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  • java looping - declaration of a Class outside / inside the loop

    - by lisak
    when looping, for instance: for ( int j = 0; j < 1000; j++) {}; and I need to instantiate 1000 objects, how does it differ when I declare the object inside the loop from declaring it outside the loop ?? for ( int j = 0; j < 1000; j++) {Object obj; obj =} vs Object obj; for ( int j = 0; j < 1000; j++) {obj =} It's obvious that the object is accessible either only from the loop scope or from the scope that is surrounding it. But I don't understand the performance question, garbage collection etc. What is the best practice ? Thank you

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  • Why Java Swing behaves different on different systems?

    - by Tom Brito
    Some swing code I write in my computer behave different on my colleague's computer, and in my PC, and in my notebook. I wonder, is there something I can do to my Swing applications behave the same in every computer? I want to have sure a algorithm I've tested in my computer will work the same way in my clients computers. E.g. Problem to focus JTextField

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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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  • Tokenize problem in Java with separator ". "

    - by user112976
    I need to split a text using the separator ". ". For example I want this string : Washington is the U.S Capital. Barack is living there. To be cut into two parts: Washington is the U.S Capital. Barack is living there. Here is my code : // Initialize the tokenizer StringTokenizer tokenizer = new StringTokenizer("Washington is the U.S Capital. Barack is living there.", ". "); while (tokenizer.hasMoreTokens()) { System.out.println(tokenizer.nextToken()); } And the output is unfortunately : Washington is the U S Capital Barack is living there Can someone explain what's going on?

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  • Java 1.5.0_16 corrupted colours when saving jpg image

    - by Coder
    Hi, i have a loaded image from disk (stored as a BufferedImage), which i display correctly on a JPanel but when i try to re-save this image using the command below, the image is saved in a reddish hue. ImageIO.write(image, "jpg", fileName); Note! image is a BufferedImage and fileName is a File object pointing to the filename that will be saved which end in ".jpg". I have read that there were problems with ImageIO methods in earlier JDKs but i'm not on one of those versions as far as i could find. What i am looking for is a way to fix this issue without updating the JDK, however having said that i would still like to know in what JDK this issue was fixed in (if it indeed is still a bug with the JDK i'm using). Thanks.

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  • Simple java syncrhonization question

    - by Misha Koshelev
    Dear All: Was wondering, which is correct: Option One class A { public void methodOne() { synchronized(this) { modifyvalue notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } Option Two class A { public void methodOne() { modifyvalue synchronized(this) { notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } and why? Thank you Misha

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  • java version of python-dateutil

    - by elhefe
    Python has a very handy package that can parse nearly any unambiguous date and provides helpful error messages on a parse failure, python-dateutil. Comparison to the SimpleDateFormat class is not favorable - AFAICT SimpleDateFormat can only handle one exact date format and the error messages have no granularity. I've looked through the Joda API but it appears Joda is the same way - only one explicit format can be parsed at a time. Is there any package or library that reproduces the python-dateutil behavior? Or am I missing something WRT Joda/SimpleDateFormat?

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  • Mouse event in Java

    - by Harish
    I am trying to move a JComponent say a label over a table.I am tracking this event using MouseMotionListener's mouseDragged method.This method perfectly helps me in tracking the item.Is there a way to track the mouse release after dragging is complete(.ie the dropping event). tktLabel1.addMouseMotionListener(new MouseMotionListener() { public void mouseDragged(MouseEvent arg0) { tktLabel1.setBounds(tktLabel1.getX() + arg0.getX(), tktLabel1.getY() + arg0.getY(), width, height); } public void mouseMoved(MouseEvent arg0) { } });

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  • Subqueries on Java GAE Datastore

    - by Dmitry
    I am trying to create a database of users with connection between users (friends list). There are 2 main tables: UserEntity (main field id) and FriendEntity with fields: - initiatorId - id of user who initiated the friendship - friendId - id of user who has been invited. Now I am trying to fetch all friends of one particular user and encountered some problems with using subqueries in JDO here. Logically the query should be something like this: SQL: SELECT * FROM UserEntity WHERE EXISTS (SELECT * FORM FriendEntity WHERE (initiatorId == UserEntity.id && friendId == userId) || (friendId == UserEntity.id && initiatorId == userId)) or SELECT * FROM UserEntity WHERE userId IN (SELECT * FROM FriendEntity WHERE initiatorId == UserEntity.id) OR userId IN (SELECT * FROM FriendEntity WHERE friendId == UserEntity.id) So to replicate the last query in JDOQL, I tried to do the following: Query friendQuery = pm.newQuery(FriendEntity.class); friendQuery.setFilter("initiatorId == uidParam"); friendQuery.setResult("friendId"); Query initiatorQuery = pm.newQuery(FriendEntity.class); initiatorQuery.setFilter("friendId == uidParam"); initiatorQuery.setResult("initiatorId"); Query query = pm.newQuery(UserEntity.class); query.setFilter("initiatorQuery.contains(id) || friendQuery.contains(id)"); query.addSubquery(initiatorQuery, "List initiatorQuery", null, "String uidParam"); query.addSubquery(friendQuery, "List friendQuery", null, "String uidParam"); query.declareParameters("String uidParam"); List<UserEntity> friends = (List<UserEntity>) query.execute(userId); In result I get the following error: Unsupported method while parsing expression. Could anyone help with this query please?

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  • SwingWorker in Java (beginner question)

    - by Malachi
    I am relatively new to multi-threading and want to execute a background task using a Swingworker thread - the method that is called does not actually return anything but I would like to be notified when it has completed. The code I have so far doesn't appear to be working: private void crawl(ActionEvent evt) { try { SwingWorker<Void, Void> crawler = new SwingWorker<Void, Void>() { @Override protected Void doInBackground() throws Exception { Discoverer discover = new Discoverer(); discover.crawl(); return null; } @Override protected void done() { JOptionPane.showMessageDialog(jfThis, "Finished Crawling", "Success", JOptionPane.INFORMATION_MESSAGE); } }; crawler.execute(); } catch (Exception ex) { JOptionPane.showMessageDialog(this, ex.getMessage(), "Exception", JOptionPane.ERROR_MESSAGE); } } Any feedback/advice would be greatly appreciated as multi-threading is a big area of programming that I am weak in.

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  • Type conversion between PHP client and Java webservice

    - by a1ex07
    I have a web service implemented as EJB. One of it's methods returns Map<String,String>. On client side I use php : $client = new SoapClient($wsdl,array("cache_wsdl"=>WSDL_CACHE_NONE)); $result = $client->foo($params); Everything works fine, but I would like $result-return to be an associative array. Now it looks like array(10) { [0]=> object(stdClass)#46 (2) { ["key"]=> string(4) "key1" ["value"]=> string(4) "val1" } .... I want array(10) {"key1"=>"value1", "key2"=>"value2", .... } The obvious solution is to iterate through this array and create a new array $arr = array(); foreach ($result->return as $val) $arr[$val->key] = $val->value; But I wonder if there is a better way to get an assosicative array ? Thanks in advance.

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  • How to re-use a thread in Java ?

    - by David
    I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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  • Arduino crashes when sending bytes from Java [on hold]

    - by francisaugusto
    I used the sample program from the arduino website in order to send and receive data via serial to my Arduino one. However, for some reason, even when I try to send only one byte, the Arduino crashes after a while. It doesn't happen if I send the chars manually via the IDE's own serial monitor. I wrote the following method to output the character to Arduino: public synchronized void serialWrite(char sendIt){ try { output.write((byte)'0'); output.flush(); for (int j=0;j<1000000000;j++){ } }catch (Exception e){System.out.println("Not connected...");} notify(); } What I try above is to send just one character when the method is called. I send just a '0' char for testing. After manually calling the method two or three times, Arduino crashes. Is there anything I should be looking into? The Arduino code: #include <SoftwareSerial.h> int buttonState=0; int lastButtonState=0; int buttonPushCounter=0; long previousMillis=0; long interval=250; int ledState=LOW; int ledState2=LOW; int ledState3=LOW; long timeElapsed=0; SoftwareSerial portOne(10,11); void setup(){ pinMode(3,OUTPUT); pinMode(4,OUTPUT); pinMode(5,OUTPUT); pinMode(2,INPUT); Serial.begin(9600); portOne.begin(9600); } boolean turnoff; void loop(){ if(portOne.overflow()){ Serial.println("There's an overflow here!"); } buttonState= digitalRead(2); if(buttonState!=lastButtonState){ if (buttonState==HIGH){ buttonPushCounter++; } } lastButtonState=buttonState; if (turnoff){ unsigned long currentMillis=millis(); if (currentMillis-previousMillis>0 && currentMillis-previousMillis<interval){ ledState=HIGH; ledState2=LOW; ledState3=LOW; }else if (currentMillis-previousMillis>interval && currentMillis-previousMillis<interval*2){ ledState=LOW; ledState2=LOW; ledState3=HIGH; }else if (currentMillis-previousMillis>interval*2 && currentMillis-previousMillis<interval*3){ ledState=LOW; ledState2=HIGH; ledState3=LOW; }else if (currentMillis-previousMillis>interval*3){ previousMillis=currentMillis; } digitalWrite(3,ledState); digitalWrite(4,ledState2); digitalWrite(5,ledState3); }else{ digitalWrite(3,LOW); digitalWrite(4,LOW); digitalWrite(5,LOW); } if (buttonPushCounter==1){ Serial.print("Button pressed!\n"); turnoff=!turnoff; buttonPushCounter=0; } noInterrupts(); char ch=Serial.read(); delay(1); if(ch=='0'){ Serial.println("Changed by serial"+turnoff); Serial.println(ch); turnoff=!turnoff; } interrupts(); }

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  • What's wrong with this JAVA code for android?

    - by Umair Ashraf
    I have written this piece of code to break an image into 9 pieces and it gives me runtime error. There is no error in LogCat and I am stuck. The error comes at line 7 line from bottom (Bitmap.createBitmap(...);). public Bitmap[] getPieces(Bitmap bmp) { Bitmap[] bmps = new Bitmap[9]; int width = bmp.getWidth(); int height = bmp.getHeight(); int rows = 3; int cols = 3; int cellHeight = height / rows; int cellWidth = width / cols; int piece = 0; for (int x = 0; x <= width; x += cellWidth) { for (int y = 0; y <= height; y += cellHeight) { Bitmap b = Bitmap.createBitmap(bmp, x, y, cellWidth, cellHeight, null, false); bmps[piece] = b; piece++; } } return bmps; }

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  • How do I detect unicode characters in a Java string to resolve sax parser exception

    - by Madhumita
    Suppose I have a string that contains '¿'. How would I find all those unicode characters? Should I test for their code? How would I do that? I want to detect it to avoid sax parser exception which I am getting it while parsing the xml saved as a clob in oracle 10g database. Exception javax.servlet.ServletException: org.xml.sax.SAXParseException: Invalid byte 1 of 1-byte UTF-8 sequence.

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  • Java: Altering UI fonts (Nimbus) doesn't work!

    - by ivan_ivanovich_ivanoff
    Hello! I'm referring to this Nimbus reference. I tried to set global Font to be slightly larger: UIManager.put("defaultFont", new Font(Font.SANS_SERIF, 0, 16)); ...works only for the menu but nothing else (buttons, labels). I tried to change labels and buttons fonts with UIManager.put("Button.font", new Font(Font.SANS_SERIF, 0, 16)); UIManager.put("Label.font", new Font(Font.SANS_SERIF, 0, 16)); but the font remains. The only thing that worked for me was deriving a font: someButton.setFont(someButton.getFont().deriveFont(16f)); But this is not an option, since this must be done for each element manually. Note, that deriving a font for UIManager doesn't work either: UIManager.put("Label.font", UIManager.getFont("Label.font").deriveFont(16f)); I tested everything under Linux and Windows: same behavior. I just can't understand how an API can be so messy. If a method is called setFont(..) then I expect it to set the font. If this method fails to set the font in any thinkable circumstances, then it should be deprecated. EDIT: The problem not only applies to Nimbus, but also to the default LAF.

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  • Reducing Time Complexity in Java

    - by Koeneuze
    Right, this is from an older exam which i'm using to prepare my own exam in january. We are given the following method: public static void Oorspronkelijk() { String bs = "Dit is een boodschap aan de wereld"; int max = -1; char let = '*'; for (int i=0;i<bs.length();i++) { int tel = 1; for (int j=i+1;j<bs.length();j++) { if (bs.charAt(j) == bs.charAt(i)) tel++; } if (tel > max) { max = tel; let = bs.charAt(i); } } System.out.println(max + " keer " + let); } The questions are: what is the output? - Since the code is just an algorithm to determine the most occuring character, the output is "6 keer " (6 times space) What is the time complexity of this code? Fairly sure it's O(n²), unless someone thinks otherwise? Can you reduce the time complexity, and if so, how? Well, you can. I've received some help already and managed to get the following code: public static void Nieuw() { String bs = "Dit is een boodschap aan de wereld"; HashMap<Character, Integer> letters = new HashMap<Character, Integer>(); char max = bs.charAt(0); for (int i=0;i<bs.length();i++) { char let = bs.charAt(i); if(!letters.containsKey(let)) { letters.put(let,0); } int tel = letters.get(let)+1; letters.put(let,tel); if(letters.get(max)<tel) { max = let; } } System.out.println(letters.get(max) + " keer " + max); } However, I'm uncertain of the time complexity of this new code: Is it O(n) because you only use one for-loop, or does the fact we require the use of the HashMap's get methods make it O(n log n) ? And if someone knows an even better way of reducing the time complexity, please do tell! :)

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  • Java socketserver: How to handle many incoming connections?

    - by SlappyTheFish
    I am writing a simple multithreaded socketserver and I am wondering how best to handle incoming connections: create a new thread for each new connection. The number of concurrent threads would be limited and waiting connections limited by specifying a backlog add all incoming connections into a queue and have a pool of worker threads that process the queue I am inclined to go for option 2 because I really don't want to refuse any connections, even under high loads, but I am wondering if there are any considerations I should be aware of with accepting effectively unlimited connections?

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