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  • Handling a binary operation that makes sense only for part of a hierarchy.

    - by usersmarvin_
    I have a hierarchy, which I'll simplify greatly, of implementations of interface Value. Assume that I have two implementations, NumberValue, and StringValue. There is an average operation which only makes sense for NumberValue, with the signature NumberValue average(NumberValue numberValue){ ... } At some point after creating such variables and using them in various collections, I need to average a collection which I know is only of type NumberValue, there are three possible ways of doing this I think: Very complicated generic signatures which preserve the type info in compile time (what I'm doing now, and results in hard to maintain code) Moving the operation to the Value level, and: throwing an unsupportedOperationException for StringValue, and casting for NumberValue. Casting at the point where I know for sure that I have a NumberValue, using slightly less complicated generics to insure this. Does anybody have any better ideas, or a recommendation on oop best practices?

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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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  • troubles reading other apps config files

    - by Aivlis
    Hi guys, I have a problem. I have to access to the data folder of other applications from my application to read configuration's file and so on but it seems it's possible only to read data from the sdcard and my application's data folder. Can you suggest me how to solve this problem?

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  • Should i use lock.lock(): in this method?

    - by user962800
    I wrote this method whose purpose is to give notice of the fact that a thread is leaving a specific block of code A thread stands for a car which is leaving a bridge so other cars can traverse it . The bridge is accessible to a given number of cars (limited capacity) and it's one way only. public void getout(int diection){ // release the lock semaphore.release(); try{ lock.lock(); //access to shared data if(direction == Car.NORTH) nNordTraversing--; //decreasing traversing threads else nSudTraversing--; bridgeCond.signal(); }finally{ lock.unlock(); } } My question is: should I use lock.lock(); or it's just nonsense? thanks in advance

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  • best way to avoid sql injection

    - by aauser
    I got similar domain model 1) User. Every user got many cities. @OneToMany(targetEntity=adv.domain.City.class...) 2) City. Every city got many districts @OneToMany(targetEntity=adv.domain.Distinct.class) 3) Distintc My goal is to delete distinct when user press delete button in browser. After that controller get id of distinct and pass it to bussiness layer. Where method DistinctService.deleteDistinct(Long distinctId) should delegate deliting to DAO layer. So my question is where to put security restrictions and what is the best way to accomplish it. I want to be sure that i delete distinct of the real user, that is the real owner of city, and city is the real owner of distinct. So nobody exept the owner can't delete ditinct using simple url like localhost/deleteDistinct/5. I can get user from httpSession in my controller and pass it to bussiness layer. After that i can get all cities of this user and itrate over them to be sure, that of the citie.id == distinct.city_id and then delete distinct. But it's rather ridiculous in my opinion. Also i can write sql query like this ... delete from t_distinct where t_distinct.city_id in (select t_city.id from t_city left join t_user on t_user.id = t_city.owner_id where t_user.id = ?) and t_distinct.id = ? So what is the best practice to add restrictions like this. I'm using Hibernate, Spring, Spring MVC by the way.. Thank you

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  • Can a plain servlet be configured to as a seam component?

    - by stacker
    I created a plain servlet within a seam-gen (2.1.2) application, now I would like to use injection. Thus I annotated it with @Name and it's recognized as component: INFO [Component] Component: ConfigReport, scope: EVENT, type: JAVA_BEAN, class: com.mycompany.servlet.ConfigReport Unfortunatly the injection of the logger doesn't work NullPointerException in init() import org.jboss.seam.annotations.Logger; import org.jboss.seam.annotations.Name; import org.jboss.seam.log.Log; @Name("ConfigReport") public class ConfigReport extends HttpServlet { @Logger private Log log; public void init(ServletConfig config) throws ServletException { log.info( "BOOM" ); } } Is my approach abusive? What would be the alternatives (the client sending requests to the servlet is curl, not a browser)?

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  • Thread help with Android game

    - by Ciph3rzer0
    I need some help dealing with three Threads in Android One thread is the main thread, the other is the GLThread, and the other is a WorkerThread I created to update the game state. The problem I have is they all need to access the same LinkedList of game objects. Both the GLThread and my WorkerThread only read from the LinkedList, so no problem there, but occasionally I have the main thread adding in another game object to the list. How can I manage this? I tried using synchronized in front of the functions involved but it really slows down the application. For some reason, just catching the errors and not rendering or updating the game state that frame, causes it to start lagging permanently. Anyone have any great ideas?

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  • Is there a standard place to store Spring library jar files?

    - by richj
    I've downloaded Spring 3.0.2 with dependencies and found that it contains 405 jar files. I usually keep third party libraries in a "lib" subdirectory, but there are so many Spring jars that it seems sensible to keep them separately so that they don't swamp the other libraries and to simplify version upgrades. I suspect that I want to keep the full set of libraries in Subversion, but only deploy the subset that is actually used. Do Spring users have a standard way to deal with this problem?

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  • Best practice when removing entity regarding mappedBy collections?

    - by Daniel Bleisteiner
    I'm still kind of undecided which is the best practice to handle em.remove(entity) with this entity being in several collections mapped using mappedBy in JPA. Consider an entity like a Property that references three other entities: a Descriptor, a BusinessObject and a Level entity. The mapping is defined using @ManyToOne in the Property entity and using @OneToMany(mappedBy...) in the other three objects. That inverse mapping is defined because there are some situations where I need to access those collections. Whenever I remove a Property using em.remove(prop) this element is not automatically removed from managed entities of the other three types. If I don't care about that and the following page load (webapp) doesn't reload those entities the Property is still found and some decisions might be taken that are no longer true. The inverse mappings may become quite large and though I don't want to use something like descriptor.getProperties().remove(prop) because it will load all those properties that might have been lazy loaded until then. So my currently preferred way is to refresh the entity if it is managed: if (em.contains(descriptor)) em.refresh(descriptor) - which unloads a possibly loaded collection and triggers a reload upon the next access. Is there another feasible way to handle all those mappedBy collections of already loaded entites?

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  • Scanner class is skipping lines

    - by user2403304
    I'm new to programing and I'm having a problem with my scanner class. This code is in a loop and when the loop comes around the second, third whatever time I have it set to it skips the first title input. I need help please why is it skipping my title scanner input in the beginning? System.out.println("Title:"); list[i].title=keyboard.nextLine(); System.out.println("Author:"); list[i].author=keyboard.nextLine(); System.out.println("Album:"); list[i].album=keyboard.nextLine(); System.out.println("Filename:"); list[i].filename=keyboard.nextLine();

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  • What is the common way to program action listeners?

    - by Roman
    I just started to learn how to use action listeners. To my understanding it works in the following way: There are some classes which contains "addActionListener" method by default (for example classes for buttons). Using this method we add an action listener to an object. For example: listenedObject.addActionListener(listeningObject). When an action with the "listenedObject" is performed, the "actionPerformed" method of the "listeningObject" will be called. So, it means that when we program a class for the listeningObject, we need to put there "actionPerformed" method. What is not clear to me, should we create a new class for every object that we want to listen. It does not seem to me as an elegant solution. On the other hand, if we have one action listener class for all (or at least many) object, than we have a problem since a instance of this class will not know which object is calling the "actionPerformed" method (and we need to know that since actions performed by the actionPerformed differs depending on who is called for this method). In my opinion, for every listened object we need to create are "personal" action listener and we can do it by setting a specific value to the corresponding field of the action listener. But I am not sure that it is a standard way to go? How do usually people do it?

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  • JFileChooser select directory but show files

    - by Jeff Storey
    I feel like there should be a simple way to do this but I can't figure it out. I have a JFileChooser that allows the user to select directories. I want to show all the files in the directories to give the user some context, but only directories should be accepted as selections (maybe the Open button would be disabled when a file is selected). Is there an easy way of doing this?

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  • Exception during processing XSLT transformation!

    - by Artic
    I'm using this code to generate contents file. try { StreamResult result = new StreamResult(); TransformerFactory tf = TransformerFactory.newInstance(); Templates templ = tf.newTemplates(xsltSource); Transformer transf = templ.newTransformer(); for (String item: groups){ item = item.replaceAll(" ", "-").toLowerCase(); result.setOutputStream(new FileOutputStream(path+item+".html")); transf.clearParameters(); transf.setParameter("group", item); transf.transform(xmlSource, result); } } catch (TransformerConfigurationException e) { throw new SinkException(e.getMessage()); } catch (TransformerException e) { throw new SinkException(e.getMessage()); } But on second iteration I have an exception ERROR: javax.xml.transform.TransformerException: com.sun.org.apache.xml.internal.utils.WrappedRuntimeException: Read error Cann't understand what is the reason?

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  • Creating Pages with unique PageMaps

    - by Michael Krauklis
    I have a wicket Application that has long lived Pages. I would like each instance of this Page to be created with a unique PageMap for reasons I won't get into here, but when I try to specify a PageMap on the constructor of my Page I end up getting OOM and StackOverflow errors. Here is the code: public <CTOR>() { super(Session.get().newPageMap("" + System.currentTimeMillis())); ... I'm using a custom BookmarkablePageLink (custom in that it does not pass on the current PageMap name to the new Page) to effectively abandon the old Page/PageMap and create a new one with a new PageMap. The errors seem to be coming from page serialization after only two or three pages have been created. Can anyone find issue with this approach?

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  • Scrolling down an awt.List

    - by nico
    As from subject, I have an awt.List object. When I add something to the list I would like to scroll it down to show the last inserted object. For instance: myList.add("sometext"); myList.select(myList.getItemCount()-1); myList.showSelectedItem(); // Or something like that The documentation does not seem to list any method that does something like that, can anybody help please?

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  • Php security question

    - by Camran
    I have a linux server, and I am about to upload a classifieds website to it. The website is php based. That means php code adds/removes classifieds, with the help of the users offcourse. The php-code then adds/removes a classified to a database index called Solr (like MySql). Problem is that anybody can currently access the database, but I only want the website to access the database (solr). Solr is on port 8983 as standard btw. My Q is, if I add a rule in my firewall (iptables), to only allow connections coming from the servers IP to the Solr port nr, would this solve my issue? Thanks

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  • How to remove strings of certain lengths

    - by Macosx Iam
    So I have this array, and I want to delete strings that are 2 or 4 characters in length (strings that contain 2 or 4 characters). I am doing this method, and it doesn't work, even though logically, it SHOULD work. public static void main(String[] args) { ArrayList<String> list = new ArrayList<String>(); list.add("This"); list.add("is"); list.add("a"); list.add("test"); for (int i=0; i<list.size(); i++) { if(list.get(i).length()==2 || list.get(i).length()==4) { list.remove(i); } } } I'd like to stick to this method of doing it. Can you please give me some suggestions as to how to correct this code? The output of this code when I run it is: [is, a] Even though I want the output to be [a] because "is" is 2 characters long.

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  • How to have a run in an Service?

    - by user1497664
    I have implemented an service that runs in a seperate process. This service contains a separate thread where i have a socket connection. This thread has a run() where it is continuously sending data to the port. My problem is after triggering the run() in the thread i don't get any contact with it anymore, i can see in the program that have open the socket that it consciously sends the data but the idea was that i while it is running i could change data that it sends for an example time. here is my run in the external thread: public void run() { if(run) { // Team and player names message is sent when entering in a game setBaseMessage(); SendMessageToCOMPort(base_message + CalculateCRC(base_message)); sleep(); // waits for 100 ms } } Anyone have any idea what might be wrong ?

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  • Junit test that creates other tests

    - by Benju
    Normally I would have one junit test that shows up in my integration server of choice as one test that passes or fails (in this case I use teamcity). What I need for this specific test is the ability to loop through a directory structure testing that our data files can all be parsed without throwing an exception. Because we have 30,000+ files that that 1-5 seconds each to parse this test will be run in its own suite. The problem is that I need a way to have one piece of code run as one junit test per file so that if 12 files out of 30,000 files fail I can see which 12 failed not just that one failed, threw a runtimeexception and stopped the test. I realize that this is not a true "unit" test way of doing things but this simulation is very important to make sure that our content providers are kept in check and do not check in invalid files. Any suggestions?

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  • How is it possible my array is broken?

    - by user1812765
    I have this piece of code: public lot merge (lot otherlot){ wafer[] mWaferarray = new wafer[16]; byte[] bytearray = new byte[16]; wafer resultwafer = new wafer(bytearray); wafer w1; wafer w2; int i; int[][] assignmentmatrix = HungarianAlgorithm.computeAssignments(convertinttofloat (solutionmatrix(otherlot))); for (i=0; i != assignmentmatrix.length ;i++){ w1 = otherlot.getWaferarray()[assignmentmatrix[i][0]]; w2 = getWaferarray()[assignmentmatrix[i][1]]; resultwafer.setWafer(w1.wafercompare(w2)); mWaferarray[i] = resultwafer; mWaferarray[i].print(); } System.out.println("HERE\n"); mWaferarray[5].toString(); resultlot = new lot(mWaferarray); resultlot.print();// Problem occurs here. return resultlot; } As you can see I create an array of wafers (selfdefined class). Then I fill this up with new wafers. When I print this array (mWaferarray[i].print()) it gives me the wanted results. But when I go out of the "for"-loop the array is broken and it is as if the last item I add to mWaferarray fills it up (the entire array, 16 long, is filled with this wafer). So if run this program this is what I get: 1011110010111100 0011011111111110 0111110111101101 1010111001101111 0110110111101111 1010110101111010 1010110111011110 1011111010111100 1111110011101110 0111111111011011 1111111111011010 1101111011111010 1010110101011110 0101111011011010 1011111011011000 0101111011011010 HERE 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 0101111011011010 As you can see it is as if the array is filled with the last wafer. I have been looking at this for some time now, I hope you guy can help me out. Thx in advance PS: my print functions are written like this: void print(){ int j; for (j=0; j != waferarray.length ;j++){ waferarray[j].print(); } } EDIT: added code for lot this is the beginning of the lot class public class lot { wafer[] waferarray = new wafer[16]; lot resultlot; public lot (wafer wafer1,wafer wafer2,wafer wafer3,wafer wafer4, wafer wafer5,wafer wafer6,wafer wafer7,wafer wafer8, wafer wafer9,wafer wafer10,wafer wafer11,wafer wafer12, wafer wafer13,wafer wafer14,wafer wafer15,wafer wafer16){ waferarray[0] = wafer1; waferarray[1] = wafer2; waferarray[2] = wafer3; waferarray[3] = wafer4; waferarray[4] = wafer5; waferarray[5] = wafer6; waferarray[6] = wafer7; waferarray[7] = wafer8; waferarray[8] = wafer9; waferarray[9] = wafer10; waferarray[10] = wafer11; waferarray[11] = wafer12; waferarray[12] = wafer13; waferarray[13] = wafer14; waferarray[14] = wafer15; waferarray[15] = wafer16; } public lot (wafer[] thiswaferarray){ waferarray = thiswaferarray; }

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