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  • Class.getArrayType in Java?

    - by ???
    I use the following trick to get the array type of a specific class: @SuppressWarnings("unchecked") public static <T> Class<T[]> getArrayType(Class<T> componentType) { String arrayClassName = "[L" + componentType.getName() + ";"; try { return (Class<T[]>) Class.forName(arrayClassName); } catch (ClassNotFoundException e) { throw new UnexpectedException("Can't get the array type for " + componentType, e); } } But, is there any more elegant way to get this?

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  • Java: empty ArrayLists in a foor loop

    - by Patrick
    hi, I'm reusing the same ArrayList in a for loop, and I use for loop results = new ArrayList<Integer>(); experts = new ArrayList<Integer>(); output = new ArrayList<String>(); .... to create new ones. I guess this is wrong, because I'm allocating new memory. Is this correct ? If yes, how can I empty them ? Added: another example I'm creating new variables each time I call this method. Is this good practice ? I mean to create new precision, relevantFound.. etc ? Or should I declare them in my class, outside the method to not allocate more and more memory ? public static void computeMAP(ArrayList results, ArrayList experts) { //compute MAP double precision = 0; int relevantFound = 0; double sumprecision = 0; thanks

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  • valid xml element in java replaceAll doesnt seem working well

    - by John
    Im trying to create a xml file from a POJO , in which i have a property that stores urls, I have been using the below method to replace all & in the url String to make the xml conform to standards and pass it as an html char entity but the string does not change. public static String forHrefAmpersand(String aURL){ return aURL.replaceAll("&", "&"); } the value might be www.abc.com/controller?a=1&next=showResults I have even tried changing the above method to use "/" as i read replaceAll uses regular expression but replaceAll is not working as exprected, Can anyone tell me what is the mistake im doing ? Thanks in advance

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  • Simple stream read/write question in java

    - by Marius
    Hi, I'm trying to upload a file via URLConnection, but i need to read/write it as a binary file without any encoding changes. So i've tried to read byte[] array from FileInputStream, but now i have an issue. The PrintWriter object i use for outputing to the server does not allow me to do writer.write(content) (where content is of type byte[]). How can i fix this? Or is there another way to quickly copy binary data from a FileInputStream to a PrintWriter? Thank you

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  • Sending arbitrarily long string over Java TCP socket

    - by bibismcbryde
    I have an Android app that communicates over a TCP socket with a server I wrote. The method I'm using now to read and write output works fine for smaller strings (up to 60kB) but I get an exception thrown when the string is much longer than that. Here is the relevant part of what I have for the server and client: Server: DataInputStream dis = null; DataOutputStream dos = null; try { dis = new DataInputStream(server.getInputStream()); dos = new DataOutputStream(server.getOutputStream()); String input = ""; input = dis.readUTF(); handle_input info = new handle_input(input, id); String xml = info.handle(); dos.writeUTF(xml); server.close(); } Client: Socket socket = null; DataOutputStream dos = null; DataInputStream dis = null; Boolean result; try { socket = new Socket(ip, port); dos = new DataOutputStream(socket.getOutputStream()); dis = new DataInputStream(socket.getInputStream()); dos.writeUTF(the_text); String in = ""; while (in.equals("")) { in += dis.readUTF(); } } How can I modify it to deal with potentially enormous Strings? I've been looking around and can't seem to find a clear answer. Thanks.

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  • inputMismatchException Java reading doubles from plain text file

    - by user939287
    Using double variable = inputFile.nextDouble(); Gives the mismatch error and I can't figure out why... Anyone know what's up? The input file is just a bunch of doubles like 5.0... Okay here is the code snippet String fileName; Scanner scanner = new Scanner(System.in); System.out.println("\nEnter file name that contains the matrix and vector: "); fileName = scanner.nextLine(); Scanner inputFile = new Scanner(fileName); double a1 = inputFile.nextDouble(); the input file is a plain text document .txt in this format 5.0 4.0 -3.0 4.0 2.0 5.0 6.0 5.0 -2.0 -13.0 4.0 12.0 I don't understand why it wouldn't take those as doubles... As far as what its expecting the format of the file to be... I suppose binary? isn't that the default? I didn't specify in the code...

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  • Good ACL implementation in Java

    - by yonconf
    Hi All. I'm implementing a web based document management system and I'd like to implement ACLs in my system. My formal requirements are hierarchal permissions (documents inherit permissions from their folders) user groups (users can dynamically create groups and associate users with groups). Such groups can have permissions on objects in the system. My code will query permission on objects in two cases: 1. Manipulating a single document 2. Listing all documents where a manipulation is possible The latter requirement seems the achilles heel for Spring Security ACLs (their method seems likely to incur multiple DB hits for each document I manage) Anyone know of another ACL implementation? Thanks!

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  • Why fill() and copy() of Collections in java is implemented this way

    - by Priyank Doshi
    According to javadoc... Collections.fill() is written as below : public static <T> void fill(List<? super T> list, T obj) { int size = list.size(); if (size < FILL_THRESHOLD || list instanceof RandomAccess) { for (int i=0; i<size; i++) list.set(i, obj); } else { ListIterator<? super T> itr = list.listIterator(); for (int i=0; i<size; i++) { itr.next(); itr.set(obj); } } } Its easy to understand why they didn't use listIterator for if (size < FILL_THRESHOLD || list instanceof RandomAccess) condition as of RandomAccess. But whats the use of size < FILL_THRESHOLD in above? I mean is there any significant performance benefit over using iterator for size>=FILL_THRESHOLD and not for size < FILL_THRESHOLD ? I see the same approach for Collections.copy() also : public static <T> void copy(List<? super T> dest, List<? extends T> src) { int srcSize = src.size(); if (srcSize > dest.size()) throw new IndexOutOfBoundsException("Source does not fit in dest"); if (srcSize < COPY_THRESHOLD || (src instanceof RandomAccess && dest instanceof RandomAccess)) { for (int i=0; i<srcSize; i++) dest.set(i, src.get(i)); } else { ListIterator<? super T> di=dest.listIterator(); ListIterator<? extends T> si=src.listIterator(); for (int i=0; i<srcSize; i++) { di.next(); di.set(si.next()); } } } FYI: private static final int FILL_THRESHOLD = 25; private static final int COPY_THRESHOLD = 10;

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  • Type casting problem with java for-each loop

    - by pharma_joe
    Hi, I have traced an issue with an application I am developing, it is giving me a type cast exception. Funny thing is it is saying it cannot cast "entities.Movie cannot be cast to entities.Movie"?! movies is an ArrayList. try { movies = getMovies(); } catch (Exception e) { e.printStackTrace(System.out); } finally { try { for (Movie movie : movies) { output.append(" <tr>\n"); output.append(" <td>" + movie.getId() + "</td>"); output.append(" </tr>\n"); } } catch (Exception e) { e.printStackTrace(System.out); } }

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  • How ensure if java program uses UTF-8 encoding

    - by Nayn
    Hi, I recently discovered that relying on default encoding of JVM causes bugs. I should explicitly use specific encoding ex. UTF-8 while working with String, InputStynreams etc. I have a huge codebase to scan for ensuring this. Could somebody suggest me some simpler way to check this than searching the whole codebase. Thanks Nayn

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  • replace \n and \r\n with <br /> in java

    - by Bala R
    This has been asked several times for several languages but I can't get it to work. I have a string like this String str = "This is a string.\nThis is a long string."; And I'm trying to replace the \n with <br /> using str = str.replaceAll("(\r\n|\n)", "<br />"); but the \n is not getting replaced. I tried to use this RegEx Tool to verify and I see the same result. The input string does not have a match for "(\r\n|\n)". What am i doing wrong ?

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  • Java - multithreaded access to a local value store which is periodically cleared

    - by Telax
    I'm hoping for some advice or suggestions on how best to handle multi threaded access to a value store. My local value storage is designed to hold onto objects which are currently in use. If the object is not in use then it is removed from the store. A value is pumped into my store via thread1, its entry into the store is announced to listeners, and the value is stored. Values coming in on thread1 will either be totally new values or updates for existing values. A timer is used to periodically remove any value from the store which is not currently in use and so all that remains of this value is its ID held locally by an intermediary. Now, an active element on thread2 may wake up and try to access a set of values by passing a set of value IDs which it knows about. Some values will be stored already (great) and some may not (sadface). Those values which are not already stored will be retrieved from an external source. My main issue is that items which have not already been stored and are currently being queried for may arrive in on thread1 before the query is complete. I'd like to try and avoid locking access to the store whilst a query is being made as it may take some time.

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  • Getting a java collection of objects in Alphabetical order

    - by MichaelMcCabe
    I have a question that I dont really know where to start. So I thought i'd ask it here. Basically, I have a drop down with names in it. I want these names to be in alphabetical order. Populating the drop down happens as follows; I query a database and pull down an Id and Name, make a object called "UserList", and set the name and id variables with what I get back. I then add this object to an ArrayList. I do this over and over. I then convert this collection to an array, and pass it to my JSP page using session.setAttribute("userList", UserList); I then populate the drop down as below. <c:forEach items="${usersCompanysList}" var="c" > There probably is a simple answer but how to I sort these names?

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  • Slowing process creation under Java?

    - by oconnor0
    I have a single, large heap (up to 240GB, though in the 20-40GB range for most of this phase of execution) JVM [1] running under Linux [2] on a server with 24 cores. We have tens of thousands of objects that have to be processed by an external executable & then load the data created by those executables back into the JVM. Each executable produces about half a megabyte of data (on disk) that when read right in, after the process finishes, is, of course, larger. Our first implementation was to have each executable handle only a single object. This involved the spawning of twice as many executables as we had objects (since we called a shell script that called the executable). Our CPU utilization would start off high, but not necessarily 100%, and slowly worsen. As we began measuring to see what was happening we noticed that the process creation time [3] continually slows. While starting at sub-second times it would eventually grow to take a minute or more. The actual processing done by the executable usually takes less than 10 seconds. Next we changed the executable to take a list of objects to process in an attempt to reduce the number of processes created. With batch sizes of a few hundred (~1% of our current sample size), the process creation times start out around 2 seconds & grow to around 5-6 seconds. Basically, why is it taking so long to create these processes as execution continues? [1] Oracle JDK 1.6.0_22 [2] Red Hat Enterprise Linux Advanced Platform 5.3, Linux kernel 2.6.18-194.26.1.el5 #1 SMP [3] Creation of the ProcessBuilder object, redirecting the error stream, and starting it.

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  • Java ThreadPool for multiple identical tasks

    - by tdimmig
    I have 1 thread who sole job is to grab DatagramPackets off of a socket and stick them in a buffer. Another thread works out of that buffer, processing the DatagramPackets. I'd like to have a pool of threads working out of that buffer. I had thought to use a fixed thread pool to do this. To do so, do I need to create the pool, then submit enough runnables for execution to fill it up? I had hoped for a way to say "this is the thread/runnable that I want you to execute, this is how many I want running, GO!". Is there such a method of doing this? Is something other than a fixed thread pool better suited?

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  • Create a java executable with Eclipse

    - by Micah
    This is a totally newbie question. I'm running Eclipse on Ubuntu. I created a test project that I want to compile to an executable (whataver the linux equivalent is of a Windows .exe file). Here's the contents of my program: public class MyTest { public static void main(String[] args) { System.out.println("You passed in: " + args[0]); } } I want to know how to compile it and then how to execute it from the command line. Thanks!

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  • Java Swing Visual Editor HELP please

    - by bat
    How would i call this function in my main? private JFrame getMainpageframe1() { if (mainpageframe1 == null) { mainpageframe1 = new JFrame(); mainpageframe1.setSize(new Dimension(315, 306)); mainpageframe1.setContentPane(getMainpage()); mainpageframe1.setTitle("Shopping For Less: Main Page"); mainpageframe1.setVisible(true); mainpageframe1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } return mainpageframe1; } public static void main(String[] args) { //call that function to output the JFrame? } thanks

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