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  • Compilers behave differently with a null parameter of a generic method

    - by Eyal Schneider
    The following code compiles perfectly with Eclipse, but fails to compile with javac: public class HowBizarre { public static <P extends Number, T extends P> void doIt(P value) { } public static void main(String[] args) { doIt(null); } } I simplified the code, so T is not used at all now. Still, I don't see a reason for the error. For some reason javac decides that T stands for Object, and then complains that Object does not conform to the bounds of T (which is true): HowBizarre.java:6: incompatible types; inferred type argument(s) java.lang.Number,java.lang.Object do not conform to bounds of type variable (s) P,T found : <P,T>void required: void doIt(null); ^ Note that if I replace the null parameter with a non-null value, it compiles fine. Which of the compilers behaves correctly and why? Is this a bug of one of them?

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  • Any way to use a class extension method to support an interface method in C#?

    - by dudeNumber4
    Console app below compiles, but the interface cast fails at run time. Is there an easy way to make this work? namespace ConsoleApplication1 { class Monkey { public string Shock { get { return "Monkey has been shocked."; } } } static class MonkeyExtensionToSupportIWombat { public static string ShockTheMonkey( this Monkey m ) { return m.Shock; } } interface IWombat { string ShockTheMonkey(); } class Program { static void Main( string[] args ) { var monkey = new Monkey(); Console.WriteLine( "Shock the monkey without the interface: {0}", monkey.Shock ); IWombat wombat = monkey as IWombat; Console.WriteLine( "Shock the monkey with the interface: {0}", wombat.ShockTheMonkey() ); Console.ReadLine(); } } }

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  • Problem in using C# generics with method overloading

    - by Siva Chandran
    I am trying to call an overloaded method based on the generic type. I've been doing this in C++ without any pain. But I really don't understand why am not able to do this in C# with generics. Can anybody help me how can I achieve this in C# with generics? class Test<T> { public T Val; public void Do(T val) { Val = val; MainClass.Print(Val); } } class MainClass { public static void Print(UInt16 val) { Console.WriteLine("UInt16: " + val.ToString()); } public static void Print(UInt32 val) { Console.WriteLine("UInt32: " + val.ToString()); } public static void Print(UInt64 val) { Console.WriteLine("UInt64: " + val.ToString()); } public static void Main (string[] args) { Test<UInt16> test = new Test<UInt16>(); test.Do(); } }

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  • Most Efficient Alternative Method of Storing Settings for iPhone Apps

    - by JPK
    I am not using the Settings bundle to store the settings for my app, as I prefer to allow the user to access the settings within the app (they may be changed fairly often). I do realize that there is the option to do both, but for now, I am trying to find the most optimal place to store the settings within the app. I have a good number of settings (from what I have read, probably too many for NSUserDefaults), and the two main options I am considering are: 1) storing the settings in a dictionary in the plist, loading the settings into a NSDictionary property in the app delegate and accessing them via the sharedDelegate 2) storing the settings in a Core Data entity (1 row on Settings entity), loading the settings into a Settings object in the app delegate and accessing them via the sharedDelegate Of these two, which would be the optimal method, performance wise?

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  • Call the method of base Class which was over ridden

    - by Abhijith Venkata
    I have illustrated my question in this example class Car { public void start(){ System.out.println("Car Started!!!"); } } class Mercedes extends Car { public void start(){ System.out.println("Mercedes Started!!!"); } } Now, in my main program, I write Mercedes m = new Mercedes(); m.start(); It prints: Mercedes Started!!! How do I call the start() method of Car class using the same object so that the output can be Car Started!!!. Edit: Actually It was asked in an interview I attended. I gave the super keyword answer. But the interviewer denied it. He said he'd give me a hint and said Virtual Function. I have no idea how to use that hint.

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  • Getting progress status out of a class library method

    - by Richard
    This app that I am doing uses a class library (if I dare call it that) to do the bulk of the work: 2 main methods in there (DoWork and UndoWork) use the other classes to achieve thier goal. Now that that works, I want to get out of the Console test enviroment and do a GUI. How would I get the status of say, the DoWork() method to update a progress bar? Should I multilate the class library (which currently works with the Console and Windows.Forms) to update? The problem with that is that I would surely have to make the class library use Window.Forms which will mess up the console testing apps (And there are lots of them - I tested all the way through, and then all together). Could you suggest some ideas, or places I can read up about ideas (the whole point of writing this this program is to learn, afer all)? Oh, by the way, suggestions like "foresight" or "planning" probably won't help here...(now, anywyay!) - But certainly will in future projects!

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  • C# generics method invocation

    - by Firat KÜÇÜK
    Hi, i have some polymorphic methods and i want to call via using an intermediate method. Following class is the simplified version of my program. class Program { public class A { } public class B { } public class C { } public void SomeMethod(A value) { Console.WriteLine("A value"); } public void SomeMethod(B value) { Console.WriteLine("B value"); } public void SomeMethod(C value) { Console.WriteLine("C value"); } static void Main(string[] args) { Program p = new Program(); // code block p.IntermediateMethod<A>(new A()); p.IntermediateMethod<B>(new B()); p.IntermediateMethod<C>(new C()); } public void IntermediateMethod<T>(T value) { // code block SomeMethod(value); // code block } }

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  • Difference in techniques for setting a stubbed method's return value with Rhino Mocks

    - by CRice
    What is the main difference between these following two ways to give a method some fake implementation? I was using the second way fine in one test but in another test the behaviour can not be achieved unless I go with the first way. These are set up via: IMembershipService service = test.Stub<IMembershipService>(); so (the first), using (test.Record()) //test is MockRepository instance { service.GetUser("dummyName"); LastCall.Return(new LoginUser()); } vs (the second). service.Stub(r => r.GetUser("dummyName")).Return(new LoginUser()); Edit The problem is that the second technique returns null in the test, when I expect it to return a new LoginUser. The first technique behaves as expected by returning a new LoginUser. All other test code used in both cases is identical.

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  • How can I selectively override a django .count() method

    - by Tom Viner
    I'm using postGresSQL and my main table has about 20,000 rows. Sometimes count() methods can take ages or even timeout. Mod.manager.filter(...).count() I need to selectively override the count() method depending on what filter has been applied. Just having a cache of results would be a great gain but I'd like to be able to say: if filter query is just {'enabled'=True} then return 20,000 without touching the db. Note: I can't prevent the call to .count() as it's inside django's pagination, which always does a count.

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  • Java static method parameters

    - by Blitzkr1eg
    Why does the following code return 100 100 1 1 1 and not 100 1 1 1 1 ? public class Hotel { private int roomNr; public Hotel(int roomNr) { this.roomNr = roomNr; } public int getRoomNr() { return this.roomNr; } static Hotel doStuff(Hotel hotel) { hotel = new Hotel(1); return hotel; } public static void main(String args[]) { Hotel h1 = new Hotel(100); System.out.print(h1.getRoomNr() + " "); Hotel h2 = doStuff(h1); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); h1 = doStuff(h2); System.out.print(h1.getRoomNr() + " "); System.out.print(h2.getRoomNr() + " "); } } Why does it appear to pass Hotel by-value to doStuff() ?

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  • Updating Activity UI from Different Activity Method?

    - by stormin986
    I have a tab widget where one of the tabs is a chat-type feature. I want to update the chat data at an interval (variable depending on whether the chat tab is active or not). The best approach seemed to be using an AsyncTask in my main TabActivity class, as that would avoid any issues of the chat activity being destroyed while in the background, while an AsyncTask was running. I wanted to ensure that the Activity isn't destroyed and recreated, thus causing my AsyncTask to be unable to modify the actual active Activity's data. However, now that my AsyncTask is in the TabActivity activity, I don't have a direct way to call my Chat's ListAdapter notifyDataSetChanged() from my onPostExecute() method anymore. Is there a way to get a reference to a given Tab's current Activity from the TabHost/TabActivity? Or, alternatively, can I assume my chat activity will never be destroyed as a child activity of the TabActivity activity (well, never destroyed while the TabActivity is active at least), and then just put the AsyncTask in the Chat Activity?

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  • non-static method setPrzechowaj(java.lang.String) cannot be referenced froma a static context

    - by bigbluedragon
    hey i have problem with JDialogForm. I have created it using netbeans 6.8. That JDialogForm have textfield and button below it. and here is some code... private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) { String sciezka = jTextField1.getText(); if (sciezka.length() > 0) { Zmienne_pomocnicze.setPrzechowaj(sciezka); } } Now i want to copy that string "sciezka" to my main window but if I do it like this public class Zmienne_pomocnicze { public String n; public void setPrzechowaj (String neew) { n = neew; } public String getPrzechowaj () { return n; } } i get error in jButton1: non-static method setPrzechowaj(java.lang.String) cannot be referenced froma a static context any ideas?

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  • Why baseclass calls method of subclass?

    - by twlkyao
    I encounter some code like the following: BaseClass: public class BaseClass { String name = "Base"; public BaseClass() { printName(); } public void printName() { System.out.println(name + "——Base"); } } DrivedClass: public class SubClass extends BaseClass { String name = "Sub"; public SubClass() { printName(); } public void printName() { System.out.println(name + "——Sub"); } public static void main(String[] args) { new SubClass(); } } When run the code, the output is: null——Sub Sub——Sub while it should be: Base——Base Sub——Sub I wonder why the BaseClass constructor calls the SubClass method, can anybody explain this? Thanks in advance.

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  • interface as a method parameter in Java

    - by PeterYu
    Hi all, I had an interview days ago and was thrown a question like this. Q: Reverse a linked list. Following code is given: public class ReverseList { interface NodeList { int getItem(); NodeList nextNode(); } void reverse(NodeList node) { } public static void main(String[] args) { } } I was confused because I did not know an interface object could be used as a method parameter. The interviewer explained a little bit but I am still not sure about this. Could somebody enlighten me?

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  • java overloaded method

    - by Sean Nguyen
    Hi, I have an abstract template method: class abstract MyTemplate { public void something(Object obj) { doSomething(obj) } protected void doSomething(Object obj); } class MyImpl extends MyTemplate { protected void doSomething(Object obj) { System.out.println("i am dealing with generic object"); } protected void doSomething(String str) { System.out.println("I am dealing with string"); } } public static void main(String[] args) { MyImpl impl = new MyImpl(); impl.something("abc"); // --> this return "i am dealing with generic object" } How can I print "I am dealing with string" w/o using instanceof in doSomething(Object obj)? Thanks,

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  • Need help: input int from console and pass it into method in different class

    - by christophe
    i'm a beginner, Need help, Please!!! I want to read number "a" from console and then store them in variable to use as passing to a different class (different .java file). How do i code the 2 classes? thanks public class PassedInMethod{ private int a; . public PAssMethod(int a) { a = a; // TODO: where to get the a? System.out.println("a was passed in!"+a); } public class Mainclass{ public static void main( String args[] ){ Scanner input = new Scanner( System.in ); int a; System.out.print( "Enter your nember: " ); a = input.nextInt(); PassedInMethod(int a); }

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  • Method sscanf() ambiguous behavior

    - by Carmen Cojocaru
    I am trying to understand how sscanf() works. I ran some examples from this page: http://docs.roxen.com/pike/7.0/tutorial/strings/sscanf.xml and they don't work on my platform. I can't understand why. For instance: "sscanf("4711bar", "%d%s", a, b);" makes the program exit with an error... Here is one of the examples that work: "sscanf("foo", "f%s", a);". Does anybody know why? Do they work on your platforms? Thank you. This is my code: int main(void){ char *b = (char*)malloc(sizeof(char)*100); int a = 0; sscanf("4711bar", "%d%s", a, b); printf("%d", a); printf("%s", b); }

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  • Java Swing UI Changing Method

    - by vigilant
    I would like to use Swing to program a simple learning game. I am wondering what would be best way to switch between UI screens. For example, I would have a screen for the Main Menu, and then when the user presses a button on that screen, I would swap out the whole screen for a completely different one. Then, arbitrary screens can be swapped in at any moment, and all of their event handlers would be reactivated while the inactive screen's event handlers will be deactivated. What type of Swing component/control would I use for each of the 'screens'. Is this even doable?

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  • Use of class definitions inside a method in Java

    - by Bragaadeesh
    Hi public class TestClass { public static void main(String[] args) { TestClass t = new TestClass(); } private static void testMethod(){ class TestMethodClass{ int a; int b; int c; } TestMethodClass testMethodClass = new TestMethodClass(); } } I found out that the above piece of code is perfectly legal in Java. I have the following questions. What is the use of ever having a class definition inside a method? Will a class file be generated for TestMethodClass Its hard for me to imagine this concept in an Object Oriented manner. Having a class definition inside a behavior. Probably can someone tell me with equivalent real world examples. Thanks

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  • How to update a vector in method

    - by gurpinars
    I'm new to C++ and trying to understand vectors. My goal is to update a vector in method: #include <vector> #include <iostream> using namespace std; void test(vector<int>& array){ for(int i=0;i<10;i++){ array.push_back(i); } } int main(){ // some integer value vector<int> array(10); test(array); for(int i=0;i<array.size();++i) cout<<array.at(i)<<endl; cout<<"array size:"<<array.size()<<endl; return 0; } output: 0 0 0 0 0 0 0 0 0 0 0 1 2 3 4 5 6 7 8 9 array size:20 I haven't figure out why 10 zeros add vector at first?

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  • Secure method for linking to image files uploaded via custom CMS

    - by letseatfood
    How does one provide a direct URL for an image file (JPEG) that is secure? For example, if a PHP script writes uploaded images to directory http://www.somehost.com/images, is it okay to provide http://www.somehost.com/images/someimage.jpg as the URL, or is there a more secure way to do this? Should I look into something like the permalink feature that is a part of Wordpress? I am not sure if that is related. The main reason I ask is that I have a custom PHP/MySQL CMS for managing images. I would like for the client to be able to copy a link to the image they want and then include it in a TinyMCE text editor for inserting the image in their website. Thanks!

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  • Why javabeans framework create the IndexedPropertyDescriptor for the NON index method

    - by George Macus
    I'm not familiar with java beans framework, in the below scenario, I got the IndexedPropertyDescriptor for the method getFooWithX, could someone explain why? public class IntrospectorTest { public static void main(String[] args) throws IntrospectionException { BeanInfo info = Introspector.getBeanInfo(SubClass.class); PropertyDescriptor[] descriptors = info.getPropertyDescriptors(); for (int i = 0; i < descriptors.length; i++) { System.out.println(descriptors[i].getClass().getName() + ":" + descriptors[i].getName()); } } } abstract class BaseClass { public abstract Object getFoo(); } abstract class SubClass extends BaseClass { public Object getFooWithX(int x) { return null; } } and the result will be: java.beans.PropertyDescriptor:class java.beans.PropertyDescriptor:foo java.beans.IndexedPropertyDescriptor:fooWithX Why?

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  • Confusing calling method in Java

    - by vBx
    class Parent { private void method1() { System.out.println("Parent's method1()"); } public void method2() { System.out.println("Parent's method2()"); method1(); } } class Child extends Parent { public void method1() { System.out.println("Child's method1()"); } } class test { public static void main(String args[]) { Parent p = new Child(); p.method2(); } } I'm confuse why does in Parent::method2() when invoking method1() it will cal Parents method1() and not Childs method1 ? I see that this happens only when method1() is private? Can someone explain me why ? Thanks you.

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  • aptitude update gives 404's for intrepid

    - by dotjoe
    I'm having issues trying to update my packages. I haven't used this server since last September and now I'm getting 404 errors on all the intrepid repos. How do I fix this? Thanks aptitude update Err http://security.ubuntu.com intrepid-security/main Packages 404 Not Found [IP: 91.189.92.166 80] Err http://security.ubuntu.com intrepid-security/restricted Packages 404 Not Found [IP: 91.189.92.166 80] Err http://security.ubuntu.com intrepid-security/main Sources 404 Not Found [IP: 91.189.92.166 80] Err http://security.ubuntu.com intrepid-security/restricted Sources 404 Not Found [IP: 91.189.92.166 80] Err http://security.ubuntu.com intrepid-security/universe Packages 404 Not Found [IP: 91.189.92.166 80] Err http://security.ubuntu.com intrepid-security/universe Sources 404 Not Found [IP: 91.189.92.166 80] Ign http://us.archive.ubuntu.com intrepid-updates/multiverse Packages Ign http://us.archive.ubuntu.com intrepid-updates/multiverse Sources Err http://us.archive.ubuntu.com intrepid/main Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/restricted Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/main Sources 404 Not Found [IP: 91.189.88.31 80] Err http://security.ubuntu.com intrepid-security/multiverse Packages 404 Not Found [IP: 91.189.92.166 80] Err http://us.archive.ubuntu.com intrepid/restricted Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/universe Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/universe Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/multiverse Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid/multiverse Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/main Packages 404 Not Found [IP: 91.189.88.31 80] Err http://security.ubuntu.com intrepid-security/multiverse Sources 404 Not Found [IP: 91.189.92.166 80] Err http://us.archive.ubuntu.com intrepid-updates/restricted Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/main Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/restricted Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/universe Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/universe Sources 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/multiverse Packages 404 Not Found [IP: 91.189.88.31 80] Err http://us.archive.ubuntu.com intrepid-updates/multiverse Sources 404 Not Found [IP: 91.189.88.31 80] Reading package lists... sources.list # # deb cdrom:[Ubuntu-Server 8.10 _Intrepid Ibex_ - Release i386 (20081028.1)]/ intrepid main restricted # deb cdrom:[Ubuntu-Server 8.10 _Intrepid Ibex_ - Release i386 (20081028.1)]/ intrepid main restricted # See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to # newer versions of the distribution. deb http://us.archive.ubuntu.com/ubuntu/ intrepid main restricted deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid main restricted ## Major bug fix updates produced after the final release of the ## distribution. deb http://us.archive.ubuntu.com/ubuntu/ intrepid-updates main restricted deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-updates main restricted ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team. Also, please note that software in universe WILL NOT receive any ## review or updates from the Ubuntu security team. deb http://us.archive.ubuntu.com/ubuntu/ intrepid universe deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid universe deb http://us.archive.ubuntu.com/ubuntu/ intrepid-updates universe deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-updates universe ## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu ## team, and may not be under a free licence. Please satisfy yourself as to ## your rights to use the software. Also, please note that software in ## multiverse WILL NOT receive any review or updates from the Ubuntu ## security team. deb http://us.archive.ubuntu.com/ubuntu/ intrepid multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid multiverse deb http://us.archive.ubuntu.com/ubuntu/ intrepid-updates multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-updates multiverse ## Uncomment the following two lines to add software from the 'backports' ## repository. ## N.B. software from this repository may not have been tested as ## extensively as that contained in the main release, although it includes ## newer versions of some applications which may provide useful features. ## Also, please note that software in backports WILL NOT receive any review ## or updates from the Ubuntu security team. # deb http://us.archive.ubuntu.com/ubuntu/ intrepid-backports main restricted universe multiverse # deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-backports main restricted universe multiverse ## Uncomment the following two lines to add software from Canonical's ## 'partner' repository. This software is not part of Ubuntu, but is ## offered by Canonical and the respective vendors as a service to Ubuntu ## users. # deb http://archive.canonical.com/ubuntu intrepid partner # deb-src http://archive.canonical.com/ubuntu intrepid partner deb http://us.archive.ubuntu.com/ubuntu/ intrepid-security main restricted deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-security main restricted deb http://us.archive.ubuntu.com/ubuntu/ intrepid-security universe deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-security universe deb http://us.archive.ubuntu.com/ubuntu/ intrepid-security multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ intrepid-security multiverse

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