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  • Establishing persistent connection to a database in Java

    - by gmile
    I've ran through several examples over the web, and found that every single time I need something from the DB, I should write the following code: try { // Step 1: Load the JDBC driver. Class.forName("mysql_driver_name"); // Step 2: Establish the connection to the database. String url = "jdbc:string_to_mysql_server"; Connection conn = DriverManager.getConnection(url,"user1","password"); // fetch from the DB ... } catch (Exception e) { System.err.println("Got an exception! "); System.err.println(e.getMessage()); } It's very annoying to put up this code every time I want something from the DB, so the question is - is there a way to only once connect entirely all my app to the DB somehow at the very start point, avoiding copy-pasting mentioned code, and then be able to do everything I want with DB? I've quickly looked through NetBeans's Project menu, but didn't find any clue on how to configurate a persistent connection to a selected DB. If it's important, i'm writing a purely desktop app, i.e. using Java EE. Also, it's worth mentioning that I'm a kinda beginner in Java.

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  • Java hangs when trying to close a ProcessBuilder OutputStream

    - by Jeff Bullard
    I have the following Java code to start a ProcessBuilder, open an OutputStream, have the process write a string to an OutputStream, and then close the OutputStream. The whole thing hangs indefinitely when I try to close the OutputStream. This only happens on Windows, never on Mac or Linux. Some of the related questions seem to be close to the same problem I'm having, but I haven't been able to figure out how to apply the answers to my problem, as I am a relative newbie with Java. Here is the code. You can see I have put in a lot of println statements to try to isolate the problem. System.out.println("GenMic trying to get the input file now"); System.out.flush(); OutputStream out = child.getOutputStream(); try { System.out.println("GenMic getting ready to write the input file to out"); System.out.flush(); out.write(intext.getBytes()); System.out.println("GenMic finished writing to out"); System.out.flush(); out.close(); System.out.println("GenMic closed OutputStream"); System.out.flush(); } catch (IOException iox) { System.out.println("GenMic caught IOException 2"); System.out.flush(); String detailedMessage = iox.getMessage(); System.out.println("Exception: " + detailedMessage); System.out.flush(); throw new RuntimeException(iox); } And here is the output when this chunk is executed: GenMic trying to get the input file now GenMic getting ready to write the input file to out GenMic finished writing to out

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  • java applet stops running on exceptions

    - by Marius
    I've developed a simple applet that imports an image from the clipboard. When i run the class file from NetBeans, everything works fine. But when i try to run it as an applet ... it gives me lots of errors in the java console and does not run ... - The applet is signed - There is a static method in one class, called getImageFromClipboard(). When the applet runs, it calls this method. - getImageFromClipboard() method has a try-catch block and suppresses all errors. It simply returns either a BufferedImage or null. - When applet runs, it does some visual adjustments before calling getImageFromClipboard() Now the scenario is as follows: the class from netbeans runs, fails to import the image and adjusts the interface accordingly (displays an error in a label) But when i run it in a browser, java console is filled with errors and nothing after the getImageFromClipboard() line works. Although the applet itself loads and does everything it's supposed do do before importing the image. So why am i getting errors if i accept the certificate and all of the possible errors are in try-catch blocks? None of this code should throw any exceptions. Any ideas why this is happening? Or do you need to see the errors to tell? UPDATE I've managed to find out the problem myself. The class that i'm using is not in the jar file :( How do i add it in? I'm using "add jar folder" in netbeans on the libraries package to import it but it does not seem to get copied to the jar.

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  • Over ride default look and feel Java

    - by Aizaz
    I want to over ride java look and feel. I just want to show the buttons differently. I want all the features of Windows Look and Feel but only buttons differently. I hope you get my point. Color color = new Color(220, 220, 220, 200); UIManager.put("OptionPane.background", color); UIManager.put("Panel.background", color); UIManager.put("Button.foreground", new Color(255, 255, 255, 255)); List<Object> gradients = new ArrayList<Object>(5); gradients.add(0.00f); gradients.add(0.00f); gradients.add(new Color(0xC1C1C1)); gradients.add(new Color(0xFFFFFF)); gradients.add(new Color(0x5C5D5C)); UIManager.put("Button.gradient", gradients); UIManager.put("Button.highlight",Color.RED); UIManager.setLookAndFeel(com.sun.java.swing.plaf.windows.WindowsLookAndFeel);

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  • Silverlight 3 + Java WebService

    - by Heko
    Hello! I have a Silverlight 3 project, and I need to call a Java WebService - the bindings are ok (SOAP 1.1 and basicHttpBinding): ClientConfig File: <configuration> <system.serviceModel> <bindings> <basicHttpBinding> <binding name="SkyinfoTestInterfaceExport2_SkyinfoTestInterfaceHttpBinding" maxBufferSize="2147483647" maxReceivedMessageSize="2147483647"> <security mode="None"> <transport> <extendedProtectionPolicy policyEnforcement="Never" /> </transport> </security> </binding> </basicHttpBinding> </bindings> <client> <endpoint address="myAddress" binding="basicHttpBinding" bindingConfiguration="SkyinfoTestInterfaceExport2_SkyinfoTestInterfaceHttpBinding" contract="SkyInfoServiceReference.SkyinfoTestInterface" name="SkyinfoTestInterfaceExport2_SkyinfoTestInterfaceHttpPort" /> </client> </system.serviceModel> When I call a method on client I get this Policy error: An error occurred while trying to make a request to URI '...'. This could be due to attempting to access a service in a cross-domain way without a proper cross-domain policy in place, or a policy that is unsuitable for SOAP services. You may need to contact the owner of the service to publish a cross-domain policy file and to ensure it allows SOAP-related HTTP headers to be sent. This error may also be caused by using internal types in the web service proxy without using the InternalsVisibleToAttribute attribute. Please see the inner exception for more details. I know about those 2 policy XML filesbut Java EE service which I'm trying to call is hosted on a IBM WebSphere Process Server to which I don't have access. Does anybody know how to work around this policy exception?

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  • Creating a QMainWindow from Java using JNI

    - by ebasconp
    Hi everybody: I'm trying to create a Qt main windows from Java using JNI directly and I got a threading error. My code looks like this: Test class: public class Test { public static void main(String... args) { System.out.println(System.getProperty("java.library.path")); TestWindow f = new TestWindow(); f.show(); } } TestWindow class: public class TestWindow { static { System.loadLibrary("mylib"); } public native void show(); } C++ impl: void JNICALL Java_testpackage_TestWindow_show (JNIEnv *, jobject) { int c = 0; char** a = NULL; QApplication* app = new QApplication(c, a); QMainWindow* mw = new QMainWindow(); mw->setWindowTitle("Hello"); mw->setGeometry(150, 150, 400, 300); mw->show(); QApplication::exec(); } and I get my window painted but frozen (it does not receive any event) and the following error message when instantiating the QMainWindow object: QCoreApplication::sendPostedEvents: Cannot send posted events for objects in another thread I know all the UI operations must done in the UI thread but in my example I created the QApplication in the only thread I have running, so, everything should work properly. I did some tests executing the code of my "show" method from a QMetaObject::invokeMethod stuff using Qt::QueuedConnection but nothing works properly. I know I could use Jambi... but I know that it could be done natively too and that is what I want to do :) Any ideas on this? Thanks in advance! Ernesto

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  • How to read XML using XPath in Java

    - by kaibuki
    Hi guys, I want to read XML data using XPath in Java, so for the information I have gathered I am not able to parse XML according to my requirement. here is what I want to do: Get XML file from online via its URL, then use XPath to parse it, I want to create two methods in it. One is in which I enter a specific node attribute id, and I get all the child nodes as result, and second is suppose I just want to get a specific child node value only <?xml version="1.0"?><howto> <topic name="Java"> <url>http://www.rgagnonjavahowto.htm</url> <car>taxi</car> </topic> <topic ame="PowerBuilder"> <url>http://www.rgagnon/pbhowto.htm</url> <url>http://www.rgagnon/pbhowtonew.htm</url> </topic> <topic name="Javascript"> <url>http://www.rgagnon/jshowto.htm</url> </topic> <topic name="VBScript"> <url>http://www.rgagnon/vbshowto.htm</url> </topic></howto> In above example I want to read all the elements if I search via @name and also one function in which I just want the url from @name 'Javascript' only return one node element. I hope I cleared my question :) Thanks. Kai

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  • BitShifting with BigIntegers in Java

    - by ThePinkPoo
    I am implementing DES Encryption in Java with use of BigIntegers. I am left shifting binary keys with Java BigIntegers by doing the BigInteger.leftShift(int n) method. Key of N (Kn) is dependent on the result of the shift of Kn-1. The problem I am getting is that I am printing out the results after each key is generated and the shifting is not the expected out put. The key is split in 2 Cn and Dn (left and right respectively). I am specifically attempting this: "To do a left shift, move each bit one place to the left, except for the first bit, which is cycled to the end of the block. " It seems to tack on O's on the end depending on the shift. Not sure how to go about correcting this. Results: c0: 11110101010100110011000011110 d0: 11110001111001100110101010100 c1: 111101010101001100110000111100 d1: 111100011110011001101010101000 c2: 11110101010100110011000011110000 d2: 11110001111001100110101010100000 c3: 1111010101010011001100001111000000 d3: 1111000111100110011010101010000000 c4: 111101010101001100110000111100000000 d4: 111100011110011001101010101000000000 c5: 11110101010100110011000011110000000000 d5: 11110001111001100110101010100000000000 c6: 1111010101010011001100001111000000000000 d6: 1111000111100110011010101010000000000000 c7: 111101010101001100110000111100000000000000 d7: 111100011110011001101010101000000000000000 c8: 1111010101010011001100001111000000000000000 d8: 1111000111100110011010101010000000000000000 c9: 111101010101001100110000111100000000000000000 d9: 111100011110011001101010101000000000000000000 c10: 11110101010100110011000011110000000000000000000 d10: 11110001111001100110101010100000000000000000000 c11: 1111010101010011001100001111000000000000000000000 d11: 1111000111100110011010101010000000000000000000000 c12: 111101010101001100110000111100000000000000000000000 d12: 111100011110011001101010101000000000000000000000000 c13: 11110101010100110011000011110000000000000000000000000 d13: 11110001111001100110101010100000000000000000000000000 c14: 1111010101010011001100001111000000000000000000000000000 d14: 1111000111100110011010101010000000000000000000000000000 c15: 11110101010100110011000011110000000000000000000000000000 d15: 11110001111001100110101010100000000000000000000000000000

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  • Optimizing processing and management of large Java data arrays

    - by mikera
    I'm writing some pretty CPU-intensive, concurrent numerical code that will process large amounts of data stored in Java arrays (e.g. lots of double[100000]s). Some of the algorithms might run millions of times over several days so getting maximum steady-state performance is a high priority. In essence, each algorithm is a Java object that has an method API something like: public double[] runMyAlgorithm(double[] inputData); or alternatively a reference could be passed to the array to store the output data: public runMyAlgorithm(double[] inputData, double[] outputData); Given this requirement, I'm trying to determine the optimal strategy for allocating / managing array space. Frequently the algorithms will need large amounts of temporary storage space. They will also take large arrays as input and create large arrays as output. Among the options I am considering are: Always allocate new arrays as local variables whenever they are needed (e.g. new double[100000]). Probably the simplest approach, but will produce a lot of garbage. Pre-allocate temporary arrays and store them as final fields in the algorithm object - big downside would be that this would mean that only one thread could run the algorithm at any one time. Keep pre-allocated temporary arrays in ThreadLocal storage, so that a thread can use a fixed amount of temporary array space whenever it needs it. ThreadLocal would be required since multiple threads will be running the same algorithm simultaneously. Pass around lots of arrays as parameters (including the temporary arrays for the algorithm to use). Not good since it will make the algorithm API extremely ugly if the caller has to be responsible for providing temporary array space.... Allocate extremely large arrays (e.g. double[10000000]) but also provide the algorithm with offsets into the array so that different threads will use a different area of the array independently. Will obviously require some code to manage the offsets and allocation of the array ranges. Any thoughts on which approach would be best (and why)?

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  • Running commands over ssh with Java

    - by Ichorus
    Scenerio: I'd like to run commands on remote machines from a Java program over ssh (I am using OpenSSH on my development machine). I'd also like to make the ssh connection by passing the password rather than setting up keys as I would with 'expect'. Problem: When trying to do the 'expect' like password login the Process that is created with ProcessBuilder cannot seem to see the password prompt. When running regular non-ssh commands (e.g 'ls') I can get the streams and interact with them just fine. I am combining standard error and standard out into one stream with redirectErrorStream(true); so I am not missing it in standard error...When I run ssh with the '-v' option, I see all of the logging in the stream but I do not see the prompt. This is my first time trying to use ProcessBuilder for something like this. I know it would be easier to use Python, Perl or good ol' expect but my boss wants to utilize what we are trying to get back (remote log files and running scripts) within an existing Java program so I am kind of stuck. Thanks in advance for the help!

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  • Applet Not Loading In Java 1.6.0_16

    - by Wayne Hartman
    I am running a Java applet compiled in 1.5 and am experiencing odd behavior when running it on computers running 1.6.0_07 and 1.6.0_16. On the *_07 version, the applet initializes and loads in the browser perfectly fine. However, computers with the *_16 are not loading at all. Even more strange, there is nothing in the Java Console to indicate any problems will loading the applet in the browser. If I run the applet from as a standalone app on said machines, it loads up just fine. The compatibility mode in the JNLP is set to 1.5+. Firefox reports no errors attempting to load the applet. Even with full tracing and logging set to all, nothing is reported in the console window. Quick facts: The JAR is signed Compiled in 1.5 Works flawlessly in browsers (FF & IE) running *_07 Does not work in browsers (FF & IE) running *_16 Works running as stand alone app in *_16 JNLP set to 1.5+ Clients are mixed *_07, *_16, and other version of 1.6 Things I have tried: Forcing the JVM to use version 1.6.0_07. This requires the user to download *_07. In my situation this is not an option, unfortunately. Ran the app on *_16 as a standalone app. This works fine, but this needs to run as an applet. Ideas?

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  • java.lang.ClassNotFoundException: org.springframework.ui.ModelMap

    - by aelshereay
    I create a simple webapp using tomcat 6, spring 2.5.6 and maven. The problem is when I boot up tomcat, I am getting the following errors: SEVERE: StandardWrapper.Throwable java.lang.NoClassDefFoundError: org/springframework/ui/ModelMap ... Caused by: java.lang.ClassNotFoundException: org.springframework.ui.ModelMap The ModelMap class does exist in spring-2.5.6.jar and spring-context-2.5.6.jar, I also have some other spring jars. All of them are being deployed to tomcat correctly, when I check the application WEB-INF (deployed to tomcat) I found all those jars there! I have only one @Controller that has a @RequestMapping("/home.htm") showForm(ModelMap model) method. My applicationContext is quite simple: <?xml version="1.0" encoding="utf-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xmlns:dwr="http://www.directwebremoting.org/schema/spring-dwr" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd http://www.directwebremoting.org/schema/spring-dwr http://www.directwebremoting.org/schema/spring-dwr-3.0.xsd" default-autowire="byName"> <context:component-scan base-package="org.myapp"/> <bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping"/> <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"></property> <property name="prefix" value="/WEB-INF/view/"></property> <property name="suffix" value=".jsp"></property> </bean> </beans>

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  • how do I get eclipse to use a different compiler version for Java?

    - by codeman73
    It seems like this should be a simple task, with the options in the Preferences menu for different JREs and the ability to set different compiler and build paths per project. However, it also seems to simply not work. For example, I have my JAVA_HOME set to a jre for Java 1.6. It's still not clear to me how Eclipse uses this, but it appears to be defaulting to this and not taking the project overrides. I have also installed Java 1.5, and added a JRE for this in eclipse in the Java-Installed JREs section. In my project, I've set the compiler compliance level to 1.5. In the build path for the project, I've added the System Library for the Java 1.5 JRE. However, I'm getting compile errors for a class that implements PreparedStatement for not implementing abstract methods that only exist in Java 1.6 PreparedStatement. Specifically, the methods setAsciiStream(int, InputStream, long) and setAsciiStream(int, InputStream) Strangely enough, it worked when we were compiling it against Java 1.4, which it was originally written for. We added the JREs for Java 1.4 and referenced that system library in the project, and set the project's compiler level to 1.4, and it works fine. But when I do the same changes to try to point to Java 1.5, it instead uses 1.6. Any ideas why?

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  • Getting a lightweight installation of java eclipse.

    - by liam
    Having dealt with yet another stupid eclipse problem, I want to try to get the lightest, most minimal eclipse installation as possible. To be clear, I use eclipse for two things: - Editing Java - Debugging Java Everything else I do through emacs/zsh (editing jsp/xml/js, file management, svn check-in, etc). I have not found any aspect of working in eclipse to do these tasks to be efficient or even reliable, so I do not want plug-ins that relate to it. From the eclipse.org site, this is the lightest install of eclipse that they have, and I don't want any of those things (bugzilla, mylyn, cvs, xml_ui), and have actually had problems with each of them even though I do not use them. So what is the minimal build I can get that will: 1) Ignore svn metadata 2) Includes the full-featured editor (intellisense and type-finding) 3) Includes the full-featured debugger (standard eclipse/jdk) Does not have any extra plug-ins, platforms, or "integrations" with other platforms, specifically, I don't want to deal with plug-ins relating to: Maven, JSP Validation, Javascript editing or validation, CVS or SVN, Mylyn, Spring or Hibernate "natures", app servers like a bundled tomcat/glassfish/etc, J2EE tools, or anything of the like. I do primarily spring/hibernate/web-mvc apps, and have never dealt with an eclipse plug-in that handles any of it gracefully, I can work effectively with my own toolset, but eclipse extensions do nothing but get in the way. I have worked with plain eclipse up to Ganymede, MyEclipse (up to 7.5), and the latest version of Spring-SourceTools, and find that they are all saddled with buggy useless plug-ins (though the combination is always different). Switching to netbeans/intellij is not an option, and my teammates work with svn-controlled .class/.project files, so it pretty much has to be eclipse. Does anyone have any good advice on how I can save a few grey hairs?

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  • Regex help in java validations

    - by user1697113
    Hi i want to do some validations.I used to put regex in JS but im new to regex in java, so i tried to make up a code on similar lines in java. Here is what i did. 1)Check whether first character in string is alphanumeric. 2)Check whether the string atleast 1 number. so i wrote a code, but it is always returning false.I am not sure if i'm doing this correctly. private static boolean checkEmbeddedPassword(final String field) { boolean returnValue=true; String testpatternAlpha="/^[A-Za-z0-9].+$/"; String testNumber="/[0-9]/"; Pattern pattern=Pattern.compile(testpatternAlpha); Pattern pattern2=Pattern.compile(testNumber); Matcher matcher = pattern.matcher(field); Matcher matcher2 = pattern2.matcher(field); boolean firstChar=matcher.matches(); boolean numberFlag=matcher2.matches(); System.out.println("-----the value of pwd iss-----"+field); System.out.println("---------Regex---------Out--put-----"+firstChar); System.out.println("---------Regex---------Out- for numeral-put-----"+numberFlag); if(firstChar){ returnValue=false; } else if(field.contains(" ")) { System.out.println("-----------cannot have space------"); returnValue=false; } else if(numberFlag) { returnValue=false; } return returnValue; }

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  • Java Random Slowdowns on Mac OS cont'd

    - by javajustice
    I asked this question a few weeks ago, but I'm still having the problem and I have some new hints. The original question is here: http://stackoverflow.com/questions/1651887/java-random-slowdowns-on-mac-os Basically, I have a java application that splits a job into independent pieces and runs them in separate threads. The threads have no synchronization or shared memory items. The only resources they do share are data files on the hard disk, with each thread having an open file channel. Most of the time it runs very fast, but occasionally it will run very slow for no apparent reason. If I attach a CPU profiler to it, then it will start running quickly again. If I take a CPU snapshot, it says its spending most of its time in "self time" in a function that doesn't do anything except check a few (unshared unsynchronized) booleans. I don't know how this could be accurate because 1, it makes no sense, and 2, attaching the profiler seems to knock the threads out of whatever mode they're in and fix the problem. Also, regardless of whether it runs fast or slow, it always finishes and gives the same output, and it never dips in total cpu usage (in this case ~1500%), implying that the threads aren't getting blocked. I have tried different garbage collectors, different sizings the parts of the memory space, writing data output to non-raid drives, and putting all data output in threads separate the main worker threads. Does anyone have any idea what kind of problem this could be? Could it be the operating system (OS X 10.6.2) ? I have not been able to duplicate it on a windows machine, but I don't have one with a similar hardware configuration.

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  • Java: Efficiency of the readLine method of the BufferedReader and possible alternatives

    - by Luhar
    We are working to reduce the latency and increase the performance of a process written in Java that consumes data (xml strings) from a socket via the readLine() method of the BufferedReader class. The data is delimited by the end of line separater (\n), and each line can be of a variable length (6KBits - 32KBits). Our code looks like: Socket sock = connection; InputStream in = sock.getInputStream(); BufferedReader inputReader = new BufferedReader(new InputStreamReader(in)); ... do { String input = inputReader.readLine(); // Executor call to parse the input thread in a seperate thread }while(true) So I have a couple of questions: Will the inputReader.readLine() method return as soon as it hits the \n character or will it wait till the buffer is full? Is there a faster of picking up data from the socket than using a BufferedReader? What happens when the size of the input string is smaller than the size of the Socket's receive buffer? What happens when the size of the input string is bigger than the size of the Socket's receive buffer? I am getting to grips (slowly) with Java's IO libraries, so any pointers are much appreciated. Thank you!

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  • Multiple elements with the same name with SimpleXML and Java

    - by LouieGeetoo
    I'm trying to use SimpleXML to parse an XML document (an ItemLookupResponse for a book from the Amazon Product Advertising API) which contains the following element: <ItemAttributes> <Author>Shane Conder</Author> <Author>Lauren Darcey</Author> <Manufacturer>Pearson Educacion</Manufacturer> <ProductGroup>Book</ProductGroup> <Title>Android Wireless Application Development: Barnes & Noble Special Edition</Title> </ItemAttributes> My problem is that I don't know how to deal with the multiple possible Author elements. Here's what I have right now for the corresponding POJO (Plain Old Java Object), keeping in mind that it's not handling the case of multiple Authors: @Element public class ItemAttributes { @Element public String Author; @Element public String Manufacturer; @Element public String Title; } (I don't care about the ProductGroup, so it's not in the class -- I'm just setting SimpleXML's strict mode to off to allow for that.) I couldn't find an example in the documentation that corresponded with such a case. Using an ElementList with (inline=true) seemed along the right lines, but I didn't see how to do it for String (as opposed to a separate Author class, which I have no need for and don't see how it would even work). Here's a similar question and answer, but for PHP: php - simpleXML how to access a specific element with the same name as others? I don't know what the Java equivalent would be to the accepted answer. Thanks in advance.

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  • java.io.StreamCorruptedException: invalid stream header: 7371007E

    - by Alex
    Hello, this is pprobably a simple question . I got a client Server application which communicate using objects. when I send only one object from the client to server all works well. when I attempt to send several objects one after another on the same stream I get StreamCorruptedException. can some one direct me to the cause of this error . Thanks client write method private SecMessage[] send(SecMessage[] msgs) { SecMessage result[]=new SecMessage[msgs.length]; Socket s=null; ObjectOutputStream objOut =null; ObjectInputStream objIn=null; try { s=new Socket("localhost",12345); objOut=new ObjectOutputStream( s.getOutputStream()); for (SecMessage msg : msgs) { objOut.writeObject(msg); } objOut.flush(); objIn=new ObjectInputStream(s.getInputStream()); for (int i=0;i<result.length;i++) result[i]=(SecMessage)objIn.readObject(); } catch(java.io.IOException e) { alert(IO_ERROR_MSG+"\n"+e.getMessage()); } catch (ClassNotFoundException e) { alert(INTERNAL_ERROR+"\n"+e.getMessage()); } finally { try {objIn.close();} catch (IOException e) {} try {objOut.close();} catch (IOException e) {} } return result; } server read method //in is an inputStream Defined in the server SecMessage rcvdMsgObj; rcvdMsgObj=(SecMessage)new ObjectInputStream(in).readObject(); return rcvdMsgObj; and the SecMessage Class is public class SecMessage implements java.io.Serializable { private static final long serialVersionUID = 3940341617988134707L; private String cmd; //... nothing interesting here , just a bunch of fields , getter and setters }

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  • Java try finally variations

    - by Petr Gladkikh
    This question nags me for a while but I did not found complete answer to it yet (e.g. this one is for C# http://stackoverflow.com/questions/463029/initializing-disposable-resources-outside-or-inside-try-finally). Consider two following Java code fragments: Closeable in = new FileInputStream("data.txt"); try { doSomething(in); } finally { in.close(); } and second variation Closeable in = null; try { in = new FileInputStream("data.txt"); doSomething(in); } finally { if (null != in) in.close(); } The part that worries me is that the thread might be somewhat interrupted between the moment resource is acquired (e.g. file is opened) but resulting value is not assigned to respective local variable. Is there any other scenarios the thread might be interrupted in the point above other than: InterruptedException (e.g. via Thread#interrupt()) or OutOfMemoryError exception is thrown JVM exits (e.g. via kill, System.exit()) Hardware fail (or bug in JVM for complete list :) I have read that second approach is somewhat more "idiomatic" but IMO in the scenario above there's no difference and in all other scenarios they are equal. So the question: What are the differences between the two? Which should I prefer if I do concerned about freeing resources (especially in heavily multi-threading applications)? Why? I would appreciate if anyone points me to parts of Java/JVM specs that support the answers.

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  • Interpreting java.lang.NoSuchMethodError message

    - by Doog
    I get the following runtime error message (along with the first line of the stack trace, which points to line 94). I'm trying to figure out why it says no such method exists. java.lang.NoSuchMethodError: com.sun.tools.doclets.formats.html.SubWriterHolderWriter.printDocLinkForMenu( ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc; Ljava/lang/String;Z)Ljava/lang/String; at com.sun.tools.doclets.formats.html.AbstractExecutableMemberWriter.writeSummaryLink( AbstractExecutableMemberWriter.java:94) Line 94 of writeSummaryLink is shown below. QUESTIONS What does "ILcom" or "Z" mean? Why there are four types in parentheses (ILcom/sun/javadoc/ClassDoc;Lcom/sun/javadoc/MemberDoc;Ljava/lang/String;Z) and one after the parentheses Ljava/lang/String; when the method printDocLinkForMenu clearly has five parameters? CODE DETAIL The writeSummaryLink method is: protected void writeSummaryLink(int context, ClassDoc cd, ProgramElementDoc member) { ExecutableMemberDoc emd = (ExecutableMemberDoc)member; String name = emd.name(); writer.strong(); writer.printDocLinkForMenu(context, cd, (MemberDoc) emd, name, false); // 94 writer.strongEnd(); writer.displayLength = name.length(); writeParameters(emd, false); } Here's the method line 94 is calling: public void printDocLinkForMenu(int context, ClassDoc classDoc, MemberDoc doc, String label, boolean strong) { String docLink = getDocLink(context, classDoc, doc, label, strong); print(deleteParameterAnchors(docLink)); }

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  • In Java it seems Public constructors are always a bad coding practice

    - by Adam Gent
    This maybe a controversial question and may not be suited for this forum (so I will not be insulted if you choose to close this question). It seems given the current capabilities of Java there is no reason to make constructors public ... ever. Friendly, private, protected are OK but public no. It seems that its almost always a better idea to provide a public static method for creating objects. Every Java Bean serialization technology (JAXB, Jackson, Spring etc...) can call a protected or private no-arg constructor. My questions are: I have never seen this practice decreed or written down anywhere? Maybe Bloch mentions it but I don't own is book. Is there a use case other than perhaps not being super DRY that I missed? EDIT: I explain why static methods are better. .1. For one you get better type inference. For example See Guava's http://code.google.com/p/guava-libraries/wiki/CollectionUtilitiesExplained .2. As a designer of the class you can later change what is returned with a static method. .3. Dealing with constructor inheritance is painful especially if you have to pre-calculate something.

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  • Problems initializing a final variable in Java

    - by froadie
    I keep running into slight variations of a problem in Java and it's starting to get to me, and I can't really think of a proper way to get around it. I have an object property that is final, but dynamic. That is, I want the value to be constant once assigned, but the value can be different each runtime. So I declare the class level variable at the beginning of the class - say private final FILE_NAME;. Then, in the constructor, I assign it a value - say FILE_NAME = buildFileName(); The problem begins when I have code in the buildFileName() method that throws an exception. So I try something like this in the constructor: try{ FILE_NAME = buildFileName(); } catch(Exception e){ ... System.exit(1); } Now I have an error - "The blank final field FILE_NAME may not have been initialized." This is where I start to get slightly annoyed at Java's strict compiler. I know that this won't be a problem because if it gets to the catch the program will exit... But the compiler doesn't know that and so doesn't allow this code. If I try to add a dummy assignment to the catch, I get - "The final field FILE_NAME may already have been assigned." I clearly can't assign a default value before the try-catch because I can only assign to it once. Any ideas...?

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  • Generate java class and call it's method dynamically

    - by Jacob
    package reflection; import java.io.*; import java.lang.reflect.*; class class0 { public void writeout0() { System.out.println("class0"); } } class class1 { public void writeout1() { System.out.println("class1"); } } class class2 { public void writeout2() { System.out.println("class2"); } } class class3 { public void run() { try { BufferedReader reader= new BufferedReader(new InputStreamReader (System.in)); String line=reader.readLine(); Class cls=Class.forName(line); //define method here } catch(Exception ee) { System.out.println("here "+ee); } } public void writeout3() { System.out.println("class3"); } } class class4 { public void writeout4() { System.out.println("class4"); } } class class5 { public void writeout5() { System.out.println("class5"); } } class class6 { public void writeout6() { System.out.println("class6"); } } class class7 { public void writeout7() { System.out.println("class7"); } } class class8 { public void writeout8() { System.out.println("class8"); } } class class9 { public void writeout9() { System.out.println("class9"); } } class testclass { public static void main(String[] args) { System.out.println("Write class name : "); class3 example=new class3(); example.run(); } } Question is ; third class will read the name of the class as String from console. Upon reading the name of the class, it will automatically and dynamically generate that class and call its writeout method.If that class is not read from input, it will not be initialized. but I can't continue any more ; i need to more something for 3.class, what can i do? Thanks;

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  • algorithim for simple colision detection in Java

    - by Bob Twinkles
    I'm not very experienced with Java, just started a couple weeks ago, but I have a simple applet that has two user controlled balls, drawn through java.awt and I need a way to detect a collision with between them. I have an algorithm for detecting collision with the walls: while (true){ if (xPositon > (300 - radius)){ xSpeed = -xSpeed; } else if (xPositon < radius){ xSpeed = -xSpeed; } else if (yPositon > (300 - radius)) { ySpeed = -ySpeed; } else if (yPositon < radius){ ySpeed = -ySpeed; } xPositon += xSpeed; yPositon += ySpeed; and for the second ball if (xPositon2 > (300 - radius)){ xSpeed2 = -xSpeed2; } else if (xPositon2 < radius){ xSpeed2 = -xSpeed2; } else if (yPositon2 > (300 - radius)) { ySpeed2 = -ySpeed2; } else if (yPositon2 < radius){ ySpeed2 = -ySpeed2; } xPositon2 += xSpeed2; yPositon2 += ySpeed2; the applet is 300 pixels by 300 pixels radius stores the radius of the circles xPositon and xPositon2 store the x cordanents for the two balls yPositon and yPositon store the y cordanents for the two balls xSpeed and xSpeed2 store the x velocities for the two balls ySpeed and ySpeed2 store the y velocities for the two balls I've only taken algebra 1 so please no advanced math or physics.

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