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  • JNI cached jclass global reference variables being garbage collected?

    - by bubbadoughball
    I'm working in the JNI Invocation API, calling into Java from C. I have some upfront initialization to cache 30+ Java classes into global references. The results of FindClass are passed into NewGlobalRef to acquire a global reference to the class. I'm caching these class variables to reuse them later. I have 30+ global references to classes (and 30+ global methodIDs for the class constructors). In the following sample, I've removed exception handling as well as JNI invocation for the purpose of shortening the code snippet. My working code has exception checks after every JNI call and I'm running with -Xcheck:jni. Here's the snippet: jclass aClass; jclass bClass; jmethodID aCtor; jmethodID bCtor; void getGlobalRef(const char* clazz, jclass* globalClass) { jclass local = (*jenv)->FindClass(jenv,clazz); if (local) { *globalClass = (jclass) (*jenv)->NewGlobalRef(jenv,local); (*jenv)->DeleteLocalRef(jenv,local); } } methodID getMethodID(jclass clazz, const char* method, const char* sig) { return (*jenv)->GetMethodID(jenv,clazz,method,sig); } void initializeJNI() { getGlobalRef("MyProj/Testclass1", &aclass); getGlobalRef("MyProj/Testclass2", &bclass); . . aCtor = getMethodID(aclass,"<init>","()V"); bCtor = getMethodID(bclass,"<init>","(I)V"); } The initializeJNI() function sets the global references for jclasses and method IDs for constructors as well as some jfieldID's and some initialization of C data structures. After initialization, when I call into a JNI function using some of the cached jclasses and ctor jmethodIDs, I get a bad global or local reference calling reported from the -Xcheck:jni. In gdb, I break at the last line of initializeJNI(), and print all jclasses and jmethodIDs and the ones causing problems look to have been turned into garbage or garbage-collected (i.e. 0x00 or 0x06). Is it possible for global references to be gc'ed? Any suggestions?

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  • Regular Expression :match string containing only non repeating words

    - by nash
    I have this situation(Java code): 1) a string such as : "A wild adventure" should match. 2) a string with adjacent repeated words: "A wild wild adventure" shouldn't match. With this regular expression: .* \b(\w+)\b\s*\1\b.* i can match strings containing adjacent repeated words. How to reverse the situation i.e how to match strings which do not contain adjacent repeat words

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  • Will this ever result in a stack overflow error?

    - by David
    Will incrementing the instance variables of an object ever lead to a stack overflow error? For example: This method (java) will cause a stack overflow error: class StackOverflow { public static void StackOverflow (int x) { System.out.println (x) ; StackOverflow(x+1) ; } public static void main (String[]arg) { StackOverflow (0) ; } but will this?: (..... is a gap that i've put in to shorten the code. its long enough as it is.) import java.util.*; class Dice { String name ; int x ; int[] sum ; .... public Dice (String name) { this.name = name ; this.x = 0 ; this.sum = new int[7] ; } .... public static void main (String[] arg) { Dice a1 = new Dice ("a1") ; for (int i = 0; i<6000000; i++) { a1.roll () ; printDice(a1) ; } } .... public void roll () { this.x = randNum(1, this.sum.length) ; this.sum[x] ++ ; } public static int randNum (int a, int b) { Random random = new Random() ; int c = (b-a) ; int randomNumber = ((random.nextInt(c)) + a) ; return randomNumber ; } public static void printDice (Dice Dice) { System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; printValues (Dice) ; } public static void printValues (Dice Dice) { for (int i = 0; i<Dice.sum.length; i++) System.out.println ("#of "+i+"'s: "+Dice.sum[i]) ; } } The above doesn't currently cause a stack overflow error but could i get it too if i changed this line in main: for (int i = 0; i<6000000; i++) so that instead of 6 million something sufficiently high were there?

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  • question on rss feed application

    - by molleman
    Hello Guys i just want to create a simple application that will allow a user to input a url to a rss feed and display the contents to a user. what would be a good java library to enable me to read rss feeds? cheers

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  • Conditional operator in if-statement?

    - by Pindatjuh
    I've written the following if-statement in Java: if(methodName.equals("set" + this.name) || isBoolean() ? methodName.equals("is" + this.name) : methodName.equals("get" + this.name)) { ... } Is this a good practice to write such expressions in if, to separate state from condition? And can this expression be simplified?

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  • How do I format a String in an email so Outlook will print the line breaks?

    - by MattGrommes
    I'm trying to send an email in Java but when I read the body of the email in Outlook, it's gotten rid of all my linebreaks. I'm putting \n at the ends of the lines but is there something special I need to do other than that? The receivers are always going to be using Outlook. I found a page on microsoft.com that says there's a 'Remove line breaks' "feature" in Outlook so does this mean there's no solution to get around that other than un-checking that setting? Thanks

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  • Progress bar while applet loads

    - by Dan
    OK so, let's say I have a Java applet that takes a while to load (~5 secs). It's getting the mysql-connector.jar and it's loading. Well.. instead of the gray box with the coffee logo... can I make it have a simple progress bar with the percent? Thanks.

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  • Find out what variable is throwing a NullPointerException programatically

    - by Hectoret
    I know I can find out if a variable is null in Java using these techniques: if (var==null) - too much work try { ... } catch (NullPointerException e) { ...} - it tells me what line is throwing the exception using the debugger - by hand, too slow Consider this line of code: if (this.superSL.items.get(name).getSource().compareTo(VIsualShoppingList.Source_EXTRA)==0) { I would like to know if there's a generic way to find out programatically what variable (not just the line) is throwing the NullPointerException in a certain area of code. In the example, knowing that

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  • JBoss AS 5 "Failed to add Resource"

    - by Mark
    Hello - We are stumped and looking for advice.. Were running: jdk1.6.0_20 , jboss-5.1.0.GA, messaging-2.0.0.BETA4 And trying to add a Topic or Queue but we are getting this error: Failed to add Resource: java.lang.IllegalStateException:Failed to find template for: TopicTemplate any advice?

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  • NamespaceContext and using namespaces with XPath

    - by Jherico
    Resolving an xpath that includes namepsaces in Java appears to require the use of a NamespaceContext object, mapping prefixes to namespace urls and vice versa. But I can find no mechanism for getting a NamespaceContext other than implementing it myself. This seems counter-intuitive. Is there any easy way to acquire a NamespaceContext from a document, or to create one, or failing that, to forgo prefixes altogether and specify the xpath with fully qualified names?

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  • How does Eclipse/IDEA/etc. debugger obtain the information about local variable values and watch exp

    - by Bubba88
    I always thought that varibales are mapped to stack locations once your Java source is compiled; additionally, they may include the info about the variable names and their scope in classfiles, but that's optional AFAIK. The question is - how do my Eclipse/IDEA IDEs allow me to set a watch expression containing the local variable name? To me, it's hard to understand :)

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  • How to replace the deprecated csc ant task

    - by GrGr
    I have a mixed Java / C# project and use an ant script that contains a csc task to compile the dll. This works, but I get a warning [csc] This task is deprecated and will be removed in a future version [csc] of Ant. It is now part of the .NET Antlib: [csc] http://ant.apache.org/antlibs/dotnet/index.html How can I replace the csc task? I can surely create an exec task calling nant with a project.build file, but that feels completely wrong.

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  • Image.createImage problem in J2ME

    - by Michael
    Hi All, I tried this on J2ME try { Image immutableThumb = Image.createImage( temp, 0, temp.length); } catch (Exception ex) { System.out.println(ex); } I hit this error: java.lang.IllegalArgumentException: How do I solve this?

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  • int datatype in 64bit JVM. Is it more "inefficient" than long?

    - by Zwei Steinen
    I heard that using shorts on 32bit system is just more inefficient than using ints. Is this the same for ints on a 64bit system? Python recently(?) basically merged ints with long and has basically a single datatype long, right? If you are sure that your app. will only run on 64bit then, is it even conceivable (potentially a good idea) to use long for everything in Java?

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  • Output on namespaced xpath

    - by user347928
    Hi there, I have the following code and have had some trouble with a specific field and it's output. The namespace is connected but doesn't seem to be outputting on the required field. Any info on this would be great. import org.w3c.dom.Document; import org.xml.sax.SAXException; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.ParserConfigurationException; import javax.xml.xpath.XPathFactory; import javax.xml.xpath.XPath; import javax.xml.xpath.XPathExpressionException; import java.io.ByteArrayInputStream; import java.io.IOException; public class test { public static void main(String args[]) { String xmlStr = "<aws:UrlInfoResponse xmlns:aws=\"http://alexa.amazonaws.com/doc/2005-10-05/\">\n" + " <aws:Response xmlns:aws=\"http://awis.amazonaws.com/doc/2005-07-11\">\n" + " <aws:OperationRequest>\n" + " <aws:RequestId>blah</aws:RequestId>\n" + " </aws:OperationRequest>\n" + " <aws:UrlInfoResult>\n" + " <aws:Alexa>\n" + " <aws:TrafficData>\n" + " <aws:DataUrl type=\"canonical\">harvard.edu/</aws:DataUrl>\n" + " <aws:Rank>1635</aws:Rank>\n" + " </aws:TrafficData>\n" + " </aws:Alexa>\n" + " </aws:UrlInfoResult>\n" + " <aws:ResponseStatus xmlns:aws=\"http://alexa.amazonaws.com/doc/2005-10-05/\">\n" + " <aws:StatusCode>Success</aws:StatusCode>\n" + " </aws:ResponseStatus>\n" + " </aws:Response>\n" + "</aws:UrlInfoResponse>"; DocumentBuilderFactory xmlFact = DocumentBuilderFactory.newInstance(); xmlFact.setNamespaceAware(true); DocumentBuilder builder = null; try { builder = xmlFact.newDocumentBuilder(); } catch (ParserConfigurationException e) { e.printStackTrace(); } Document doc = null; try { doc = builder.parse( new ByteArrayInputStream( xmlStr.getBytes())); } catch (SAXException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } System.out.println(doc.getDocumentElement().getNamespaceURI()); System.out.println(xmlFact.isNamespaceAware()); String xpathStr = "//aws:OperationRequest"; XPathFactory xpathFact = XPathFactory.newInstance(); XPath xpath = xpathFact.newXPath(); String result = null; try { result = xpath.evaluate(xpathStr, doc); } catch (XPathExpressionException e) { e.printStackTrace(); //To change body of catch statement use File | Settings | File Templates. } System.out.println("XPath result is \"" + result + "\""); } } Thanks Tony

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  • Hadoop: Processing large serialized objects

    - by restrictedinfinity
    I am working on development of an application to process (and merge) several large java serialized objects (size of order GBs) using Hadoop framework. Hadoop stores distributes blocks of a file on different hosts. But as deserialization will require the all the blocks to be present on single host, its gonna hit the performance drastically. How can I deal this situation where different blocks have to cant be individually processed, unlike text files ?

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  • assigning a specific record in a ResultSet to a variable

    - by kilhra
    Hi I want to retrieve a set of records from a database, do a rs.next() and then assign the result of this to a variable to pass to a method that will use this record, in the same way that I would without assigning it to a variable and passing it to a method is there any way to do this? I'm using JAVA (1.5)

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  • Projects with browsable source using dependency injection w/ guice?

    - by André
    I often read about dependency injection and I did research on google and I understand in theory what it can do and how it works, but I'd like to see an actual code base using it (Java/guice would be preferred). Can anyone point me to an open source project, where I can see, how it's really used? I think browsing the code and seeing the whole setup shows me more than the ususal snippets in the introduction articles you find around the web. Thanks in advance!

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