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  • Passing parametrized ArrayList to a function in java

    - by user150505
    I have the following fucntion. func(ArrayList <String> name) { ........ } The function fills the ArrayList. (I don't want to return the ArrayList) However, in the caller function the ArrayList obtained has all items of ArrayList as null. For eg. 1 name = new ArrayList[num]; 2 func(name); 3 System.out.println(name[0]); I get NullPointerException at line 3. Is this because of line 1, i.e. I am not parametrizing? If yes, is there another way this can be done? Because java does not allow creating a generic array of parametrized ArrayList.

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  • Java: Parse Australian Street Addresses

    - by bguiz
    Looking for a quick and dirty way to parse Australian street addresses into its parts: 3A/45 Jindabyne Rd, Oakleigh, VIC 3166 should split into: "3A", 45, "Jindabyne Rd" "Oakleigh", "VIC", 3166 Suburb names can have multiple words, as can street names. See: http://stackoverflow.com/questions/1739746/parse-a-steet-address-into-components Has to be in Java, cannot make http requests (e.g. to web APIs). EDIT: Assume that format specified is always followed. I have no issue with spitting incorrectly formatted strings back at the user with a message telling them to follow the format (which I've described above).

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  • Run java thread at specific times

    - by rmarimon
    I have a web application that synchronizes with a central database four times per hour. The process usually takes 2 minutes. I would like to run this process as a thread at X:55, X:10, X:25, and X:40 so that the users knows that at X:00, X:15, X:30, and X:45 they have a clean copy of the database. It is just about managing expectations. I have gone through the executor in java.util.concurrent but the scheduling is done with the scheduleAtFixedRate which I believe provides no guarantee about when this is actually run in terms of the hours. I could use a first delay to launch the Runnable so that the first one is close to the launch time and schedule for every 15 minutes but it seems that this would probably diverge in time. Is there an easier way to schedule the thread to run 5 minutes before every quarter hour?

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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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  • 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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  • SocketTimeOutException while creating socket, java

    - by Sunil Kumar Sahoo
    Hi All, I have created a sample java socket application. I used Socket s = new Socket(ip, port) Now it works fine. but when my internet connection is very slow that time after a long interval (even if sometimes after 2 minutes) i used to get SocketTimeOutException in that line. means it gives that error while creating socket. I want the exception should be handled properly means if internet connection is very slow then if that error occurs it happens very late now . I want if this type of error occurs then it should be caught very fast means the error should not come at such a delay interval of time rather it should come immediately. How to achieve this. Thanks Sunil Kumar Sahoo

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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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  • Books recommendation to learn about java networking

    - by elec
    In order to cover for my (glaring) lack of knowledge in the basics of networking, I'm looking for a book which would ideally cover: - 1 or 2 chapters on the transport layer: tcp, udp... - 1 or 2 chapters on the application layer: http, dns... - rest of the book would be devoted to pratical way of sending data across the wire using Java-related technologies. This would involve discussions about existing products (eg. hessian, protobuf, thrift, tibco...) , performances comparisons, case studies...etc.. Does such a book exist ?

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  • Java: Local Enums

    - by bruno conde
    Today, I found myself coding something like this ... public class LocalEnums { public LocalEnums() { } public void foo() { enum LocalEnum { A,B,C }; // .... // class LocalClass { } } } and I was kind of surprised when the compiler reported an error on the local enum: The member enum LocalEnum cannot be local Why can't enums be declared local like classes? I found this very useful in certain situations. In the case I was working, the rest of the code didn't need to know anything about the enum. Is there any structural/design conflict that explains why this is not possible or could this be a future feature of Java?

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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 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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  • 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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  • 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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  • 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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  • 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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