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  • fail-fast iterator

    - by joy
    I get this definition : As name suggest fail-fast Iterators fail as soon as they realized that structure of Collection has been changed since iteration has begun. what it mean by since iteration has begun? is that mean after Iterator it=set.iterator() this line of code? public static void customize(BufferedReader br) throws IOException{ Set<String> set=new HashSet<String>(); // Actual type parameter added **Iterator it=set.iterator();**

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  • OPTICS Clustering algorithm. How to get the best epsilon

    - by Marco Galassi
    I am implementing a project which needs to cluster geographical points. OPTICS algorithm seems to be a very nice solution. It needs just 2 parameters as input(MinPts and Epsilon), which are, respectively, the minimum number of points needed to consider them as a cluster, and the distance value used to compare if two points are in can be placed in same cluster. My problem is that, due to the extreme variety of the points, I can't set a fixed epsilon. Just look at the image below. The same points structure but in a different scale would result very different. Suppose to set MinPts=2 and epsilon = 1Km. On the left, the algorithm would create 2 clusters(red and blue), but on the right it would create one single cluster containing all of the points(red), but I would like to obtain 2 clusters even on the right. So my question is: is there any kind of way to calculate dynamically the epsilon value to get this result? Thank you very much and excuse my for my poor english. Marco

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  • Display values inside a JList -

    - by sharon Hwk
    I have a method that returns a HashMap, and is defined as follows; public HashMap<Integer, Animal> allAnimal(){ return returnsAHashMap; } Animal will have the following values in its class: public Animal{ int animalID; String animalName; // i have declared getters/setters } I have a GUI screen which has a JList and it's defined as: l = new JList(); l.setModel(new AbstractListModel() { String[] v = new String[] {"animal id 1", "2", "3"}; public int getSize() { return v.length; } public Object getElementAt(int index) { return v[index]; } }); What I want to do is to display the AnimalID's in the JList. I need to find a way to call the allAnimal() method and display all its Animal Id's in the JList. How can i do this ?

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  • What to do when ServerSocket throws IOException and keeping server running

    - by s5804
    Basically I want to create a rock solid server. while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... } catch (IOException e) { e.printStackTrace(); // NOW WHAT? } } In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT); However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating. EDIT: After some answers, here my attempt to deal with the IOException. Would the implementation be guaranteeing keeping the server up and only re-create server socket when only necessary? while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... bindExceptionCounter = 0; } catch (IOException e) { e.printStackTrace(); recreateServerSocket(); } } private void recreateServerSocket() { while (keepRunning) { try { logger.info("Try to re-create Server Socket"); ServerSocket socket = ServerSocketFactory.getDefault().createServerSocket(RateTableServer.RATE_EVENT_SERVER_PORT); // No exception thrown, then use the new socket. serverSocket = socket; break; } catch (BindException e) { logger.info("BindException indicates that the server socket is still good.", e); bindExceptionCounter++; if (bindExceptionCounter < 5) { break; } } catch (IOException e) { logger.warn("Problem to re-create Server Socket", e); e.printStackTrace(); try { Thread.sleep(30000); } catch (InterruptedException ie) { logger.warn(ie); } } } }

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  • ExecutorService memory leak on exception

    - by TofuBeer
    I am having a hard time tracking this down since the profiler keeps crashing (hotspot error). Before I go too deep into figuring it out I'd like to know if I really have a problem or not :-) I have a few thread pools created via: Executors.newFixedThreadPool(10); The threads connect to different web sites and, on occasion, I get connection refused and wind up throwing an exception. When I later on call Future.get() to get the result it will then catch the ExecutionException that wraps the exception that was thrown when the connection could not be made. The program uses a fairly constant amount of memory up until the point in time that the exceptions get thrown (they tend to happen in batches when a particular site is overloaded). After that point the memory again remains constant but at a higher level. So my question is along the lines of is the memory behaviour (reported by "top" on Unix) expected because the exceptions just triggered something or do I probably have an actual leak that I'll need to track down? Additionally when Future.get() throws an exception is there anything else I need to do besides catch the exception (such as call Future.cancel() on it)?

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  • Return value changed after finally

    - by Nestor
    I have the following code: public bool ProcessData(String data) { try { result= CheckData(data); if (TextUtils.isEmpty(result)) { summary="Data is invalid"; return false; } ... finally { Period period = new Period(startTime, new LocalDateTime()); String duration = String.format("Duration: %s:%s", period.getMinutes(), period.getSeconds()); LogCat(duration); } return true; As I learned from this question, the finally block is executed after the return statement. So I modified my code according to that, and in the finally I inserted code that does not modify the output. Strangely, the code OUTSIDE the finally block does. My method always returns true. As suggested, it is not a good idea to have 2 return. What should I do?

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  • Resolve naming conflict in included XSDs for JAXB compilation

    - by Jason Faust
    I am currently trying to compile with JAXB (IBM build 2.1.3) a pair of schema files into the same package. Each will compile on it's own, but when trying to compile them together i get a element naming conflict due to includes. My question is; is there a way to specify with an external binding a resolution to the naming collision. Example files follow. In the example the offending element is called "Common", which is defined in both incA and incB: incA.xsd <?xml version="1.0" encoding="UTF-8"?> <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.example.org/" xmlns:tns="http://www.example.org/" elementFormDefault="qualified"> <complexType name="TypeA"> <sequence> <element name="ElementA" type="string"></element> </sequence> </complexType> <!-- Conflicting element --> <element name="Common" type="tns:TypeA"></element> </schema> incB.xsd <?xml version="1.0" encoding="UTF-8"?> <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.example.org/" xmlns:tns="http://www.example.org/" elementFormDefault="qualified"> <complexType name="TypeB"> <sequence> <element name="ElementB" type="int"></element> </sequence> </complexType> <!-- Conflicting element --> <element name="Common" type="tns:TypeB"></element> </schema> A.xsd <?xml version="1.0" encoding="UTF-8"?> <schema targetNamespace="http://www.example.org/" elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tns="http://www.example.org/"> <include schemaLocation="incA.xsd"></include> <complexType name="A"> <sequence> <element ref="tns:Common"></element> </sequence> </complexType> </schema> B.xsd <?xml version="1.0" encoding="UTF-8"?> <schema targetNamespace="http://www.example.org/" elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tns="http://www.example.org/"> <include schemaLocation="incB.xsd"></include> <complexType name="B"> <sequence> <element ref="tns:Common"></element> </sequence> </complexType> </schema> Compiler error when both are compiled from one evocation of xjb: [ERROR] 'Common' is already defined line 9 of file:/C:/temp/incB.xsd [ERROR] (related to above error) the first definition appears here line 9 of file:/C:/temp/incA.xsd (For reference, this is a generalization to resolve an issue with compiling the OAGIS8 SP3 package)

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  • Better to use constructor or method factory pattern?

    - by devoured elysium
    I have a wrapper class for the Bitmap .NET class called BitmapZone. Assuming we have a WIDTH x HEIGHT bitmap picture, this wrapper class should serve the purpose of allowing me to send to other methods/classes itself instead of the original bitmap. I can then better control what the user is or not allowed to do with the picture (and I don't have to copy the bitmap lots of times to send for each method/class). My question is: knowing that all BitmapZone's are created from a Bitmap, what do you find preferrable? Constructor syntax: something like BitmapZone bitmapZone = new BitmapZone(originalBitmap, x, y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.From(originalBitmap, x , y, width, height); Factory Method Pattern: BitmapZone bitmapZone = BitmapZone.FromBitmap(originalBitmap, x, y, width, height); Other? Why? Thanks

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  • Resized image degrades in quality.

    - by Venkats
    I resized an image using Java2D Graphics class. But it doesn't look right. BufferedImage resizedImage = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, type); Graphics2D g = resizedImage.createGraphics(); g.drawImage(originalImage, 0, 0, IMG_WIDTH, IMG_HEIGHT, null); g.dispose(); Is it possible to scale an image without introducing artifacts?

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  • How to create new account using servlets

    - by Alvin
    I want to know how can I create new account using servlets in post method? I'm currently following MVC design pattern, and I want to know if I pass the required data to register new account from JSP page, then how can I get that data in post method? As request.getParameter() method returning me null. How can I know that post method is calling to create new account? How can I pass all the relevant user information from servlets to model class for registering data to the database table?

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  • How do I execute a sequence of servlets?

    - by Legend
    I have some servlets that act as individual URLs for populating a database for some dummy testing. Something of the form: public class Populate_ServletName extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { resp.setContentType("text/plain"); //Insert records //Print confirmation } } I have about 6 such servlets which I want to execute in a sequence. I was thinking of using setLocation to set the next page to be redirected but was not sure if this is the right approach because the redirects should happen after the records have been inserted. Specifically, I am looking for something like this: public class Populate_ALL extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { resp.setContentType("text/plain"); //Call Populate_1 //Call Populate_2 //Call Populate_3 //... } } Any suggestions?

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  • Retrieve only the superclass from a class hierarchy

    - by user1792724
    I have an scenario as the following: @Entity @Table(name = "ANIMAL") @Inheritance(strategy = InheritanceType.JOINED) public class Animal implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_ANIMAL") @SequenceGenerator(name = "S_ANIMAL", sequenceName = "S_ANIMAL", allocationSize = 1) public int getNumero() { return numero; } public void setNumero(int numero) { this.numero = numero; } . . . } and as the subclass: @Entity @Table(name = "DOG") public class Dog extends Animal { private static final long serialVersionUID = -7341592543130659641L; . . . } I have a JPA Select statement like this: SELECT a FROM Animal a; I'm using Hibernate 3.3.1 As I can see the framework retrieves instances of Animal and also of Dog using a left outer join. Is there a way to Select only the "part" Animal? I mean, the previous Select will get all the Animals, those that are only Animals but not Dogs and those that are Dogs. I want them all, but in the case of Dogs I want to only retrieve the "Animal part" of them. I found the @org.hibernate.annotations.Entity(polymorphism = PolymorphismType.EXPLICIT) but as I could see this only works if Animal isn't an @Entity. Thanks a lot.

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  • In a bidirectional JPA OneToMany/ManyToOne association, what is meant by "the inverse side of the as

    - by Bytecode Ninja
    In these examples on TopLink JPA Annotation Reference: Example 1-59 @OneToMany - Customer Class With Generics @Entity public class Customer implements Serializable { ... @OneToMany(cascade=ALL, mappedBy="customer") public Set<Order> getOrders() { return orders; } ... } Example 1-60 @ManyToOne - Order Class With Generics @Entity public class Order implements Serializable { ... @ManyToOne @JoinColumn(name="CUST_ID", nullable=false) public Customer getCustomer() { return customer; } ... } It seams to me that the Customer entity is the owner of the association. However, in the explanation for the mappedBy attribute in the same document, it is written that: if the relationship is bidirectional, then set the mappedBy element on the inverse (non-owning) side of the association to the name of the field or property that owns the relationship as Example 1-60 shows. However, if I am not wrong, looks like in the example the mappedBy is actually specified on the owning side of the association, rather than the non-owning side. So my question is basically: In a bidirectional (one-to-many/many-to-one) association, which of the entities is the owner? How can we designate the One side as the owner? How can we designate the Many side as the owner? What is meant by "the inverse side of the association"? How can we designate the One side as the inverse? How can we designate the Many side as the inverse? Thanks in advance.

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  • Is selling a "website screen scraper" illegal?

    - by Yatendra Goel
    I have coded a "website screen scraper" and want to sell it commercially. I know that webpages scraped by the screen scraper are restricted to be scraped by the webmaser of that website. The robots.txt file of the website says that its webpages must not be scraped. So my question is whether selling that screen scraper is a crime or using that screen scraper is a crime in legal terms. I know that this question is related to law but I thought the software experts on SO must also have answer to this question.

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  • How to remove duplicate line in a file

    - by Abs
    Hi I'm using the below method to write to a file from the Jtextarea and I call this method every 30 second within a Timer but instead to add only new line in file it rewrite the entire lines contained in Jtextarea so then I have duplicate lines. I want to avoid this and update the file just with new lines. Could you help me please. public void loger() { FileWriter writer = null; try { writer = new FileWriter("MBM_Log_"+date()+".txt" , true); textArea.write(writer); } catch (IOException exception) { System.err.println("log error"); exception.printStackTrace(); } finally { if (writer != null) { try { writer.close(); } catch (IOException exception) { System.err.println("Error closing writer"); exception.printStackTrace(); } } } }

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  • Source code versioning with comments (organizational practice) - leave or remove?

    - by ADTC
    Before you start admonishing me with "DON'T DO IT," "BAD PRACTICE!" and "Learn to use proper source code control", please hear me out first. I am fully aware that the practice of commenting out old code and leaving it there forever is very bad and I hate such practice myself. But here's the situation I'm in. A few months ago I joined a company as software developer. I had worked in the company for few months as an intern, about a year before joining recently. Our company uses source code version control (CVS) but not properly. Here's what happened both in my internship and my current permanent position. Each time I was assigned to work on a project (legacy, about 8-10 years old). Instead of creating a CVS account and letting me check out code and check in changes, a senior colleague exported the code from CVS, zipped it up and passed it to me. While this colleague checks in all changes in bulk every few weeks, our usual practice is to do fine-grained versioning in the actual source code itself (each file increments in versions independent from the rest). Whenever a change is made to a file, old code is commented out, new code entered below it, and this whole section is marked with a version number. Finally a note about the changes is placed at the top of the file in a section called Modification History. Finally the changed files are placed in a shared folder, ready and waiting for the bulk check-in. /* * Copyright notice blah blah * Some details about file (project name, file name etc) * Modification History: * Date Version Modified By Description * 2012-10-15 1.0 Joey Initial creation * 2012-10-22 1.1 Chandler Replaced old code with new code */ code .... //v1.1 start //old code new code //v1.1 end code .... Now the problem is this. In the project I'm working on, I needed to copy some new source code files from another project (new in the sense that they didn't exist in destination project before). These files have a lot of historical commented out code and comment-based versioning including usually long or very long Modification History section. Since the files are new to this project I decided to clean them up and remove unnecessary code including historical code, and start fresh at version 1.0. (I still have to continue the practice of comment-based versioning despite hating it. And don't ask why not start at version 0.1...) I have done similar something during my internship and no one said anything. My supervisor has seen the work a few times and didn't say I shouldn't do such clean-up (if at all it was noticed). But a same-level colleague saw this and said it's not recommended as it may cause downtime in the future and increase maintenance costs. An example is when changes are made in another project on the original files and these changes need to be propagated to this project. With code files drastically different, it could cause confusion to an employee doing the propagation. It makes sense to me, and is a valid point. I couldn't find any reason to do my clean-up other than the inconvenience of a ridiculously messy code. So, long story short: Given the practice in our company, should I not do such clean-up when copying new files from project to project? Is it better to make changes on the (copy of) original code with full history in comments? Or what justification can I give for doing the clean-up? PS to mods: Hope you allow this question some time even if for any reason you determine it to be unfit in SO. I apologize in advance if anything is inappropriate including tags.

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  • RSA encryption/ Decryption in a client server application

    - by user308806
    Hi guys, probably missing something very straight forward on this, but please forgive me, I'm very naive! Have a client server application where the client identifies its self with an RSA encrypted username & password. Unfortunately I'm getting a "bad padding exception: data must start with zero" when i try to decrypt with the public key on the client side. I'm fairly sure the key is correct as I have tested encrypting with public key then decrypting with private key on the client side with no problems at all. Just seems when I transfer it over the connection it messses it up somehow?! Using PrintWriter & BufferedReader on the sockets if thats of importance. EncodeBASE64 & DecodeBASE64 encode byte[] to 64base and vice versa respectively. Any ideas guys?? Client side: Socket connectionToServer = new Socket("127.0.0.1", 7050); InputStream in = connectionToServer.getInputStream(); DataInputStream dis = new DataInputStream(in); int length = dis.readInt(); byte[] data = new byte[length]; // dis.readFully(data); dis.read(data); System.out.println("The received Data*****************************************"); System.out.println("The length of bits "+ length); System.out.println(data); System.out.println("***********************************************************"); Decryption d = new Decryption(); byte [] ttt = d.decrypt(data); System.out.print(data); String ss = new String(ttt); System.out.println("***********************"); System.out.println(ss); System.out.println("************************"); Server Side: in = connectionFromClient.getInputStream(); OutputStream out = connectionFromClient.getOutputStream(); DataOutputStream dataOut = new DataOutputStream(out); LicenseList licenses = new LicenseList(); String ValidIDs = licenses.getAllIDs(); System.out.println(ValidIDs); Encryption enc = new Encryption(); byte[] encrypted = enc.encrypt(ValidIDs); byte[] dd = enc.encrypt(ValidIDs); String tobesent = new String(dd); //byte[] rsult = enc.decrypt(dd); //String tt = String(rsult); System.out.println("The sent data**********************************************"); System.out.println(dd); String temp = new String(dd); System.out.println(temp); System.out.println("*************************************************************"); //BufferedWriter bf = new BufferedWriter(OutputStreamWriter(out)); //dataOut.write(ValidIDs.getBytes().length); dataOut.writeInt(ValidIDs.getBytes().length); dataOut.flush(); dataOut.write(encrypted); dataOut.flush(); System.out.println("********Testing**************"); System.out.println("Here are the ids:::"); System.out.println(licenses.getAllIDs()); System.out.println("**********************"); //bw.write("it is working well\n");

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  • 500 Worker Threads, what kind of thread pool?

    - by Submerged
    I am wondering if this is the best way to do this. I have about 500 threads that run indefinitely, but Thread.sleep for a minute when done one cycle of processing. ExecutorService es = Executors.newFixedThreadPool(list.size()+1); for (int i = 0; i < list.size(); i++) { es.execute(coreAppVector.elementAt(i)); //coreAppVector is a vector of extends thread objects } The code that is executing is really simple and basically just this class aThread extends Thread { public void run(){ while(true){ Thread.sleep(ONE_MINUTE); //Lots of computation every minute } } } I do need a separate threads for each running task, so changing the architecture isn't an option. I tried making my threadPool size equal to Runtime.getRuntime().availableProcessors() which attempted to run all 500 threads, but only let 8 (4xhyperthreading) of them execute. The other threads wouldn't surrender and let other threads have their turn. I tried putting in a wait() and notify(), but still no luck. If anyone has a simple example or some tips, I would be grateful! Well, the design is arguably flawed. The threads implement Genetic-Programming or GP, a type of learning algorithm. Each thread analyzes advanced trends makes predictions. If the thread ever completes, the learning is lost. That said, I was hoping that sleep() would allow me to share some of the resources while one thread isn't "learning"

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  • Draw a position from a 2d Array on respected canvas location

    - by Anon
    Background: I have two 2d arrays. Each index within each 2d array represents a tile which is drawn on a square canvas suitable for 8 x 8 tiles. The first 2d array represents the ground tiles and is looped and drawn on the canvas using the following code: //Draw the map from the land 2d array map = new Canvas(mainFrame, 20, 260, 281, 281); for(int i=0; i < world.length; i++){ for(int j=0; j < world[i].length; j++){ for(int x=0; x < 280; x=x+35){ for(int y=0; y < 280; y=y+35){ Point p = new Point(x,y); map.add(new RectangleObject(p,35,35,Colour.green)); } } } } This creates a grid of green tiles 8 x 8 across as intended. The second 2d array represents the position on the ground. This 2d array has everyone of its indexes as null apart from one which is comprised of a Person class. Problem I am unsure of how I can draw the position on the grid. I was thinking of a similar loop, so it draws over the previous 2d array another set of 64 tiles. Only this time they are all transparent but the one tile which isn't null. In other words, the tile where Person is located. I wanted to use a search throughout the loop using a comparative if statement along the lines of if(!(world[] == null)){ map.add(new RectangleObject(p,35,35,Colour.red));} However my knowledge is limited and I am confused on how to implement it.

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