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  • 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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  • Is it possible to use the values method for a HashMap if the values are ArrayLists?

    - by Denman
    I'm stuck trying to get something to work in an assignment. I have a HashMap<Integer, ArrayList<Object>> called sharedLocks and I want to check whether a certain value can be found in any ArrayList in the HashMap. The following code obviously wouldn't work because Object[] can't be cast to ArrayList[], but it is a demonstration of the general functionality that I want. ArrayList[] values = (ArrayList[]) sharedLocks.values().toArray(); boolean valueExists = false; for (int i = 0; i < values.length; i++) { if (values[i].contains(accessedObject)) { valueExists = true; } } Is there a way for me to check every ArrayList in the HashMap for a certain value? I'm not sure how to use the values method for HashMaps in this case. Any help would be much appreciated.

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  • Should filters write to the response during or after filtering?

    - by Mark
    I have a filter which processes generated HTML and rewrites certain elements. For example, it adds class attributes to some anchors. Finally, it writes the processed HTML to the response (a subclass of HttpServletResponseWrapper). Naturally, this means that the processed HTML is a different length after it has passed through the filter. I can see two ways of approaching this. One is to iterate over the HTML, using a StringBuilder to build up the processed HTML, and write the processed HTML to the response once all filtering is complete. The other is to iterate over the HTML but to write it to the response as soon as each element has been processed. Which is the better way for this operation, or is there another option which would be preferable? I am looking to minimise temporary memory usage primarily.

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  • Adding a MouseOverHandler to an Element?

    - by JP
    I would like to listen for the mouse over event in GWT 1.6. Since GWT 1.6 has introduced handlers and deprecated listeners I'm unsure as to how I can accomplish this with what little information exists. Note: I have an Element object. That's what I need to add the mouse handler to. I apologize for my lack of clarity. Thanks!

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  • What is the command-line input to produce the javadoc?

    - by Bernard
    After writing all the comments inside the code about the javadoc such as /** * This method compares the student's answer to the standard answer * @param ans The student's answer * @return True for correct answer; False for incorrect answer */ boolean compareAnswer(int ans); I guess it starts with : javadoc [optionss] [packages|files] I'm not sure what is the regular or default [option] and how can I say to produce it in my current home directory?

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  • Project Euler #3

    - by Alex
    Question: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143? I found this one pretty easy, but running the file took an extremely long time, it's been going on for a while and the highest number I've got to is 716151937. Here is my code, am I just going to have a wait or is there an error in my code? //User made class public class Three { public static boolean checkPrime(long p) { long i; boolean prime = false; for(i = 2;i<p/2;i++) { if(p%i==0) { prime = true; break; } } return prime; } } //Note: This is a separate file public class ThreeMain { public static void main(String[] args) { long comp = 600851475143L; boolean prime; long i; for(i=2;i<comp/2;i++) { if(comp%i==0) { prime = Three.checkPrime(i); if(prime==true) { System.out.println(i); } } } } }

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  • Returning and instance of a Class given its .class (MyClass.class)

    - by jax
    I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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  • What is the easiest straightforward way of telling which version performs better?

    - by Peter Perhác
    I have an application, which I have re-factored so that I believe it is now faster. One can't possibly feel the difference, but in theory, the application should run faster. Normally I would not care, but as this is part of my project for my master's degree, I would like to support my claim that the re-factoring did not only lead to improved design and 'higher quality', but also an increase in performance of the application (a small toy-thing - a train set simulation). I have toyed with the latest VisualVM thing today for about four hours but I couldn't get anything helpful out of it. There isn't (or I haven't found it) a way to simply compare the profiling results taken from the two versions (pre- and post- refactoring). What would be the easiest, the most straightforward way of simply telling the slower from the faster version of the application. The difference of the two must have had an impact on the performance. Thank you.

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  • Redirects in Glassfish (adding trailing slash)

    - by echox
    Is it possible to add a trailing slash to the default context of an application? Example: http://www.uri.com/foo -> http://www.uri.com/foo/ I added the following redirect to the server properties: redirect_1: from=/foo url-prefix=/foo/ and this ends up in a loop... Several other configurations also didn't work :-/ I'm using glassfish v2.1-b60e.

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  • new Integer vs valueOf

    - by LB
    Hi, I was using Sonar to make my code cleaner, and it pointed that I'm using new Integer(1) instead of Integer.valueOf(1). Because it seems that valueOf does not instantiate a new object so is more memory-friendly. How can valueOf not instantiate a new object ? How does it work ? Is this true for all integers ? thanks.

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  • recursion resulting in extra unwanted data

    - by spacerace
    I'm writing a module to handle dice rolling. Given x die of y sides, I'm trying to come up with a list of all potential roll combinations. This code assumes 3 die, each with 3 sides labeled 1, 2, and 3. (I realize I'm using "magic numbers" but this is just an attempt to simplify and get the base code working.) int[] set = { 1, 1, 1 }; list = diceroll.recurse(0,0, list, set); ... public ArrayList<Integer> recurse(int index, int i, ArrayList<Integer> list, int[] set){ if(index < 3){ // System.out.print("\n(looping on "+index+")\n"); for(int k=1;k<=3;k++){ // System.out.print("setting i"+index+" to "+k+" "); set[index] = k; dump(set); recurse(index+1, i, list, set); } } return list; } (dump() is a simple method to just display the contents of list[]. The variable i is not used at the moment.) What I'm attempting to do is increment a list[index] by one, stepping through the entire length of the list and incrementing as I go. This is my "best attempt" code. Here is the output: Bold output is what I'm looking for. I can't figure out how to get rid of the rest. (This is assuming three dice, each with 3 sides. Using recursion so I can scale it up to any x dice with y sides.) [1][1][1] [1][1][1] [1][1][1] [1][1][2] [1][1][3] [1][2][3] [1][2][1] [1][2][2] [1][2][3] [1][3][3] [1][3][1] [1][3][2] [1][3][3] [2][3][3] [2][1][3] [2][1][1] [2][1][2] [2][1][3] [2][2][3] [2][2][1] [2][2][2] [2][2][3] [2][3][3] [2][3][1] [2][3][2] [2][3][3] [3][3][3] [3][1][3] [3][1][1] [3][1][2] [3][1][3] [3][2][3] [3][2][1] [3][2][2] [3][2][3] [3][3][3] [3][3][1] [3][3][2] [3][3][3] I apologize for the formatting, best I could come up with. Any help would be greatly appreciated. (This method was actually stemmed to use the data for something quite trivial, but has turned into a personal challenge. :) edit: If there is another approach to solving this problem I'd be all ears, but I'd also like to solve my current problem and successfully use recursion for something useful.

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  • Naked Objects. Good or Bad

    - by Midhat
    I have recently been exposed to naked objects. It looks like a pretty decent framework. However I do not see it in widespread use like say, Spring. So why is this framework not getting any mainstream application credit. What are its shortcomings as you see?

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  • j2me: How to use setCommandListener on a TextField?

    - by SmRndGuy
    I wanted to make it so that when I select a specific TextField in a Form, I get a specific list of Commands, for example TextField: OK, CancelTextField2: OK, Back, Help And I succeeded by using addCommand() on each of TextFields but I can't tell it what to happen when when I activate one of these commands since there is no setCommandListener method for them. It throws a NullPointerException when I click it.I also tried to get the commands from their Form but it is receiving only the commands that it contains, not the commands that TextFields have Any help how to get arround this? Thanks in advance

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  • how to add list to button

    - by priya
    hi... how to add a list to a button.. for example if i have four button like classic, western, jazz,pop.if i click classic button i should get subtitle .or if i click western i should get sub title... so how to creat

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  • Mapping restful ajax requests to spring

    - by Diones
    I have this piece of code: @RequestMapping(value = "/test.json", method = RequestMethod.GET) @ResponseStatus(HttpStatus.OK) public @ResponseBody Object[] generateFile(@RequestParam String tipo) { Object[] variaveis = Variavel.getListVariavelByTipo(tipo); return variaveis; } As far as I know it should take a request to test.json?tipo=H and return the JSON representation of Variavel[], however when I make such request I get: HTTP Status 406 - type Status report message descriptionThe resource identified by this request is only capable of generating responses with characteristics not acceptable according to the request "accept" headers () By using the following function I can get the expected json: @RequestMapping(value = "/teste.json") public void testeJson(Model model, @RequestParam String tipo) { model.addAttribute("data", Variavel.getListVariavelByTipo("H")); } What I'm doing wrong?

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  • Why the generated key size is not constant?

    - by Tom Brito
    The following code prints randomly 634, 635, 636, each time I run it. Why its not constant? public static void main(String[] args) throws Exception { KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA", "BC"); keyPairGen.initialize(1024); RsaKeyPair keyPair = new RsaKeyPair(keyPairGen.generateKeyPair()); System.out.println(keyPair.getPrivate().getEncoded().length); }

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  • Which is the 'correct' way to do this (if statement)

    - by frinkz
    I've got plenty of these lying around, and I'm wondering if I'm going to face any trouble - or performance problems. I have method A: MyClass monkey; ... if(monkey != null) { ... } Or method B: boolean hasMonkey; //This is set to TRUE when monkey is not null MyClass monkey; ... if(hasMonkey) { ... } On a functional level, they both do the same thing. Right now, I'm using method A. Is that a bad way of doing things? Which is going to perform better?

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  • Making html tags selectable in GWT

    - by Zoja
    I'm trying to display an html source ( without interpretation ) and I'd like all the nodes to be selectable (p, div, etc..). Something like in firebug where if I click on a node I can get it's properties. Does anybody have an idea how to do that or where to start ?

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  • multiplying all elements in an array by an outside number?

    - by prodo
    I need to multiple all the values in an array by 3000 which in turn would create a new array that I will use to subtract from another array. I've tried to create a separate method that would do that for me but all I got back in the multiplied array was a bunch of numbers and symbols strangely? here is the code that I wrote public static void main(String[] args) { int numberOfTaxpayers = Integer.parseInt(JOptionPane.showInputDialog("Enter how many users you would like to calculate taxes for: "); int[] usernumChild = new int[numberOfTaxPayers]; for (int i = 0; i < usernumChild.length; i++) { usernumChild[i] = Integer.parseInt(JOptionPane.showInputDialog("Enter number of children for user "+ (i+1) +": ")); }//this for loop finds out the number of children per user so we can later multiply each input by 3000 to create an array that determine dependency exemption for each user int[] depndExemp = multiply(usernumChild, 3000);//this was the calling of the multiply method... somewhere here is the error!! }//end main method public static int[] multiply(int[] children, int number) { int array[] = new int[children.length]; for( int i = 0; i < children.length; i++) { children[i] = children[i] * number; }//end for return array; }//this is the method that I was shown in a previous post on how to create return an array in this the dependency exemption array but when I tested this by printing out the dependency array all I received were a jumble of wrong numbers.

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