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  • How would you code a washing machine?

    - by Dan
    Imagine I have a class that represents a simple washing machine. It can perform following operations in the following order: turn on - wash - centrifuge - turn off. I see two basic alternatives: A) I can have a class WashingMachine with methods turnOn(), wash(int minutes), centrifuge(int revs), turnOff(). The problem with this is that the interface says nothing about the correct order of operations. I can at best throw InvalidOprationException if the client tries to centrifuge before machine was turned on. B) I can let the class itself take care of correct transitions and have the single method nextOperation(). The problem with this on the other hand, is that the semantics is poor. Client will not know what will happen when he calls the nextOperation(). Imagine you implement the centrifuge button’s click event so it calls nextOperation(). User presses the centrifuge button after machine was turned on and ups! machine starts to wash. I will probably need a few properties on my class to parameterize operations, or maybe a separate Program class with washLength and centrifugeRevs fields, but that is not really the problem. Which alternative is better? Or maybe there are some other, better alternatives that I missed to describe?

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  • What is the best practice of using return keyword?

    - by Artic
    What is the best practice of using return keyword? If i need to return something from method which pattern is better to use? public boolean method(){ if (case1){ return true; } if (case 2){ return false; } return false; } or public boolean method(){ boolean result = false; if (case1){ result = true; } if (case 2){ result = false; } return result; }

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  • How do I subtract a binding using a Guice module override?

    - by Jimmy Yuen Ho Wong
    So according to my testing, If you have something like: Module modA = new AbstractModule() { public void configure() { bind(A.class).to(AImpl.class); bind(C.class).to(ACImpl.class); bind(E.class).to(EImpl.class); } } Module modB = New AbstractModule() { public void configure() { bind(A.class).to(C.class); bind(D.class).to(DImpl.class); } } Guice.createInjector(Modules.overrides(modA, modB)); // gives me binding for A, C, E AND D with A overridden to A->C. But what if you want to remove the binding for E in modB? I can't seem to find a way to do this without having to break the bind for E into a separate module. Is there a way?

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  • Security when using GWT RPC

    - by gerdemb
    I have an POJO in Google Web Toolkit like this that I can retrieve from the server. class Person implements Serializable { String name; Date creationDate; } When the client makes changes, I save it back to the server using the GWT RemoteServiceServlet like this: rpcService.saveObject(myPerson,...) The problem is that the user shouldn't be able to change the creationDate. Since the RPC method is really just a HTTP POST to the server, it would be possible to modify the creationDate by changing the POST request. A simple solution would be to create a series of RPC functions like changeName(String newName), etc., but with a class with many fields would require many methods for each field, and would be inefficient to change many fields at once. I like the simplicity of having a single POJO that I can use on both the server and GWT client, but need a way to do it securely. Any ideas?

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  • Max Daily Budget exceeded and Billing Status "Changing Daily Budget"

    - by draftpik
    We've exceeded the Max Daily Budget for our app, but we can't increase the budget due to a serious flaw in Google's billing system. Google App Engine and Google Wallet do not have very capable support for multiple sign-in. As a result, I went to change the budget, but it used the wrong Google Wallet account (a different Google Account I was signed in as). I had to go back and try again, but now our GAE app shows the following status: Billing Status: Changing Daily Budget Your account has been locked while we process your budget changes. If you were redirected to Google Checkout but did not complete the process, your settings will remain unchanged. (You will be able to make changes to your budget settings again once the outstanding payment is processed.) Now I'm completely prevented from making any billing changes, our app is shut off (over quota), and I have NOTHING I can do to fix it. This is a seriously fundamental flaw in App Engine's billing system and Google Wallet integration. Has anyone run into this before? Is there a workaround anyone is aware of? Right now, our production app is completely down thanks to this issue. Any help you can offer would be greatly appreciated? If you're from Google and you might be able to help on the backend, our app id is "nhldraftpik". Thanks! Brian

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  • Is there a way to see which Project Wizard was used to create a given Eclipse Project?

    - by Bears will eat you
    Every time I start working on a new J2EE web application, I need to create the various Eclipse projects that I'll fill up. This includes the top-level project that generates the EAR, a WAR project, etc. I usually only have to do this every couple of months, so I never remember the exact steps - specifically, which Eclipse Project Wizards to use for each project in the webapp. I have enough old J2EE projects laying around that they could serve as good reference if only I could actually see which Wizard created them. Is there a way to recover this information?

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  • Any way of working with Eclipse WTP that does not mean redeploying the _WHOLE_ application when a J

    - by Thorbjørn Ravn Andersen
    I have migrated a Web Application from MyEclipse to Eclipse WTP, and I am now in the middle of the first major upgrade to the code base and web pages after the migration, and it is frankly driving me mad that saving a JSP page causes a redeployment of the WHOLE application, as it takes time and that my backend connection does not survive the serialization-deserialization of the session object (which is non-trivial to fix). In addition to that the JSP-editor is insanely slow so I frequently have to pause to let the editor catch up to be certain where my edits go in a small JSP using JavaServer Faces. Disabling validation did not help. The Eclipse Dynamic Web Project depends on several library eclipse projects so I cannot just tell e.g. Jetty to use the WebRoot folder, as several dependencies are then missing from the classpath. The question is: Is there a way of working - ANY way of working - with the Eclipse WTP system that does NOT imply redeploying everything every time any file is saved? I can use Tomcat 5.5 or Jetty 6 as servers.

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  • Running server-program from a .jar file

    - by skiwi
    I have created and am working on a server-application that monitors for specific folders and takes appropriate actions whenever files are being added. Now I come to the point where I want to be able to shutdown the program, for example for applying a patch. The server runs simply in a command prompt, how can I signal that I want to perform maintenance on it? I do not think reading System.In is feasible as I am also outputting text in the prompt. Regards.

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  • How to store some of the entity's values in another table using hibernate?

    - by nimcap
    Hi guys, is there a simple way to persist some of the fields in another class and table using hibernate. For example, I have a Person class with name, surname, email, address1, address2, city, country fields. I want my classes to be: public class Person { private String name; private String surname; private String email; private Address address; // .. } public class Address { private Person person; // to whom this belongs private String address1; private String address2; private String city; private Address country; // .. } and I want to store Address in another table. What is the best way to achieve this? Edit: I am using annotations. It does not have to be the way I described, I am looking for best practices. PS. If there is a way to make Address immutable (to use as a value object) that is even better, or maybe not because I thought everything from wrong perspective :)

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  • How would I set up this enum to return the image I want?

    - by Justen
    I'm trying to set up this enum so that it has the ability to return the correct image, though I'm struggling with a way to incorporate the context since it is in a separate class. public enum CubeType { GREEN { public Drawable getImage() { return Context.getResources().getDrawable( R.drawable.cube_green ); } }; abstract public Drawable getImage(); } The error I'm getting is: Cannot make a static reference to the non-static method getResources() from the type Context

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  • How can I get the size?

    - by Sanju
    I got a class. Lets say its named Class1 Here I create another class, Class2 Class2 has an arrya[] No my question is. When I create Class2 I cant have any size of the array with me in. How can I then know how big I want the array to be??? Out in Class1 I know how big it is. Thanks in Advance.

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  • Having a different action for each button dynamically created in a loop

    - by Oliver
    Hi, use this website a lot but first time posting. My program creates a number of buttons depending on the number of records in a file. E.g. 5 records, 5 buttons. The buttons are being created but i'm having a problem with the action listener. If add the action listener in the loop every button does the same thing; but if I add the action listener outside the loop it just adds the action listener to last button. Any ideas? Here is what I have code-wise (I've just added the for loop to save space): int j=0; for(int i=0; i<namesA.size(); i++) { b = new JButton(""+namesA.get(i)+""); conPanel.add(b); conFrame.add(conPanel); b.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent ae2){ System.out.println(namesA.get(j)); } }}); j++; } Much Appreciated

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  • chat website in jsp/servlet

    - by akshay
    I want to devlelop a chat website using JSP/Servlets and Tomcat. I have following questions: Can the website handle load (1000 people at one time) without slowing down? Will it cause the website to slow down? What is the ideal server configuration for this kind of website? Note that I don't have a huge budget to host. How can I implement server push? Will PHP or JSP be ideal for such website?

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  • Adding exclusive filter for <static initializer> in findbugs

    - by MilanAleksic
    Hi all, I want my findbugs report not show the following error: DM_NUMBER_CTOR: Method invokes inefficient Number constructor; use static valueOf instead The problem is that this happens in groovy-generated code files, so I can't control the source code - that is why I want to exclude it and add it to my exclude filter. I do not want to add explicitly class (since I make API that many tools will use, I want my filter to be generic). I would not like to completely remove this bug from the report by type, I would really like to only exclude this bug from appearing if it happenned in "static initializer" methods. Any idea? I tried the filter below but no luck, maybe somebody has better idea? <Match> <Method name="~.*static initializer.*" /> <Bug pattern="DM_NUMBER_CTOR" /> </Match> Here is the "stacktrace" of FindBugs in that case: In class net.milanaleksic.cuc.tools.sound.SoundPlayerTool In method net.milanaleksic.cuc.tools.sound.SoundPlayerTool.() Called method new Long(long) Should call Long.valueOf(long) instead In SoundPlayerTool.groovy

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  • UI not updated while using ProgressMonitorInputStream in Swing to monitor compressed file decompress

    - by Bozhidar Batsov
    I'm working on swing application that relies on an embedded H2 database. Because I don't want to bundle the database with the app(the db is frequently updated and I want new users of the app to start with a recent copy), I've implemented a solution which downloads a compressed copy of the db the first time the application is started and extracts it. Since the extraction process might be slow I've added a ProgressMonitorInputStream to show to progress of the extraction process - unfortunately when the extraction starts, the progress dialog shows up but it's not updated at all. It seems like to events are getting through to the event dispatch thread. Here is the method: public static String extractDbFromArchive(String pathToArchive) { if (SwingUtilities.isEventDispatchThread()) { System.out.println("Invoking on event dispatch thread"); } // Get the current path, where the database will be extracted String currentPath = System.getProperty("user.home") + File.separator + ".spellbook" + File.separator; LOGGER.info("Current path: " + currentPath); try { //Open the archive FileInputStream archiveFileStream = new FileInputStream(pathToArchive); // Read two bytes from the stream before it used by CBZip2InputStream for (int i = 0; i < 2; i++) { archiveFileStream.read(); } // Open the gzip file and open the output file CBZip2InputStream bz2 = new CBZip2InputStream(new ProgressMonitorInputStream( null, "Decompressing " + pathToArchive, archiveFileStream)); FileOutputStream out = new FileOutputStream(ARCHIVED_DB_NAME); LOGGER.info("Decompressing the tar file..."); // Transfer bytes from the compressed file to the output file byte[] buffer = new byte[1024]; int len; while ((len = bz2.read(buffer)) > 0) { out.write(buffer, 0, len); } // Close the file and stream bz2.close(); out.close(); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException ex) { ex.printStackTrace(); } try { TarInputStream tarInputStream = null; TarEntry tarEntry; tarInputStream = new TarInputStream(new ProgressMonitorInputStream( null, "Extracting " + ARCHIVED_DB_NAME, new FileInputStream(ARCHIVED_DB_NAME))); tarEntry = tarInputStream.getNextEntry(); byte[] buf1 = new byte[1024]; LOGGER.info("Extracting tar file"); while (tarEntry != null) { //For each entry to be extracted String entryName = currentPath + tarEntry.getName(); entryName = entryName.replace('/', File.separatorChar); entryName = entryName.replace('\\', File.separatorChar); LOGGER.info("Extracting entry: " + entryName); FileOutputStream fileOutputStream; File newFile = new File(entryName); if (tarEntry.isDirectory()) { if (!newFile.mkdirs()) { break; } tarEntry = tarInputStream.getNextEntry(); continue; } fileOutputStream = new FileOutputStream(entryName); int n; while ((n = tarInputStream.read(buf1, 0, 1024)) > -1) { fileOutputStream.write(buf1, 0, n); } fileOutputStream.close(); tarEntry = tarInputStream.getNextEntry(); } tarInputStream.close(); } catch (Exception e) { } currentPath += "db" + File.separator + DB_FILE_NAME; if (!currentPath.isEmpty()) { LOGGER.info("DB placed in : " + currentPath); } return currentPath; } This method gets invoked on the event dispatch thread (SwingUtilities.isEventDispatchThread() returns true) so the UI components should be updated. I haven't implemented this as an SwingWorker since I need to wait for the extraction anyways before I can proceed with the initialization of the program. This method get invoked before the main JFrame of the application is visible. I don't won't a solution based on SwingWorker + property changed listeners - I think that the ProgressMonitorInputStream is exactly what I need, but I guess I'm not doing something right. I'm using Sun JDK 1.6.18. Any help would be greatly appreciated.

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  • Call the method of base Class which was over ridden

    - by Abhijith Venkata
    I have illustrated my question in this example class Car { public void start(){ System.out.println("Car Started!!!"); } } class Mercedes extends Car { public void start(){ System.out.println("Mercedes Started!!!"); } } Now, in my main program, I write Mercedes m = new Mercedes(); m.start(); It prints: Mercedes Started!!! How do I call the start() method of Car class using the same object so that the output can be Car Started!!!. Edit: Actually It was asked in an interview I attended. I gave the super keyword answer. But the interviewer denied it. He said he'd give me a hint and said Virtual Function. I have no idea how to use that hint.

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  • Autocomplete server-side implementation

    - by toluju
    What is a fast and efficient way to implement the server-side component for an autocomplete feature in an html input box? I am writing a service to autocomplete user queries in our web interface's main search box, and the completions are displayed in an ajax-powered dropdown. The data we are running queries against is simply a large table of concepts our system knows about, which matches roughly with the set of wikipedia page titles. For this service obviously speed is of utmost importance, as responsiveness of the web page is important to the user experience. The current implementation simply loads all concepts into memory in a sorted set, and performs a simple log(n) lookup on a user keystroke. The tailset is then used to provide additional matches beyond the closest match. The problem with this solution is that it does not scale. It currently is running up against the VM heap space limit (I've set -Xmx2g, which is about the most we can push on our 32 bit machines), and this prevents us from expanding our concept table or adding more functionality. Switching to 64-bit VMs on machines with more memory isn't an immediate option. I've been hesitant to start working on a disk-based solution as I am concerned that disk seek time will kill performance. Are there possible solutions that will let me scale better, either entirely in memory or with some fast disk-backed implementations? Edits: @Gandalf: For our use case it is important the the autocompletion is comprehensive and isn't just extra help for the user. As for what we are completing, it is a list of concept-type pairs. For example, possible entries are [("Microsoft", "Software Company"), ("Jeff Atwood", "Programmer"), ("StackOverflow.com", "Website")]. We are using Lucene for the full search once a user selects an item from the autocomplete list, but I am not yet sure Lucene would work well for the autocomplete itself. @Glen: No databases are being used here. When I'm talking about a table I just mean the structured representation of my data. @Jason Day: My original implementation to this problem was to use a Trie, but the memory bloat with that was actually worse than the sorted set due to needing a large number of object references. I'll read on the ternary search trees to see if it could be of use.

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  • How to set the email protocol in JavaMail

    - by Dusk
    If I need to get inbox messages by passing request from servlets to javamail API , how can I know the protocol in which to retrieve inbox messages? Do I have to state the protocol in request URL? I've already checked in gmail, where they haven't stated any protocol, then How can I get inbox messages based on particular protocol like: POP3 or IMAP

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  • How can I find out if two arguments are instances of the same, but unknown class?

    - by Ingmar
    Let us say we have a method which accepts two arguments o1 and o2 of type Object and returns a boolean value. I want this method to return true only when the arguments are instances of the same class, e.g.: foo(new Integer(4),new Integer(5)); Should return true, however: foo(new SomeClass(), new SubtypeSomeClass()); should return false and also: foo(new Integer(3),"zoo"); should return false. I believe one way is to compare the fully qualified class names: public boolean foo(Object o1, Object o2){ Class<? extends Object> c1 = o1.getClass(); Class<? extends Object> c2 = o2.getClass(); if(c1.getName().equals(c2.getName()){ return true;} return false; } An alternative conditional statement would be : if (c1.isAssignableFrom(c2) && c2.isAssignableFrom(c1)){ return true; } The latter alternative is rather slow. Are there other alternatives to this problem?

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