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  • Should I use a modified singleton design pattern that only allows one reference to its instance?

    - by Graham
    Hi, I have a class that would normally just generate factory objects, however this class should only used once throughout the program in once specifix place. What is the best design pattern to use in this instance? I throught that having a modified singleton design which only allows one reference to instance throughout the program would be the correct way to go. So only the first call to getInstance() returns the factory library. Is this a good or bad idea? Have I missed out another fundermental design pattern for solving this problem? Thanks for your help.

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  • What to do when ServerSocket throws IOException

    - by s5804
    Basically I want to create a rock solid server. while (keepRunning.get()) { try { Socket clientSocket = serverSocket.accept(); ... spawn a new thread to handle the client ... } catch (IOException e) { e.printStackTrace(); // NOW WHAT? } } In the IOException block, what to do? Is the Server socket at fault so it need to be recreated? For example wait a few seconds and then serverSocket = ServerSocketFactory.getDefault().createServerSocket(MY_PORT); However if the server socket is still OK, then it is a pity to close it and kill all previously accepted connections that are still communicating.

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  • toString() Method question

    - by cdominguez13
    I've been working on this assignemnt here's code: public class Student { private String fname; private String lname; private String studentId; private double gpa; public Student(String studentFname,String studentLname,String stuId,double studentGpa) { fname = studentFname; lname = studentLname; studentId = stuId; gpa = studentGpa; } public double getGpa() { return gpa; } public String getStudentId() { return studentId; } public String getName() { return lname + ", " + fname; } public void setGpa(double gpaReplacement) { if (gpaReplacement >= 0.0 && gpaReplacement <= 4.0) gpa = gpaReplacement; else System.out.println("Invalid GPA! Please try again."); System.exit(0); } } Now I need to create a toString() method that returns a String formatted something like this: Name: Wilson, Mary Ann ID number: 12345 GPA: 3.5

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  • Why is my quick sort so slow?

    - by user513075
    Hello, I am practicing writing sorting algorithms as part of some interview preparation, and I am wondering if anybody can help me spot why this quick sort is not very fast? It appears to have the correct runtime complexity, but it is slower than my merge sort by a constant factor of about 2. I would also appreciate any comments that would improve my code that don't necessarily answer the question. Thanks a lot for your help! Please don't hesitate to let me know if I have made any etiquette mistakes. This is my first question here. private class QuickSort implements Sort { @Override public int[] sortItems(int[] ts) { List<Integer> toSort = new ArrayList<Integer>(); for (int i : ts) { toSort.add(i); } toSort = partition(toSort); int[] ret = new int[ts.length]; for (int i = 0; i < toSort.size(); i++) { ret[i] = toSort.get(i); } return ret; } private List<Integer> partition(List<Integer> toSort) { if (toSort.size() <= 1) return toSort; int pivotIndex = myRandom.nextInt(toSort.size()); Integer pivot = toSort.get(pivotIndex); toSort.remove(pivotIndex); List<Integer> left = new ArrayList<Integer>(); List<Integer> right = new ArrayList<Integer>(); for (int i : toSort) { if (i > pivot) right.add(i); else left.add(i); } left = partition(left); right = partition(right); left.add(pivot); left.addAll(right); return left; } }

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  • Playing Ogg Sound in Android

    - by baba tenor
    In my application, I am trying to play a sound file in ogg format, stored in raw folder in res directory of my application. When I press the button that calls below function, it just freezes with the button pressed and does not respond. In the end, I have to terminate the application from Eclipse. Nothing about an error or exception in Logcat. In debugging mode, it enters create function and never comes back. What am I doing wrong? private void playbeep() { mPlayer = MediaPlayer.create(this, R.raw.beep); mPlayer.start(); mPlayer.release(); }

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  • How to collect and inject all beans of a given type in Spring XML configuration

    - by GrzegorzOledzki
    One of the strongest accents of the Spring framework is the Dependency Injection concept. I understand one of the advices behind that is to separate general high-level mechanism from low-level details (as announced by Dependency Inversion Principle). Technically, that boils down to having a bean implementation to know as little as possible about a bean being injected as a dependency, e.g. public class PrintOutBean { private LogicBean logicBean; public void action() { System.out.println(logicBean.humanReadableDetails()); } //... } <bean class="PrintOutBean"> <property name="loginBean" ref="ShoppingCartBean"/> </bean> But what if I wanted to a have a high-level mechanism operating on multiple dependent beans? public class MenuManagementBean { private Collection<Option> options; public void printOut() { for (Option option:options) { // do something for option } //... } } I know one solution would be to use @Autowired annotation in the singleton bean, that is... @Autowired private Collection<Option> options; But doesn't it violate the separation principle? Why do I have to specify what dependents to take in the very same place I use them (i.e. MenuManagementBean class in my example)? Is there a way to inject collections of beans in the XML configuration like this (without any annotation in the MMB class)? <bean class="MenuManagementBean"> <property name="options"> <xxx:autowire by-type="MyOptionImpl"/> </property> </bean>

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  • Hibernate database connection configuration

    - by Alvin
    We have 2 different server environments using the same Hibernate configuration. One server has JNDI support for datasource, but the other does not. Currently the Hibernate configuration is configured to use JNDI, which is causing problem on the server that does not support JNDI. I have also tried to put the direct JDBC configuration together with JNDI configuration into the configuration file, but it looks like hibernate always favors JNDI over direct JDBC configuration if both exist. My question is, will it be the same if both JNDI and connection_provider configuration both exists? Will Hibernate still use JNDI over connection_provider? Or is there any way to change the precedence of the database connection property? I do not have access to the server all the time, so I thought I do ask the question before my window of the sever time. Thanks in advance.

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  • Best practice for passing configuration to each GUI object

    - by Laimoncijus
    Hi, I am writing an application, where I do have few different windows implemented, where each window is a separate class. Now I need somehow to pass a single configuration object to all of them. My GUI is designed in way, where I have one main window, which may create some child windows of its own, and these child windows can have their own childs (so there is no possibility to create all windows in initialization part and feed the config object to all of them from the very beginning)... What would be best practice for sharing this configuration object between them? Always passing via constructor or maybe making it somewhere as final public static and let each window object to access it when needed? Thanks

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  • Ensuring all waiting threads complete

    - by Daniel
    I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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  • hibernate modeling relationships managed through an intermediate table

    - by shikarishambu
    I have a datamodel that has an intermediate table to manage relationships between entities. For example, tables Person and Organization are related through the Relationship table Party (table) - ID Person (table) - ID (references Party.ID) - name Organization (table) -ID (references Party.ID) -name Relationship (table) -ID (PK) -type (references relationshiptype lookup) -fromID (references Party.ID) -ToID (references Party.ID) -fromDate -ToDate Type+fromID+ToID+fromDate+ToDate is guaranteed to be unique. How do I manage this using hibernate? TIA

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  • Unit test helper methods?

    - by Aly
    Hi, I have classes which prviously had massive methods so i subdivided the work of this method into 'helper' methods. These helper methods are declared private to enforce encapsulation - however I want to unit test the big public methods, is it good to unit test the helper methods too as if one of them fail the public method that calls it will also fail - but this way we can identify why it failed. Also in order to test these using a mock object I would need to change their visibility from private to protected, is this desirable?

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  • How can i make projects bound to eachother in eclipse?

    - by ikky
    Hi! I have 3 projects in Eclipse that are bound to eachother. With bound i mean this: Everytime i add a class in one of the projects, the other projects also updates themselves and add the class Now i want to add another project to these, but i don't know how to bind it together with the other projects. Any suggestions? Thanks in advance!

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  • not able to select hidden link - selenium

    - by Maddy
    I have to select web link when i mouse hover to particular frame in the webpage, the button(link to next page) will be visible. WebElement mainElement = driver.findElement(By.xpath(<frame xpath >)); Actions builder = new Actions(driver); builder.moveToElement(mainElement); WebElement button1 = driver.findElement(By.xpath("//*[@id='currentSkills']/div[1]/div/a")); builder.moveToElement(button1).click().perform(); I am still unable to select the particular link when i execute, the following error am getting org.openqa.selenium.ElementNotVisibleException: Element is not currently visible and so may not be interacted with (WARNING: The server did not provide any stacktrace information) Command duration or timeout: 131 milliseconds But when i hover mouse pointer to the particular frame during AUT(just to move to particular frame without clicking anything), then test is executing sucessfully. I know this can be handled by JS. But i want to find out is there any solution within selenium webdriver Your help is much appreciated... Thanks Madan

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  • hibernate annotation bi-directional mapping

    - by smithystar
    I'm building a web application using Spring framework and Hibernate with annotation and get stuck with a simple mapping between two entities. I'm trying to create a many-to-many relationship between User and Course. I followed one of the Hibernate tutorials and my implementation is as follows: User class: @Entity @Table(name="USER") public class User { private Long id; private String email; private String password; private Set<Course> courses = new HashSet<Course>(0); @Id @GeneratedValue @Column(name="USER_ID") public Long getId() { return id; } public void setId(Long id) { this.id = id; } @Column(name="USER_EMAIL") public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } @Column(name="USER_PASSWORD") public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } @ManyToMany(cascade = CascadeType.ALL) @JoinTable(name = "USER_COURSE", joinColumns = { @JoinColumn(name = "USER_ID") }, inverseJoinColumns = { @JoinColumn(name = "COURSE_ID") }) public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } } Course class: @Entity @Table(name="COURSE") public class Course { private Long id; private String name; @Id @GeneratedValue @Column(name="COURSE_ID") public Long getId() { return id; } public void setId(Long id) { this.id = id; } @Column(name="NAME") public String getName() { return name; } public void setName(String name) { this.name = name; } } The problem is that this implementation only allows me to go one way user.getCourses() What do I need to change, so I can go in both directions? user.getCourses() course.getUsers() Any help would be appreciated.

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  • Can I use Pub/Sub model with Many Publishers and Only One Subscriber?

    - by rauch
    I need to send some files from different machines to only one Server. As I understand, I can use JMS api + (for example) ActiveMQ as broker. There are two models: p2p and pub/sub. I would like to use pub/sub model, but the problem is that I haven`t few subscribers, I have only one Subscriber(Server) and many Publishers. The question is the following: can I use pub/sub model for my situation and How can I send files from different machines to Only One Topic, on that Server sibscribed? May be any other ideas, thanks a lot.

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  • Implementing clone on a LinkedList

    - by devoured elysium
    I am trying to implement a clone() method on a DoubleLinkedList. Now, the problem is that implementing it by "the convention" is a lot more troublesome than just creating a new DoubleLinkedList and filling it with all the elements of my current DoubleLinkedList. Is there any inconvenient I am not seeing when doing that? Here is my current approach: @Override public DoubleLinkedList<T> clone() { DoubleLinkedList<T> dll = new DoubleLinkedList<T>(); for (T element : dll) { dll.add(element); } return dll; } Here is what it would be by the convention: @Override public DoubleLinkedList<T> clone() { try { DoubleLinkedList<T> dll = (DoubleLinkedList<T>)super.clone(); //kinda complex code to copy elements return dll; } catch (CloneNotSupportedException e) { throw new InternalError(e.toString()); } }

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  • Double multiplied by 100 and then cast to long is giving wrong value

    - by xyz
    I have the following code: Double i=17.31; long j=(long) (i*100); System.out.println(j); O/P : 1730 //Expected:1731 Double i=17.33; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1733 Double i=17.32; long j=(long) (i*100); System.out.println(j); O/P : 1732 //Expected:1732{As expected} Double i=15.33; long j=(long) (i*100); System.out.println(j); O/P : 1533 //Expected:1533{as Expected} I have tried to Google but unable to find reason.I am sorry if the question is trivial.

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  • How Netbeans Editors know that file is not modified after undo?

    - by Ha
    Netbeans uses standart UndoManager API for implementation of undo functionality. But neither standart javax.swing.undo.UndoManager nor org.openide.awt.UndoRedo.Manager doesn't have any method to mark states as saved and check modified status. Nonetheless if you change the file and press undo, the file is marked as unmodified. How do they do that? I need the same functionality for my (non-text) editors if the Netbeans RCP application.

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  • JButtons re-enable themselves after being disabled

    - by Anarchist
    I have an array of JButtons which form a keypad interface. After six numbers are entered I want to disable the keypad so that no further numbers can be entered by the user. I have written the code and the buttons do disable until the mouse hovers above any of them, then the buttons seem to re-enable themselves and run actionEvents added to them. The full code is available here. Possible things that I think are wrong. There is some sort of MouseListener which is ignoring when I set button.setEnabled(false); I haven't separated attributes from the buildGUI(); correctly, I only did this anyway so that the inner class could access them. Possibly something to do with the gridLayout as disabling the buttons seems to work for my services JPanel buttons.

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