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  • Are hashCodes unique for Strings?

    - by Batty
    Recently, I came across a piece of code, where Map<Integer, String> is used, where Integer(key) is hashCode of some string and String value corresponding to that. Is this right thing to do? Because now, equals will not be called for the String when calling get. (get is also done using hashCode() method on String object. Or, hashCode(s) are unique for unique Strings? I checked equals od String class. There is logic written for that. I am confused.

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  • Are Interfaces "Object"?

    - by PrashantGupta
    package inheritance; class A{ public String display(){ return "This is A!"; } } interface Workable{ public String work(); } class B extends A implements Workable{ public String work(){ return "B is working!"; } } public class TestInterfaceObject{ public static void main(String... args){ B obj=new B(); Workable w=obj; //System.out.println(w.work()); //invoking work method on Workable type reference System.out.println(w.display()); //invoking display method on Workable type reference //System.out.println(w.hashCode()); // invoking Object's hashCode method on Workable type reference } } As we know that methods which can be invoked depend upon the type of the reference variable on which we are going to invoke. Here, in the code, work() method was invoked on "w" reference (which is Workable type) so method invoking will compile successfully. Then, display() method is invoked on "w" which yields a compilation error which says display method was not found, quite obvious as Workable doesn't know about it. Then we try to invoke the Object class's method i.e. hashCode() which yields a successful compilation and execution. How is it possible? Any logical explanation?

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  • JDBC delete statement with multiple columns

    - by user1643033
    It says I ended this statement wrong when if I input it into sql plus with just the addition of ; it works perfectly. What am I doing wrong? Statement statement = connection.createStatement(); statement.executeUpdate("delete from aplbuk MODEL = '"+ textField_4.getText() + "'AND year = '" + textField_1.getText() + "' AND Litres = '" + textField_2.getText() + "' AND ENGINE_TYPE = '" + textField_3.getText() + "'"); statement.close();

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  • Enumerate all k-partitions of 1d array with N elements?

    - by user301217
    This seems like a simple request, but google is not my friend because "partition" scores a bunch of hits in database and filesystem space. I need to enumerate all partitions of an array of N values (N is constant) into k sub-arrays. The sub-arrays are just that - a starting index and ending index. The overall order of the original array will be preserved. For example, with N=4 and k=2: [ | a b c d ] (0, 4) [ a | b c d ] (1, 3) [ a b | c d ] (2, 2) [ a b c | d ] (3, 1) [ a b c d | ] (4, 0) I'm pretty sure this isn't an original problem (and no, it's not homework), but I'd like to do it for every k <= N, and it'd be great if the later passes (as k grows) took advantage of earlier results. If you've got a link, please share.

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  • Traversing ORM relationships returns duplicate results

    - by NKing253
    I have 4 tables -- store, catalog_galleries, catalog_images, and catalog_financials. When I traverse the relationship from store --> catalog_galleries --> catalog_images in other words: store.getCatalogGallery().getCatalogImages() I get duplicate records. Does anyone know what could be the cause of this? Any suggestions on where to look? The store table has a OneToOne relationship with catalog_galleries which in turn has a OneToMany relationship with catalog_images and an eager fetch type. The store table also has a OneToMany relationship with catalog_financials.

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  • Solr authentication possible? (or apache port authentication would also work)

    - by Camran
    Currently anybody can access the solr admin page by going to my_ip:8983/solr I can't have it like that, so how can I make it prompt for password or something? I have setup my servers apache2.conf file to prompt for password whenever my site is accessed by www.mydomain.com. But when using another port, the "require password" wont show up. Any ideas how to secure this? Don't point me to the SolrSecurity wiki because it's simply too outdated. I have tried it without luck. Thanks

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  • programming help

    - by user208639
    class Person holds personal data Its constructor receives 3 parameters, two Strings representing first and last names and an int representing age public Person(String firstName, String lastName, int age) { its method getName has no parameters and returns a String with format "Lastname, Firstname" its method getAge takes no parameters and returns an int representing the current age its method birthday increases age value by 1 and returns the new age value Create the class Person and paste the whole class into the textbox below public class Person { public Person(String first, String last, int age) { getName = "Lastname, Firstname"; System.out.print(last + first); getAge = age + 1; return getAge; System.out.print(getAge); birthday = age + 1; newAge = birthday; return newAge; } } im getting errors such as "cannot find symbol - variable getName" but when i declare a variable it still not working, i also wanted to ask if i am heading in the right direction or is it all totally wrong? im using a program called BlueJ to work on.

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  • How do I create new variables based on the size of a List?

    - by GK
    I have a List with say size n, and i have to dynamically create n variables ie i want to dynamically create the variables depending upon the size of the list. How can i achieve this? Say i have List as List year with n elements in it; then i have to create the n Integer variables from the above list. thanks.

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  • getting panel color

    - by user161004
    I have a program where i have a button to change the background color to red and another button to set back the default panel color. How do i get back the default color for panel??

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  • How can I add to List<? extends Number> data structures?

    - by kunjaan
    I have a List which is declared like this : List<? extends Number> foo3 = new ArrayList<Integer>(); I tried to add 3 to foo3. However I get an error message like this: The method add(capture#1-of ? extends Number) in the type List<capture#1-of ? extends Number> is not applicable for the arguments (ExtendsNumber)

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  • Calendar add() vs roll() when do we use it?

    - by Pentium10
    I know add() adds the specified (signed) amount of time to the given time field, based on the calendar's rules. And roll() adds the specified (signed) single unit of time on the given time field without changing larger fields. I can't think of an everyday usage of roll() I would do everything by add(). Can you help me out with examples when do we use roll() and when add()?

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  • Column moved [finished] event in JTable

    - by chown
    How should I detect that column moved action is finished in JTable? I've added columnModeListener to my column model but the problem is columnMoved method is called every time a column moves (by certain pixels). I don't want this behavior. I just want to detect when the column dragging is finished. columnModel.addColumnModelListener(new TableColumnModelListener() { public void columnAdded(TableColumnModelEvent e) { } public void columnRemoved(TableColumnModelEvent e) { } public void columnMoved(TableColumnModelEvent e) { //this is called so many times //I don't want this, but something like column moved finished event System.out.println("Moved "+e.getFromIndex()+", "+e.getToIndex()); } public void columnMarginChanged(ChangeEvent e) { } public void columnSelectionChanged(ListSelectionEvent e) { } }); I hope it is clear what I'm looking for. Thanks.

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  • gmail app 504 server timeout

    - by Hui
    this is the part of code I use for getting info from gmail, it's working alright on my localhost, but somehow when i deploy it online, I got 504 gateway timeout error. Did I missed something in my code? can someone give some advices , thanks a lot public class GetGmail { static String last = null; public static ArrayList run(String username, String password, String lastloggin)throws Exception { ArrayList result = null; System.out.println("Getting Gmail......"); last = lastloggin; Properties props = System.getProperties(); props.setProperty("mail.store.protocol", "imaps"); try { Session session = Session.getDefaultInstance(props, null); Store store = session.getStore("imaps"); store.connect("imap.googlemail.com", username, password); result = readMessage(store); store.close(); } catch (NoSuchProviderException e) { e.printStackTrace(); return null; } catch (MessagingException e) { e.printStackTrace(); return null; } return result; } }

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  • String[] initialized by null???

    - by Esmond
    Hi i encountered this problem whereby when i initialized my String[], there seems to be a null in the String[] before i do anything. How do i initialized the String[] to be completely empty,i.e. without the null at the start? The output for the following code is: nullABC nullABC nullABC nullABC nullABC public static void main(String[] args){ String[] inputArr = new String[5]; for (int i = 0; i< inputArr.length; i++){ inputArr[i] += "ABC"; } for (int i = 0; i< inputArr.length; i++){ System.out.println(inputArr[i]); } } }

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  • 1:M relationship in Hibernate and cascading operations

    - by EugeneP
    Table SUBCOURSE references COURSE COURSE(id, name) SUBCOURSE(id, course_id, name) So, 1:M. Hibernate generates for Course: @OneToMany(fetch = FetchType.LAZY, mappedBy = "course", cascade = CascadeType.ALL) public Set getSubCourses() { return this.subCourses; } for Subcourse it generates @ManyToOne(fetch = FetchType.LAZY) @JoinColumn(name = "course_id", nullable = false) public Course getCourse() { return this.course; } Now the problem is that cascading does not work as expected. I want to create a collection of SubCourse objects (Set), fill it and then bind it to setSubCourses() of Course object. Though, having ManyToOne thing in a Subcourses table, I need to manually setCourse() before adding to collection on each object. If I do not do so, an exception is raised. What can you recommend me?

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  • What happens if we load already loaded class again?

    - by GK
    I mean we have a class which is already loaded in JVM. and in some other method we are unknowingly trying to load that same class, So in this situation what happens? ie will there be any error or exception saying its already loaded. If not, then is it possible that we can have modified class with some extra features and load it whenever it is required that is Hot Deployment.

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  • How do I compare a string in an array to a string?

    - by user1641312
    EDIT: IT'S FIXED, THANKS FOR THE HELP! So basically I have an array of strings, a question and an answer public static String[][] triviaData = { {"Question2", "Answer1"}, {"Question2", "Answer2"}, {"Question3", "Answer3"}, }; And I am trying to make a method that validates an entered input, lets call the entered input enteredAnswer. enteredAnswer is stored as a String. I am trying to validate that the enteredAnswer is the same as the second index of the array. if (enteredAnswer.equalsIgnoreCase(triviaData[Config.CurrentQuestion][1])) { This is the code I tried, but I get the error "Cannot invoke equalsIgnoreCase(String) on the array type String[]" I am a beginner programmer so if you could help me out it would be highly appreciated. Thanks. enteredAnswer is stored as public String[] enteredAnswer;

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