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  • Modular Inverse and BigInteger division

    - by dano82
    I've been working on the problem of calculating the modular inverse of an large integer i.e. a^-1 mod n. and have been using BigInteger's built in function modInverse to check my work. I've coded the algorithm as shown in The Handbook of Applied Cryptography by Menezes, et al. Unfortunately for me, I do not get the correct outcome for all integers. My thinking is that the line q = a.divide(b) is my problem as the divide function is not well documented (IMO)(my code suffers similarly). Does BigInteger.divide(val) round or truncate? My assumption is truncation since the docs say that it mimics int's behavior. Any other insights are appreciated. This is the code that I have been working with: private static BigInteger modInverse(BigInteger a, BigInteger b) throws ArithmeticException { //make sure a >= b if (a.compareTo(b) < 0) { BigInteger temp = a; a = b; b = temp; } //trivial case: b = 0 => a^-1 = 1 if (b.equals(BigInteger.ZERO)) { return BigInteger.ONE; } //all other cases BigInteger x2 = BigInteger.ONE; BigInteger x1 = BigInteger.ZERO; BigInteger y2 = BigInteger.ZERO; BigInteger y1 = BigInteger.ONE; BigInteger x, y, q, r; while (b.compareTo(BigInteger.ZERO) == 1) { q = a.divide(b); r = a.subtract(q.multiply(b)); x = x2.subtract(q.multiply(x1)); y = y2.subtract(q.multiply(y1)); a = b; b = r; x2 = x1; x1 = x; y2 = y1; y1 = y; } if (!a.equals(BigInteger.ONE)) throw new ArithmeticException("a and n are not coprime"); return x2; }

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  • Android: Prompt user to save changes when Back button is pressed

    - by chriskopec
    I have an activity that contains several user editable items (an EditText field, RatingBar, etc). I'd like to prompt the user if the back/home button is pressed and changes have been made that have not yet been saved. After reading through the android documentation, it seems like this piece of code should go in the onPause method. I've tried putting an AlertDialog in the onPause however the dialog gets shown and then immediately tears down because nothing is there to block the pause from completing. This is what I've come up with so far: @Override protected void onPause() { super.onPause(); AlertDialog ad = new AlertDialog.Builder(this).setMessage( R.string.rating_exit_message).setTitle( R.string.rating_exit_title).setCancelable(false) .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { // User selects OK, save changes to db } }).setNeutralButton(android.R.string.cancel, new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int whichButton) { // User selects Cancel, discard all changes } }).show(); } Am I on the right track or is there another way to accomplish what I'm trying to do here? Any help would be great!

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  • Problem detaching entire object graph in GAE-J with JDO

    - by tempy
    I am trying to load the full object graph for User, which contains a collection of decks, which then contains a collection of cards, as such: User: @PersistenceCapable(detachable = "true") @Inheritance(strategy = InheritanceStrategy.SUBCLASS_TABLE) @FetchGroup(name = "decks", members = { @Persistent(name = "_Decks") }) public abstract class User { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) protected Key _ID; @Persistent protected String _UniqueIdentifier; @Persistent(mappedBy = "_Owner") @Element(dependent = "true") protected Set<Deck> _Decks; protected User() { } } Each Deck has a collection of Cards, as such: @PersistenceCapable(detachable = "true") @FetchGroup(name = "cards", members = { @Persistent(name = "_Cards") }) public class Deck { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent String _Name; @Persistent(mappedBy = "_Parent") @Element(dependent = "true") private Set<Card> _Cards = new HashSet<Card>(); @Persistent private Set<String> _Tags = new HashSet<String>(); @Persistent private User _Owner; } And finally, each card: @PersistenceCapable public class Card { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Key _ID; @Persistent private Text _Question; @Persistent private Text _Answer; @Persistent private Deck _Parent; } I am trying to retrieve and then detach the entire object graph. I can see in the debugger that it loads fine, but then when I get to detaching, I can't make anything beyond the User object load. (No Decks, no Cards). At first I tried without a transaction to simply "touch" all the fields on the attached object before detaching, but that didn't help. Then I tried adding everything to the default fetch group, but that just generated warnings about GAE not supporting joins. I tried setting the fetch plan's max fetch depth to -1, but that didn't do it. Finally, I tried using FetchGroups as you can see above, and then retrieving with the following code: PersistenceManager pm = _pmf.getPersistenceManager(); pm.setDetachAllOnCommit(true); pm.getFetchPlan().setGroup("decks"); pm.getFetchPlan().setGroup("cards"); Transaction tx = pm.currentTransaction(); Query query = null; try { tx.begin(); query = pm.newQuery(GoogleAccountsUser.class); //Subclass of User query.setFilter("_UniqueIdentifier == TheUser"); query.declareParameters("String TheUser"); List<User> results = (List<User>)query.execute(ID); //ID = Supplied parameter //TODO: Test for more than one result and throw if(results.size() == 0) { tx.commit(); return null; } else { User usr = (User)results.get(0); //usr = pm.detachCopy(usr); tx.commit(); return usr; } } finally { query.closeAll(); if (tx.isActive()) { tx.rollback(); } pm.close(); } This also doesn't work, and I'm running out of ideas...

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  • Can't add libraries to Eclipse Android project

    - by neuromancer
    I'm trying to get the Hackbook for Android project to work in Eclipse. One of the things I need to do is remove that invalid reference and include that project I made. I did this before, but then I started over and now it doesn't work. Here is where I add the project. If I click "Apply" and then "OK" everything seems to be fine, but it isn't, because when I go back to this screen, none of the changes I made are there. Why isn't it saving my changes? How am I supposed to do this?

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  • How to use SQLiteOpenHelper without or less restrictive use of Context?

    - by Pentium10
    If you extend SQLiteOpenHelper, for the Constructor you have to use a Context. I am wondering if there is a way to leave this out, and be able to work with database tables without a Context. Or at least be least restrictive, I mean a way of project/class structure that will make history the several context passings I have to do now. As it is my application has several level of classes, chained in each other, and there are a few that connects to the database, but have no whatsoever influence on the interface, so they don't actually need the Context. Are you creating your classes in the way that you pass each time a Context to them? If not, how you do, how you reuse a Context in a short class?

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  • How can I force the text go to the button of the panel?

    - by Roman
    At the moment I have the following code which works fine. label = new JLabel(panelLabel,SwingConstants.CENTER); outputPanel.add(label,BorderLayout.CENTER); I get the text in the center of the panel (in terms of the left-right position as well as in terms of the top-bottom). Now I want to set the position to the bottom (and center in terms of "left-right"). I tried to use SOUTH instead of the CENTER in the first line. Compiler does not complains but during the execution i get IllegalArgumentException: HorizontalAlignment. What is that?

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  • Use of mouselisteners in a jTable

    - by eli1987
    I have a jTable with columns 'Job_no' and 'Status'with values such as: Job_no Status 1 Active 2 Pending 3 Pending I would like it so that if a user clicks on a Status say in this case the first 'Pending'(where Job_no = 2) an inputDialog pops up allowing the user to change the status of the cell clicked-how can I do this? Bear in mind you will also have to retrieve the Job_no(that corresponds to that status) somehow, and that, though I'm OK with JOptionPane's, I'm new to JTables. I'm using JDBC(mySQL) and have a table 'Jobs' which amongst other things, has column Job_no and status. Thanks for your help.

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  • RAD - Websphere Application server won't start

    - by Caroline
    I am having issues with RAD7. My server will not start for me today. I am working from home and connected to the VPN. Everything works except my server in RAD. It worked fine yesterday in work and had previously worked when I was at home but that was a few weeks ago. Are there any settings that I should look out for? I have disabled my proxy settings in RAD and turned off everything in my firewall. I can ping all the DBs that the server is connecting to. I have even removed all the projects from the server and it will still not start. It keeps trying and then times out after 300s. Any suggestions?

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  • Creating objects makes the VM faster?

    - by Sudhir Jonathan
    Look at this piece of code: MessageParser parser = new MessageParser(); for (int i = 0; i < 10000; i++) { parser.parse(plainMessage, user); } For some reason, it runs SLOWER (by about 100ms) than for (int i = 0; i < 10000; i++) { MessageParser parser = new MessageParser(); parser.parse(plainMessage, user); } Any ideas why? The tests were repeated a lot of times, so it wasn't just random. How could creating an object 10000 times be faster than creating it once?

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  • change a frame's attribute by pressing a button

    - by asavu
    Hi. Suppose we have a JFrame named frame1 with a String attribute named credentials set inittially to null. I have a jButton named button1 attached to the frame and I want to change the frame1 String credentials attribute by pressing button1. I need some piece of advice regarding the ActionListener code especially. Could you guys pls help me? Thank you.

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  • arrayListOutOfBoundsException... Please Help?

    - by Jacob
    This is my class Debugger. Can anyone try and run it and see whens wrong? Ive spent hours on it already. :( public class Debugger { private String codeToDebug = ""; public Debugger(String code) { codeToDebug = code; } /** * This method itterates over a css file and adds all the properties to an arraylist */ public void searchDuplicates() { boolean isInside = false; ArrayList<String> methodStorage = new ArrayList(); int stored = 0; String[] codeArray = codeToDebug.split(""); try { int i = 0; while(i<codeArray.length) { if(codeArray[i].equals("}")) { isInside = false; } if(isInside && !codeArray[i].equals(" ")) { boolean methodFound = false; String method = ""; int c = i; while(!methodFound) { method += codeArray[c]; if(codeArray[c+1].equals(":")) { methodFound = true; } else { c++; } } methodStorage.add(stored, method); System.out.println(methodStorage.get(stored)); stored++; boolean stillInside = true; int skip = i; while(stillInside) { if(codeArray[skip].equals(";")) { stillInside = false; } else { skip++; } } i = skip; } if(codeArray[i].equals("{")) { isInside = true; } i++; } } catch(ArrayIndexOutOfBoundsException ar) { System.out.println("------- array out of bounds exception -------"); } } /** * Takes in String and outputs the number of characters it contains * @param input * @return Number of characters */ public static int countString(String input) { String[] words = input.split(""); int counter = -1; for(int i = 0; i<words.length; i++){ counter++; } return counter; } public static void main(String[] args) { Debugger h = new Debugger("body {margin:;\n}"); h.searchDuplicates(); } }

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  • Does it mean JVM Suspended?

    - by Joe.wang
    When my application run . I got a message says : Ping: Timed out waiting for signal from JVM. The JVM was launched with debug options so this may be because the JVM is currently suspended by a debugger. Any future timeouts during this JVM invocation will be silently ignored. What does that mean? It seems it will block any web request from outside? because when I upload a file to it, it failed. help me .

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  • Wait between tasks with SingleThreadExecutor

    - by Lord.Quackstar
    I am trying to (simply) make a blocking thread queue, where when a task is submitted the method waits until its finished executing. The hard part though is the wait. Here's my 12:30 AM code that I think is overkill: public void sendMsg(final BotMessage msg) { try { Future task; synchronized(msgQueue) { task = msgQueue.submit(new Runnable() { public void run() { sendRawLine("PRIVMSG " + msg.channel + " :" + msg.message); } }); //Add a seperate wait so next runnable doesn't get executed yet but //above one unblocks msgQueue.submit(new Runnable() { public void run() { try { Thread.sleep(Controller.msgWait); } catch (InterruptedException e) { log.error("Wait to send message interupted", e); } } }); } //Block until done task.get(); } catch (ExecutionException e) { log.error("Couldn't schedule send message to be executed", e); } catch (InterruptedException e) { log.error("Wait to send message interupted", e); } } As you can see, there's alot of extra code there just to make it wait 1.7 seconds between tasks. Is there an easier and cleaner solution out there or is this it?

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  • Does thread pool size keep growing for scheduledthreadpoolexecutor?

    - by Sourajit Basak
    Imagine a situation where tasks are being added to scheduledthreadpoolexecutor. Each of these tasks will keep on running at different periodic intervals. Although all such tasks will not be running at the same time because each is set at different intervals, there may be a situation where a high number of threads are competing for execution. Is there any restriction on total number of threads ? It seems there is a restriction on the total number of idle threads. And does this concept of idle thread imply that long running tasks (thread) may be destroyed and recreated when needed ?

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  • What features EJB3 bring and also how does EJB3 stack up with Spring Framework ?

    - by Rachel
    I have never worked on ejb, when I started programming Spring was already arrived and all my projects have been with Spring only, recently I had one interview and they wanted knowledge of EJB3.0 and so I want to know how does EJB3.0 stack up with Spring Framework and why many projects now a day are with Spring Framework and not with EJB3.0, do not quote me here as I can be wrong I would really appreciate if difference and benefits of using one over another could be explained from practical perspective.

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  • Jaxb to generate the XML directly to the OutputStream

    - by sonu
    Hi, I have a 500Mb csv file. I need to convert it into XML file. I am using the Jaxb to created the xml file. It is working fine for small amout of data. but for large amout of data like 300 mb it is throwing out of memory exception. Can anyone tell me that How can I create each element and write it into a file without creating the whole tree using the jaxb?" Thanks Sonu

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  • How to select item in jComboBox

    - by jtnire
    Hi folks, I have a jComboBox that I am populating with some objects. The objects are of a type which I have made myself, and include a String and an int. The object's toString method returns the String, which is displayed in the Combo Box. Now, I wish to select an item in the Combo Box with code. How do I do this? There are multiple items starting with the same letter Thanks

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  • Best Design Pattern to Implement while Mapping Actions in MVC

    - by FidEliO
    What could be the best practices of writing the following case: We have a controller which based on what paths users take, take different actions. For example: if user chooses the path /path1/hello it will say hello. If a user chooses /path1/bye?name="Philipp" it will invoke sayGoodBye() and etc. I have written a switch statement inside the controller which is simple, however IMO not efficient. What are the best way to implement this, considering that paths are generally String. private void takeAction() { switch (path[1]) { case "hello": //sayHello(); break; case "bye": //sayBye(); break; case "case3": //Blah(); break; ... } }

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