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  • Java many to many association map

    - by Raphael Jolivet
    Hi, I have to classes, ClassA and ClassB and a "many to many" AssociationClass. I want to use a structure to hold the associations between A and B such as I can know, for each instance of A or B, which are their counterparts. I thought of using a Hashmap, with pair keys: Hasmap<Pair<ClassA, ClassB>, AssociationClass> associations; This way, I can add and remove an association between two instances of ClassA and ClassB, and I can query a relation for two given instances. However, I miss the feature of getting all associations defined for a given instance of ClassA or ClassB. I could do it by brute force and loop over all keys of the map to search for associations between a given instance, but this is inefficient and not elegant. Do you know of any data structure / free library that enables this ? I don't want to reinvent the wheel. Thanks in advance for your help, Raphael NB: This is not a "database" question. These objects are pure POJO used for live computation, I don't need persistence stuff.

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  • Java paint speed relative to color model

    - by Jon
    I have a BufferedImage with an IndexColorModel. I need to paint that image onto the screen, but I've noticed that this is slow when using an IndexColorModel. However, if I run the BufferedImage through an identity affine transform it creates an image with a DirectColorModel and the painting is significantly faster. Here's the code I'm using AffineTransformOp identityOp = new AffineTransformOp(new AffineTransform(), AffineTransformOp.TYPE_BILINEAR); displayImage = identityOp.filter(displayImage, null); I have three questions 1. Why is painting the slower on an IndexColorModel? 2. Is there any way to speed up the painting of an IndexColorModel? 3. If the answer to 2. is no, is this the most efficient way to convert from an IndexColorModel to a DirectColorModel? I've noticed that this conversion is dependent on the size of the image, and I'd like to remove that dependency. Thanks for the help

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  • Multiple consecutive alerts in Java ME

    - by Casebash
    According to the documentation, Display.setCurrent doesn't work if the current displayable is an alert. Does anyone know how to work around this so that we can go from one alert to another? I am using CLDC 1.0 and MIDP 2.0. My attempt The spec does allow us to edit an alert while it is on screen, but some Nokia phones don't handle it well at all. So I am now trying to go from the alert to a canvas, then back to the alert. Of course I don't want the user to interact with the previous canvas, so it seems that I am forced to create a new blank canvas. As a sidenote, this has the slight disadvantage of looking worse on phones which still have the previous screen when an alert is shown. The bigger problem is how to transition from the blank canvas back to an alert once the canvas is loaded. Testing on the Motorola emulator revealed that showNotify is not called after returning from an alert to the previous screen. I guess I could create the next alert in the paint method, but this seems like a ugly hack.

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  • get eigenvalue pca with java

    - by Muhamad Burhanudin
    I try use PCA to reduce dimention, and i use jama for help me using matrix. but, i got problem when get eigenvalue with jama. for example i hava 2 image dimention 100x100, then i create single matrix 2 image x (100x100). there is 20.000 pixel. and how to get reduction with eigenvalue? this is sample my code : public static void main(String[] args) { BufferedImage bi; int[] rgb; int R, G, B; // int[] jum; double[][] gray = new double[500][500] ; String[] baris = new String[1000]; try { //bi = ImageIO.read(new File("D:\\c.jpg")); int[][] pixelData = new int[bi.getHeight() * bi.getWidth()][3]; int counter = 0; for (int i = 0; i < bi.getHeight(); i++) { for (int j = 0; j < bi.getWidth(); j++) { gray[i][j] = getPixelData(bi, i, j); // R = getR(bi, i, j); //G = getG(bi, i, j); //B = getB(bi, i, j); //jum = R + G + B; // gray[counter] = Double.toString(R + G + B / 3); // System.out.println("Gray " +gray); //for (int k = 0; k < rgb.length; k++) { // pixelData[counter][k] = rgb[k]; // } counter++; } } } catch (IOException e) { e.printStackTrace(); } Matrix matrix = new Matrix(gray); PCA pca = new PCA(matrix); pca.getEigenvalue(6); String n = pca.toString(); System.err.println("nilai n "+n); //double dete = pcadete(matrix,3600); } private static int getPixelData(BufferedImage bi, int x, int y) { int argb = bi.getRGB(y, x); int r, g, b; int gray; int rgb[] = new int[]{ (argb >> 16) & 0xff, //red (argb >> 8) & 0xff, //green (argb) & 0xff //blue }; r = rgb[0]; g = rgb[1]; b = rgb[2]; gray = (r + g + b) / 3; System.out.println("gray: " + gray); return gray; } when i show eigenvalue in this code : PCA pca = new PCA(matrix); pca.getEigenvalue(6); String n = pca.toString(); System.err.println("nilai n "+n); Result is : nilai n PCA@c3e9e9 Can, u tell me what way to get eigenvalue and reduction dimension.

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  • Do Websites need Local Databases Anymore?

    - by viatropos
    If there's a better place to ask this, please let me know. Every time I build a new website/blog/shopping-cart/etc., I keep trying to do the following: Extract out common functionality into reusable code (Rubygems and jQuery plugins mostly) If possible, convert that gem into a small service so I never have to deal with a database for the objects involved (by service, I mean something lean and mean, usually built with the Sinatra Web Framework with a few core models). My assumption is, if I can remove dependencies on local databases, that will make it easier and more scalable in the long run (scalable in terms of reusability and manageability, not necessarily database/performance). I'm not sure if that's a good or bad assumption yet. What do you think? I've made this assumption because of the following reason: Most serious database/model functionality has been built on the internet somewhere. Just to name a few: Social Network API: Facebook Messaging API: Twitter Mailing API: Google Event API: Eventbrite Shopping API: Shopify Comment API: Disqus Form API: Wufoo Image API: Picasa Video API: Youtube ... Each of those things are fairly complicated to build from scratch and to make as optimized, simple, and easy to use as those companies have made them. So if I build an app that shows pictures (picasa) on an Event page (eventbrite), and you can see who joined the event (facebook events), and send them emails (google apps api), and have them fill out monthly surveys (wufoo), and watch a video when they're done (youtube), all integrated into a custom, easy to use website, and I can do that without ever creating a local database, is that a good thing? I ask because there's two things missing from the puzzle that keep forcing me to create that local database: Post API RESTful/Pretty Url API While there's plenty of Blogging systems and APIs for them, there is no one place where you can just write content and have it part of some massive thing. For every app, I have to use code for creating pretty/restful urls, and that saves posts. But it seems like that should be a service! Question is, is that what the website is? ...That place to integrate the worlds services for my specific cause... and, sigh, to store posts that only my site has access to. Will everyone always need "their own blog"? Why not just have a profile and write lots of content on an established platform like StackOverflow or Facebook? ... That way I can write apps entirely without a database and know that I'm doing it right. Note: Of course at some point you'd need a database, if you were doing something unique or new. But for the case where you're just rewiring information or creating things like videos, events, and products, is it really necessary anymore??

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  • Java: why can't iterate over an iterator?

    - by noamtm
    I read http://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable and http://stackoverflow.com/questions/27240/why-arent-enumerations-iterable, but I still don't understand why this: void foo(Iterator<X> it) { for (X x : it) { bar(x); baz(x); } } was not made possible. In other words, unless I'm missing something, the above could have been nice and valid syntactic sugar for: void foo(Iterator<X> it) { for (X x; it.hasNext();) { x = it.next(); bar(x); baz(x); } }

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  • Is it possible to run Weblogic with 8gb heap size in a 64bit java/linux environment

    - by Per Arneng
    Setup: 64bit Linux 64bit SUN Jvm 1.6.0_20 Weblogic 10.3 Is it possible to run Weblogic 10.3 in this setup with a maximum heap size of 8gb? We have recived answers from oracle support that states that it might not be possible to address more than 4gb with this setup. Please submit any official links that support any statements that it is possible to run this setup with more than 4gb of heap size. We can not find any documentation of any limits of heap size when running with this setup. Thanx

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  • Java: Implement own message queue (threadsafe)

    - by derMax
    The task is to implement my own messagequeue that is thread safe. My approach: public class MessageQueue { /** * Number of strings (messages) that can be stored in the queue. */ private int capacity; /** * The queue itself, all incoming messages are stored in here. */ private Vector<String> queue = new Vector<String>(capacity); /** * Constructor, initializes the queue. * * @param capacity The number of messages allowed in the queue. */ public MessageQueue(int capacity) { this.capacity = capacity; } /** * Adds a new message to the queue. If the queue is full, it waits until a message is released. * * @param message */ public synchronized void send(String message) { //TODO check } /** * Receives a new message and removes it from the queue. * * @return */ public synchronized String receive() { //TODO check return "0"; } } If the queue is empty and I call remove(), I want to call wait() so that another thread can use the send() method. Respectively, I have to call notifyAll() after every iteration. Question: Is that possible? I mean does it work that when I say wait() in one method of an object, that I can then execute another method of the same object? And another question: Does that seem to be clever?

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  • Sorting an arraylist in Java language

    - by Computeristic
    Hi, I have an arraylist set up. I have input instuctions set up too, so that the user can enter one string, then one integer, then one string (the first name, the age, and the last name). I need to sort the arraylist by the last name. The code I have entered so far is all under the main method:- public static void main(String[] args) { Name Name[] = new Name[50]; int count = 0; for (int i=0; i<50; i++) NewName[i] = new Name(); //ADD NEW TO ARRAYLIST NAME String FName = JOptionPane.showInputDialog("first name"); int age = Integer.parseInt(JOptionPane.showInputDialog("age")); String LName = JOptionPane.showInputDialog("last name"); NewName[count] = new Name(FName, age, LName); count = count++; } //ITEMS SORT BY LAST NAME //CODE FOR SORT GOES HERE

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  • Grails or Play! for an ex-RoR developer ?

    - by Kedare
    Hello, I plan to begin learning a Java web framework (I love the Java API), I already used Rails and Django. I want something close to Java, but without all the complexity of J2EE. I've found 2 framework that could be good for me : Grails : Grails looks great, it use Groovy that is better than Java for web application (I think..), but it's slower, that use pure-java components (Hibernate, Strut, Spring), it looks pretty simple to deploy (send .war and it's ok !), the GSP is great ! It's a bit harder to debug (need to restart the server at each modification, and the stacktrace is a mix of Java and Groovy stack that is not always understandable..) Play! : This framework also looks great, it's faster than Grails (It's use directly Java), but I don't really like how it use Java, it modify the source code to transform the properties call as setXXX/getXXX, I'm not kind of that... The framework also have caching function that Grails don't (alreary) has. I don't really like the Template Engine. It's also easer to debug (no need to restart the server, and the stacktrace is clear) What do you recommend for ? I am looking for something easy to learn (I used a lot ruby and java, but a little bit java (But I love the Java API)), that is full featured (That's no a problem with all the Java Library availables, but if it's bundle and integrated I prefer), that scale and that is not too slow (faster than ruby), and if possible I would want something with a decent community to easily find support and answer to my questions ;) PS: No JRuby on Rails Thank you !

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  • Java: downloading issue using BufferedInputStream, BufferedOutputStream

    - by nkr1pt
    When downloading a rar file from the internet with the code below, the downloaded file is larger than it actually is. Not sure what causes this? bis = new BufferedInputStream(urlConn.getInputStream()); bos = new BufferedOutputStream(new FileOutputStream(outputFile)); eventBus.fireEvent(this, new DownloadStartedEvent(item)); int read; byte[] buffer = new byte[2048]; while ((read = bis.read(buffer)) != -1) { bos.write(buffer); } eventBus.fireEvent(this, new DownloadCompletedEvent(item));

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  • Loading all files in a directory in a Java applet

    - by WarrenB
    How would one go about programatically loading all the resource files in a given directory in a JAR file for an applet? The resources will probably change several times over the lifetime of the program so I don't want to hardcode names in. Normally I would just traverse the directory structure using File.list(), but I get permission issues when trying to do that within an applet. I also looked at using an enumeration with something line ClassLoader.getResources() but it only finds files of the same name within the JAR file. Essentially what I want to do is (something like) this: ClassLoader imagesURL = this.getClass().getClassLoader(); MediaTracker tracker = new MediaTracker(this); Enumeration<URL> images = imagesURL.getResources("resources/images/image*.gif"); while (images.hasMoreElements()){ tracker.add(getImage(images.nextElement(), i); i++; } I know I'm probably missing some obvious function, but I've spent hours searching through tutorials and documentation for a simple way to do this within an unsigned applet.

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  • Is this a Java DateFormat bug?

    - by anonymous
    The pattern is "dd-MM-yyyy" I think the string "01-01-2010mwwwwwwwwwwwwwww" does not satisfy the pattern, but the following code shows the contrary. Anyone can explain why? public static void main(String[] args) throws Exception { SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy"); Date date = df.parse("01-01-2010mwwwwwwwwwwwwwww"); System.out.println(date); } Thanks

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  • special debugging lines (java)

    - by David
    Recently i've found myself writing a lot of methods with what i can only think to call debugging scaffolding. Here's an example: public static void printArray (String[] array, boolean bug) { for (int i = 0; i<array.lenght; i++) { if (bug) System.out.print (i) ; //this line is what i'm calling the debugging scaffolding i guess. System.out.println(array[i]) ; } } in this method if i set bug to true, wherever its being called from maybe by some kind of user imput, then i get the special debugging text to let me know what index the string being printed as at just in case i needed to know for the sake of my debugging (pretend a state of affairs exists where its helpful). All of my questions more or less boil down to the question: is this a good idea? but with a tad bit more objectivity: Is this an effective way to test my methods and debug them? i mean effective in terms of efficiency and not messing up my code. Is it acceptable to leave the if (bug) stuff ; code in place after i've got my method up and working? (if a definition of "acceptability" is needed to make this question objective then use "is not a matter of programing controversy such as ommiting brackets in an if(boolean) with only one line after it, though if you've got something better go ahead and use your definition i won't mind) Is there a more effective way to accomplish the gole of making debugging easier than what i'm doing? Anything you know i mean to ask but that i have forgotten too (as much information as makes sense is appreciated).

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  • Control - C exception in Java

    - by Phil
    I need to catch that exception but I can't figure out which one it is. The IDE i'm using right now doesn't allow for a program interrupt that way. I know how to user try/catch, but I don't actually know what I'm trying to catch.. Can anyone help me with this?

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  • How to access struts interceptor parameters in Java?

    - by Ricardo
    I have the following code in struts.xml: <interceptor-ref name="checkTabsStack"> <param name="tabName">availability</param> </interceptor-ref> and I want to access the parameter tabName in the interceptor routine, how do i do that? i tried Map params = ActionContext.getContext().getParameters(); but params comes empty... Thanks!

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  • Java appending XML data

    - by Travis
    I've already read through a few of the answers on this site but none of them worked for me. I have an XML file like this: <root> <character> <name>Volstvok</name> <charID>(omitted)</charID> <userID>(omitted)</userID> <apiKey>(omitted)</apiKey> </character> </root> I need to add another <character> somehow. I'm trying this but it does not work: public void addCharacter(String name, int id, int userID, String apiKey){ Element newCharacter = doc.createElement("character"); Element newName = doc.createElement("name"); newName.setTextContent(name); Element newID = doc.createElement("charID"); newID.setTextContent(Integer.toString(id)); Element newUserID = doc.createElement("userID"); newUserID.setTextContent(Integer.toString(userID)); Element newApiKey = doc.createElement("apiKey"); newApiKey.setTextContent(apiKey); //Setup and write newCharacter.appendChild(newName); newCharacter.appendChild(newID); newCharacter.appendChild(newUserID); newCharacter.appendChild(newApiKey); doc.getDocumentElement().appendChild(newCharacter); }

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  • Java Swing - Problem in disabling JCheckbox

    - by Yatendra Goel
    I am disabling a JCheckbox and then enabling it with the help of setEnabled(...) method. But the problem is if I disable a unselected checkbox, then it becomes selected after I enable it. I want all of them to have the same state after being enabled that they had before being disabled.

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  • Would a Centralized Blogging Service Work?

    - by viatropos
    If there's a better place to ask this, please let me know. Every time I build a new website/blog/shopping-cart/etc., I keep trying to do the following: Extract out common functionality into reusable code (Rubygems and jQuery plugins mostly) If possible, convert that gem into a small service so I never have to deal with a database for the objects involved (by service, I mean something lean and mean, usually built with the Sinatra Web Framework with a few core models. My assumption is, if I can remove dependencies on local databases, that will make it easier and more scalable in the long run (scalable in terms of reusability and manageability, not necessarily database/performance). I'm not sure if that's a good or bad assumption yet. What do you think? I've made this assumption because of the following reason: Most serious database/model functionality has been built on the internet somewhere. Just to name a few: Social Network API: Facebook Messaging API: Twitter Mailing API: Google Event API: Eventbrite Shopping API: Shopify Comment API: Disqus Form API: Wufoo Image API: Picasa Video API: Youtube ... Each of those things are fairly complicated to build from scratch and to make as optimized, simple, and easy to use as those companies have. So if I build an app that shows pictures (picasa) on an Event page (eventbrite), and you can see who joined the event (facebook events), and send them emails (google apps api), and have them fill out monthly surveys (wufoo), and watch a video when they're done (youtube), all integrated into a custom, easy to use website, and I can do that without ever creating a local database, is that a good thing? I ask because there's two things missing from the puzzle that keep forcing me to create that local database: Post API RESTful/Pretty Url API While there's plenty of Blogging systems and APIs for them, there is no one place where you can just write content and have it part of some massive thing. For every app, I have to use code for creating pretty/restful urls, and that saves posts. But it seems like that should be a service! Question is, is that the main point of a website? Will everyone always need "their own blog"? Why not just have a profile and write lots of content on an established platform like StackOverflow or Facebook?

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  • Filling a byte array in Java

    - by Corleone
    Hey all! For part of a project I'm working on I am implementing a RTPpacket where I have to fill the header array of byte with RTP header fields. //size of the RTP header: static int HEADER_SIZE = 12; // bytes //Fields that compose the RTP header public int Version; // 2 bits public int Padding; // 1 bit public int Extension; // 1 bit public int CC; // 4 bits public int Marker; // 1 bit public int PayloadType; // 7 bits public int SequenceNumber; // 16 bits public int TimeStamp; // 32 bits public int Ssrc; // 32 bits //Bitstream of the RTP header public byte[] header = new byte[ HEADER_SIZE ]; This was my approach: /* * bits 0-1: Version * bit 2: Padding * bit 3: Extension * bits 4-7: CC */ header[0] = new Integer( (Version << 6)|(Padding << 5)|(Extension << 6)|CC ).byteValue(); /* * bit 0: Marker * bits 1-7: PayloadType */ header[1] = new Integer( (Marker << 7)|PayloadType ).byteValue(); /* SequenceNumber takes 2 bytes = 16 bits */ header[2] = new Integer( SequenceNumber >> 8 ).byteValue(); header[3] = new Integer( SequenceNumber ).byteValue(); /* TimeStamp takes 4 bytes = 32 bits */ for ( int i = 0; i < 4; i++ ) header[7-i] = new Integer( TimeStamp >> (8*i) ).byteValue(); /* Ssrc takes 4 bytes = 32 bits */ for ( int i = 0; i < 4; i++ ) header[11-i] = new Integer( Ssrc >> (8*i) ).byteValue(); Any other, maybe 'better' ways to do this?

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  • Java: JPQL select statement

    - by bguiz
    select x from X x where x.a.id = :a_id -- Always 0 objects selected Why does the above JPQL statement not work, but the one below work? select a from A a where a.id = :a_id -- a_obj select x from X x where x.a = :a_obj -- Always correct number of objects selected Neither query throws an exception during execution, but a different number of results are obtained. Thanks

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