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• 2d String Array NullPointerException (java)

  - by Student01

  I am currently creating a java application in which I have a 2d array which I want to get some data into. I am creating the 2d array as such String[][] addressData; and then when I am trying to put data in I am using reference the exact position in the 2d array I want to enter the data into e.g addressData[0][0] = "String Data"; The program compiles yet when I run I get a NullPointerException error. Am I using the wrong method to enter data into this 2d array?

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• Java Polymorphism - Selecting correct method based on subtype

  - by Marty Pitt

  Hi Given the following Class and Service layer signatures: public class PersonActionRequest { PersonVO person // ... other fields } public class MyServiceLayerClass { public void requestAction(PersonActionRequest request) { PersonVO abstractPerson = request.getPerson(); // call appropriate executeAction method based on subclass of PersonVO } private void executeAction(PersonVO person) {} private void executeAction(EmployeeVO employee) {} private void executeAction(ManagerVO manager) {} private void executeAction(UnicornWranglerVO unicornWrangler) {} } As discussed here, java will select the best method based on type info at compile time. (Ie., it will always select executeAction(PersonVO person) ). What's the most appropriate way to select the correct method? The internet tells me that using instanceof gets me slapped. However, I don't see the appropraite way to select the method without explictly casting abstractPerson to one of the other concrete types. Thanks Marty

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• Working with arrays of lists pattern in java

  - by Mad Wombat

  I am writing a card game in java where I need to spread cards from a deck into several columns until I have fixed amount of cards left. This is how I do this. public class Column extends ArrayList {} List deck = Cards.createNewDeck(); Column[] columns = new Column[10]; int c = 0; while (deck.size() 50) { if (c == 10) { c = 0; } if (columns[c] == null) { columns[c] = new Column(); } columns[c].add(Cards.dealTopCard(deck)); c += 1; } This somehow seems clunky. Is there a more readable/comprehensive way of doing the same thing?

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• Java exception reading xml file

  - by xain

  Hi, I have the following xml file: <?xml version="1.0" encoding="UTF-8"?> <c1> <c2 id="0001" n="CM" urlget="/at/CsM" urle="/E/login.jsp"> </c2> <c2 id="0002" n="C2M" urlget="/a2t/CsM" urle="/E2/login.jsp"> </c2> </c1> I'm trying to load c2's attributes this way: Document d = DocumentBuilderFactory.newInstance() .newDocumentBuilder() .parse("epxy.xml"); Element c1 = d.getDocumentElement(); Element c2 = (Element)c1.getFirstChild(); while (c2 != null) { ... c2 = (Element)c2.getNextSibling(); } But I get the exception java.lang.ClassCastException: org.apache.xerces.dom.DeferredTextImpl incompatible with org.w3c.dom.Element in the line Element c2 = (Element)c1.getFirstChild(); before the loop. Any hints ? Thanks.

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• groovy call private method in Java super class

  - by Jeff Storey

  I have an abstract Java class MyAbstractClass with a private method. There is a concrete implementation MyConcreteClass. public class MyAbstractClass { private void somePrivateMethod(); } public class MyConcreteClass extends MyAbstractClass { // implementation details } In my groovy test class I have class MyAbstractClassTest { void myTestMethod() { MyAbstractClass mac = new MyConcreteClass() mac.somePrivateMethod() } } I get an error that there is no such method signature for somePrivateMethod. I know groovy can call private methods but I'm guessing the problem is that the private method is in the super class, not MyConcreteClass. Is there a way to invoke a private method in the super class like this (other than using something like PrivateAccessor)? thanks Jeff

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• Java portable media detection

  - by quosoo

  I would like to write a piece of java code that synchronizes files between local hard drive and a usb storage. I would like to have a different synchronization configuration depending on which usb storage is plugged in and I would like to have apropriate configuration to be selected automatically rather than chosen by the user. I've just read the JSR-80 and jUSB documentation as well as a bunch of articles and SO posts, but all of those are very old and it seems that since that time (around 2005) all the efforts have been abandoned especially for Windows platform, while the OS-independence is quite important to me (at least Windows and Linux need to be supported). Do I really need to use any of the USB APIs to recognize external drives that are connected to the system? I need something that is more unique than file path, drive letter or drive label... And if yes which one would you recommend (unless I missed something jUnit is actually the only for which Windows support exists).

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• Play wave file using AudioFormat in java

  - by angelina

  Dear all, I m getting following exception while running my code on linux operating system.This code works fine on windows operating system.below is the exception and code used. java.lang.IllegalArgumentException: No line matching interface Clip supporting format PCM_SIGNED unknown sample rate, 16 bit, stereo, 4 bytes/frame, big-endian is supported. AudioFormat format = sourceaudio.getFormat(); format = new AudioFormat( AudioFormat.Encoding.PCM_SIGNED, format.getSampleRate(), format.getSampleSizeInBits() * 2, format.getChannels(), format.getFrameSize() * 2, format.getFrameRate(), true); AudioFileFormat.Type targettype = AudioFileFormat.Type.WAVE; AudioInputStream targetaudiostream = AudioSystem.getAudioInputStream(format, sourceaudio); sourceaudio.close(); targetaudiostream.close(); System.out.println("55555555"); URL url = new URL("http://localhost:8084/newvideo/PCMfile.wav"); Clip clip = AudioSystem.getClip(); AudioInputStream ais = AudioSystem.getAudioInputStream(url); clip.open(ais); System.out.println("seconds: " + (clip.getMicrosecondLength() / 1000000));

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• What to do of exceptions when implementing java.lang.Iterator

  - by Vincent Robert

  The java.lang.Iterator interface has 3 methods: hasNext, next and remove. In order to implement a read-only iterator, you have to provide an implementation for 2 of those: hasNext and next. My problem is that these methods does not declare any exceptions. So if my code inside the iteration process declares exceptions, I must enclose my iteration code inside a try/catch block. My current policy has been to rethrow the exception enclosed in a RuntimeException. But this has issues because the checked exceptions are lost and the client code no longer can catch those exceptions explicitly. How can I work around this limitation in the Iterator class? Here is a sample code for clarity: class MyIterator implements Iterator { @Override public boolean hasNext() { try { return implementation.testForNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } @Override public boolean next() { try { return implementation.getNext(); } catch ( SomethingBadException e ) { throw new RuntimeException(e); } } ... }

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• When using the getInstance() method of the abstract java.text.NumberFormat class, what is the actual

  - by iamchuckb

  This question expands upon the one at abstract-class-numberformat-very-confused-about-getinstance. I feel that this question is different enough to merit being asked on its own. In the answers to that question, it was stated that a code statement such as NumberFormat en = NumberFormat.getInstance(Locale.US); returns an object that is a subclass of the java.text.NumberFormat class. It makes sense to me why the return type can't be just an instance of NumberFormat since that is an abstract class. Rather, it was stated that the returned object is at least an instance of NumberFormat, but actually something else. My question is this: what specifically is the class of the object that is returned? In the Sun documentation the only subclasses I see are ChoicesFormat and DecimalFormat. Is there some sort of behind the scenes compiler voodoo going on here? Thanks in advance!

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• java/swing: Shape questions: serializing and combining

  - by Jason S

  I have two questions about java.awt.Shape. Suppose I have two Shapes, shape1 and shape2. How can I serialize them in some way so I can save the information to a file and later recreate it on another computer? (Shape is not Serializable but it does have the getPathIterator() method which seems like you could get the information out but it would be kind of a drag + I'm not sure how to reconstruct a Shape object afterwards.) How can I combine them into a new Shape so that they form a joint boundary? (e.g. if shape1 is a large square and shape2 is a small circle inside the square, I want the combined shape to be a large square with a small circular hole)

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• Java - binary compatibility of abstract class & subclasses

  - by thSoft

  In Java, I define an abstract class with both concrete and abstract methods in it, and it has to be subclassed independently by third-party developers. Just to be sure: are there any changes I could make to the abstract class that are source compatible with their classes but not binary compatible? In other words: after they have compiled their subclasses, could I change the abstract class - apart from e.g. adding an abstract method to it or removing a protected method from it that is called by subclasses, which are of course source incompatible - in a way that could force them to recompile their subclasses?

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• java keytool question

  - by user384706

  Hi, I created a java keystore programmatically of type jks (i.e. default type). It is initially empty so I created a DSA certificate. keytool -genkey -alias myCert -v -keystore trivial.keystore How can I see the public and private keys? I.e. is there a command that prints the private key of my certificate? I could only find keytool -certreq which in my understanding prints the certificate as a whole: -----BEGIN NEW CERTIFICATE REQUEST----- MIICaTCCAicCAQAwZTELMAkGA1UEBhMCR1IxDzANBgNVBAgTBkdyZWVjZTEPMA0GA1UEBxMGQXRo BQADLwAwLAIUQZbY/3Qq0G26fsBbWiHMbuVd3VICFE+gwtUauYiRbHh0caAtRj3qRTwl -----END NEW CERTIFICATE REQUEST----- I assume this is the whole certificate. How can I see private (or public key) via keytool? Thank you

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• Writing out BMP files with DataBuffer.TYPE_FLOAT or DataBuffer.TYPE_DOUBLE in java

  - by Basil Dsouza

  Hi Guys, I had a problem working with the image classes in java. I am creating a buffered image with DataBuffer.TYPE_DOUBLE. This all works fine in memory (I think). But the problem starts when I try to write it using ImageIO.write. Initially I was getting no exception at all and instead was only getting an empty output file for my troubles.. After a bit of poking around in the code, i found out that the bmp writer doesnt support writing type_double type of files. From: BMPImageWriterSpi.canEncodeImage: if (dataType < DataBuffer.TYPE_BYTE || dataType > DataBuffer.TYPE_INT) return false; So my question is, does anyone have a way of writing out those kind of images to disk? any documentation or tutorial, or link would be helpful. Thanks, Basil Dsouza

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• Extending Throwable in Java

  - by polygenelubricants

  Java lets you create an entirely new subtype of Throwable, e.g: public class FlyingPig extends Throwable { ... } Now, very rarely, I may do something like this: throw new FlyingPig("Oink!"); and of course elsewhere: try { ... } catch (FlyingPig porky) { ... } My questions are: Is this a bad idea? And if so, why? What could've been done to prevent this subtyping if it is a bad idea? Since it's not preventable (as far as I know), what catastrophies could result? If this isn't such a bad idea, why not? How can you make something useful out of the fact that you can extends Throwable?

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• Eclipse Java Profiler

  - by Jeff Storey

  I know this has been asked before, but I have not found anything recent that really gives a good answer. I'm trying to find a free profiler for eclipse that works well. I would like a graphical breakdown of execution time in particular. I've tried TPTP but have had no luck at all with GUI apps (it took almost a minute for a GUI app to start and was virtually unusable on screen - it uses a lot of Java OpenGL, so I'm not sure if it has to do with that). I liked YourKit, but unfortunately it's not free. I even tried switching to NetBeans since they have a built in profiler. If anyone has had success with particular profilers (even if it was TPTP), I'd like to hear about it. Any recommendations would be greatly appreciated. thanks, Jeff

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• Read data from a text file using Java

  - by Saran

  I need to read a text file line by line using Java. I use available() method of FileInputStream to check and loop over the file. But while reading, the loop terminates after the line before the last one. i.e., if the file has 10lines, the loop reads only the first 9 lines. Snippet used : while(fis.available() > 0) { char c = (char)fis.read(); ..... ..... }

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• What causes "java.lang.IncompatibleClassChangeError: vtable stub"?

  - by JimN

  What causes "java.lang.IncompatibleClassChangeError: vtable stub"? In our application, we have seen this error pop up randomly and very seldom (just twice so far, and we run it a lot). It is not readily reproducible, even when restarting the app, using the same jvm/jars without rebuilding. As for our build process, we clean all classes/jars and rebuild them, so it's not the same problem as others have encountered where they made a change in one class and didn't recompile some other dependent classes. This is unlike some of the other questions related to IncompatibleClassChangeError -- none of them mention "vtable stub". In fact, there are surprisingly few google results when searching for "IncompatibleClassChangeError "vtable stub"".

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• javax script how to call a function in JavaScript from Java

  - by Dan Howard

  Hi All, I'm trying to call a function in JavaScript via Java. This works fine when directly reading a script as a string but I'm using CompiledScripts. When I do this with a compiled script it gives me method not found if I also add bindings. Without bindings it works but of course the function fails because it needs the bindings. Any ideas? CompiledScript script = ... get script.... Bindings bindings = script.getEngine().createBindings(); Logger scriptLogger = LogManager.getLogger("TEST_SCRIPT"); bindings.put("log", scriptLogger); //script.eval(bindings); -- this way fails script.eval(); // -- this way works Invocable invocable = (Invocable) script.getEngine(); invocable.invokeFunction(methodName); TIA

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• java.io.IOException: Server returned HTTP response code: 403 for URL

  - by Adao

  I want to download the mp3 file from url : "http://upload13.music.qzone.soso.com/30671794.mp3", i always got java.io.IOException: Server returned HTTP response code: 403 for URL. But it's ok when open the url using browser. Below is part of my code: BufferedInputStream bis = null; BufferedOutputStream bos = null; try { URL url = new URL(link); URLConnection urlConn = url.openConnection(); urlConn.addRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)"); String contentType = urlConn.getContentType(); System.out.println("contentType:" + contentType); InputStream is = urlConn.getInputStream(); bis = new BufferedInputStream(is, 4 * 1024); bos = new BufferedOutputStream(new FileOutputStream( fileName.toString()));? Anyone could help me? Thanks in advance!

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• Using Java server-side with PHP-generated front-end

  - by Storm

  Hi!  Does anyone have a real-world experience in building such a project? I'd like to move away questions about "is it good idea or not", but focus on possible solutions. I see one simple way - HTTP GET/POST + xml/json - and one more elegant - AJAX/DWR. As for the first one - I understand that it is possible, but needs quite a lot coding. As for second way - is it possible to use Java DWR engine with PHP front-end? Is DWR language-independent for client side (as it uses just JavaScript)?  Would it be a problem, that client page was generated by one web server (for example, apache+php) and served on server-side by another (for example, tomcat)? I suspect, that Tomcat will complain about sessions. Can this problem be fixed with allowing cross-domain AJAX? Thank you in advance. Denis.

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• Sugar CRM integration with Java - How to add relationship

  - by Arun P Johny

  Hi, I'm trying to integrate Sugar CRM with one of my projects. I'm using Apache Axis as my SOAP client. I've created the Sugar CRM client Stub classes using Apache Axis. I'm able to login and add Leads, Opportunities, Accounts and Contacts. But I'm unable to add a relation ship between my Account and Opportunity. I've found following method in the SugarsoapPortType port.set_relationship(session, module_name, module_id, link_field_name, related_ids, name_value_list, delete) but I cannot understand the different parameters required by this method. Most of the online documents suggests a simple way as given below $result = $client->call('set_relationship',array("session"=>$session _id,array("module1"=>"Emails","module1_id"=>"<module1_id>","module2"=>"Accounts","module2_id"=> "<module2_id>"))); how can I achieve this using Java Thanks

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• HPC (mainly on Java)

  - by Insectatorious

  I'm looking for some way of using the number-crunching ability of a GPU (with Java perhaps?) in addition to using the multiple cores that the target machine has. I will be working on implementing (at present) the A* Algorithm but in the future I hope to replace it with a Genetic Algorithm of sorts. I've looked at Project Fortress but as I'm building my GUI in JavaFX, I'd prefer not to stray too far from a JVM. Of course, should no feasible solution be available, I will migrate to the easiest solution to implement.

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• Java library to encode / decode AMF

  - by Ceilingfish

  Hi chaps, I currently have a Java server that talks to a Flash client by passing JSON encoded data over a binary socket connection. Is there a way on either side to encode / decode packets as AMF instead of JSON? It seems to me that there should be some native support in Flash player for doing this? All the implementations I have found of AMF serialization seem to be embedded inside an application framework. Simiarly so, does anyone know if it's possible to decode AMF packets independently of a connection implementation in Flash?

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• Java framework "suggestion" for persisting the results from an Oracle 9i stored procedure using Apac

  - by chocksaway

  Hello, I am developing a Java servlet which calls an Oracle stored procedure. The stored procedure is likely to "grow" over time, and I have concerns the amount of time taken to "display the results on a web page". While I am at the implementation stage, I would like some suggestions of a Persistence framework which will work on Apache Tomcat 5.5? I see two approaches to persisting the database results. A scheduled database query every N minutes, or something which utilises triggers. Hibernate seems like the obvious answer, but I have never called stored procedures from Hibernate (HQL and Criteria). Is there a more appropriate framework which can be used? Thank you. cheers Miles.

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• Java - Parsing a Date from a String

  - by Yatendra Goel

  I want to parse a java.util.Date from a String. I tried the following code but got unexpected output: Date getDate() { Date date = null; SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd"); try { date = sdf.parse("Sat May 11"); } catch (ParseException ex) { Logger.getLogger(URLExtractor.class.getName()).log(Level.SEVERE, null, ex); return null; } return date; } When I run the above code, I got the following output: Mon May 11 00:00:00 IST 1970

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