image will appear and fog all elements.) Is there any efficient way to handle this? Currently I'm using the following function to wait till the loading image disappears, public void wait_for_ajax_loading() throws Exception { try{ Thread.sleep(2000); if(selenium.isElementPresent("id=loadingPanel")) while(selenium.isElementPresent("id=loadingPanel")&&selenium.isVisible("id=loadingPanel"))//wait till the loading screen disappears { Thread.sleep(2000); System.out.println("Loading...."); }} catch(Exception e){ Logger.logPrint("Exception in wait_for_ajax_loading() "+e); Logger.failedReport(report, e); driver.quit(); System.exit(0); } } But I don't know exactly when to call the above function, calling it at a wrong time will fail. Is there any efficient way to check if an element is actually clickable? or the loading image is present? Thanks..

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  • Java Persistence: Cast to something the result of Query.getResultList() ?

    - by GuiSim
    Hey everyone, I'm new to persistence / hibernate and I need your help. Here's the situation. I have a table that contains some stuff. Let's call them Persons. I'd like to get all the entries from the database that are in that table. I have a Person class that is a simple POJO with a property for each column in the table (name, age,..) Here's what I have : Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = lQuery.getResultList(); However, I get a warning saying that this is an unchecked conversion from List to List<Person> I thought that simply changing the code to Query lQuery = myEntityManager.createQuery("from Person") List<Person> personList = (List<Person>)lQuery.getResultList(); would work.. but it doesn't. Is there a way to do this ? Does persistence allow me to set the return type of the query ? (Through generics maybe ? )

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  • Convert bit vector (array of booleans) to an integer, and integer to bit vector, in Java.

    - by dreeves
    What's the best way to unstub the following functions? // Convert a bit-vector to an integer. int bitvec2int(boolean[] b) { [CODE HERE] } // Convert an integer x to an n-element bit-vector. boolean[] int2bitvec(int x, int n) { [CODE HERE] } Or is there a better way to do that sort of thing than passing boolean arrays around? This comes up in an Android app where we need an array of 20 booleans to persist and the easiest way to do that is to write an integer or string to the key-value store. I'll post the way we (Bee and I) wrote the above as an answer. Thanks!

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  • How can two programs talk to each other in Java?

    - by Arnon
    I want to ?reduce? the CPU usage/ROM usage/RAM usage - generally?, all system resources that my app uses - who doesn't? :) For this reason I want to split the preferences window from the rest of the application, and let the preferences window to run as ?independent? program. The preferences program ?should? write to a Property file(not a problem at all) and to send a "update signal" to the main program - which means it should call the update method (that i wrote) that found in the Main class. How can I call the update method in the Main program from the preferences program? To put it another way, is a way to build preferences window that take system resources just when the window appears? Is this approach - of separating programs and let them talk to each other (somehow) - the right approach for speeding up my programs?

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  • Is there an easy way to copy an iterator into a list in Java?

    - by Space_C0wb0y
    I want something like this: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); fooList.addAll(fooIterator); } which should be equivalent to: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); while(fooIterator.hasNext()) fooList.add(fooIterator.next()); } Is there any method in the API to achieve that, or is this the only way?

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  • Is there a way to launch an aggressive and complete garbage collection in Java?

    - by Gnoupi
    For memory optimization reasons, I'm launching myself the garbage collector during profiling, to check if objects are correctly cleaned after disposing of them. The call to garbage collector is not enough, though, and it seems that there is no guarantee of what it will clean. Is there a way to call it, to be sure it will recover as much as it can, in profiling conditions (this would have no point in production, of course)? Or is "calling it several times" the only way to be "almost sure"? Or did I simply misunderstand something about the Garbage Collector?

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  • How to access a subset of XML data in Java when the XML data is too large to fit in memory?

    - by Michael Jones
    What I would really like is a streaming API that works sort of like StAX, and sort of like DOM/JDom. It would be streaming in the sense that it would be very lazy and not read things in until needed. It would also be streaming in the sense that it would read everything forwards (but not backwards). Here's what code that used such an API would look like. URL url = ... XMLStream xml = XXXFactory(url.inputStream()) ; // process each <book> element in this document. // the <book> element may have subnodes. // You get a DOM/JDOM like tree rooted at the next <book>. while (xml.hasContent()) { XMLElement book = xml.getNextElement("book"); processBook(book); } Does anything like this exist?

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  • Java JIT compiler compiles at compile time or runtime ?

    - by Tony
    From wiki: In computing, just-in-time compilation (JIT), also known as dynamic translation, is a technique for improving the runtime performance of a computer program. So I guess JVM has another compiler, not javac, that only compiles bytecode to machine code at runtime, while javac compiles sources to bytecode,is that right?

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  • Extracting two strings from quotations in Java using regex?

    - by user656710
    Hi everyone, I'm new to using patterns and looked everywhere on the internet for an explanation to this problem. Say I have a string: String info = "Data I need to extract is 'here' and 'also here'"; How would I extract the words: here also here without the single quotes using a pattern? This is what I have so far... Pattern p = Pattern.compile("(?<=\').*(?=\')"); But it returns ( here and 'also here ) minus the brackets, that is just for viewing. It skips over the second piece of data and goes straight to the last quote... Thank you!

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  • Why am I getting a Java NoSuchPortException when the port exists?

    - by user258526
    Got the following production code below, I'm using it for a new driver. portName is COM4 and this port exists on the PC (and I can connect to it with hyperterminal), so why does Javacomm throw a NoSuchPortException? COM4 shows up fine in device mgr. too final String portName = getSerialPort(); try { final CommPortIdentifier id = CommPortIdentifier.getPortIdentifier(portName); port = (SerialPort) id.open(getName(), 1000); } catch (NoSuchPortException nspe) { report(SeverityCode.LEVEL2, getName(), "PIN Pad is not connected to " + portName + " port, or the port does not exist."); return; } catch (PortInUseException piue) { report(SeverityCode.LEVEL2, getName(), portName + " port is already in-use by some other device. Reason: " + piue.getMessage()); return; }

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  • How to implement event listener in background of the main program in java?

    - by Johny
    Hi im a beginner so sorry for my question if it sounds naive. I want to implement a thread that runs in the background and listens all the time. By listening i mean, say it keeps check on a value returned from main thread and if the vaue exceeds certain figure, it executes some method, or say exits the program. If you could give me some idea or at least refer me to something useful, that'll be great.

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  • Can you tell on runtime if you're running java from within a jar?

    - by Dikla
    Hi, I have an application that some of my users run from Eclipse, and others run it by using a jar file. I want some actions to be done when running from within the jar, but I don't want them to be done when running from Eclipse. Is there a way to know on runtime whether the current application is running from within a jar? Thanks! Dikla

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  • Whats the difference between theese two java code snippets?

    - by Joe Hopfgartner
    I have this code i am doing for university. The first code works as expected, the second one provides different results. I can not see what they are doing differently?? first: public Mat3 getNormalMatrix() { return new Mat3(this.getInverseMatrix()).transpose(); } second: public Mat3 getNormalMatrix() { Mat4 mat = this.getInverseMatrix(); Mat3 bla = new Mat3(mat); bla.transpose(); return bla; }

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