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• Performance implications of finalizers on JVM

  - by Alexey Romanov

  According to this post, in .Net, Finalizers are actually even worse than that. Besides that they run late (which is indeed a serious problem for many kinds of resources), they are also less powerful because they can only perform a subset of the operations allowed in a destructor (e.g., a finalizer cannot reliably use other objects, whereas a destructor can), and even when writing in that subset finalizers are extremely difficult to write correctly. And collecting finalizable objects is expensive: Each finalizable object, and the potentially huge graph of objects reachable from it, is promoted to the next GC generation, which makes it more expensive to collect by some large multiple. Does this also apply to JVMs in general and to HotSpot in particular?

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• Is it possible to include JButton in a JTable?

  - by Benjamin Confino

  I have a JTable that stores the results of a database query, so far so good. What I want is for the last column in each table to have a clickible JButton that will open the edit screen for the object represented in that row, and that means the button will need to know the details of the first column in the table from its own row (the ID from the database). Any advice? I already tried just adding JButtons but they turned into Text when I tried to run it.

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• How do I prevent JDialog from showing in gnome-panel(Linux)?

  - by aeter

  I have a class: public class ANote extends JDialog{...} In GNOME(Linux) it shows an entry in the gnome-panel. I want it to show nothing (the same way it does in the taskbar in Windows), because there may be present several instances of the class simultaneously, and this overcrowds the gnome-panel. How do I prevent it from showing an instance in the gnome-panel? EDIT: So far I have tried playing with the modality, which hides it from the gnome-panel, but blocks the main frame of the application behind the ANote instances.

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• E-commerce web site with J2EE

  - by Acharf

  hello everybody, I need to create a Ecommerce web site with J2EE. So any one has a source code, tutorial any things can help.

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• Strategies for dealing with Circular references caused by JPA relationships?

  - by ams

  I am trying to partition my application into modules by features packaged into separate jars such as feature-a.jar, feature-b.jar, ... etc. Individual feature jars such as feature-a.jar should contain all the code for a feature a including jpa entities, business logic, rest apis, unit tests, integration test ... etc. The problem I am running into is that bi-directional relationships between JPA entities cause circular references between the jar files. For example Customer entity should be in customer.jar and the Order should be in order.jar but Customer references order and order references customer making it hard to split them into separate jars / eclipse projects. Options I see for dealing with the circular dependencies in JPA entities: Option 1: Put all the entities into one jar / one project Option 2: Don't map certain bi-directianl relationships to avoid circular dependencies across projects. Questions: What rules / principles have you used to decide when to do bi-directional mapping vs. not? Have you been able to break jpa entities into their own projects / jar by features if so how did you avoid the circular dependencies issues?

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• How to write a jUnit test for this class?

  - by flash

  Hi, I would like to know what's the best approach to test the method "pushEvent()" in the following class with a jUnit test. My problem is, that the private method "callWebsite()" always requires a connection to the network. How can I avoid this requirement or refactor my class that I can test it without a connection to the network? class MyClass { public String pushEvent (Event event) { //do something here String url = constructURL (event); //construct the website url String response = callWebsite (url); return response; } private String callWebsite (String url) { try { URL requestURL = new URL (url); HttpURLConnection connection = null; connection = (HttpURLConnection) requestURL.openConnection (); String responseMessage = responseParser.getResponseMessage (connection); return responseMessage; } catch (MalformedURLException e) { e.printStackTrace (); return e.getMessage (); } catch (IOException e) { e.printStackTrace (); return e.getMessage (); } } }

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• What is annotations and how do it actually works for frameworks like Spring ?

  - by Rachel

  I am new to Spring and now a days I hear a lot about Spring Framework. I have two sets of very specific questions: Set No. 1: What are annotations in general ? How does annotations works specifically with Spring framework ? Can annotations be used outside Spring Framework or are they Framework specific ? Set No. 2: What module of Spring Framework is widely used in Industry ? I think it is Spring MVC but why it is the most used module, if am correct or correct me on this ? I am newbie to Spring and so feel free to edit this questions to make more sense.

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• byte stream and character stream

  - by JavaUser

  Hi, Please explain byte stream and character stream files. What exactly these means , is microsoft word document is byte oriented or character oriented ? Thanks

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• Keeping messages in queue in case of receiver crash

  - by John Doe

  Hi, We've a Spring JMS message listener container for receiving messages asynchronously. Using DefaultMessageListenerContainer and in sessionTransacted mode. I understand being in sessionTransacted mode means in case of an exception the message will be put back into the queue. But how can I make sure the message won't be deleted from the queue even if the receiver (which is picked the message) crashes or just the machine running it looses power? At first I thought CLIENT_ACKNOWLEDGE acknowledge mode should save me, but apparently it's not the case, Spring calls .acknowledge() no matter what. So here's my question, how can I guarantee the delivery? Using a custom MessageListenerContainer? Using a transaction manager?

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• how to know JToolbar's status?

  - by 5YrsLaterDBA

  How to check the JToolbar is docked on my JFrame or it is draged out with its own window?

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• Extracting startup errors from Spring contexts

  - by sehugg

  Consider the following output from a Tomcat server under Eclipse: INFO: Initializing Coyote HTTP/1.1 on http-8080 INFO: Initialization processed in 634 ms INFO: Starting service Catalina INFO: Starting Servlet Engine: Apache Tomcat/6.0.20 SEVERE: Error listenerStart SEVERE: Context [/MyServlet] startup failed due to previous errors I would like to figure out what exception caused "Error listenerStart", but Spring seems to be preventing me from finding the error via Eclipse. I'd love to start Catalina manually, but that doesn't seem to do anything. What's the best way to find the hidden exception? I'm not afraid to use torture methods.

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• How to mock object?

  - by Gandalf StormCrow

  How to mock object for testing if the class you're testing is abstract? you can't instantiate from it ?

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• Implement the business logic in an app server with spring

  - by HenryOS

  Hi everybody, i have a doub... Is posible implement the business logic in an App Server remote using pojos instead of either EJB or Servlets???. The main idea is apply a model of 3 layers where the clients may be both web browsers and desktop applications, and they share the business logic in an App Server. Sorry for my english... im from Argentina and my english is poor. Thank you to everybody and i hope that anybody can help me soon. Regards! this would be the architecture browser----- Web Server --------|App Server(Business Logic common)|-------|RDBMS common| desktop App(Swing for example)-|App Server(Business Logic common)|-------|RDBMS common|

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• business object and codelist

  - by feiroox

  Hi How to design a business object? I have a library which returns me an Object which have ten lists of other different objects. I need to store it into database all. List of objects are often like: class Item { private int id; private String name; private double point; } But the name is often the same. Like basic title of the product or code. Containing from 3 characters up to 70characters. Should I make conversion for every Object to: (or something similar) class ConvertedItem { private int id; private int code; private double point; } And have a separated table of codes ( I guess around 60). Or do not bother with duplicated stuff? It's not mission critical app. What would you do in my case? thanks in advance

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• How to get icons for entities from eclipse?

  - by fastcodejava

  I am writing an eclipse plugin. How do I get the various images from eclipse library? So I don't have have keep a local set of images for the standard entities, e.g classes, interfaces, junits, etc. EDIT : I used PlatformUI.getWorkbench().getSharedImages().getImage(ISharedImages.IMG_OBJ_FILE) from the article : http://www.eclipse.org/articles/Article-Using%20Images%20In%20Eclipse/Using%20Images%20In%20Eclipse.html. That did not work.

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• Using exponential smoothing with NaN values

  - by Eric

  I have a sample of some kind that can create somewhat noisy output. The sample is the result of some image processing from a camera, which indicates the heading of a blob of a certain color. It is an angle from around -45° to +45°, or a NaN, which means that the blob is not actually in view. In order to combat the noisy data, I felt that exponential smoothing would do the trick. However, I'm not sure how to handle the NaN values. On the one hand, involving them in the math would result in a NaN average, which would then prevent any meaningful results. On the other hand, ignoring NaN values completely would mean that a "no-detection" scenario would never be reported. And just to complicate things, the data is also noisy in that it can get false NaN value, which ideally would be smoothed somehow to prevent random noise. Any ideas about how I could implement such an exponential smoother?

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• Two pass JSP page rendering

  - by dotsid

  Suppose an example. I have following interface: public interface DataSource<T> { Future<T> fetch(); } This datasource can do asynchronous data fetching. And we have following tag for using datasource in JSP: <html> <d:fetch from="${orderDS}" var="orders"> <c:foreach in="${orders}" var="order"> <div class="order"> <c:out value="${order.title}" /> </div> </c:foreach> </d:fetch> </html> So, what I want? I want JSP rendering engine to call my custom tag (FetchTag in this example) twice. On first call FetchTag will do DataSource.fetch() call and save Future locally as a object field. On second call FetchTag do Future.get() call and will be blocked until data becomes available. Is there any way to do such a thing?

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• HIbernate query language problem.....

  - by mslatf

  I have a Project class that has a Set of userstories called userStories12many. I'm having troubles trying to get the project that has a certain userstory in its set getComponent(int userStoryID) I think im on the right track but i dont know what i did wrong public Projects getComponent(int userStoryID) { Session session = SessionFactoryHelper.getSessionFactory() .getCurrentSession(); session.beginTransaction(); List<Projects> compo = session.createQuery("select p " + "from Projects as p inner join fetch p.userStories12many as u " + "where u.storyId='" + userStoryID + "'").list(); session.getTransaction().commit(); return compo.get(0); }

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• ExecutorSerrvice memory leak on exception

  - by TofuBeer

  I am having a hard time tracking this down since the profiler keeps crashing (hotspot error). Before I go too deep into figuring it out I'd like to know if I really have a problem or not :-) I have a few thread pools created via: Executors.newFixedThreadPool(10); The threads connect to different web sites and, on occasion, I get connection refused and wind up throwing an exception. When I later on call Future.get() to get the result it will then catch the ExecutionException that wraps the exception that was thrown when the connection could not be made. The program uses a fairly constant amount of memory up until the point in time that the exceptions get thrown (they tend to happen in batches when a particular site is overloaded). After that point the memory again remains constant but at a higher level. So my question is along the lines of is the memory behaviour (reported by "top" on Unix) expected because the exceptions just triggered something or do I probably have an actual leak that I'll need to track down? Additionally when Future.get() throws an exception is there anything else I need to do besides catch the exception (such as call Future.cancel() on it)?

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• Grails query not using GORM

  - by Tihom

  What is the best way to query for something without using GORM in grails? I have query that doesn't seem to fit in the GORM model, the query has a subquery and a computed field. I posted on stackoverflow already with no response so I decided to take a different approach. I want to query for something not using GORM within a grails application. Is there an easy way to get the connection and go through the result set?

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• Identifying the GeoPoint that trigger an onTap call

  - by Akroy

  I'm developing a Google Maps app on Android. I have a number of GeoPoints that I'm displaying by adding them as OverlayItems to an ItemizedOverlay. This works well for displaying them and bringing up a nice box when I click them, however I'm trying to put info in the box it brings up. Thus, I've extended ItemizedOverlay with my own class, and I'm overriding onTap (final GeoPoint p, final MapView mapView). At first I thought that this would be very simple, as one of the parameters is the GeoPoint, so I would know exactly which GeoPoint was clicked. However, from what I can tell, the GeoPoint argument there is the GeoPoint for where the user actually touched. Given the range the user can touch and still trigger the onTap, that GeoPoint isn't very helpful for knowing precisely which GeoPoint was actually touched. I'm currently checking the parameter GeoPoint against all my existing GeoPoints and seeing which it's closest to. This seems like a super hacky abstraction inversion. Is there a better way to know what was actually tapped?

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• PDFBox: Problem with converting pdf page into image

  - by user552910

  My mission is pretty simple: converting every single page of a pdf file into images. I tried using icepdf open source version to generate the images but they don't generate the image with the correct font. So I start using PDFBox instead. The code is the following: PDDocument document = PDDocument.load(new File("testing.pdf")); List<PDPage> pages = document.getDocumentCatalog().getAllPages(); for (int i = 0; i < pages.size(); i++) { PDPage singlePage = pages.get(i); BufferedImage buffImage = convertToImage(singlePage, 8, 12); ImageIO.write(buffImage, "png", new File(PdfUtil.DATA_OUTPUT_DIR+(count++)+".png")); } The font looks good, but the pictures within the pdf file look fainted out (See the attachment). I look into the source code but I still have no clue how to fix it. Do you guys have any idea what's going on? Please help. Thanks!!

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• Time complexity O() of isPalindrome()

  - by Aran

  I have this method, isPalindrome(), and I am trying to find the time complexity of it, and also rewrite the code more efficiently. boolean isPalindrome(String s) { boolean bP = true; for(int i=0; i<s.length(); i++) { if(s.charAt(i) != s.charAt(s.length()-i-1)) { bP = false; } } return bP; } Now I know this code checks the string's characters to see whether it is the same as the one before it and if it is then it doesn't change bP. And I think I know that the operations are s.length(), s.charAt(i) and s.charAt(s.length()-i-!)). Making the time-complexity O(N + 3), I think? This correct, if not what is it and how is that figured out. Also to make this more efficient, would it be good to store the character in temporary strings?

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• Android, Quick question on service binding

  - by moppel

  Is there a way to find out if an activity is bound to a service? Something like boolean isBoundToService(ServiceConnection sc)? Sometimes when I play around with my app I get an exception when it tries to unbind a service which is not bound.

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• How to properly encode "[" and "]" in queries using Apache HttpClient?

  - by Jason Nichols

  I've got a GET method that looks like the following: GetMethod method = new GetMethod("http://host/path/?key=[\"item\",\"item\"]"); Such a path works just fine when typed directly into a browser, but the above line when run causes an IllegalArgumentException : Invalid URI. I've looked at using the URIUtils class, but without success. Is there a way to automatically encode this (or to add a query string onto the URL without causing HttpClient to barf?).

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