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  • Java Generics Type Safety warning with recursive Hashmap

    - by GC
    Hi, I'm using a recursive tree of hashmaps, specifically Hashmap map where Object is a reference to another Hashmap and so on. This will be passed around a recursive algorithm: foo(String filename, Hashmap<String, Object> map) { //some stuff here for (Entry<String, Object> entry : map.entrySet()) { //type warning that must be suppressed foo(entry.getKey(), (HashMap<String, Object>)entry.getValue()); } } I know for sure Object is of type Hashmap<String, Object> but am irritated that I have to suppress the warning using @SuppressWarnings("unchecked"). I'll be satisfied with a solution that does either a assert(/*entry.getValue() is of type HashMap<String, Object>*/) or throws an exception when it isn't. I went down the Generics route for compile type safety and if I suppress the warning then it defeats the purpose. Thank you for your comments, ksb

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  • What are some Java memory management best practices?

    - by Ascalonian
    I am taking over some applications from a previous developer. When I run the applications through Eclipse, I see the memory usage and the heap size increase a lot. Upon further investigation, I see that they were creating an object over-and-over in a loop as well as other things. I started to go through and do some clean up. But the more I went through, the more questions I had like "will this actually do anything?" For example, instead of declaring a variable outside the loop mentioned above and just setting its value in the loop... they created the object in the loop. What I mean is: for(int i=0; i < arrayOfStuff.size(); i++) { String something = (String) arrayOfStuff.get(i); ... } versus String something = null; for(int i=0; i < arrayOfStuff.size(); i++) { something = (String) arrayOfStuff.get(i); } Am I incorrect to say that the bottom loop is better? Perhaps I am wrong. Also, what about after the second loop above, I set "something" back to null? Would that clear out some memory? In either case, what are some good memory management best practices I could follow that will help keep my memory usage low in my applications? Update: I appreciate everyones feedback so far. However, I was not really asking about the above loops (although by your advice I did go back to the first loop). I am trying to get some best practices that I can keep an eye out for. Something on the lines of "when you are done using a Collection, clear it out". I just really need to make sure not as much memory is being taken up by these applications.

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  • Java servlet and UTF-8 problem

    - by Gabriele
    I have some problem with UTF-8. My client (realized in GWT) make a request to my servlet, with some parametres in the URL, as follow: http://localhost:8080/servlet?param=value When in the servlet I retrieve the URL, I have some problem with UTF-8 characters. I use this code: protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); String reqUrl = request.getRequestURL().toString(); String queryString = request.getQueryString(); System.out.println("Request: "+reqUrl + "?" + queryString); ... So, if I call this url: http://localhost:8080/servlet?param=così the result is like this: Request: http://localhost:8080/servlet?param=cos%C3%AC What can I do to set up properly the character encoding?

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  • Exception hierarchy in java

    - by Abhishek Jain
    As Error and Exception are subclass of throwable class, we can throw any error, runtime ex and other ex. Also we can catch any of these type. Why do we usually catch only checked Exception? Can somebody provide me good links for exception with examples?

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  • Using a priority queue in Java

    - by Bharat
    Forgive me if this is a tried question, but I'm having a little difficulty figuring it out. I currently have a class Node, and each 'node' is a square in a maze. I'm trying to implement the A* algorithm, so each of these nodes will have an f-cost (int) data member inside of it. I was wondering if there's a way that I can create a priority queue of these nodes, and set up the f-cost variable as the comparator? I've looked at examples online, but all I can find are String priority queues. Can I implement Comparator for the Node class? Would this allow me to access the data member stored inside it? Many Thanks!

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  • java: <identifier> expected with ArrayList

    - by A-moc
    I have a class named Storage. Storage contains an arraylist of special objects called Products. Each product contains information such as name, price, etc. My code is as follows: class Storage{ Product sprite = new Product("sprite",1.25,30); Product pepsi = new Product("pepsi",1.85,45); Product orange = new Product("orange",2.25,36); Product hershey = new Product("hershey",1.50,33); Product brownie = new Product("brownie",2.30,41); Product apple = new Product("apple",2.00,15); Product crackers = new Product("peanut",3.90,68); Product trailmix = new Product("trailmix",1.90,45); Product icecream = new Product("icecream",1.65,28); Product doughnut = new Product("doughnut",2.75,18); Product banana = new Product("banana",1.25,32); Product coffee = new Product("coffee",1.30,40); Product chips = new Product("chips",1.70,35); ArrayList<Product> arl = new ArrayList<Product>(); //add initial elements to arraylist arl.add(sprite); arl.add(pepsi); arl.add(orange); arl.add(hershey); arl.add(brownie); arl.add(apple); arl.add(peanut); arl.add(trailmix); arl.add(icecream); arl.add(doughnut); arl.add(banana); arl.add(coffee); arl.add(chips); } Whenever I compile, I get an error message on lines 141-153 stating <identifier> expected. I know it's an elementary problem, but I can't seem to figure this out. Any help is much appreciated.

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  • Java-Swing: Change getSource() in ActionListener

    - by Brandon
    I have a class that contains a JButton. This can't be changed. The problem is this: The actionListener calls getSource() and gets the JButton, not the container class. Can I change what getSource retrieves, before the actionListener is added? OR can JButtons have a variable reference to its container? I can't make a class extend a JButton. It caused bugs for drawing purposes... story of my week.

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  • Java Prepared Statement arguments!

    - by Epitaph
    I am planning to replace repeatedly executed Statement objects with PreparedStatement objects to improve performance. I am using arguments like the MySQL function now(), and string variables. Most of the PreparedStatement queries I have seen contained constant values (like 10, and strings like "New York") as arguments used for the "?" in the queries. How would I go about using functions like now(), and variables as arguments? Is it necessary to use the "?"s in the queries instead of actual values? I am quite confounded.

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  • Recursive String Function (Java)

    - by Jake Brooks
    Hi, I am trying to design a function that essentially does as follows: String s = "BLAH"; store the following to an array: blah lah bah blh bla bl ba bh ah al So basically what I did there was subtract each letter from it one at a time. Then subtract a combination of two letters at a time, until there's 2 characters remaining. Store each of these generations in an array. Hopefully this makes sense, Jake

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  • Java ArrayList<Double> IndexOutOfBoundsException Problem

    - by Sebastian Bechtel
    Hello, I've got a Problem with ArrayList. I need it to store a result. Because I want to start with element n I tryed to give the ArrayList a capacity with ensureCapacity(n+1) to use set(n,x) but I get an IndexOutOfBoundsException. I tryed to store n add(x) before the use of set and this works. So I'd like to know why it doesn't work on my way and how to solve this because put n times a add(x) isn't a good style ;-) Best regards, Sebastian

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  • Java HashSet<Integer> to int array

    - by jackweeden
    I've got a HashSet with a bunch of (you guessed it) integers in it. I want to turn it into an array, but calling hashset.toArray(); returns an array of Object type. This is fine, but is there a better way to cast it to an array of int, other than iterating through every element manually? A method I want to pass it to void doSomething(int[] arr) Won't accept the Object[] array, even if I try casting it like doSomething((int[]) hashSet.toArray());

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  • Java SQL database independence.

    - by Paul
    Hello, I have been looking for an alternative to Hibernate for various reasons. I came across Liquibase and i like the idea so i am willing to try it. Liquibase will cater for database creation/modification in a SQL independent fashion. My main question is how does my code in my application execute SQL statements without being database dependent? Is there some other project that acts like Hibernates Dialect classes? Thanks, Paul

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  • Message Driven Bean with Java Message Queue down

    - by Rafa de Castro
    I have the following problem deploying my application. It uses JMS and a remote openMQ for communication between servers. The problem is that the connection is not fully reliable so it can be up or down. For reconnecting I set the jms reconnect glassfish property so it reconnects if at some moment the connection gets lost. The problem arises when i try to deploy the application and there is no connection. It looks like it keeps retrying the connection but the application does not finish deployment until connection is available. Is it possible to configure it in any way that the deployment continues even if there is no connection and keeps retrying until there is connection available? Thanks a lot.

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  • Task queue java

    - by user268515
    Hi i'm new to Task queue concepts when i referred the guide I got struck on this line queue.add( DatastoreServiceFactory.getDatastoreService().getCurrentTransaction(), TaskOptions().url("/path/to/my/worker")); what is TaskOptions() method. Is it default method are method created manually what will TaskOptions() method will return. I created a method called TaskOption() when i to return a string value its saying error as "The method url(String) is undefined for the type String" In url what i want to specify servlet are any other. My doubt may be stupid but plz clarify it. Thank you, sharun.

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  • Bind a Java Collection to xQuery sequence from xQuery

    - by jtzero
    declare function Error:toString($this as javaObject) as xs:string external; the previous binds a return String() to xs:string. is it possible to return a collection and bind it to an xQuery Sequence, say the following declare function Error:toList($this as javaObject) as squenceType external; so that it can be run through a flwr?

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  • Permutation algorithm without recursion? Java

    - by Andreas Hornig
    Hi, I would like to get all combination of a number without any repetation. Like 0.1.2, 0.2.1, 1.2.0, 1.0.2, 2.0.1, 2.1.0. I tried to find an easy scheme but couldn't find so I drawed a graph/tree for it and this screams to use recursion. But I would like to do it without, if this is possible. So could anyone please help me how to do that? Thank you in advance, Andreas

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  • Java .split() Method To Split XML Parameters

    - by Buzz Lightyear
    I have this line from an XML document: <?xml version="1.0" encoding="UTF-8"?> <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" contentScriptType="text/ecmascript" width="1024" zoomAndPan="magnify" contentStyleType="text/css" viewBox="0 0 1024 768" height="768" preserveAspectRatio="xMidYMid meet" version="1.0"> I want to be able to split it up, using the split method. For example i want to save each parameter into a String array. So i'd like: contentScriptType="text/ecmascript" width="1024" zoomAndPan="magnify" contentStyleType="text/css" viewBox="0 0 1024 768" height="768" etc etc to be saved into a string array, is there anyway to do this using the split method, or can anybody suggest an easier, more efficient way to do this?

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  • Invoking methods on objects in java.

    - by David
    If i have a class called Dice which contains this method: public void roll () { this.x = randNum(1, this.sum.length) ; this.sum[x] ++ ; } And i am in a diferent class how do i invoke this method? I am currently trying InstanceOfObjectName.Dice.roll and its not working. What should i do?

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  • Measure heap used by each object in Java

    - by Fazal
    Can some suggest a good a free memory profiling tool which will show memory being used by each object in the heap separately. We are trying to profile our application and I used jconsole but its gives me total memory usage only. I am using Eclipse and OC4J

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  • Syntax highlight in java for android

    - by Mohit Deshpande
    I want to build an notepad-style application on android that will have syntax highlighting. But when I search around the web, I find the syntax highlighting can be done only through use of an awt class. How could I syntax highlight in maybe a custom EditText or TextView view? I know that the release of a syntax highlighter is sort of anticipated, so I want to add my syntax highlighter on the market.

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  • Implement a RSA algorithm in Java

    - by Robin Monjo
    Hello everyone. I want to implement a RSA algorithm to encrypt an image (byte[]). To generate my two keys I used this piece of code : KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA"); keygen.initialize(512); keyPair = keygen.generateKeyPair(); Once public and private key are generated, I would like to show them to the user so he can distribute the public key and use the private key to decode. How can I get back those key? Using keygen.getPrivateKey() and keygen.getPublicKey() give me all the information of the RSA algorithm, not only the keys I need. Thanks

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  • Permutatation algorithm without recursion? Java

    - by Andreas Hornig
    Hi, I would like to get all combination of a number without any repetation. Like 0.1.2, 0.2.1, 1.2.0, 1.0.2, 2.0.1, 2.1.0. I tried to find an easy scheme but couldn't find so I drawed a graph/tree for it and this screams to use recursion. But I would like to do it without, if this is possible. So could anyone please help mw how to do that? Thank you in advance, Andreas

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  • Java: how to register a listener that listen to a JFrame movement

    - by cocotwo
    How can you track the movement of a JFrame itself? I'd like to register a listener that would be called back every single time JFrame.getLocation() is going to return a new value. Here's a skeleton that compiles and runs, what kind of listener should I add so that I can track every JFrame movement on screen? import javax.swing.*; public class SO { public static void main( String[] args ) throws Exception { SwingUtilities.invokeAndWait( new Runnable() { public void run() { final JFrame jf = new JFrame(); final JPanel jp = new JPanel(); final JLabel jl = new JLabel(); updateText( jf, jl ); jp.add( jl ); jf.add( jp ); jf.pack(); jf.setVisible( true ); } } ); } private static void updateText( final JFrame jf, final JLabel jl ) { jl.setText( "JFrame is located at: " + jf.getLocation() ); jl.repaint(); } }

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