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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: 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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  • Using two threads and controlling one from the other in java?

    - by sidra
    Can someone please help me out. I need to use two threads in a way that one thread will run permanently while(true) and will keep track of a positioning pointer (some random value coming in form a method). This thread has a logic, if the value equals something, it should start the new thread. And if the value does not equal it should stop the other thread. Can someone give me some code snippet (block level) about how to realize this?

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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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  • What is my error in a map in java?

    - by amveg
    Hello everyone I am trying to solve this problem: http://www.cstutoringcenter.com/problems/problems.php?id=4, but I cant figure out why my code doesnt solve this, I mean in the "for" how can I can multiply the letters? what is my error?, It just tell always 7, but I want to multiple all the letters, I hope you can help me enter code here public class ejercicio3 { public static void main(String args[]) { Map<Character, Integer> telefono = new HashMap<Character, Integer>(); telefono.put('A', 2); telefono.put('B', 2); telefono.put('C', 2); telefono.put('D', 3); telefono.put('E', 3); telefono.put('F', 3); telefono.put('G', 4); telefono.put('H', 4); telefono.put('I', 4); telefono.put('J', 5); telefono.put('K', 5); telefono.put('L', 5); telefono.put('M', 6); telefono.put('N', 6); telefono.put('O', 6); telefono.put('P', 7); telefono.put('R', 7); telefono.put('S', 7); telefono.put('T', 8); telefono.put('U', 8); telefono.put('V', 8); telefono.put('W', 9); telefono.put('X', 9); telefono.put('Y', 9); String mensaje = "Practice"; int producto = 1; for (char c : mensaje.toCharArray()) { if (telefono.containsKey(c)) { producto = telefono.get(c) * producto; System.out.println(producto); } } } }

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  • Java Swing: Resize JMenuItem's icon, either automatically or programatically?

    - by TGP1994
    It seems that JMenuItems don't automatically resize any image icon that's assigned to them, and from what I can tell, there isn't a property that makes them automatically do that, either. Is anyone aware of a way that I can programatically resize the Icon for a JMenuItem? It seems like the Icon object is lacking functionality as it is, unless there's some other function that can actually deal with Icon objects.

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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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  • Is it expensive to hold on to PreparedStatements? (Java & JDBC)

    - by sbook
    I'm trying to figure out if it's efficient for me to cache all of my statements when I create my database connection or if I should only create those that are most used and create the others if/when they're needed.. It seems foolish to create all of the statements in all of the client threads. Any feedback would be greatly appreciated.

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  • Is it possible to write a generic +1 method for numeric box types in Java?

    - by polygenelubricants
    This is NOT homework. Part 1 Is it possible to write a generic method, something like this: <T extends Number> T plusOne(T num) { return num + 1; // DOESN'T COMPILE! How to fix??? } Short of using a bunch of instanceof and casts, is this possible? Part 2 The following 3 methods compile: Integer plusOne(Integer num) { return num + 1; } Double plusOne(Double num) { return num + 1; } Long plusOne(Long num) { return num + 1; } Is it possible to write a generic version that bound T to only Integer, Double, or Long?

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  • Java: How to display a multi-line ToolTip with AWT?

    - by Martijn Courteaux
    Hi, I wrote an application and now I'm making a tray-icon. Now I want to set a multi-line tooltiptext to the tray-icon. But I don't know how. I know how to do this with Swing: component.setToolTipText("<html>Line 1<br>Line2</html>"); But this doesn't work with AWT. Also serarating lines by \n doesn't work. Any help would be very appreciated. Thanks

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  • Trying to use a list iterator to print out entire linked list in Java. Infinite loop for some reaso

    - by Matt
    I created my list: private static List list = new LinkedList(); and my iterator: ListIterator itr = list.listIterator(); and use this code to try to print out the list... Only problem is, it never comes out of the loop. When it reaches the tail, shouldn't it come out of the loop, because there is no next? Or is it going back to the head like a circular linked list? It is printing so quickly and my computer locks up shortly after, so I can't really tell what is going on. while (itr.hasNext()) System.out.println(itr.next());

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  • How can I get relative path of the folders in my project? (java)

    - by masterkapu
    How can I get the relative path of the folders in my project (using code)? I created new folder in my project and I want its relative path so no matter where is the app the path will be correct. Maybe this can be useful: I trying to do it not inside any function just inside the class and I want to init with it a final variable. the app is android and the class is "extends Activity" thanks

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  • C or C++: how do loaders/wrappers work?

    - by guitar-
    Here's an example of what I mean... User runs LOADER.EXE program LOADER.EXE downloads another EXE but keeps it all in memory without saving it to disk Runs the downloaded EXE just as it would if it were executed from disk, but does it straight from memory I've seen a few applications like this, and I've never seen an example or an explanation of how it works. Does anyone know? Another example is having an encrypted EXE embedded in another one. It gets extracted and decrypted in memory, without ever being saved to disk before it gets executed. I've seen that one used in some applications to prevent piracy.

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  • Java: Superclass to construct a subclass on certain conditions, possible?

    - by ramihope
    I have this condition public class A { public action() { System.out.println("Action done in A"); } } public class B extends A { public action() { System.out.println("Action done in B"); } } when I create an instance of B, the action will do just actions in B, as it overrides the action of the superclass. the problem is that in my project, the super class A is already used too many times, and I am looking for a way that under certain conditions, when i create an instance of A it makes a check and if it is true, replace itself with B. public class A { public A() { if ([condition]) { this = new B(); } } public action() { System.out.println("Action done in A"); } } A a = new A(); a.action(); // expect to see "Action done in B"... is this possible in some way?

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  • What goes into the "Controller" in "MVC"?

    - by P72endragon
    I think I understand the basic concepts of MVC - the Model contains the data and behaviour of the application, the View is responsible for displaying it to the user and the Controller deals with user input. What I'm uncertain about is exactly what goes in the Controller. Lets say for example I have a fairly simple application (I'm specifically thinking Java, but I suppose the same principles apply elsewhere). I organise my code into 3 packages called app.model, app.view and app.controller. Within the app.model package, I have a few classes that reflect the actual behaviour of the application. These extends Observable and use setChanged() and notifyObservers() to trigger the views to update when appropriate. The app.view package has a class (or several classes for different types of display) that uses javax.swing components to handle the display. Some of these components need to feed back into the Model. If I understand correctly, the View shouldn't have anything to do with the feedback - that should be dealt with by the Controller. So what do I actually put in the Controller? Do I put the public void actionPerformed(ActionEvent e) in the View with just a call to a method in the Controller? If so, should any validation etc be done in the Controller? If so, how do I feedback error messages back to the View - should that go through the Model again, or should the Controller just send it straight back to View? If the validation is done in the View, what do I put in the Controller? Sorry for the long question, I just wanted to document my understanding of the process and hopefully someone can clarify this issue for me!

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