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  • deleting a file in java while uploading it in other thread

    - by user369507
    i'm trying to build a semi file sharing program, when each computer acts both as a server and as a client. I give multiple threads the option to DL the file from my system. also, i've got a user interface that can recieve a delete message. my problem is that i want that the minute a delete message receieved, i wait for all the threads that are DL the file to finish DL, and ONLY than excute file.delete(). what is the best way to do it? I thought about some database that holds and iterate and check if the thread is active, but it seems clumsy. is there a better way? thanks

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  • Java generics conversion

    - by LittleGreenMan
    I have build a generic datacontainer and now I want to manipulate data depending on their type. However, I get an incompatable types warning. What am I doing wrong? Type _Value; public void set(Type t) throws Exception { if (_Value instanceof Integer && t instanceof Integer) { _Value = (((Integer) t - _MinValue + getRange()) % getRange()) + _MinValue; } else if (_Value instanceof Boolean && t instanceof Boolean) { _Value = t; } else throw new Exception("Invalid type"); }

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  • Java for loop with multiple incrementers

    - by user2517280
    Im writing a program which combines the RGB pixel values for 3 images, e.g. red pixel of image 1, green pixel of image 2 and blue pixel of image 3 and I want to then create a final image of it. Im using the code below, but this seems to be incrementing x2 and x3 whilst x1 is the same, i.e. not giving the right pixel value for same co-ordinate for each image. for (int x = 0; x < image.getWidth(); x++) { for (int x2 = 0; x2 < image2.getWidth(); x2++) { for (int x3 = 0; x3 < image3.getWidth(); x3++) { for (int y = 0; y < image.getHeight(); y++) { for (int y2 = 0; y2 < image2.getHeight(); y2++) { for (int y3 = 0; y3 < image3.getHeight(); y3++) { So I was wondering if anyone can tell me how to iterate through each of the 3 images on the same co-ordinate, so for example read 1, 1 of each image and record the red, green and blue value accordingly. Apologies if it doesnt make complete sense, its a bit hard to explain. I can iterate the values for one image fine but when I add in another, things start to go a bit wrong as obviously its quite a bit more complicated! I was thinking it might be easier to create an array and replace the according values in that just not sure how to do that effectively either. Thanks

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  • java - find out the type of class which implements of other classes

    - by Johnzzz
    i have a kind of specific problem, let's say, that i have public interface A { } //------------------------------ public class B implements A{ static int countx = 0; } //---------------------------------- public class C implements A{ static int county = 0; } //---------------------------------- public class Arc { public A from; public A to; //======================================== and now I have an object a (which is an instance of Arc) and I want to find out whether it is an instance of B or C and get to the atributes countX or countY (stg like a.from.countX) any ideas? :)

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  • Java Generics Issue (w/ Spring)

    - by drewzilla
    I think I may be a victim of type erasure but thought I'd check with others here first. I have the requirement to do something like this: public interface FooFactory { public <T extends Bar> Foo<T> createFoo( Class<T> clazz ); } It is perfectly valid to write this code. However, I'm trying to implement this functionality using a Spring BeanFactory and I can't do it. What I'd like to do is this... public class FooFactoryImpl implements BeanFactoryAware { private BeanFactory beanFactory; public <T extends Bar> Foo<T> createFoo( Class<T> clazz ) { return beanFactory.getBean( ????????? ); } public void setBeanFactory( BeanFactory beanFactory ) { this.beanFactory = beanFactory; } } As you can see, I've put in ???????? where I'd like to retrieve a bean of type Foo<T>, where T extends Bar. However, it is not possible to derive a Class object of type Foo<T> and so I assume what I'm trying to do is impossible? Anyone else see a way round this or an alternative way of implementing what I'm trying to do? Thanks, Andrew

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  • Return an Object in Java

    - by digby12
    I've been struggling to work out how to return an object. I have the following array of objects. ArrayList<Object> favourites; I want to find an object in the array based on it's "description" property. public Item finditem(String description) { for (Object x : favourites) { if(description.equals(x.getDescription())) { return Object x; else { return null; Can someone please show me how I would write this code. Thanks.

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  • What is a good "Error Checking" Pattern (Java)?

    - by Jack
    I'll explain what I mean by input error checking. Say you have a function doSomething(x). If the function completes successfully doSomething does something and returns nothing. However, if there are errors I'd like to be notified. That is what I mean by error checking. I'm looking for, in general, the best way to check for errors. I've thought of the following solutions, each with a potential problem. Flag error checking. If doSomething(x) completes successfully return null. Otherwise, it returns a boolean or an error string. Problem: Side effects. Throwing an exception. Throw an exception if doSomething(x) encounters an error. Problem: If you are performing error checking for parameters only, throwing an IllegalArgumentExceptionseems inappropriate. Validating input prior to function call. If the error checking is only meant for the parameters of the function, then you can call a validator function before calling the doSomething(x) function. Problem: What if a client of the class forgets to call the validator function before calling doSomething(x)? I often encounter this problem and any help or a point in the right direction would be much appreciated.

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  • what databases can be used with java?

    - by aadersh patel
    I am doing an undergrad final project, and need to justify my choice of MySQL for the database element of my project. Truth is, it's the only one I can really use, and hence I went for it. What other database systems could I have used? Any advantages and disadvantages of these over MySQL?

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  • Java Detect Variable Change Using PropertyChangeSupport and PropertyChangeListener

    - by Sam
    I'm trying to print out debug statements when some third party code changes a variable. For example, consider the following: public final class MysteryClass { private int secretCounter; public synchronized int getCounter() { return secretCounter; } public synchronized void incrementCounter() { secretCounter++; } } public class MyClass { public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // add code here to detect calls to incrementCounter and print a debug message } I don't have the ability to change the 3rd party MysteryClass, so I thought that I could use PropertyChangeSupport and PropertyChangeListener to detect changes to the secretCounter: public class MyClass implements PropertyChangeListener { private PropertyChangeSupport propertySupport = new PropertyChangeSupport(this); public MyClass() { propertySupport.addPropertyChangeListener(this); } public void propertyChange(PropertyChangeEvent evt) { System.out.println("property changing: " + evt.getPropertyName()); } public static void main(String[] args) { MysteryClass mysteryClass = new MysteryClass(); // do logic which involves increment and getting the value of MysteryClass } } Unfortunately, this did not work and I have no debug messages printed out. Does anyone see what is wrong with my implementation of the PropertyChangeSupport and Listener interfaces? I want to print a debug statement whenever incrementCounter is called or the value of secretCounter changes.

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  • How to analyze evenness/oddness of numbers in Java

    - by appreciation
    I have to write a program which reads in 3 numbers (using input boxes), and depending on their values it should write one of these messages: All 3 numbers are odd OR All 3 numbers are even OR 2 numbers are odd and 1 is even OR 1 number is odd and 2 are even This is what I have so far: import javax.swing.JOptionPane; class program3 { public static void main(String[] args) { String num1 = JOptionPane.showInputDialog("Enter first number."); String num2 = JOptionPane.showInputDialog("Enter second number."); String num3 = JOptionPane.showInputDialog("Enter third number."); boolean newnum1 = Integer.parseInt(num1); boolean newnum2 = Integer.parseInt(num2); boolean newnum3 = Integer.parseInt(num3); } } This is where I am stuck. I am not sure how to use the MOD to display the messages. I think I have to also use an IF Statement too...But I'm not too sure. Please help! :D

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  • Java: How to make this Serializable?

    - by Hasslarn
    I dont know that much about Serializable, but i need this class to be. How to achieve it? package helpers; public class XY implements Comparable<XY> { public int x; public int y; public XY (int x, int y) { this.x = x; this.y = y; } public int compareTo( XY other ) { String compare1 = this.x + "-" + this.y; String compare2 = other.x + "-" + other.y; return compare1.compareTo( compare2 ); } public String toString() { return this.x + "-" + this.y; } } As of now i cant send it as an object with outputstream..I´ve tried just to implement Serializable but it doesnt do the trick!

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  • force warning in java

    - by Dustin Getz
    I'd like a mechanism to throw a compile-time warning manually. I'm using it to flag unfinished code so I can't possibly forget about it later. @Deprecated is close but warns at caller site, not at creation site. I'm using eclipse. Something like #Warning in C#.

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  • ConcurentModificationException in Java HashMap

    - by Bear
    Suppose I have two methods in my classes, writeToMap() and processKey() and both methods are called by multiple threads. writeToMap is a method to write something in hashmap and processKey() is used to do sth based on the keySet of HashMap. Inside processKey, I first copy the originalMap before getting the key set. new HashMap<String, Map<String,String>(originalMap).get("xx").keySet(); But I am still getting ConcurrentModificationException even though I always copy the hashmap. Whats the problem?

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  • Java: limit to nest classes?

    - by HH
    A very poor style to code but sometimes unavoidable. It is an extreme example. So is there some limit for nesting classes? are they equivalent? how do you deal with such situations? Create library? Code new FileObject().new Format().new Words().new Some().new Continue someThing; ((((new FileObject()).new Format()).new Words()).new Some()).new Continue someThing;

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  • Java - Thread - Problem in one of the Sun's tutorial

    - by Yatendra Goel
    I was reading this Sun's tutorial on Thread. I found a block of code there which I think can be replaced by a code of fewer lines. I wonder why Sun's expert programmers followed that long way when the task can be accomplished with a code of fewer lines. I am asking this question so as to know that if I am missing something that the tutorial wants to convey. The block of code is as follows: t.start(); threadMessage("Waiting for MessageLoop thread to finish"); //loop until MessageLoop thread exits while (t.isAlive()) { threadMessage("Still waiting..."); //Wait maximum of 1 second for MessageLoop thread to //finish. t.join(1000); if (((System.currentTimeMillis() - startTime) > patience) && t.isAlive()) { threadMessage("Tired of waiting!"); t.interrupt(); //Shouldn't be long now -- wait indefinitely t.join(); } } threadMessage("Finally!"); I think that the above code can be replaced by the following: t.start(); t.join(patience); // InterruptedException is thrown by the main method so no need to handle it if(t.isAlive()) { // t's thread couldn't finish in the patience time threadMessage("Tired of waiting!"); t.interrupt(); t.join(); } threadMessage("Finally!");

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  • Java connecting to Http which method to use?

    - by jax
    I have been looking around at different ways to connect to URLs and there seem to be a few. My requirements are to do POST and GET queries on a URL and retrieve the result. I have seen URL class DefaultHttpClient class And there were some others in apache commons which method is best?

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  • java - Depth First Search - Perform DFS on a tree

    - by DJDonaL3000
    Im trying to perform DFS on a Minimum Spanning Tree which contains 26 nodes. Nodes are named 'A' to 'Z' and the tree is undirected. I have an empty function called DFS here that I am trying to write, which (i presume) takes in the tree (a 2D array) a startNode (randomly selected node 'M') and the endNode (randomly selected node 'Z'). The weights of connected nodes are identified in the 2D array parameter, but how do I actually get started visiting nodes? All that is required is to print each nodeName in the order of the DFS traversal. Do I need to create a Node_class for each node in the 2d array??

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  • using itext how to extracta string in java

    - by user2455183
    I am finding the string in between 123 and 321 and making it as bold. For that I used the Pattern to get the string before 123, text between 123 and 321 and text after 321. Could anyone please help me get all the strings between 123 and 321. Pattern p = Pattern.compile("^.*?(123)"); Matcher m = p.matcher(meredithEditorialSectionSegment); while (m.find()) { String desc = m.group(); String segDesc = (desc.substring(0, desc.length() - 3)); segmentDesc.add(new Chunk(segDesc, sectionDescriptionFont)); } descBold = meredithEditorialSectionSegment.substring(meredithEditorialSectionSegment.indexOf("123") + 3); descBold = descBold.substring(0, descBold.indexOf("321")); segmentDesc.add(new Chunk(descBold, sectionDescriptionBoldFont)); Matcher matcher = Pattern.compile("(?<=321).*").matcher(meredithEditorialSectionSegment); matcher.find(); segmentDesc.add(new Chunk(matcher.group(), sectionDescriptionFont));

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  • How to introduce multi-column constraint with JPA annotations?

    - by plouh
    I am trying to introduce a multi-key constraint on a JPA-mapped entity: public class InventoryItem { @Id private Long id; @Version private Long version; @ManyToOne @JoinColumn("productId") private Product product; @Column(nullable=false); private long serial; } Basically (product, serial) pair should be unique, but I only found a way to say that serial should be unique. This obviously isn't a good idea since different products might have same serial numbers. Is there a way to generate this constraint via JPA or am I forced to manually create it to DB?

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  • Java giving incorrect year values

    - by whistler
    Something very, very strange is occurring in my program, and I'm wondering if anyone out there has seen this occur before. And, if so, how to fix it. Basically, I am parsing an csv file...no problem there. One column contains a date and I am taking it in as a String and changing to a Date object. Again, no problem there. The code is as follows: SimpleDateFormat dateFormat = new SimpleDateFormat("MM/dd/yy hh:mm"); Date initialDate = new Date(); try { initialDate = dateFormat.parse(rows.get(0)[8]); System.out.println(initialDate); } catch (ParseException e) { // TODO Auto-generated catch block e.printStackTrace(); } Of course, I'm parsing other columns as well (and those are working fine). So, when I run my program for a small csv file (2.8 MB), the dates come out (i.e. are parsed) perfectly. However, when I run the program for a large csv file (25 MB), the dates are a hot mess. For example, take a look at the year values I am getting (the following is just a tiny portion of the println output from the code above): 1000264 at Sun Nov 05 15:30:00 EST 2186 1000320 at Sat Mar 04 17:30:00 EST 2169 1000347 at Sat Apr 01 09:45:00 EDT 2169 1000413 at Tue Jul 09 13:00:00 EDT 2182 1000638 at Fri Dec 11 13:45:00 EST 2167 1000667 at Wed Dec 10 10:00:00 EST 2188 1000690 at Mon Jan 02 13:00:00 EST 2169 1000843 at Thu Feb 11 13:30:00 EST 2196 In actuality, the years are in the realm of 1990-2006 or so. Again, this does not happen with the small csv file. Does anyone know what's going on here and how I can fix it? I need to process the large csv file (the small one was just for testing purposes). By request, here are the actual dates in the csv file and after that the value given by the code above: 5/20/03 15:30 5/20/03 15:30 8/30/04 9:00 8/30/04 9:00 12/20/04 10:30 12/20/04 10:30 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Sun Nov 05 15:30:00 EST 2186 Thu Dec 08 09:00:00 EST 2196 Tue Dec 12 10:30:00 EST 2186 Tue Dec 12 10:30:00 EST 2186

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  • Calling class in Java after editing file used in as source for table

    - by user2892290
    I'm currently working on a project, I'll try to subrscibe first. I save data into text file, that I use as a source for browser of that data. The browser is based on table that contains the data. I have to rewrite the source file everytime I delete or edit data. That's where the problem comes in. After deleting or editing data I call a method to create the table again, but the table never creates. Is it possibly made by editing the file and calling the method right after that? If I restart my app the table is successfully created with right data. Take in note that I don't get any error message. This is the method I use for loading data from source file: try (BufferedReader input1 = new BufferedReader(new FileReader("./src/data.src"))) { int lines = 0; while (input1.read() != -1) { if (!(input1.readLine()).equals("")) { lines++; } } input1.close(); if (lines == 0) { JOptionPane.showMessageDialog(null, "No data to load, create a note first!"); new Writer().build(frame); } else { try (BufferedReader input = new BufferedReader(new FileReader("./src/data.src"))) { Game[] g = new Game[lines]; String currentLine; String[] help; int counter = 0; while (lines > 0) { currentLine = input.readLine(); help = currentLine.split("#"); g[counter] = new Game(help[0],help[1], help[2], help[3], help[4], help[5], help[6], help[7], help[8], help[9]); counter++; lines--; } input.close(); final JButton bButton = new backButton().create(frame, mPanel); build(g, frame, bButton); mPanel.add(panel); mPanel.add(panel2); mPanel.add(searchPanel); mPanel.add(bButton); bButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { frame.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR)); panel.removeAll(); frame.setCursor(Cursor.getDefaultCursor()); } }); mPanel.setPreferredSize(new Dimension(1000, 750)); panel.setBorder(new EmptyBorder(10, 10, 10, 10)); frame.setLayout(new FlowLayout()); frame.add(mPanel); frame.pack(); JMenuBar menuBar = new Menu().create(frame, mPanel); frame.setJMenuBar(menuBar); frame.setVisible(true); Rectangle rec = GraphicsEnvironment.getLocalGraphicsEnvironment().getMaximumWindowBounds(); int width = (int) rec.getWidth(); int height = (int) rec.getHeight(); frame.setBounds(1, 3, width, height); frame.addComponentListener(new ComponentAdapter() { @Override public void componentMoved(ComponentEvent e) { frame.setLocation(1, 3); } }); And this is the method I use for creating the table: String[][] tableData = new String[g.length][9]; for (int i = 0; i < tableData.length; i++) { tableData[i][0] = g[i].getChampion(); tableData[i][1] = g[i].getRole(); tableData[i][2] = g[i].getEnemy(); tableData[i][3] = g[i].getDifficulty(); tableData[i][4] = g[i].getResult(); tableData[i][5] = g[i].getScore(); tableData[i][6] = g[i].getGameType(); tableData[i][7] = g[i].getPoints(); tableData[i][8] = g[i].getLeague(); } final JLabel searchLabel = new JLabel("Search for champion played."); final JButton searchButton = new JButton("Search"); final JTextField searchText = new JTextField(20); frame.setTitle("LoL Notepad - reading your notes"); JTable table = new JTable(tableData, columnNames); final JScrollPane scrollPane = new JScrollPane(table); scrollPane.setPreferredSize(new Dimension(980, 500)); panel2.setPreferredSize(new Dimension(1000, 550)); panel2.setVisible(false); panel2.setBorder(new EmptyBorder(10, 10, 10, 10)); panel3.setVisible(false); panel.setLayout(new FlowLayout()); panel.add(scrollPane); searchPanel.add(searchLabel); searchPanel.add(searchText); searchPanel.add(searchButton); searchButton.addActionListener(new ActionListener() { @Override public void actionPerformed(ActionEvent e) { try { frame.setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR)); search(g, searchText.getText(), frame, bButton); frame.setCursor(Cursor.getDefaultCursor()); } catch (IOException ex) { Logger.getLogger(Reader.class.getName()).log(Level.SEVERE, null, ex); } } }); table.addMouseListener(new MouseAdapter() { @Override public void mousePressed(MouseEvent e) { if (e.getClickCount() == 1) { JTable target = (JTable) e.getSource(); panel.setVisible(false); searchPanel.setVisible(false); bButton.setVisible(false); int row = target.getSelectedRow(); specific(row, g, frame, bButton); } } });

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  • Java reading files......

    - by user69514
    Ok this is a homework questions, but I cannot find the answer anywhere, not even in the book. Path to Files If the user wants to specify a path for a file, the typical forward slash is replaced by ________. can you help?

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  • Java Null Pointer Exception :-(

    - by John-Michael Reed
    I've got a Null Pointer Exception in my main that just won't go away and I'm totally out of ideas. The error is on the line "Board[x][y].color = 2;" in which Board is a public, static array of piece objects that contain instance variables like the one "color" that is being set to 2 in the above statement. Pieces is not static - that is there are many different copies of pieces, each with its own data, but only one board. The array has been initialized and defined as both public Piece[][] Board = new Piece[8][8] and public static Piece[][] Board = new Piece[8][8], but no matter how I mess around with it (getting rid of static, putting the variable in another object, etc.), I can't seem to get the error to go away. Help?

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