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  • Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

    - by Marcos
    I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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  • Velocity templates seem to fail with UTF-8

    - by steve
    Hi, i have been trying to use a velocity Template with the following content: Sübjäct $item everything works fine except the translation of the tow unicode characters. The result string printed on the commandline looks like: Sübjäct foo I searched the velocity website and the web an this issue, and came uo with differnt font encoding options, which i added to my code. But those won't help. This is the actuall code: velocity.setProperty("file.resource.loader.path", absPath); velocity.setProperty("input.encoding", "UTF-8"); velocity.setProperty("output.encoding", "UTF-8"); Template t = velocity.getTemplate("subject.vm"); t.setEncoding("UTF-8"); StringWriter sw = new StringWriter(); t.merge(null, sw); System.out.println(sw.getBuffer()); Can anyone give me some hints, how to fix this issue?

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  • Project Euler #119 Make Faster

    - by gangqinlaohu
    Trying to solve Project Euler problem 119: The number 512 is interesting because it is equal to the sum of its digits raised to some power: 5 + 1 + 2 = 8, and 8^3 = 512. Another example of a number with this property is 614656 = 28^4. We shall define an to be the nth term of this sequence and insist that a number must contain at least two digits to have a sum. You are given that a2 = 512 and a10 = 614656. Find a30. Question: Is there a more efficient way to find the answer than just checking every number until a30 is found? My Code int currentNum = 0; long value = 0; for (long a = 11; currentNum != 30; a++){ //maybe a++ is inefficient int test = Util.sumDigits(a); if (isPower(a, test)) { currentNum++; value = a; System.out.println(value + ":" + currentNum); } } System.out.println(value); isPower checks if a is a power of test. Util.sumDigits: public static int sumDigits(long n){ int sum = 0; String s = "" + n; while (!s.equals("")){ sum += Integer.parseInt("" + s.charAt(0)); s = s.substring(1); } return sum; } program has been running for about 30 minutes (might be overflow on the long). Output (so far): 81:1 512:2 2401:3 4913:4 5832:5 17576:6 19683:7 234256:8 390625:9 614656:10 1679616:11 17210368:12 34012224:13 52521875:14 60466176:15 205962976:16 612220032:17

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  • Help choosing the right data structure

    - by devoured elysium
    I need a data structure with the following requirements: Needs to be able to get elements by index (like a List). I will always just add / remove elements from the end of the structure. I am inclined to use an ArrayList. In this situation, it seems to be O(1) both to read elements (they always are?), remove elements (I only need to remove them at the end of the list) and to add(I only add to the end of the list). There is only the problem that time to time the ArrayList will have a performance penalty when it's completly full and I need to add more elements to it. Is there any other better idea? I don't think of a data structure that'd beat the ArrayList here. Thanks

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  • Getting the type of a parametrized class parameter?

    - by GuidoMB
    I have the following class public class MyClass<T> { public Class<T> getDomainClass() { GET THE CLASS OF T } } I've googled this problem and all the answers I could find told me to use getGenericSuperClass(), but the problem of this method is that I must have a second class that extends MyClass and I don't want to do this. What I need is to get the parametrized type of a concrete class?

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  • how to make an array of arrays

    - by yuliya
    hi, how would you write an array of values to other array. In instance, I have a list of IPs and list of requests. I want to have something like [{ip1, request1}, {ip2, request2}, ....]. It's how I would do it, but sure obj will change every time and array will have all the time the same values. ArrayList array = new ArrayList(); Object[] obj = new Object[2]; for (int i=0; i<listSize; i++){ obj[0] = ipList.get(i).toString(); obj[1] = requestList.get(i); array.add(obj);

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  • Counting the number of occurrences of characters in an array

    - by Anthony Pittelli
    This is what I have but it is not working, this is confusing for me. If you scroll down I commented on someones post the exact problem I am having and what I am trying to do. I was thinking maybe the problem is my code to generate the random characters: public void add (char fromChar, char toChar){ Random r = new Random(); //creates a random object int randInt; for (int i=0; i<charArray.length; i++){ randInt = r.nextInt((toChar-fromChar) +1); charArray[i] = (char) randInt; //casts these integers as characters } }//end add public int[] countLetters() { int[] count = new int[26]; char current; for (int b = 0; b <= 26; b++) { for (int i = 97; i <= 123; i++) { char a = (char) i; for (int ch = 0; ch < charArray.length; ch++) { current = charArray[ch]; if (current == a) { count[b]++; } } } } return count; }

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  • executorservice to read data from database in chuncks and run process on them

    - by TazMan
    I'm trying to write a process that would read data from a database and upload it onto a cloud datastore. How can I decide the partition strategy of the data? I want to query the table in chunks and process each chunk in 10 threads. Each thread basically will send the data to an individual node on a 10 node cluster on the cloud.. Where in the below multi threading code will the dataquery to extract and send 10 concurrent requests for uploading data to cloud would be? public class Caller { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(10); for (int i = 0; i < 10; i++) { Runnable worker = new DomainCDCProcessor(i); executor.execute(worker); } executor.shutdown(); while (!executor.isTerminated()) { } System.out.println("Finished all threads"); } }

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  • Interview question : What is the fastest way to generate prime number recursively ?

    - by hilal
    Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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  • How to use ASTRewrite split one field declaration into two?

    - by user307598
    For example: private long p, q, g, h; I want to split this field declaration as: private long p; private long q, g, h; How can I use ASTRewrite to do it? I tried to use ASTNode copyFd = rewriter.createCopyTarget(fd) to copy the field declaration, modify it, then add to field declaration list, but my modification on copyFd is not seen. It's just the same to fd. Why? Anybody can help?

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  • null pointer exception on list.add

    - by Eric
    I've been working on this one error for a few hours so I thought I'd pick the brains of some pros. I am getting a null pointer exception at the modelData.add(i, es) method. I know from debugging that es isn't null. I'm really confused, thanks. public class EventTableModel extends AbstractTableModel { //private int rowCount = 0; protected List<EventSeat> modelData; private static final int COLUMN_COUNT = 3; private Event e; Event j = GUIpos.m; int i = 1; public EventTableModel(Event e) { this.e = e; try { System.out.println(modelData); for (EventSeat es : e.getEventSeats()) { modelData.add(i, es); i++; } } catch (DataException ex) { Logger.getLogger(EventTableModel.class.getName()).log(Level.SEVERE, null, ex); } }

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  • How to execute maven tasks in eclipse (Sonatype plugin)

    - by Bruce
    Hi all I know it must be something simple, but I just can't figure it out.. I'm using the Sonatype maven plugin on eclipse. When I want to build a war file for a webapp project, the only way I know to do it is to use the command line and type mvn package. I've looked all through the right click menu and I can't find any way to do it from eclipse. There's a maven submenu that seems to have no options to do with building, and there's a run menu that doesn't seem right - I don't want to run my project - I just want to build it. There is a maven build option in the run menu, but if I run it, a configuration window pops up for me to enter goals in.. How I do I just do a simple mvn package, but through gui? What am I missing? Thanks!

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  • Not able to get the data from the JSON in OpenSocial App!

    - by Abhishek
    I have follwing JSON: {"mykey":[{name:"Jak",interests:"movies"}]} and following opensocial app code: <script type="text/os-template" require="mykey"> <ul> <li repeat="${mykey}"> <span>Offer id: ${Cur.name}</span> <span>Offer: ${Cur.interests}</span> </li> </ul> </script> but the App is not able to get the data from the JSON? Not able to find out the issue!

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  • Recursively determine average value

    - by theva
    I have to calculate an average value of my simulation. The simulation is ongoing and I want (for each iteration) to print the current average value. How do I do that? I tried the code below (in the loop), but I do not think that the right value is calculated... int average = 0; int newValue; // Continuously updated value. if(average == 0) { average = newValue; } average = (average + newValue)/2; I also taught about store each newValue in an array and for each iteration summarize the whole array and do the calculation. However, I don't think that's a good solution, because the loop is an infinity loop so I can't really determine the size of the array. There is also a possibility that I am thinking too much and that the code above is actually correct, but I don't think so...

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  • How to clean up my code

    - by simion
    Being new to this i realy am trying to learn how to keep code as simple as possible, whilst doing the job its supposed to. The question i have done is from project eulur, it says Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... Find the sum of all the even-valued terms in the sequence which do not exceed four million. Here is my code below, i was wondering what the best way of simplifying this would be, for a start removing all of the .get(list.length()-1 )..... stuff would be a good start if possible but i dont really no how to? Thanks public long fibb() { ArrayList<Integer> list = new ArrayList<Integer>(); list.add(1); list.add(2); while((list.get(list.size() - 1) + (list.get(list.size() - 2)) < 4000000)){ list.add((list.get(list.size()-1)) + (list.get(list.size() - 2))); } long value = 0; for(int i = 0; i < list.size(); i++){ if(list.get(i) % 2 == 0){ value += list.get(i); } } return value; }

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  • Using low level api for datastore in google app engine ? is it bad ?

    - by Chez
    There is little documentation on how to use the low level api for datastore and quite a lot on JPA and JDO and how it translates to it. My question is: is there any advantage in coding against the JPA or JDO specs instead of accessing directly the low level api for datastore ? From an initial look, it seems simple and straight forward but I am not sure if there are good reasons why not to do it. Thanks Cx

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  • Reading http file on url

    - by Nkunzis
    I am trying to read an xml file on an http url. "Unexpected end of file from server" keeps on coming . the page is password protected, I would like to know if I am properly giving in my url authentication details. I tried with non protected pages and I can read them properly. Here is my code: URL url = new URL("http://username:[email protected]:0000/test.xml"); URLConnection yc = url.openConnection(); BufferedReader in = new BufferedReader(new InputStreamReader(yc.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close();

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  • Is there a file diff tool that allows for exceptions?

    - by Kevin
    We currently use Beyond Compare 3.0 and I am quite pleased with it. However, it would be great if I could easily specify an exclusion for a specific one-time case. This is needed when I am doing a code review of some refactoring. For instance: Old code doSomething(ConstantsInterface.FOOBAR); New code: doSomething(BetterEnumeration.FOOBAR); In this case, I have hundreds of changes that I am reviewing that are essentially all the same exact change and I just want to see the exceptions. It would be great if I could easily specify an exception that indicates these two cases are equal. I know of a way to do it in the grammar, but it is tedious and cumbersome in the case where there are ten or so exceptions. Any other tips?

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  • What are the suggested alternatives for Class<T>.isAssignableFrom(Class<?> cls)?

    - by Wing C. Chen
    Currently I am doing the profiling to a piece of code. During the profiling, I discovered that this very method call, Class<T>.isAssignableFrom(Class<?> cls) takes up to quite amount of the entire time. Because this is a method from reflection, it takes a lot of time compared to normal keywords or method calls. I am wondering if there are some good alternatives for this method calls?

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  • A file is being http posted, how can I reference the parameter by index?

    - by Blankman
    An XML file is being posted to a url that my spring mvc is responding to. In .NET, I could do this: request.Form[0] request.Form["abc"] or request.QueryString[0] request.QueryString["some_key"] Now with spring/servlets it seems I can only do this: request.getParameter("some_key") or get all the names or values. When someone is posting a file to a url, using http post, won't this be just a single request parameter then? Can I get the parameter using index with servlets?

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  • Tomcat memory issue

    - by user305210
    Hello, I have noticed that my application that is running on Tomcat 5 starts with 1gig of memory and as soon as it starts receiving requests from client, the memory starts dropping until it is down to 100MBs and troubles start from there. I am looking at /manager/status page of tomcat under JVM section where "Free Memory", "Total Memory", "Max Memory" is listed. Is this an indicator of memory leak? Memory does not seem to be freed-up automatically even if there are no requests coming from client machines.

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