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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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  • How can I tell what is using the memory when there is a heap overflow in Java?

    - by Grae
    Hi all, I know a little about profiling, but what I am particularlly insterest in, is what has all the memory when I get these heap over flow exceptions. I will start getting them after about a hour of debugging. I am hoping there is some sort of dump or something, that I can use to get a list of what instances are around at the time the program starts. By the way, sorry if this is a lazy question. I really shoud put sometime in learning about profiling. Grae

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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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  • Why does Java think my object is a variable?

    - by user2896898
    Ok so I'm trying to make a simple pong game. I have a paddle that follows the mouse and a ball that bounces around. I wrote a method collidesWith(Sprite s) inside of my Sprite class that checks if the ball collides with the paddle (this works and isn't the problem). I have two objects extending my sprite class, a ball and a paddle object. So inside of my ball class I'm trying to check if it collides with the paddle. So I've tried if(this.collidesWith(paddle) == true){ System.out.println("They touched"); } I've also tried ball.collidesWith(paddle) and other combinations but it always says the same thing about the paddle (and the ball when I use ball.collidesWith) "Cannot find symbol. Symbol: variable paddle(or ball). Location: class Ball" So if I'm reading this right, it thinks that the paddle (and ball) are variables and it's complaining because it can't find them. How can I make it understand I am passing in objects, not variables? For extra information, an earlier assignment had me make two boxes and for them to change colors when they were colliding. In that assignment I used very similar code to above with if(boxOne.collidesWith(boxTwo) == true){ System.out.println("yes"); } And in this code it worked just fine. The program knew that boxOne and boxTwo were child classes of my Sprite class. Anyone know why they wouldn't work the same?

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  • C# compiler fails to recognize a class is implementing an interface

    - by Freek
    The following code fails to compile (using VS2010) and I don't see why. The compiler should be able to infer that List is 'compatible' (sorry for lack of a better word) with IEnumerable, but somehow it doesn't. What am I missing here? interface ITest { void Test(); } class TestClass : ITest { public void Test() { } } class Program { static void Test(IEnumerable<ITest> tests) { foreach(var t in tests) { Console.WriteLine(t); } } static void Main(string[] args) { var lst = new List<TestClass>(); Test(lst); // fails, why? Test(lst.Select(t=>t as ITest)); //success Test(lst.ToArray()); // success } }

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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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  • How to plot the graph(line) from a file in java?

    - by kiran
    I have a directory containing list of files. Those files have some list of values as x and y ordered as line by line. And my question is just I would like to read those files one by one and to plot line graphs based on those values. Could you please help me for that?

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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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  • 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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  • 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: 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: 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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  • Drawing lines between windows just like in Interface Builder

    - by Koning Baard
    I have two windows, each with a round NSView: ------------------ ------------ |X-+ Oscillator | |X-+ Mixer | |----------------| |----------| | | | | | O | | O | | | | | | | | | ------------------ ------------ Both windows are in a seperate NIB. I want to be able to draw a line between the two round NSViews at runtime, using drag'n'drop, just like connecting IBOutlets in Interface Builder: ------------------ ------------ |X-+ Oscillator | |X-+ Mixer | |----------------| |----------| | | | | | O-------+-----+-----O | | | | | | | | | ------------------ ------------ I also want to be able to determine to which NSViews the NSViews are connected using the drawn lines. I need this to connect Oscillators to Mixers. I also want to be able to remove the connections by dragging into empty space. Can anyone explain me how to do this? Thanks.

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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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  • 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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  • 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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