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  • singleton pattern in java- lazy Intialization

    - by flash
    public static MySingleton getInstance() { if (_instance==null) { synchronized (MySingleton.class) { _instance = new MySingleton(); } } return _instance; } 1.is there a flaw with the above implementation of the getInstance method? 2.What is the difference between the two implementations.? public static synchronized MySingleton getInstance() { if (_instance==null) { _instance = new MySingleton(); } return _instance; } I have seen a lot of answers on the singleton pattern in stackoverflow but the question I have posted is to know mainly difference of 'synchronize' at method and block level in this particular case.

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  • [Processing/Java]Visibility/Layering Issue

    - by nnash
    I'm working on a small sketch in processing where I am making a "clock" using the time functions and drawing ellipses across the canvas based on milliseconds, seconds and minutes. I'm using a for loop to draw all of the ellipses and each for loop is inside its own method. I'm calling each of these methods in the draw function. However for some reason only the first method that is called is being drawn, when ideally I would like to have them all being visibly rendered. //setup program void setup() { size(800, 600); frameRate(30); background(#eeeeee); smooth(); } void draw(){ milliParticles(); secParticles(); minParticles(); } //time based particles void milliParticles(){ for(int i = int(millis()); i >= 0; i++) { ellipse(random(800), random(600), 5, 5 ); fill(255); } } void secParticles() { for(int i = int(second()); i >= 0; i++) { fill(0); ellipse(random(800), random(600), 10, 10 ); background(#eeeeee); } } void minParticles(){ for(int i = int(minute()); i >= 0; i++) { fill(50); ellipse(random(800), random(600), 20, 20 ); } }

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  • Sequence of the Events in Java

    - by ozlegolas
    Hi, I have two events for two seperate components, but there is a problem. JTabbedPane's stateChanged event is fired before JFormattedField's focusLost event. Is there a way of making stateChange event to be fired after focusLost event. Thanks, Tuna

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  • Java using generics with lists and interfaces

    - by MirroredFate
    Ok, so here is my problem: I have a list containing interfaces - List<Interface> a - and a list of interfaces that extend that interface: List<SubInterface> b. I want to set a = b. I do not wish to use addAll() or anything that will cost more memory as what I am doing is already very cost-intensive. I literally need to be able to say a = b. I have tried List<? extends Interface> a, but then I cannot add Interfaces to the list a, only the SubInterfaces. Any suggestions? EDIT I want to be able to do something like this: List<SubRecord> records = new ArrayList<SubRecord>(); //add things to records recordKeeper.myList = records; The class RecordKeeper is the one that contains the list of Interfaces (NOT subInterfaces) public class RecordKeeper{ public List<Record> myList; }

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  • List files starting with a specific name using java

    - by user3610075
    i want to list files starting with a name like "Report" from a folder. i found this in google to list all files but i don't how to list file starting with a name. Thank you File directory = new File("C:\\Users\\kiki\\Downloads"); File[] files = directory.listFiles(); for (int index = 0; index < files.length; index++) { //Print out the name of files in the directory System.out.println(files[index].toString()); }

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  • Need help with java map and javabean

    - by techoverflow
    Hi folks, I have a nested map: Map<Integer, Map<Integer, Double>> areaPrices = new HashMap<Integer, Map<Integer, Double>>(); and this map is populated using the code: while(oResult.next()) { Integer areaCode = new Integer(oResult.getString("AREA_CODE")); Map<Integer, Double> zonePrices = areaPrices.get(areaCode); if(zonePrices==null) { zonePrices = new HashMap<Integer, Double>(); areaPrices.put(areaCode, zonePrices); } Integer zoneCode = new Integer(oResult.getString("ZONE_CODE")); Double value = new Double(oResult.getString("ZONE_VALUE")); zonePrices.put(zoneCode, value); myBean.setZoneValues(areaPrices); } I want to use the value of this Map in another method of the same class. For that I have a bean. How do I populate it on the bean, so that I can get the ZONE_VALUE in this other method In my bean I added one new field as: private Map<Integer, Map<Integer, Double>> zoneValues; with getter and setter as: public Map<Integer, Map<Integer, Double>> getZoneValues() { return zoneValues; } public void setZoneValues(Map<Integer, Map<Integer, Double>> areaPrices) { this.zoneValues = areaPrices; } What I am looking for to do in the other method is something like this: Double value = myBean.get(areaCode).get(zoneCode); How do I make it happen :(

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  • [java] run 2 threads simultaneously

    - by lamsaitat
    hi all, in the case of an IM client. i have made 2 separate threads to handle sending packets (by std io) and receiving packets. the question is how to make these 2 threads run simultaneously so that i can keep prompting for input while at the same time be ready to receive packets at any time? i have already tried setting a timer but the data is always lost receiving.

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  • How to tell if there is an available thread in a thread pool in java

    - by Gormcito
    I am trying to proccess a queue of tasks from a database table as fast as possible while also limiting the number of threads to process the tasks. I am using a fixed sized thread pool with Executors.newFixedThreadPool(N); I want to know if there is a way of knowing if the thread pool is full, by that I mean are there currently 50 threads running, if so then I'll wait for a thread to be available before starting a new one instead of sleeping the main thread. Code of what I would like to do: ExecutorService executor = Executors.newFixedThreadPool(N); ResultSet results; while( true ) { results = getWaitingTasksStmt.executeQuery(); while( results.next() && executor.notFull() ) { executor.submit( new thread( new runnableInheritedClass(results) ) ); } }

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  • Parsing query strings in Java

    - by Will
    J2EE has ServletRequest.getParameterValues(). On non-EE platforms, URL.getQuery() simply returns a string. What's the normal way to properly parse the query string in a URL when not on J2EE?

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  • java/swing: font size selection + rendering

    - by Jason S
    I want to create and fill/stroke a path that consists of an outer boundary which is a square of side d and an inner boundary that is the outline of any of the capital letters. How can I do this? (challenges = creating a mask from a font, and figuring out the right size/position to use)

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  • Constructors from extended class in Java

    - by Crystal
    I'm having some trouble with a hw assignment. In one assignment, we had to create a Person class. Mine was: public class Person { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName) { this.firstName = firstName; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public boolean equals(Object otherObject) { // a quick test to see if the objects are identical if (this == otherObject) { return true; } // must return false if the explicit parameter is null if (otherObject == null) { return false; } if (!(otherObject instanceof Person)) { return false; } Person other = (Person) otherObject; return firstName.equals(other.firstName) && lastName.equals(other.lastName) && telephone.equals(other.telephone) && email.equals(other.email); } public int hashCode() { return 7 * firstName.hashCode() + 11 * lastName.hashCode() + 13 * telephone.hashCode() + 15 * email.hashCode(); } public String toString() { return getClass().getName() + "[firstName = " + firstName + '\n' + "lastName = " + lastName + '\n' + "telephone = " + telephone + '\n' + "email = " + email + "]"; } } Now we have to extend that class and use that class in our constructor. The function protoype is: public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax, double interestRate, CAR_LOAN_TERMS length) I'm confused on how I use the Person constructor from the superclass. I cannot necessarily do super(client); in my constructor which is what the book did with some primitive types in their example. Not sure what the correct thing to do is... Any thoughts? Thanks!

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  • JAVA setlayout(null)

    - by niv zatl
    I use setLayout (null) and I'm trying to place the buttons and textfield places I know by x, y The problem when I run the program no matter what software (Eclipse, bluej) I need to run on the panel with the mouse until I stand on the position of the button and I can see it. When I find the textfield, it is small and only when I start writing it became the size I set it Does anyone know how to solve it?

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  • Example applications and benefits of using "C" , "C++" or "Java"

    - by Waltzy
    Ok, I'm revising for my upcoming year 2 exams on a CS course and its likely something like this will come up. my question is what is an ideal application that would especially benefit from the program features of each of the three languages? I have a vague idea but getting a second opinion could really help. JavaPortability, easy - good for GUIs. C++Fast but may requite significant changes in order to be moved from system to system, good for image processing. CI'm unsure here small embedded applications? Some clarification on this would be really appreciated, thanks again StackOverflow

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  • Initialize an object in java

    - by harigm
    Is it the right Way we initialise the the object? I have a class Sample I want to initialise the Object in my Sample1 Class After intialisation I dont require to use the object of Sample Class. In that Case Can I initialise that object as new Sample(); instead of Sample s = new Sample(); if I am not going to use s anywhere in my Sample1 Class My question, is this a good practice to do that? will there be any after affects

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  • Catching TransactionRolledbackLocalException in Java

    - by user271858
    I receive javax.ejb.TransactionRolledbackLocalException in Websphere 7 from the container and I wonder how is it possible to catch this exception? I have a timeout set in Websphere and get this message after this time. I run session beans. I am trying to find what SQl statement was the cause of this exception. Where can i find that?

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  • scope of variables java

    - by qxc
    Is a variable inside the main, a public variable? public static void main(String[] args) { ......... for(int i=0;i<threads.length;i++) try { threads[i].join(); } catch (InterruptedException e) { e.printStackTrace(); } long time=0; .... } i and time are they both public variables? Of course if my reasoning is correct, also any variable belonging to a public method should be considered public.. am i right? Thanks

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  • Create a java executable with Eclipse

    - by Micah
    This is a totally newbie question. I'm running Eclipse on Ubuntu. I created a test project that I want to compile to an executable (whataver the linux equivalent is of a Windows .exe file). Here's the contents of my program: public class MyTest { public static void main(String[] args) { System.out.println("You passed in: " + args[0]); } } I want to know how to compile it and then how to execute it from the command line. Thanks!

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  • Java: GatheringByteChannel advantages?

    - by Jason S
    I'm wondering when the GatheringByteChannel's write methods (taking in an array of ByteBuffers) have advantages over the "regular" WritableByteChannel write methods. I tried a test where I could use the regular vs. the gathering write method on a FileChannel, with approx 400KB/sec total in ByteBuffers of between 23-27 bytes in length in both cases. Gathering writes used an array of 64. The regular method used up approx 12% of my CPU, and the gathering method used up approx 16% of my CPU (worse than the regular method!) This tells me it's NOT useful to use gathering writes on a FileChannel around this range of operating parameters. Why would this be the case, and when would you ever use GatheringByteChannel? (on network I/O?) Relevant differences here: public void log(Queue<Packet> packets) throws IOException { if (this.gather) { int Nbuf = 64; ByteBuffer[] bbufs = new ByteBuffer[Nbuf]; int i = 0; Packet p; while ((p = packets.poll()) != null) { bbufs[i++] = p.getBuffer(); if (i == Nbuf) { this.fc.write(bbufs); i = 0; } } if (i > 0) { this.fc.write(bbufs, 0, i); } } else { Packet p; while ((p = packets.poll()) != null) { this.fc.write(p.getBuffer()); } } }

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  • Open a new panel via a button Java Swing

    - by abuteau
    I saw a lot of post on StackOverflow relating to this, but unable to solve my problem. I want to open a new Panel by clicking a button. Here is how i try to do it parameterButton = new JButton("Parametres"); parameterButton.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ createParameterPanel = new DisplayParameterPanel(); createParameterPanel.setVisible(true); add(createParameterPanel); }; }); add(parameterButton); When I click the parameterButton it doesn't open. How can I open a new panel. Thanks,

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