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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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  • Filling a byte array in Java

    - by Corleone
    Hey all! For part of a project I'm working on I am implementing a RTPpacket where I have to fill the header array of byte with RTP header fields. //size of the RTP header: static int HEADER_SIZE = 12; // bytes //Fields that compose the RTP header public int Version; // 2 bits public int Padding; // 1 bit public int Extension; // 1 bit public int CC; // 4 bits public int Marker; // 1 bit public int PayloadType; // 7 bits public int SequenceNumber; // 16 bits public int TimeStamp; // 32 bits public int Ssrc; // 32 bits //Bitstream of the RTP header public byte[] header = new byte[ HEADER_SIZE ]; This was my approach: /* * bits 0-1: Version * bit 2: Padding * bit 3: Extension * bits 4-7: CC */ header[0] = new Integer( (Version << 6)|(Padding << 5)|(Extension << 6)|CC ).byteValue(); /* * bit 0: Marker * bits 1-7: PayloadType */ header[1] = new Integer( (Marker << 7)|PayloadType ).byteValue(); /* SequenceNumber takes 2 bytes = 16 bits */ header[2] = new Integer( SequenceNumber >> 8 ).byteValue(); header[3] = new Integer( SequenceNumber ).byteValue(); /* TimeStamp takes 4 bytes = 32 bits */ for ( int i = 0; i < 4; i++ ) header[7-i] = new Integer( TimeStamp >> (8*i) ).byteValue(); /* Ssrc takes 4 bytes = 32 bits */ for ( int i = 0; i < 4; i++ ) header[11-i] = new Integer( Ssrc >> (8*i) ).byteValue(); Any other, maybe 'better' ways to do this?

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  • Returning searched results in an array in Java without ArrayList

    - by Crystal
    I started down this path of implementing a simple search in an array for a hw assignment without knowing we could use ArrayList. I realized it had some bugs in it and figured I'd still try to know what my bug is before using ArrayList. I basically have a class where I can add, remove, or search from an array. public class AcmeLoanManager { public void addLoan(Loan h) { int loanId = h.getLoanId(); loanArray[loanId - 1] = h; } public Loan[] getAllLoans() { return loanArray; } public Loan[] findLoans(Person p) { //Loan[] searchedLoanArray = new Loan[10]; // create new array to hold searched values searchedLoanArray = this.getAllLoans(); // fill new array with all values // Looks through only valid array values, and if Person p does not match using Person.equals() // sets that value to null. for (int i = 0; i < searchedLoanArray.length; i++) { if (searchedLoanArray[i] != null) { if (!(searchedLoanArray[i].getClient().equals(p))) { searchedLoanArray[i] = null; } } } return searchedLoanArray; } public void removeLoan(int loanId) { loanArray[loanId - 1] = null; } private Loan[] loanArray = new Loan[10]; private Loan[] searchedLoanArray = new Loan[10]; // separate array to hold values returned from search } When testing this, I thought it worked, but I think I am overwriting my member variable after I do a search. I initially thought that I could create a new Loan[] in the method and return that, but that didn't seem to work. Then I thought I could have two arrays. One that would not change, and the other just for the searched values. But I think I am not understanding something, like shallow vs deep copying???....

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  • Java: using endpoint to publish webservice to tomcat server

    - by Will
    hi all, i am creating a simple SOAP web service. i am to ensure that it runs on a tomcat web service. im trying to implement this with JAX-WS (see code) my question is: does the Endpoint.publish use the tomcat server to host this or is it a mini glassfish kind of server? should i be extending UnicastRemoveObject or something similiar instead? ideally it would be able to be packaged into a .WAR and dropped in the directory and just work. It doesn't seem to work with my installed tomcat server as is because it says the port is already in use. I'm using Ubuntu karmic with the tomcat6 package installed, it could also be my user doesnt have permissions to publish to the running tomcat on 8080 i hope this question is clear enough sample code: @WebService public class UserAttributes { public static void main(String[] args) { UserAttributes instance = new UserAttributes(); Endpoint.publish("http://localhost:8082/WebServices/userattributes", instance); } public string Hello() { return "Hello World"; } }

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  • Simple java syncrhonization question

    - by Misha Koshelev
    Dear All: Was wondering, which is correct: Option One class A { public void methodOne() { synchronized(this) { modifyvalue notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } Option Two class A { public void methodOne() { modifyvalue synchronized(this) { notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } and why? Thank you Misha

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  • serialize/deserialize a LinkedHashMap (android) java

    - by user348058
    So i want to pass a LinkedHashMap to an intent. //SEND THE MAP Intent singlechannel = new Intent(getBaseContext(),singlechannel.class); singlechannel.putExtra("db",shows1);//perase to startActivity(singlechannel); //GET THE MAP LinkedHashMap<String,String> db = new LinkedHashMap<String,String>(); db=(LinkedHashMap<String,String>) getIntent().getSerializableExtra("db"); This one Worked Like a charm with HashMap. But with LinkedHashMap i got a problem I got a warning "Type safety: Unchecked cast from Serializable to LinkedHashMap" But i had this warning with HashMap too? Any ideas.Any help is much appreciated Also I just saw this. https://issues.apache.org/jira/browse/HARMONY-6498

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  • Java socketserver: How to handle many incoming connections?

    - by SlappyTheFish
    I am writing a simple multithreaded socketserver and I am wondering how best to handle incoming connections: create a new thread for each new connection. The number of concurrent threads would be limited and waiting connections limited by specifying a backlog add all incoming connections into a queue and have a pool of worker threads that process the queue I am inclined to go for option 2 because I really don't want to refuse any connections, even under high loads, but I am wondering if there are any considerations I should be aware of with accepting effectively unlimited connections?

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  • Java generic Comparable where subclasses can't compare to eachother

    - by dege
    public abstract class MyAbs implements Comparable<MyAbs> This would work but then I would be able to compare class A and B with each other if they both extend MyAbs. What I want to accomplish however is the exact opposite. So does anyone know a way to get the generic type to be the own class? Seemed like such a simple thing at first... Edit: To explain it a little further with an example. Say you have an abstract class animals, then you extend it with Dogs and ants. I wouldn't want to compare ants with Dogs but I however would want to compare one dog with another. The dog might have a variable saying what color it is and that is what I want to use in the compareTo method. However when it comes to ants I would rather want to compare ant's size than their color. Hope that clears it up. Could possibly be a design flaw however.

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  • XML validation in Java - why does this fail?

    - by jd
    hi, first time dealing with xml, so please be patient. the code below is probably evil in a million ways (I'd be very happy to hear about all of them), but the main problem is of course that it doesn't work :-) public class Test { private static final String JSDL_SCHEMA_URL = "http://schemas.ggf.org/jsdl/2005/11/jsdl"; private static final String JSDL_POSIX_APPLICATION_SCHEMA_URL = "http://schemas.ggf.org/jsdl/2005/11/jsdl-posix"; public static void main(String[] args) { System.out.println(Test.createJSDLDescription("/bin/echo", "hello world")); } private static String createJSDLDescription(String execName, String args) { Document jsdlJobDefinitionDocument = getJSDLJobDefinitionDocument(); String xmlString = null; // create the elements Element jobDescription = jsdlJobDefinitionDocument.createElement("JobDescription"); Element application = jsdlJobDefinitionDocument.createElement("Application"); Element posixApplication = jsdlJobDefinitionDocument.createElementNS(JSDL_POSIX_APPLICATION_SCHEMA_URL, "POSIXApplication"); Element executable = jsdlJobDefinitionDocument.createElement("Executable"); executable.setTextContent(execName); Element argument = jsdlJobDefinitionDocument.createElement("Argument"); argument.setTextContent(args); //join them into a tree posixApplication.appendChild(executable); posixApplication.appendChild(argument); application.appendChild(posixApplication); jobDescription.appendChild(application); jsdlJobDefinitionDocument.getDocumentElement().appendChild(jobDescription); DOMSource source = new DOMSource(jsdlJobDefinitionDocument); validateXML(source); try { Transformer transformer = TransformerFactory.newInstance().newTransformer(); transformer.setOutputProperty(OutputKeys.INDENT, "yes"); StreamResult result = new StreamResult(new StringWriter()); transformer.transform(source, result); xmlString = result.getWriter().toString(); } catch (Exception e) { e.printStackTrace(); } return xmlString; } private static Document getJSDLJobDefinitionDocument() { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = null; try { builder = factory.newDocumentBuilder(); } catch (Exception e) { e.printStackTrace(); } DOMImplementation domImpl = builder.getDOMImplementation(); Document theDocument = domImpl.createDocument(JSDL_SCHEMA_URL, "JobDefinition", null); return theDocument; } private static void validateXML(DOMSource source) { try { URL schemaFile = new URL(JSDL_SCHEMA_URL); Sche maFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI); Schema schema = schemaFactory.newSchema(schemaFile); Validator validator = schema.newValidator(); DOMResult result = new DOMResult(); validator.validate(source, result); System.out.println("is valid"); } catch (Exception e) { e.printStackTrace(); } } } it spits out a somewhat odd message: org.xml.sax.SAXParseException: cvc-complex-type.2.4.a: Invalid content was found starting with element 'JobDescription'. One of '{"http://schemas.ggf.org/jsdl/2005/11/jsdl":JobDescription}' is expected. Where am I going wrong here? Thanks a lot

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  • java looping - declaration of a Class outside / inside the loop

    - by lisak
    when looping, for instance: for ( int j = 0; j < 1000; j++) {}; and I need to instantiate 1000 objects, how does it differ when I declare the object inside the loop from declaring it outside the loop ?? for ( int j = 0; j < 1000; j++) {Object obj; obj =} vs Object obj; for ( int j = 0; j < 1000; j++) {obj =} It's obvious that the object is accessible either only from the loop scope or from the scope that is surrounding it. But I don't understand the performance question, garbage collection etc. What is the best practice ? Thank you

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  • W3C dom api in Java, get child elements by name

    - by Benju
    I just realized that the method Element.getElementsByTagName("someTagName") returns a nodelist of all elements in the document that have a given tagname. What if I just want to get all child elements by tag name? For example... <person> <name>Bob</name> <car> <name>Toyota Corolla</name> </car> </person>

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  • [Java] Cannot find symbol

    - by m00st
    I've created a class called Entity this is the superclass. Actor has successfully extended Entity; now trying to do the same with Item results in the Cannot find symbol error. Here is example code: public class Actor extends Entity { Actor(String filename, int x, int y) { super(filename, x, y); } } works just fine but this doesn't: public class Item extends Entity { }

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  • Java special characters

    - by Binaryrespawn
    Hi all, this must be quite simple but I am having great difficulty. You see I am trying to find a string within another string as follows. e = input.indexOf("-->"); s = input.indexOf("<!--"); input = input.replace(input.substring(s, e + 3), " "); The integers e and s are returning -1 in that it was not found and this is causing the replace method to fail. The test string I am using is "Chartered Certified<!--lol--> Accountants (ACCA)". I tried to creat a new string object and pass in the string as an argument as follows e=input.indexOf(new String("<!--")); This yielded the same result. Any ideas ?

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  • Fast 4x4 matrix multiplication in Java with NIO float buffers

    - by kayahr
    I know there are LOT of questions like that but I can't find one specific to my situation. I have 4x4 matrices implemented as NIO float buffers (These matrices are used for OpenGL). Now I want to implement a multiply method which multiplies Matrix A with Matrix B and stores the result in Matrix C. So the code may look like this: class Matrix4f { private FloatBuffer buffer = FloatBuffer.allocate(16); public Matrix4f multiply(Matrix4f matrix2, Matrix4f result) { {{{result = this * matrix2}}} <-- I need this code return result; } } What is the fastest possible code to do this multiplication? Some OpenGL implementations (Like the OpenGL ES stuff in Android) provide native code for this but others doesn't. So I want to provide a generic multiplication method for these implementations.

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  • How do I detect unicode characters in a Java string to resolve sax parser exception

    - by Madhumita
    Suppose I have a string that contains '¿'. How would I find all those unicode characters? Should I test for their code? How would I do that? I want to detect it to avoid sax parser exception which I am getting it while parsing the xml saved as a clob in oracle 10g database. Exception javax.servlet.ServletException: org.xml.sax.SAXParseException: Invalid byte 1 of 1-byte UTF-8 sequence.

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  • java cms(opencms) and my SQL configuring problem

    - by akshay
    i have installed open cms on my local machine and it perfectly works fine. But in order to work it corre,ty it is mentioned that i have to modify the my.ini file and set max_alllowed_packed site to 32 I have done it and it works perfectly fine but can i modify this file if i use a third party hosting provider for tomcat and mysql??

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  • Reducing Time Complexity in Java

    - by Koeneuze
    Right, this is from an older exam which i'm using to prepare my own exam in january. We are given the following method: public static void Oorspronkelijk() { String bs = "Dit is een boodschap aan de wereld"; int max = -1; char let = '*'; for (int i=0;i<bs.length();i++) { int tel = 1; for (int j=i+1;j<bs.length();j++) { if (bs.charAt(j) == bs.charAt(i)) tel++; } if (tel > max) { max = tel; let = bs.charAt(i); } } System.out.println(max + " keer " + let); } The questions are: what is the output? - Since the code is just an algorithm to determine the most occuring character, the output is "6 keer " (6 times space) What is the time complexity of this code? Fairly sure it's O(n²), unless someone thinks otherwise? Can you reduce the time complexity, and if so, how? Well, you can. I've received some help already and managed to get the following code: public static void Nieuw() { String bs = "Dit is een boodschap aan de wereld"; HashMap<Character, Integer> letters = new HashMap<Character, Integer>(); char max = bs.charAt(0); for (int i=0;i<bs.length();i++) { char let = bs.charAt(i); if(!letters.containsKey(let)) { letters.put(let,0); } int tel = letters.get(let)+1; letters.put(let,tel); if(letters.get(max)<tel) { max = let; } } System.out.println(letters.get(max) + " keer " + max); } However, I'm uncertain of the time complexity of this new code: Is it O(n) because you only use one for-loop, or does the fact we require the use of the HashMap's get methods make it O(n log n) ? And if someone knows an even better way of reducing the time complexity, please do tell! :)

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  • using extends with Java Generics

    - by Sandro
    Lets say that I have the following code: public class Shelter<A extends Animal, B extends Animal> { List<A> topFloor = new Vector<A>(); List<B> bottomFloor = new Vector<B>(); public A getFirstTopFloorAnimal(){return topFloor.firstElement();} public B getFirstBottomFloorAnimal(){return bottomFloor.firstElement();} //This compiles but when I try to use it, it only returns objects public List<Animal> getAnimals() { Vector a = new Vector(topFloor); a.addAll(bottomFloor); return a; } } Now for somereason the following code compiles. But when I try to use getAnimals() I get a of objects instead of Animal. Any ideas why this is? Does this have to do with the List is NOT a List idea in the Generics tutorial? Thank you.

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  • Java Node.cloneNode()

    - by Tom Brito
    Talking about the org.w3c.dom package; When I call Node.cloneNode() method from a Element(extends Node) object, which Document is used to create the new cloned Element? Example: import org.w3c.dom; class MyClass { public static void main(String[] args) throws Exception { DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder(); Document doc = builder.newDocument(); Element element = doc.createElement("myElement"); Element cloneElement = (Element) element.cloneNode(true); } } Which Document was used to create cloneElement?

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  • How to give xpath expression in java using axiom

    - by user1811206
    <resource name="cde.xml" status="updated" isCollection="false"> <mediaType>xml</mediaType> <creator>admin</creator> <createdTime>1352783477964</createdTime> <lastUpdater>admin</lastUpdater> <lastModified>1352783477964</lastModified> <description /> <version>0</version> <content>ZGFza2QgbGQgbGt2Zmx3ZGFzamQgYWRsa2ogYWxramRrbGEgamQK </content> </resource> i want to catch nodes which are having status using xpath here is the xpath expression other part of the code is correct. I have problem with xpath expression AXIOMXPath xpathExpression = new AXIOMXPath ( "//resourse[@name]");

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  • get eigenvalue pca with java

    - by Muhamad Burhanudin
    I try use PCA to reduce dimention, and i use jama for help me using matrix. but, i got problem when get eigenvalue with jama. for example i hava 2 image dimention 100x100, then i create single matrix 2 image x (100x100). there is 20.000 pixel. and how to get reduction with eigenvalue? this is sample my code : public static void main(String[] args) { BufferedImage bi; int[] rgb; int R, G, B; // int[] jum; double[][] gray = new double[500][500] ; String[] baris = new String[1000]; try { //bi = ImageIO.read(new File("D:\\c.jpg")); int[][] pixelData = new int[bi.getHeight() * bi.getWidth()][3]; int counter = 0; for (int i = 0; i < bi.getHeight(); i++) { for (int j = 0; j < bi.getWidth(); j++) { gray[i][j] = getPixelData(bi, i, j); // R = getR(bi, i, j); //G = getG(bi, i, j); //B = getB(bi, i, j); //jum = R + G + B; // gray[counter] = Double.toString(R + G + B / 3); // System.out.println("Gray " +gray); //for (int k = 0; k < rgb.length; k++) { // pixelData[counter][k] = rgb[k]; // } counter++; } } } catch (IOException e) { e.printStackTrace(); } Matrix matrix = new Matrix(gray); PCA pca = new PCA(matrix); pca.getEigenvalue(6); String n = pca.toString(); System.err.println("nilai n "+n); //double dete = pcadete(matrix,3600); } private static int getPixelData(BufferedImage bi, int x, int y) { int argb = bi.getRGB(y, x); int r, g, b; int gray; int rgb[] = new int[]{ (argb >> 16) & 0xff, //red (argb >> 8) & 0xff, //green (argb) & 0xff //blue }; r = rgb[0]; g = rgb[1]; b = rgb[2]; gray = (r + g + b) / 3; System.out.println("gray: " + gray); return gray; } when i show eigenvalue in this code : PCA pca = new PCA(matrix); pca.getEigenvalue(6); String n = pca.toString(); System.err.println("nilai n "+n); Result is : nilai n PCA@c3e9e9 Can, u tell me what way to get eigenvalue and reduction dimension.

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