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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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  • 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 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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  • What's wrong with this JAVA code for android?

    - by Umair Ashraf
    I have written this piece of code to break an image into 9 pieces and it gives me runtime error. There is no error in LogCat and I am stuck. The error comes at line 7 line from bottom (Bitmap.createBitmap(...);). public Bitmap[] getPieces(Bitmap bmp) { Bitmap[] bmps = new Bitmap[9]; int width = bmp.getWidth(); int height = bmp.getHeight(); int rows = 3; int cols = 3; int cellHeight = height / rows; int cellWidth = width / cols; int piece = 0; for (int x = 0; x <= width; x += cellWidth) { for (int y = 0; y <= height; y += cellHeight) { Bitmap b = Bitmap.createBitmap(bmp, x, y, cellWidth, cellHeight, null, false); bmps[piece] = b; piece++; } } return bmps; }

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  • How to represent double values as circles in a 2d matrix in java

    - by marco
    Hello, so I want to write a matrix explorer which enables me to reorder rows and columns of a matrix. For this porpouse I used the Jtable class. Now the problem that I have is that it is very difficult to reorder a matrix by looking at double values, so I would like to print the matrix not with the double values but with circles in which the radius of the circle represents the value. So that I can tell the difference between big values and small values quicker. Anybody has any idea how I can turn this double values into filled circles with JTable or any table class for that matter?

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  • A linked list with multiple heads in Java

    - by Emile
    Hi, I have a list in which I'd like to keep several head pointers. I've tried to create multiple ListIterators on the same list but this forbid me to add new elements in my list... (see Concurrent Modification exception). I could create my own class but I'd rather use a built-in implementation ;) To be more specific, here is an inefficient implementation of two basic operations and the one wich doesn't work : class MyList <E { private int[] _heads; private List<E _l; public MyList ( int nbHeads ) { _heads = new int[nbHeads]; _l = new LinkedList<E(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { return _l.get(_heads[head++]); // ugly } } class MyList <E { private Vector<ListIterator<E _iters; private List<E _l; public MyList ( int nbHeads ) { _iters = new Vector<ListIterator<E(nbHeads); _l = new LinkedList<E(); for( ListIterator<E iter : _iters ) iter = _l.listIterator(); } public void add ( E e ) { _l.add(e); } public E next ( int head ) { // ConcurrentModificationException because of the add() return _iters.get(head).next(); } } Emile

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  • Extending Java Enums

    - by CaseyB
    Here's what I am looking to accomplish, I have a class that has an enum of some values and I want to subclass that and add more values to the enum. This is a bad example, but: public class Digits { public enum Digit { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 } } public class HexDigits extends Digits { public enum Digit { A, B, C, D, E, F } } so that HexDigits.Digit contains all Hex Digits. Is that possible?

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  • Who is preventing the release of Java 1.7

    - by Shawn
    I recently attended a talk by a Sun engineer Charlie Hunt regarding performance. The talk was interesting enough but one question was regarding release date of 1.7. He said it's delayed as there are parties who are refusing to sign off JSRs they own and thus preventing the 1.7 release. It apparently has something to do with the cost of determining your Sun compliance. I would be interested to know the full story if anyone knows or can point me in the right direction. What triggered my question was the amazing long release notes for 6u18. Thanks

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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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  • 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 - volatile keyword

    - by Tiyoal
    Say I have two threads and an object. One thread assigns the object: public void assign(MyObject o) { myObject = o; } Another thread uses the object: public void use() { myObject.use(); } Does the variable myObject have to be declared as volatile? I am trying to understand when to use volatile and when not, and this is puzzling me. Is it possible that the second thread keeps a reference to an old object in its local memory cache? If not, why not? Thanks a lot.

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  • How to repaint a XYPlot from JFreeChart? (JAVA)

    - by mccrank
    Hi, I'm doing a GUI that has a XYPlot (from the JFreeChart package) and when I click a button I'm trying to add some values. I add them correctly to the XYSeries that are inside the XYPlot, but the GUI doesn't change. It only changes when y maximize or minimize. Is there some kind of repaint to do this? I have been looking for it and I have found nothing.

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  • generating and unmarshalling java classes while unmarshalling input contains a DTD

    - by Hans Westerbeek
    Hi, For a Spring-based project, I have the following situation to solve: I have XML files coming in whose contents I will have to parse at runtime. Those XML files come with a DTD reference. I need to generate the classes that the unmarshaller churns out using the right at build time, using the Maven2 plugin for the unmarshalling library of choice. This is also not very hard to do, once I have generated an XSD from the DTD. I want to use spring-oxm's UnMarshaller interface to do the unmarshalling at runtime. This I understand how to do. The xml files come in with a DTD reference, and all unmarshalling libraries out there want to do unmarshalling based on an XSD. Now, as described in the castor documentation, I can convert the DTD to an XSD and keep it on the classpath. However, when an actual XML file comes into the system it will still have that DTD reference at the top, and there's nothing I can really do about that (except for string replacing which feels hacky in this case). Will this cause the unmarshaller, like Castor to fail? Am I right in suspecting that this DTD reference will cause the unmarshalling to fail? Could I do pure DTD-based unmarshalling? Or can this somehow be prevented by providing detailed configuration to the unmarshaller? Until now, I have tried castor, xmlbeans and xstream. Which would fit my purposes best? Has anyone else been in this situation? Did you also end up just doing manual DOM or SAX parsing?

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  • Passing a Java object from one Struts action to another

    - by Bernhard V
    Hello! In one of my Struts action I've got the following code in a method: ... List<Object> retrievedListOfObjects = c.getListOfObjects(); return mapping.findForward("fw_view"); } fw_view leads to a new Struts action with another Struts form. Let's say this form has got among others the following field List<Object> listOfObjects; I now want to pass the retrievedListOfObjects from within the first Struts action to the form of the following Struts action. Is this possible without storing it in the session?

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  • remove duplicate code in java

    - by Anantha Kumaran
    class A extends ApiClass { public void duplicateMethod() { } } class B extends AnotherApiClass { public void duplicateMethod() { } } I have two classes which extend different api classes. The two class has some duplicate methods(same method repeated in both class) and how to remove this duplication? Edit The ApiClass is not under my control

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  • Dijkstras Algorithm exaplination java

    - by alchemey89
    Hi, I have found an implementation for dijkstras algorithm on the internet and was wondering if someone could help me understand how the code works. Many thanks private int nr_points=0; private int[][]Cost; private int []mask; private void dijkstraTSP() { if(nr_points==0)return; //algorithm=new String("Dijkstra"); nod1=new Vector(); nod2=new Vector(); weight=new Vector(); mask=new int[nr_points]; //initialise mask with zeros (mask[x]=1 means the vertex is marked as used) for(int i=0;i<nr_points;i++)mask[i]=0; //Dijkstra: int []dd=new int[nr_points]; int []pre=new int[nr_points]; int []path=new int[nr_points+1]; int init_vert=0,pos_in_path=0,new_vert=0; //initialise the vectors for(int i=0;i<nr_points;i++) { dd[i]=Cost[init_vert][i]; pre[i]=init_vert; path[i]=-1; } pre[init_vert]=0; path[0]=init_vert; pos_in_path++; mask[init_vert]=1; for(int k=0;k<nr_points-1;k++) { //find min. cost in dd for(int j=0;j<nr_points;j++) if(dd[j]!=0 && mask[j]==0){new_vert=j; break;} for(int j=0;j<nr_points;j++) if(dd[j]<dd[new_vert] && mask[j]==0 && dd[j]!=0)new_vert=j; mask[new_vert]=1; path[pos_in_path]=new_vert; pos_in_path++; for(int j=0;j<nr_points;j++) { if(mask[j]==0) { if(dd[j]>dd[new_vert]+Cost[new_vert][j]) { dd[j]=dd[new_vert]+Cost[new_vert][j]; } } } } //Close the cycle path[nr_points]=init_vert; //Save the solution in 3 vectors (for graphical purposes) for(int i=0;i<nr_points;i++) { nod1.addElement(path[i]); nod2.addElement(path[i+1]); weight.addElement(Cost[path[i]][path[i+1]]); } }

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