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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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• 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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• 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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• How to write a virtual conditional breakpoint in java

  - by Phuong Nguyen de ManCity fan

  I'm sorry if the question title may mis-inform you, but I cannot find a proper word to explain that. If you ever working with .NET, you would know that there is Assert class that will automatically wake up and attach debugger if necessary and then have debugger (Visual Studio) pausing at the Assert command, given the Assert command failed. Given I'm running a java program and having debugger connected, then how can I have debugger to break on certain condition without manually setup a break point? I'm expecting something like that: void doSomeThing(String x){ if (x==null) breakDebuggerNow(); }

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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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• 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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• 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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• augment the factory pattern in java

  - by TP

  I am trying to use a factory pattern to create a QuestionTypeFactory where the instantiated classes will be like MultipleChoice, TrueFalseQuestion etc. The factory code looks something like this class QuestionFactory { public enum QuestionType { TrueFalse, MultipleChoice, Essay } public static Question createQuestion(QuestionType quesType) { switch (quesType) { case TrueFalse: return new TrueFalseQuestion(); case MultipleChoice: return new MultipleChoiceQuestion(); case Essay: return new EssayQuestion(); } throw new IllegalArgumentException("Not recognized."); } } This works ok for now. If I want to add another question type I will need to modify the factory class and I do not want to do that. How can I set it up so that each question class registers itself with the Factory so that when I add a new question type, I do not have to change the code for the factory? I am a bit new to java and am not sure how to do this.

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• Use of Java constructors in persistent entities

  - by Mr Morgan

  Hello I'm new to JPA and using persistence in Java anyway and I have two questions I can't quite work out: I have generated tags as: @JoinColumn(name = "UserName", referencedColumnName = "UserName") @ManyToOne(optional = false) private User userName; @JoinColumn(name = "DatasetNo", referencedColumnName = "DatasetNo") @ManyToOne(optional = false) private Dataset datasetNo; But in one of the constructors for the class, no reference is made to columns UserName or DatasetNo whereas all other columns in the class are referenced in the constructor. Can anyone tell me why this is? Both columns UserName and DatasetNo are 'foreign keys' on the entity Visualisation which corresponds to a database table of the same name. I can't quite work out the ORM. And when using entity classes, or POJO, is it better to have class variables like: private User userName; Where an instance of a class is specified or simply the key of that class instance like: private String userName; Thanks Mr Morgan.

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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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• mp3 downsampling / compression in java

  - by veenit33

  Well, i was looking forward to modify the bit rate of a mp3 file in java. I want to downsample(change its bit rate) the mp3 file from 256/384 kbps to say 64/128 kbps.. (I guess this is the only way one can achieve mp3 compression..or is there any other way.?) I searched for LameOnJ but that website is temperoraly down and so im not able to get the license file which we need to download in every 2 days. Is this possible using JMF..? What are the other option i have..? Regards, Veenit Shah

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• Creating database desktop application with data manipulation in Netbeans using Java Persistence

  - by Lulu

  It's my first time to use Persistence in developing a Java program because I usually connect via JDBC. I read that for large amounts of data, it is best to use persistence. I tried playing with the CRUD example of Netbeans. It's not very helpful thought because it only connects to the DB and allows addition and deletion of records. I need something that will allow me to manipulate the data like if the value from column C1 of table T1 is such, it will retrieve data from table t2. In short, I need to apply conditions before knowing what to retrieve exactly. The example in CRUD example already has a specific table to retrieve and only acts like a database manager. How is it possible to retrieve a specific item first then from this, will determine the next steps to be done. I'm also using embedded JavaDB/Derby as my database (also my first time to use because I usually use remote mysql)

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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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• 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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• 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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• Assigning a default value to a final variable in case of an exception in Java

  - by frenetisch applaudierend

  Why won't Java let me assign a value to a final variable in a catch block after setting the value in the try block, even if it is not possible for the final value to be written in case of an exception. Here is an example that demonstrates the problem: public class FooBar { private final int foo; private FooBar() { try { int x = bla(); foo = x; // In case of an exception this line is never reached } catch (Exception ex) { foo = 0; // But the compiler complains // that foo might have been initialized } } private int bla() { // You can use any of the lines below, neither works // throw new RuntimeException(); return 0; } } The problem is not hard to work around, but I would like to understand why the compiler does not accept this. Thanks in advance for any inputs!

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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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• 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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• 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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• 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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• Objective-C : enum like Java (int values and many others for each enum)

  - by Oliver

  In Java, you can make an enum having multiples values. In objective-C, this cannot be done easily. I've read many pages about this but I didn't found anything satisfying that would allow me to use enums by a simple way and to keep the enum declaration and their different values in the same file. I would like to write something like this in a enums.h : // ======================================== typedef enum {eRED, eGREEN, eBLUE} ColorEnum; int colorValues[] = { 0xFF0000, 0x00FF00, 0x0000FF }; NSArray *colorNames = [NSArray arrayWithObjects:@"Red color", @"light green", @"Deep blue", nil]; // ======================================== and be able to use thoses global variables to manage my stuff anywhere like : int color = colorValues[eRED]; But I don't know how to write this. I have compile errors like "ColorValues" is defines many times. Or if I just use "static", I have many "ColorValues" not used in .m file... Could you help me ?

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• Mail merge from Java

  - by Mike Q

  Hi all, Does anyone have any experience with doing mail merge from Java on a word document? I need to support both doc and docx formats. I have heard of Apache POI and docx4j. However, from reading around I'm sure how good the word support is in POI. docx4j only supports docx format as far as I can see. Can any suggest either one of the above (and correct my knowledge on support) or another appropriate library. If necessary I would be willing to use one lib for doc and another for docx. Thanks.

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• Java Math.cos() Method Does Not Return 0 When Expected

  - by dimo414

  Using Java on a Windows 7 PC (not sure if that matters) and calling Math.cos() on values that should return 0 (like pi/2) instead returns small values, but small values that, unless I'm misunderstanding, are much greater than 1 ulp off from zero. Math.cos(Math.PI/2) = 6.123233995736766E-17 Math.ulp(Math.cos(Math.PI/2)) = 1.232595164407831E-32 Is this in fact within 1 ulp and I'm simply confused? And would this be an acceptable wrapper method to resolve this minor inaccuracy? public static double cos(double a){ double temp = Math.abs(a % Math.PI); if(temp == Math.PI/2) return 0; return Math.cos(a); }

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• Gson module not found Blackberry Java application

  - by Curro

  Hi. I'm developing a simple application for Blackberry and i'm using Google's gson to retrieve some data from a server. The UI was working fine but when I added the gson part it started failing, it wont run. When I run the application in the simulator it show this error: "Uncaught: RuntimeException" on that annoying white screen of death and after holding the click button I can see that there is an alert dialog that says "Module 'gson-1.4' not found". However I did added "gson-1.4.jar" in the Project's Properties - Java Build Path - Add External JARs... also, the Gson objects are recognized at my code, no syntax errors at my code. BTW, I'm using Eclipse and the most recent Blackberry SDK Please help

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• problem with jtabbedpane in java..

  - by mani

  hai, is it possible to loading of tabs in jtabedpane dyanamically in java.. that means i have frame that consinting of one tabbedpane.. in that i have 10 tabs and in each tab consting of another tabbedpane and in that each tabbedpane has 4 tabs and each tab consisting buttons and textfields...... when i login into my project the next frame takes more time to visible.... this is happens why because i have more tabbedpanes in my frame so that it takes the lot's of time to visible.. my question is.. is it possible to load tabs content dynamically when i click the tab in tabbedpane..... or is it possible to load tabbedpanes fastly......????????

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