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  • How can I tell what is using the memory when there is a heap overflow in Java?

    - by Grae
    Hi all, I know a little about profiling, but what I am particularlly insterest in, is what has all the memory when I get these heap over flow exceptions. I will start getting them after about a hour of debugging. I am hoping there is some sort of dump or something, that I can use to get a list of what instances are around at the time the program starts. By the way, sorry if this is a lazy question. I really shoud put sometime in learning about profiling. Grae

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  • Is it possible to write a generic +1 method for numeric box types in Java?

    - by polygenelubricants
    This is NOT homework. Part 1 Is it possible to write a generic method, something like this: <T extends Number> T plusOne(T num) { return num + 1; // DOESN'T COMPILE! How to fix??? } Short of using a bunch of instanceof and casts, is this possible? Part 2 The following 3 methods compile: Integer plusOne(Integer num) { return num + 1; } Double plusOne(Double num) { return num + 1; } Long plusOne(Long num) { return num + 1; } Is it possible to write a generic version that bound T to only Integer, Double, or Long?

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  • Java-Hibernate-Newbie: How do I acces the values from this list?

    - by Mes
    I have this class mapped @Entity @Table(name = "USERS") public class User { private long id; private String userName; } and I make a query: Query query = session.createQuery("select id, userName, count(userName) from User order by count(userName) desc"); return query.list(); How can I acces the value returned by the query?

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  • Is it expensive to hold on to PreparedStatements? (Java & JDBC)

    - by sbook
    I'm trying to figure out if it's efficient for me to cache all of my statements when I create my database connection or if I should only create those that are most used and create the others if/when they're needed.. It seems foolish to create all of the statements in all of the client threads. Any feedback would be greatly appreciated.

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  • What is my error in a map in java?

    - by amveg
    Hello everyone I am trying to solve this problem: http://www.cstutoringcenter.com/problems/problems.php?id=4, but I cant figure out why my code doesnt solve this, I mean in the "for" how can I can multiply the letters? what is my error?, It just tell always 7, but I want to multiple all the letters, I hope you can help me enter code here public class ejercicio3 { public static void main(String args[]) { Map<Character, Integer> telefono = new HashMap<Character, Integer>(); telefono.put('A', 2); telefono.put('B', 2); telefono.put('C', 2); telefono.put('D', 3); telefono.put('E', 3); telefono.put('F', 3); telefono.put('G', 4); telefono.put('H', 4); telefono.put('I', 4); telefono.put('J', 5); telefono.put('K', 5); telefono.put('L', 5); telefono.put('M', 6); telefono.put('N', 6); telefono.put('O', 6); telefono.put('P', 7); telefono.put('R', 7); telefono.put('S', 7); telefono.put('T', 8); telefono.put('U', 8); telefono.put('V', 8); telefono.put('W', 9); telefono.put('X', 9); telefono.put('Y', 9); String mensaje = "Practice"; int producto = 1; for (char c : mensaje.toCharArray()) { if (telefono.containsKey(c)) { producto = telefono.get(c) * producto; System.out.println(producto); } } } }

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  • Search for all instances of certain annotation type

    - by user1064918
    Suppose I have this annotation @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface Name { String value(); } This is going to be used as follows @Name("name1") public static Foo foo = new Foo(); I have multiples of these across my project source files. Is there an fairly simple way to search and collect all those "foo"s that're preceded by @Name? In other words, I'd like to write a method that would return a Set<Foo> containing these. Thanks!!!

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  • How can I get relative path of the folders in my project? (java)

    - by masterkapu
    How can I get the relative path of the folders in my project (using code)? I created new folder in my project and I want its relative path so no matter where is the app the path will be correct. Maybe this can be useful: I trying to do it not inside any function just inside the class and I want to init with it a final variable. the app is android and the class is "extends Activity" thanks

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  • How to plot the graph(line) from a file in java?

    - by kiran
    I have a directory containing list of files. Those files have some list of values as x and y ordered as line by line. And my question is just I would like to read those files one by one and to plot line graphs based on those values. Could you please help me for that?

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  • Java: Is it possible to take a GUI Panel and output it into a picture?

    - by user369748
    So I have this chart that's a little special. Kind of like an XY plot of points but my boss wanted to look like a bunch of boxes rather than dots connected by lines. And I basically made a chart using gridlayout and a whole bunch of cells that I'll be colouring in black or white depending on the data. Now he sorta wants it to be outputted to a image file. Is there any way to save a Panel into a picture? He wants to display not only the data but also save a visual representation of the data into an image file.

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  • Java - Can i have a faster performance for this loop ?

    - by Brad
    I am reading a book and deleting a number of words from it. My problem is that the process takes long time, and i want to make its performance better(Less time), example : Vector<String> pages = new Vector<String>(); // Contains about 1500 page, each page has about 1000 words. Vector<String> wordsToDelete = new Vector<String>(); // Contains about 50000 words. for( String page: pages ) { String pageInLowCase = page.toLowerCase(); for( String wordToDelete: wordsToDelete ) { if( pageInLowCase.contains( wordToDelete ) ) page = page.replaceAll( "(?i)\\b" + wordToDelete + "\\b" , "" ); } // Do some staff with the final page that does not take much time. } This code takes around 3 minutes to execute. If i skipped the loop of replaceAll(...) i can save more than 2 minutes. So is there a way to do the same loop with a faster performance ?

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  • Java: Superclass to construct a subclass on certain conditions, possible?

    - by ramihope
    I have this condition public class A { public action() { System.out.println("Action done in A"); } } public class B extends A { public action() { System.out.println("Action done in B"); } } when I create an instance of B, the action will do just actions in B, as it overrides the action of the superclass. the problem is that in my project, the super class A is already used too many times, and I am looking for a way that under certain conditions, when i create an instance of A it makes a check and if it is true, replace itself with B. public class A { public A() { if ([condition]) { this = new B(); } } public action() { System.out.println("Action done in A"); } } A a = new A(); a.action(); // expect to see "Action done in B"... is this possible in some way?

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  • How do I make this Java code operate properly? [Multi-threaded, race condition]

    - by Fixee
    I got this code from a student, and it does not work properly because of a race condition involving x++ and x--. He added synchronized to the run() method trying to get rid of this bug, but obviously this only excludes threads from entering run() on the same object (which was never a problem in the first place) but doesn't prevent independent objects from updating the same static variable x at the same time. public class DataRace implements Runnable { static volatile int x; public synchronized void run() { for (int i = 0; i < 10000; i++) { x++; x--; } } public static void main(String[] args) throws Exception { Thread [] threads = new Thread[100]; for (int i = 0; i < threads.length; i++) threads[i] = new Thread(new DataRace()); for (int i = 0; i < threads.length; i++) threads[i].start(); for (int i = 0; i < threads.length; i++) threads[i].join(); System.out.println(x); // x not always 0! } } Since we cannot synchronize on x (because it is primitive), the best solution I can think of is to create a new static object like static String lock = ""; and enclose the x++ and x-- within a synchronized block, locking on lock. But this seems really awkward. Is there a better way?

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  • Java: Anyone know of a library that detects the quality of an internet connection?

    - by Zombies
    I know a simple URLConnection to google can detect if I am connected to the internet, after all I am confident that the internet is all well and fine If I cant connect to google. But what I am looking for at this juncture is a library that can measure how effective my connection to the internet is in terms of BOTH responsiveness and bandwidth available. BUT, I do not want to measure how much bandwidth is potentially available as that is too resource intensive. I really just need to be able to test wether or not I can recieve something like X kB's in Y amount of time. Does such a library already exist?

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  • What is the mean of @ModelAttribute annotation at method argument level?

    - by beemaster
    Spring 3 reference teaches us: When you place it on a method parameter, @ModelAttribute maps a model attribute to the specific, annotated method parameter I don't understand this magic spell, because i sure that model object's alias (key value if using ModelMap as return type) passed to the View after executing of the request handler method. Therefore when request handler method executes the model object's name can't be mapped to the method parameter. To solve this contradiction i went to stackoverflow and found this detailed example. The author of example said: // The "personAttribute" model has been passed to the controller from the JSP It seems, he is charmed by Spring reference... To dispel the charms i deployed his sample app in my environment and cruelly cut @ModelAttribute annotation from method MainController.saveEdit. As result the application works without any changes! So i conclude: the @ModelAttribute annotation is not needed to pass web form's field values to the argument's fields. Then i stuck to the question: what is the mean of @ModelAttribute annotation? If the only mean is to set alias for model object in View, then why this way better than explicitly adding of object to ModelMap?

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  • Trying to use a list iterator to print out entire linked list in Java. Infinite loop for some reaso

    - by Matt
    I created my list: private static List list = new LinkedList(); and my iterator: ListIterator itr = list.listIterator(); and use this code to try to print out the list... Only problem is, it never comes out of the loop. When it reaches the tail, shouldn't it come out of the loop, because there is no next? Or is it going back to the head like a circular linked list? It is printing so quickly and my computer locks up shortly after, so I can't really tell what is going on. while (itr.hasNext()) System.out.println(itr.next());

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