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  • Java Swing: How to add a CellRenderer for displaying a Date?

    - by HansDampf
    I have a Table: public class AppointmentTableModel extends AbstractTableModel { private int columns; private int rows; ArrayList<Appointment> appointments;... So each row of the table contains one Appointment. public class Appointment { private Date date; private Sample sample; private String comment; private ArrayList<Action> history; public Appointment(Date date, Sample sample, String comment) { this.date = date; this.sample = sample; this.comment = comment; this.history = new ArrayList<Action>(); } public Object getByColumn(int columnIndex) { switch (columnIndex) { case 0: return date;//Date: dd:mm:yyyy case 1: return date;//Time mm:hh case 2: return sample;//sample.getID() int (sampleID) case 3: return sample;//sample.getNumber string (telephone number) case 4: return sample;//sample.getName string (name of the person) case 5: return history;//newst element in history as a string case 6: return comment;//comment as string } return null; I added in comments what this one is going to mean. How would I create CellRenderers to display it like this. table.getColumnModel().getColumn(1).setCellRenderer(new DateRenderer()); I also want to add the whole row to be painted in red when the date is later then the current date. And then another column that holds a JButton to open up another screen with the corresponding Appointment as parameter.

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  • Multithreaded java cache for objects that are heavy to create ?

    - by krosenvold
    I need a cache some objects with fairly heavy creation times, and I need exactly-once creation semantics. It should be possible to create objects for different CacheKeys concurrently. I think I need something that (under the hood) does something like this: ConcurrentHashMap<CacheKey, Future<HeavyObject>> Are there any existing open-source implementations of this that I can re-use ?

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  • Java JTable, how to change cell data (write text in)?

    - by Bob Owuor
    Am looking to change a cell's data in a jtable. How can I do this? When I execute the following code I get errors. JFrame f= new JFrame(); final JTable table= new JTable(10,5); TableModelListener tl= new TableModelListener(){ public void tableChanged(TableModelEvent e){ table.setValueAt("hello world",2,2); } }; table.getModel().addTableModelListener(tl); f.add(table); f.pack(); f.setVisible(true); I have also tried this below but it still doesn't work. What gives? table.getModel().setValueAt("hello world",2,2);

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  • How do i generate thumbnail image for use with img tag ? Java web application.

    - by Nitesh Panchal
    Hello, I am using the below given code, but it is not working properly. Can anybody tell me how do i generate thumbnail of the image? because i am creating a photo album and i want only thumbnail images to be downloaded at first, not the entire 400-500 kb images. File objFile = new File(strImageFullPath); File targetFile = new File(strImageFullPathWithoutExt + "_small" + strFileExtension); Image image = ImageIO.read(objFile); final int WIDTH = 150; final int HEIGHT = 150; Image thumbnailImage = image.getScaledInstance(WIDTH, HEIGHT, Image.SCALE_DEFAULT); BufferedImage objThumbnailBufferedImage = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB); Graphics gfx = objThumbnailBufferedImage.getGraphics(); gfx.drawImage(image, 0, 0, null); gfx.dispose(); ImageIO.write(objThumbnailBufferedImage, strFileExtension.substring(1), targetFile); Just assume that few variables like strImageFullPath,strImageFullPathWithoutExt etc they exist. Thanks in advance :)

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  • How to identify/handle text file newlines in Java?

    - by rafrafUk
    Hi Everyone! I get files in different formats coming from different systems that I need to import into our database. Part of the import process it to check the line length to make sure the format is correct. We seem to be having issues with files coming from UNIX systems where one character is added. I suspect this is due to the return carriage being encoded differently on UNIX and windows platform. Is there a way to detect on which file system a file was created, other than checking the last character on the line? Or maybe a way of reading the files as text and not binary which I suspect is the issue? Thanks Guys !

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  • Which of the following Java coding fragments is better?

    - by Simon
    This isn't meant to be subjective, I am looking for reasons based on resource utilisation, compiler performance, GC performance etc. rather than elegance. Oh, and the position of brackets doesn't count, so no stylistic comments please. Take the following loop; Integer total = new Integer(0); Integer i; for (String str : string_list) { i = Integer.parse(str); total += i; } versus... Integer total = 0; for (String str : string_list) { Integer i = Integer.parse(str); total += i; } In the first one i is function scoped whereas in the second it is scoped in the loop. I have always thought (believed) that the first one would be more efficient because it just references an existing variable already allocated on the stack, whereas the second one would be pushing and popping i each iteration of the loop. There are quite a lot of other cases where I tend to scope variables more broadly than perhaps necessary so I thought I would ask here to clear up a gap in my knowledge. Also notice that assignment of the variable on initialisation either involving the new operator or not. Do any of these sorts of semi-stylistic semi-optimisations make any difference at all?

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  • Java: Is it possible to take a GUI Panel and output it into a picture?

    - by user369748
    So I have this chart that's a little special. Kind of like an XY plot of points but my boss wanted to look like a bunch of boxes rather than dots connected by lines. And I basically made a chart using gridlayout and a whole bunch of cells that I'll be colouring in black or white depending on the data. Now he sorta wants it to be outputted to a image file. Is there any way to save a Panel into a picture? He wants to display not only the data but also save a visual representation of the data into an image file.

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  • How to iterate over numerically named object properties

    - by Scott Schluer
    So I have a horribly designed class that I can't change that has properties like this: object.Color1 object.Color2 object.Color3 etc... How can I iterate through those with a for loop. In other words, something like this: for (int i = 0; i <= 40; i++) { string PropertyName = "Color" + i; if (object.PropertyName != "") { // do something } } Obviously this code wouldn't work but it gives you an idea of what I'm after. I have to do some processing on each property and I don't want to repeat my code 40 times. :) A loop would be perfect, I'm just not sure how to create the name of the property on the fly.

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  • Java: Is it possible to have a generic class that only takes types that can be compared?

    - by mr popo
    I wanted to do something along the lines of: public class MyClass<T implements Comparable> { .... } But I can't, since, apparently, generics only accept restrictions with subclasses, and not interfaces. It's important that I'm able to compare the types inside the class, so how should I go about doing this? Ideally I'd be able to keep the type safety of Generics and not have to convert the T's to Object as well, or just not write a lot of code overall. In other words, the simplest the better.

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  • Java - Can i have a faster performance for this loop ?

    - by Brad
    I am reading a book and deleting a number of words from it. My problem is that the process takes long time, and i want to make its performance better(Less time), example : Vector<String> pages = new Vector<String>(); // Contains about 1500 page, each page has about 1000 words. Vector<String> wordsToDelete = new Vector<String>(); // Contains about 50000 words. for( String page: pages ) { String pageInLowCase = page.toLowerCase(); for( String wordToDelete: wordsToDelete ) { if( pageInLowCase.contains( wordToDelete ) ) page = page.replaceAll( "(?i)\\b" + wordToDelete + "\\b" , "" ); } // Do some staff with the final page that does not take much time. } This code takes around 3 minutes to execute. If i skipped the loop of replaceAll(...) i can save more than 2 minutes. So is there a way to do the same loop with a faster performance ?

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  • How do I make this Java code operate properly? [Multi-threaded, race condition]

    - by Fixee
    I got this code from a student, and it does not work properly because of a race condition involving x++ and x--. He added synchronized to the run() method trying to get rid of this bug, but obviously this only excludes threads from entering run() on the same object (which was never a problem in the first place) but doesn't prevent independent objects from updating the same static variable x at the same time. public class DataRace implements Runnable { static volatile int x; public synchronized void run() { for (int i = 0; i < 10000; i++) { x++; x--; } } public static void main(String[] args) throws Exception { Thread [] threads = new Thread[100]; for (int i = 0; i < threads.length; i++) threads[i] = new Thread(new DataRace()); for (int i = 0; i < threads.length; i++) threads[i].start(); for (int i = 0; i < threads.length; i++) threads[i].join(); System.out.println(x); // x not always 0! } } Since we cannot synchronize on x (because it is primitive), the best solution I can think of is to create a new static object like static String lock = ""; and enclose the x++ and x-- within a synchronized block, locking on lock. But this seems really awkward. Is there a better way?

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  • Java: Best approach to have a long list of variables needed all the time without consuming memory?

    - by evilReiko
    I wrote an abstract class to contain all rules of the application because I need them almost everywhere in my application. So most of what it contains is static final variables, something like this: public abstract class appRules { public static final boolean IS_DEV = true; public static final String CLOCK_SHORT_TIME_FORMAT = "something"; public static final String CLOCK_SHORT_DATE_FORMAT = "something else"; public static final String CLOCK_FULL_FORMAT = "other thing"; public static final int USERNAME_MIN = 5; public static final int USERNAME_MAX = 16; // etc. } The class is big and contains LOTS of such variables. My Question: Isn't setting static variables means these variables are floating in memory all the time? Do you suggest insteading of having an abstract class, I have a instantiable class with non-static variables (just public final), so I instantiate the class and use the variables only when I need them. Or is what am I doing is completely wrong approach and you suggest something else?

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  • Java-Hibernate-Newbie: How do I acces the values from this list?

    - by Mes
    I have this class mapped @Entity @Table(name = "USERS") public class User { private long id; private String userName; } and I make a query: Query query = session.createQuery("select id, userName, count(userName) from User order by count(userName) desc"); return query.list(); How can I acces the value returned by the query?

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  • Java generic function for performing calculations on integer, on double?

    - by Daniel
    Is this possible? Surely if you passed in a double, any sort of function implementation code which casts an object to an Integer would not be able to work unless the cast 'Integer' was specifically used? I have a function like: public static void increment(Object o){ Integer one = (Integer)o; system.out.println(one++); } I cant see how this could be made generic for a double? I tried public static <E> void increment(E obj){ E one = (E)o; system.out.println(one++); } but it didn't like it?

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