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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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  • 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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  • 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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  • 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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  • 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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  • What is the event dispatching thread?

    - by Roman
    I know what "thread" means and if I understand the event dispatching thread (EDT) as "just a thread", it explains a lot but, apparently, it does not explain everything. I do not understand what is special about this thread. For example I do not understand why we should start a GUI in a the EDT? Why the "main" thread is bed for GUI? Well, if we just do not want to occupy the main thread why we cannot start GUI just in "another thread" why it should be some "special" thread called EDT? Then I do not understand why we cannot start the EDT like any other thread? Why we should use some special tool (called invokeLater). And why GUI, unlike any other thread, does not start immediately. We should wait until it is ready to accept our job. Is it because EDT can, potentially execute several task simultaneously? If you decide to answer this question, could you pleas use a really simple terminology because otherwise, I am afraid, I will not be able to understand the answer.

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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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  • Join data from two Lists into one object

    - by Petr Mensik
    I ran into following situation and I am wondering about best solution. Let's say I have List<Object1> and List<Object2>, these lists are result of two separated queries. Both of them have the same size and there is relationship 1:1 between elements in the lists based on ID. I know that best solution would be fetching data in one DB query but that's possible right now. So my question is, what is the best way to join these lists into let's say List<Object3>?

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  • Iterating over hashmap injsp in struts application

    - by Rozer
    I have a Hashmap object that i am getting on a jsp page. HashMap<Integer,Gift_product> gift_hm = new HashMap<Integer,Gift_product>(); gift_hm.put(17,new Gift_product("doll",67)); now i need to iterate this and display content on jsp. as Gift_product class contains two fields name and price jsp output should be serial no. product name price 17 Doll 67 How can i achieve it..

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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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  • 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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  • Rotating A Tile In A BufferedImage

    - by Eddy Freeman
    I have created a a bufferedImage of 6 tiles of 2 rows and 3 columns and i want to rotate the last tile of the second row. This tile serves as a crossing for my animation. My problems are : How can i get access to that specifc tile alone and rotate it alone without affecting others. I have googled for a while but no answer.

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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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  • Merge object from list by comparing one value

    - by Bala
    I have two List of Objects (one is master list and other is error list) and if there is a match of one value when compared two lists then merge all other error list values into mast list value (only one object). Other than iterating is there any other way to compare a value and then merge that object. Object is a Value object with some setters and getters. Appreciate your help. List<OrderVO> masterList; List<OrderVO> errorList; If errorList.OrderVO.getOrderID = masterList.OrderVO.getOrderID then masterList.OrderVO.merge(errorList.OrderVO) or copy all values of masterList.OrderVO.copy(errorList.OrderVO). Hoper this is clear

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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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  • @ExceptionHandler doesn't handle the thrown exceptions

    - by Javi
    Hello, I have a method in my controller which will handle the exceptions thrown by the application. So I have a method like this one. @Controller public class ExceptionController { @RequestMapping(value="/error") @ExceptionHandler(value={Exception.class, NullPointerException.class}) public String showError(Exception e, Model model){ return "tiles:error"; } } And to try I if it works I throw a NullPointerException in another method in other method controller: boolean a = true; if(a){ throw new NullPointerException(); } After the exception is thrown it is printed in the JSP, but it doesn't go throw my showError() method (I've set a breakpoint there and it never enters). showError() method will catch the exception and will show different error pages depending on the exception type (though now it always shows the same error page). If I go to the url /error it shows the error page so the showError() method is OK. I'm using Spring 3. What can be the problem? Thanks.

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  • What is the best way to restore(rollback) data in an application to a specified state(date) ?

    - by panzerschreck
    Hello, An example would set the context right, the example below captures the various states of the entity, which needs to be reverted(rolled back) . State 1 - Recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 State 2 - Recorded on 02-Mar-2010 Column1 Column2 Data1 0.57 State 3 - Recorded on 03-Mar-2010 Column1 Column2 Data1 0.58 User notices that state3 is not what he intended to be in, decides to revert back to state2. One approach that I can think of, without modifying the entity is via "auditing" all the inserts/updates, as below, the rollback information captures the data just before the updates/modifications on the entity, so that it can be applied in an order when you need to revert.Please note that changing the entity's schema, is not an option. Rollback - R1 recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R2 Recorded on 02-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R3 Recorded on 03-Mar-2010 Column1 Column2 Data1 0.57 So, to get to state2 , we would start with rollback information R1,apply R2 onto it. Is there a better approach to achieve this ? Thanks for your time.

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  • For a Chemical Equation Balancer App (Android), how do I count the number of atoms of each element in each term?

    - by Upas
    This is my app: If someone enters "C6H12O6+O2=CO2+H2O", then I have already written code to split the equation into terms, so in an ArrayList called rterms I have the strings: C6H12O6 CO2 and in another ArrayList called pterms, I have: CO2 H2O I need to count the number of C's in each term of the reactants, so 6 for term 1, 0 for term 2, and then the H's and then O's. How would I do this? Any help is appreciated.

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  • Can't create packages with Maven webapp

    - by cardori
    I have created a project using the following maven webapp project in eclipse: When adding a package to the project (right click project - new - package), the package gets added as a folder (I added a package named core). It does not have the usual package icon: If I try to create a new class and select a package, there are no entries in the list box. I have tried creating packages in a normal eclipse dynamic web project and these work correctly. How do I get packages in Maven enabled webapp projects?

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