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  • WeakHashMap iteration and garbage collection

    - by Shamik
    I am using a WeaekHashMap to implement a Cache. I am wondering if I am iterating over the keys of this map, and at the same time garbage collector is actively removing keys from this map, would I receive a ConcurrentModificationException ? I do not think so, because as far as I understand, concurrentmodificationexception happens because of bugs in the application code where the developer forgot to understand that the same map is shared/used by other threads and in this case, it should not happen. But wondering how would JVM handle this when WeakHashMap is not synchronized ?

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  • Can I get the full query that a PreparedStatement is about to execute?

    - by ufk
    I'm working with PreparedStatement with MySQL server. example: String myQuery = "select id from user where name = ?"; PreparedStatement stmt = sqlConnection.prepareStatement(myQuery); stmt.setString(1, "test"); stmt.executeQUery(); ResultSet rs = stmt.getResultSet(); How can I receive the full SQL query that is about to be executed on the MySQL server? thanks!

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  • Why is the output like this?

    - by javatechi
    class another { public void method(Object o) { System.out.println("This is in method which takes object"); } public void method(String s) { System.out.println("This is method which takes string"); } } public class NewClass { public static void main(String args[]) { another an = new another(); an.method(null); } } When I try to execute this, I get This is method which takes string as the output. Why not "This is in method which takes object"? Object can also be null and string can also be null, why doesn't it invoke first method?

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  • Preon library problem

    - by Kamahire
    I am using preon lib to parse binary data it contain short, int data The structure as follows @BoundNumber(size="32", byteOrder=ByteOrder.BigEndian) public int time;// @BoundString(size="2") public String alphaChar;// 2 byte array @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code1;//short @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code2;//short @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code3;//short @BoundString(size="8") public String firstName;// 8 byte array @BoundString(size="8") public String middleName;// 8 byte array @BoundString(size="8") public String lastName;// 8 byte array @BoundNumber(size="16", byteOrder=ByteOrder.BigEndian) public int code4;//short I am getting correct values for code1, code2, code3 but for code4 it not giving me correct value. It always gives me 0(Zero); When I checked with position of byte array; it shows me correct value. Is there any kind padding require?

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  • Associate activity with database ID

    - by Mohit Deshpande
    I have a main ListView that is based on an adapter from my database. Each database id is "assigned" to an Activity via the ListView. And in my AndroidManifest, each activity has an intent filter with a custom action. Now with this, I have had to create this class: public final class ActivityLauncher { private ActivityLauncher() { } public static void launch(Context c, int id) { switch(id) { case 1: Intent intent = new Intent(); intent.setAction(SomeActivity.ACTION_SOMEACTIVITY); c.startActivity(intent); break; case 2: ... break; ... } } private static void st(Context context, String action) { Intent intent = new Intent(); intent.setAction(action); context.startActivity(intent); } } So I have to manually create a new case for the switch statement. This would get troublesome if I have to rearrange or delete an id. Is there any way to get around this?

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  • Hot to set class variable to be visible to its public static methods?

    - by RCola
    Why I can noy access my variable p in mull form iterate method? How to resolve a problem? Hot to set class variable to be visible to its public static methods? public class mull { public static void main(String[] args) throws InterruptedException { final JPanel p = createAndShowGUI(); Timer timer = new Timer(1000, new MyTimerActionListener()); timer.start(); try { Thread.sleep(10000); } catch (InterruptedException e) { } timer.stop(); public static void iterate(){ for (int i = 0; i < 55; i++){ // "p cannot be resolved" p.moveSquare(i*10, i*10); p.setParamsRing(i*5, i*7, 200, 200); // p.repaint(); } } } class MyPanel extends JPanel { .... } How to access variable set in another method (in this example main())? Why Eclipse forces me to use this ((MyPanel) p).setParamsRing(i*5, i*7, 200, 200); instead of this p.setParamsRing(i*5, i*7, 200, 200);?

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  • FileInput Help/Advice

    - by user559142
    I have a fileinput class. It has a string parameter in the constructor to load the filename supplied. However it just exits if the file doesn't exist. I would like it to output a message if the file doesn't exist - but not sure how.... Here is the class: public class FileInput extends Input { /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final String fileName) { try { scanner = new Scanner(new FileInputStream(fileName)); } catch (FileNotFoundException e) { System.err.println("File " + fileName + " could not be found."); System.exit(1); } } /** * Construct <code>FileInput</code> object given a file name. */ public FileInput(final FileInputStream fileStream) { super(fileStream); } } And its implementation: private void loadFamilyTree() { out.print("Enter file name: "); String fileName = in.nextLine(); FileInput input = new FileInput(fileName); family.load(input); input.close(); }

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  • How to use AOP to intercept a method call in super on an argument?

    - by hleinone
    I'm extending a class and overriding a method. All I want to do is to call super, but with a modified argument that gets intercepted upon one of its methods is called. An example makes it more clear: // Foo is an interface and also this method is part of an interface @Override public void foo(Foo foo) { // I want to intercept the call to foo.bar() in super super.foo(foo); } I'd rather use a tool that doesn't require a compiler of its own. What would be the optimal one?

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  • Should my DAOs (Database Entities) Directly match my UI Objects?

    - by scarpacci
    I am trying to figure out best practice for N-Tier application design. When designing the objects my UI needs and those that will be persisted in the DB some of my colleagues are suggesting that the objects be one in the same. This doesn't not feel right to me and I am ultimately looking for some best practice documentation to help me in this decision. I honestly do not understand why I would want to design this way given that other applications may want to interact with my Data Access Layer....or it is just ignorance or lack of understanding on my part. Any documentation, information you could provide would be greatly appreciated. Just want to better understand these concepts and I am having a hard time finding some good information on the best practice for implementing these patterns (Or it is right in front of me on what I found and I didn't understand what was being outlined). Thanks, S

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  • Correct way to manage multiple h:inputText?

    - by Mirco Attocchi
    I've an h:dataTable to display my item information (in my case a customer support request) and for each row I'd like to put an h:inputText and h:commandButton to add a comment to the desired item. I've no problem with action, but my question is about the correct way to manage many h:inputText and related value on backbean. I'm not sure that is correct to make all h:inputText set the value to the same backbean property. Any suggestions? Thanks all.

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  • Aggregation, Association and Composition (examples of code given)

    - by Bukocen
    I have such a simple example: public class Order { private ArrayList<Product> orders = new ArrayList<Product>(); public void add(Product p) { orders.add(p); } } Is it aggregation or composition? I guess it's composition, because orders will be delated after delete of Order, right? Unfortunately it was a task and answer was different;/ Do you know why? second problem: public class Client extends Person { String adress = ""; Orders orders = new Orders(); public Client(String n, String sn) { name = n; surName = sn; } public String getAddress() { return adress; } public Orders getOrders() { return this.orders; } } Is it Association between Client and Orders? My teacher told me that this is association, but I was wondering why it's not a aggregation/composition - he told me that aggregation or composition occur only when one class contains few instances of different class - is that right? I guess not, because e.g. car contains ONE wheel and it's aggregation I guess? What type of relation is that and why? Greetings

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  • Is it a good practice to have trim in setter?

    - by zibi
    I'm doing a code review and I noticed such a code: @Entity @Table(name = "SOME_TABLE") public class SomeReportClass { @Column(name = "REPORT_NUMBER", length = 6, nullable = false) private String reportNumber; ..... public String getReportNumber() { return reportNumber; } public void setReportNumber(String reportNumber) { this.reportNumber = StringUtils.trimToNull(reportNumber); } } Every time I see trimming inside of a setter I feel that its not the clearest solution - what is the general practice with that issue?

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  • Generation of abstract class with JCodeModel

    - by SadJokerBY
    I'm trying to generate top-level abstract class with JCodeModel library, but I can't find any way to change class modifiers. It's possible for nested classes (JDefinedClass API provides methods that get modifiers as parameters). But for creation of top level classes I found only JCodeModel API methods that get fully qualified name with or without ClassType (class/interface/annotation/enum) as parameters. Does anybody can suggest me how to change modifiers of JDefinedClass to make it abstract?

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  • How to use CellRenderer for GregorianCalendar?

    - by HansDampf
    So I have been trying to use the example from Tutorial and change it so it fits my program. The getColumnValue method returns the object that holds the information that is supposed to be displayed. Is this the way to go or should it rather return the actual String to be displayed. I guess not because that way I would mix the presentation with the data, which I was trying to avoid. public class IssueTableFormat implements TableFormat<Appointment> { public int getColumnCount() { return 6; } public String getColumnName(int column) { if(column == 0) return "Datum"; else if(column == 1) return "Uhrzeit"; else if(column == 2) return "Nummer"; else if(column == 3) return "Name"; else if(column == 4) return "letzte Aktion"; else if(column == 5) return "Kommentar"; throw new IllegalStateException(); } public Object getColumnValue(Appointment issue, int column) { if(column == 0) return issue.getDate(); else if(column == 1) return issue.getDate(); else if(column == 2) return issue.getSample(); else if(column == 3) return issue.getSample(); else if(column == 4) return issue.getHistory(); else if(column == 5) return issue.getComment(); throw new IllegalStateException(); } } The column 0 and 1 contain a GregorianCalendar object, but I want column 0 to show the date and 1 to show the time. So I know using cellRenderers can help here. This is what I tried. public class DateRenderer extends DefaultTableCellRenderer { public DateRenderer() { super(); } public void setValue(Object value) { GregorianCalendar g =(GregorianCalendar) value; value=g.get(GregorianCalendar.HOUR); } } But the cell doesnt show anything, what is wrong here?

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  • What is corresponding Cron expression to fire in every X seconds, where X > 60?

    - by giolekva
    I want my jobs to execute in every X seconds, there's one to one matching between job and X. Also during runtime there can be registered new jobs with their own intervals. I've tried to write cron expression for such scenarios, but in documentation there's written that value of seconds can't be more than 69. So cron expression like this: "0/63 * * * * ?" isn't valid. At first sight solution of that problem seemed to be expression like this: "0/3 0/1 * * * ?", but it means completely different thing: trigger job in every three second of every minute. Can you suggest what is the right solution (cron expression) for that? I know I could use just simple timers, but I've to use cron jobs using Quartz.

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  • Suggestion To Stackoverflow [closed]

    - by Eddy Freeman
    Hello Stackoverflow Team, This is just a suggestion to you. In the first place i must say that you guys are doing a great job. I suggest that you build into the forum system a mail notifier(to notify users whenever there is a move/deletion of a post with the reason of the move/deletion) so that whenever you move or removed someone's post then he can be notified about the move, so that we don't spend time looking for posts that are removed. I think by so doing the number of duplicate posts and mistakes from users can be minimized. The reason is i spent hours searching through the posts to locate my posts that you have re/moved. That is why i was a little bit upset. Sorry if here is the wrong place to post my suggestion. Point me to the right place. Thanks for your work.

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  • Do running times match with O(nlogn)?

    - by user472221
    Hi I have written a class(greedy strategy) that at first i used sort method which has O(nlogn) Collections.sort(array, new SortingObjectsWithProbabilityField()); and then i used the insert method of binary search tree which takes O(h) and h here is the tree height. for different n ,the running time will be : n,running time 17,515428 33,783340 65,540572 129,1285080 257,2052216 513,4299709 which I think is not correct because for increasing n , the running time should almost increase. This method will take the running time: Exponent = -1; for(int n = 2;n<1000;n+=Math.pow(2,exponent){ for (int j = 1; j <= 3; j++) { Random rand = new Random(); for (int i = 0; i < n; i++) { Element e = new Element(rand.nextInt(100) + 1, rand.nextInt(100) + 1, 0); for (int k = 0; k < i; k++) { if (e.getDigit() == randList.get(k).getDigit()) { e.setDigit(e.getDigit() + 1); } } randList.add(e); } double sum = 0.0; for (int i = 0; i < randList.size(); i++) { sum += randList.get(i).getProbability(); } for (Element i : randList) { i.setProbability(i.getProbability() / sum); } //Get time. long t2 = System.nanoTime(); GreedyVersion greedy = new GreedyVersion((ArrayList<Element>) randList); long t3 = System.nanoTime(); timeForGreedy = timeForGreedy + t3 - t2; } System.out.println(n + "," + "," + timeForGreedy/3 ); exponent++; } thanks

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  • Unusual "static" method declaration

    - by Jason
    public class Card { public enum Rank { DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT, NINE, TEN, JACK, QUEEN, KING, ACE } public enum Suit { CLUBS, DIAMONDS, HEARTS, SPADES } private final Rank rank; private final Suit suit; private Card(Rank rank, Suit suit) { this.rank = rank; this.suit = suit; } public Rank rank() { return rank; } public Suit suit() { return suit; } public String toString() { return rank + " of " + suit; } private static final List<Card> protoDeck = new ArrayList<Card>(); // Initialize prototype deck **static** { for (Suit suit : Suit.values()) for (Rank rank : Rank.values()) protoDeck.add(new Card(rank, suit)); } public static ArrayList<Card> newDeck() { return new ArrayList<Card>(protoDeck); // Return copy of prototype deck } } I have a quick question. The code block that starts right after the static keyword declaration, what type of method is that ? I haven't ever seen that before. If anyone could enlighten me, that would be greatly appreciated. Thanks.

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  • Android app using 2.x APIs that will also run on 1.x

    - by Adam Haile
    I'm working on an Android app in which I would like to use multi-touch. However, I do not want to completely leave out those still running a 1.x OS phone. How do you program the app so that you can use the 2.x multi-touch APIs (or any other higher level API for that matter) and still allow it to gracefully degrade on 1.x systems. If you create a project in Eclipse for 1.x can you even still access the 2.x APIs? Basically I want it to show up in the marketplace and work on all 1.6 and higher phones and just allow access to the higher level functionality if available. Also, if anyone can point me to any data on the number of 1.x devices vs. 2.x devices in use, it would be greatly appreciated.

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  • Refactoring a complicated if-condition

    - by kumar kasimala
    Hi all, Can anyone suggest best way to avoid most if conditions? I have below code, I want avoid most of cases if conditions, how to do it ? any solution is great help; if (adjustment.adjustmentAccount.isIncrease) { if (adjustment.increaseVATLine) { if (adjustment.vatItem.isSalesType) { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } else { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } } else { if (adjustment.vatItem.isSalesType) { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } else { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } } } else { if (adjustment.increaseVATLine) { if (adjustment.vatItem.isSalesType) { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } else { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } } else { if (adjustment.vatItem.isSalesType) { entry2.setDebit(adjustment.total); entry2.setCredit(0d); } else { entry2.setCredit(adjustment.total); entry2.setDebit(0d); } } }

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