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• abstract class NumberFormat - very confuse about getInstance()

  - by Alex

  Hi, I'm new to Java and I have a beginner question: NumberFormat is an abstract class and so I assume I can't make an instance of it. But there is a public static (factory?) method getInstance() that allow me to do NumberFormat nf = NumberFormat.getInstance(); I'm quite confuse. I'll be glad if someone could give me hints on: 1) If there is a public method to get an instance of this abstract class, why don't we have also a constructor? 2) This is an abstract class ; how can we have this static method giving us an instance of the class? 3) Why choosing such a design? If I assume it's possible to have an instance of an abstract class (???), I don't get why this class should be abstract at all. Thank you.

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• abstract class NumberFormat - very confused about getInstance()

  - by Alex

  Hi, I'm new to Java and I have a beginner question: NumberFormat is an abstract class and so I assume I can't make an instance of it. But there is a public static (factory?) method getInstance() that allow me to do NumberFormat nf = NumberFormat.getInstance(); I'm quite confuse. I'll be glad if someone could give me hints on: 1) If there is a public method to get an instance of this abstract class, why don't we have also a constructor? 2) This is an abstract class ; how can we have this static method giving us an instance of the class? 3) Why choosing such a design? If I assume it's possible to have an instance of an abstract class (???), I don't get why this class should be abstract at all. Thank you.

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• NetBeans 6.8/6.7 UML Class Diagrams

  - by ikurtz

  i have tried to generate Class Diagrams in NetBeans 6.7 and 6.8 but all i get is: i figured out installing UML for 6.8 here: NetBeans 6.8 UML i have followed the instructions here: UML Class diagrams i so far i failed to generate anything meaningful. i have followed the tips: Open your project, then create a new UML project (choose "Reverse Engineered Java-Platform model"). After that all your classes will be available in the UML project under "Model". You can now create a new class diagram and drag your classes from "Model" onto the diagram. but nothing meaningful happens when i drag my classes to the Class Diagrams. it always represents the classes as "datatype" on the diagram and class info is not displayed. any helpful tips regarding how can i fix this? or another way of generating Java class diagrams? thank you for your time.

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• change the class loading order google app engine java

  - by Shekhar

  I am trying to create an application on google app engine using struts2. Struts2 internally uses freemarker .One of the Freemarker framework classes suppose X internally uses a class javax.swing.Treenode which is not in google app engine jre white list. Now in order to run my application i created a new class X in the same package structure as it was in freemarker framework and copied the class to WEB-INF classes.Then When i run my application it run fine. The problem is that i want to take out the class X from my application sourcecode and move it to newly created jar and place it in WEB-INF/lib folder. So that i can reuse the code in multiple project and my code remains clean of the freemarker code. But when i run the application it picks the old class X from the original freemarker framework.As a result i get ClassNotFoundException. Can anyone provide any help such that i can change the ClassLoading order such that my jar containing X class loads first.

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• ZipArchive php Class - Does it support all servers?

  - by SoLoGHoST

  Ok, just wondering on the versions of PHP that this class is built into. And if they are built into all platforms (OS's). I'm wanting an approach to search through a zip file and place files using file_put_contents in different filepaths within the webroot. In any case, I'm familiar with how to do this with the ZipArchive class, but I'm wondering if using this class would be a good solution and support MOST, if not ALL servers?? I mean, I'd rather not use a method that requires the Server to have it installed. I'm looking for a solution to this that will support at least MOST servers without having to install the class... Thanks :) Also, I'd like to support opening tar.gz and/or .tgz files if possible, but I don't think the ZipArchive class supports this, but perhaps a different built-in php class does??

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• Visual Studio: Design a UserControl class that derives from an abstract base class

  - by Marcel

  Hi All, I want to have an abstract base class for some of my custom UserControl's. The reason is obvious: they share some common properties and methods (a basic implementation of some elements of an interface actually), and I want to implement them only once. I have done this by defining my abstract base class: public abstract class ViewBase : UserControl, ISomeInterface Then I went to implement one of my views, as usual, with the designer: public partial class SpecialView : UserControl //all OK Up to here all is fine. Now I replace the derivation of my SpecialView class with the abstract base class: public partial class SpecialView : ViewBase //disrupts the designer Now, the designer in Visual Studio 2008 won't work anymore, stating: The designer must create an instance of type 'ViewBase' but it cannot because the type is declared as abstract. How can I circumvent this? I just do not want to have the same code copied for all those views. Info: there is a question question with virtual methods, instead of abstract classes, but there is no suitable solution for me.

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• Class Methods Inheritence

  - by Roman A. Taycher

  I was told that static methods in java didn't have Inheritance but when I try the following test package test1; public class Main { /** * @param args the command line arguments */ public static void main(String[] args) { TB.ttt(); TB.ttt2(); } } package test1; public class TA { static public Boolean ttt() { System.out.println("TestInheritenceA"); return true; } static public String test ="ClassA"; } package test1; public class TB extends TA{ static public void ttt2(){ System.out.println(test); } } it printed : TestInheritenceA ClassA so do java static methods (and fields have) inheritance (if you try to call a class method does it go down the inheritance chai looking for class methods). Was this ever not the case,are there any inheritance OO languages that are messed up like that for class methods?

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• C++ Class Inheritance architecture - preventing casting

  - by Some One

  I have a structure of base class and a couple of inherited classed. Base class should be pure virtual class, it should prevent instantiation. Inherited classes can be instantiated. Code example below: class BaseClass { public: BaseClass(void); virtual ~BaseClass(void) = 0; }; class InheritedClass : public BaseClass { public: InheritedClass1(void); ~InheritedClass1(void); }; class DifferentInheritedClass : public BaseClass { public: DifferentInheritedClass(void); ~DifferentInheritedClass(void); }; I want to prevent the following operations to happen: InheritedClass *inherited1 = new InheritedClass(); DifferentInheritedClass *inherited2 = new DifferentInheritedClass (); BaseClass *base_1 = inherited1; BaseClass *base_2 = inherited2; *base_1 = *base_2;

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• method __getattr__ is not inherited from parent class

  - by ??????

  Trying to subclass mechanize.Browser class: from mechanize import Browser class LLManager(Browser, object): IS_AUTHORIZED = False def __init__(self, login = "", passw = "", *args, **kwargs): super(LLManager, self).__init__(*args, **kwargs) self.set_handle_robots(False) But when I make something like this: lm["Widget[LinksList]_link_1_title"] = anc then I get an error: Traceback (most recent call last): File "<pyshell#8>", line 1, in <module> lm["Widget[LinksList]_link_1_title"] = anc TypeError: 'LLManager' object does not support item assignment Browser class have overridden method __getattr__ as shown: def __getattr__(self, name): # pass through _form.HTMLForm methods and attributes form = self.__dict__.get("form") if form is None: raise AttributeError( "%s instance has no attribute %s (perhaps you forgot to " ".select_form()?)" % (self.__class__, name)) return getattr(form, name) Why my class or instance don't get this method as in parent class?

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• jQuery to target CSS a:hover class

  - by songdogtech

  Confused here. What's the best way to change the hover CSS of the link below, and how? toggle.Class? add.Class? I want to show an image on hover. I have been able to change the color of the text with $("#menu-item-1099 a:contains('rss')").css("color", "#5d5d5d"); but can't seem to target the hover class. <div id="access"> <div class="menu-header"> <ul id="menu-main-menu" class="menu"> <li id="menu-item-1099" class="menu-item menu-item-type-custom menu-item-1099"> <a href="http://mydomain.com/feed/">rss</a></li>

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• Testing for the existence of a field in a class

  - by Brett

  Hi, i have a quick question. I have a 2D array that stores an instance of a class. The elements of the array are assigned a particular class based on a text file that is read earlier in the program. Since i do not know without looking in the file what class is stored at a particular element i could refer to a field that doesn't exist at that index (referring to appearance when an instance of temp is stored in that index). i have come up with a method of testing this, but it is long winded and requires a second matrix. Is there a function to test for the existence of a field in a class? class temp(): name = "default" class temp1(): appearance = "@"

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• Create Generic Class Instance from Static Method in a Derived Class

  - by user343547

  I have a class in C# with a template and static method similar to class BClass<T> { public static BClass<T> Create() { return new BClass<T>(); } } From this I derive a class and specify a template parameter to the base class class DClass : BClass<int> { } A problem occurs when I try to use the static method to create an instance of D class Program { static void Main(string[] args) { DClass d = DClass.Create(); } } Gives a compiler error "Cannot implicitly convert type 'Test.BClass<int ' to 'Test.DClass'." Adding the below cast leads to a runtime casting exception. DClass d = (DClass)DClass.Create(); Is there any succint way to allow the static method to create instances of the derived class? Ideally I would like the equivalent of a c++ typedef and I don't want the below syntax (which does work). BClass<int> d = DClass.Create();

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• how to get a specific class object

  - by user1275129

  I am still quite new to class concept. I have a problem here. for example, i have a class called class p{ int id; p(id){ //constructor } } now, i want to make instances of class p. After i have all the instances. i want to build a function get_p(pid) to return the specific class p which id=pid, how can i write this part? I have read c++ and java class tutorials, but i cant sort this out. please help me.

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• Possible Conflict with Class name & Property Name?

  - by coffeeaddict

  If you have a namespace that contains a property in ClassA and a class that has the name of that Property somewhere else in your project and both are in the same namespace this won't cause conflicts will it? So lets say I have a class named Car namespace Dealer { class Vehicle { // the main class that defines vehicle, so this is Dealer.Vehicle (Vehicle.cs) } } and a property over in some other class namespace Dealer { class Dealer { public Vehicle Vehicle { get { return _vehicle; } } } } so for the second it is really this for the property public Dealer.Vehicle Vehicle { get { return _car; } } so now you have Dealer.Vehicle and Dealer.Dealer.Vehicle. Wondering of that would cause a conflict ever. If both those classes are in the same namespace and

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• Figuring out what makes a C++ class abstract in VS2008

  - by suszterpatt

  I'm using VS2008 to build a plain old C++ program (not C++/CLI). I have an abstract base class and a non-abstract derived class, and building this: Base* obj; obj = new Derived(); fails with the error "'Derived': cannot instantiate abstract class". (It may be worth noting, however, that if I hover over Base with the cursor, VS will pop up a tooltip saying "class Base abstract", but hovering over Derived will only say "class Derived" (no "abstract")). The definitions of these classes are fairly large and I'd like to avoid manually checking if each method has been overridden. Can VS do this for me somehow? Any general tips on pinpointing the exact parts of the class' definition that make it abstract?

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• C++ Basic Class Layout

  - by Spencer

  Learning C++ and see the class laid out like this: class CRectangle { int x, y; public: void set_values (int,int); int area () {return (x*y);} }; void CRectangle::set_values (int a, int b) { x = a; y = b; } I know Java and methods(functions) in Java are written within the class. The class looks like a Java interface. I know I can write the class like this: class CRectangle { int x, y; public: void set_values (int a, int b) { x = a; y = b; }; int area () {return (x*y);} }; But is there a difference or standard?

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• I can't set main Class variable in onCreate Method

  - by natrollus

  Main class has two variables that want to reach another class: public class MyClassA extends Activity { int i = 1; Button b1; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); this.i = 31; this.b1 = (Button) findViewById(R.id.btn1); ~~ } } Second class want to call variables in mainClass object: public class MyclassB implements OnClickListener{ MyClassA mainClass = new MyClassA(); Button btn = mainClass.b1; int n = mainClass.i; public void OnClick(View arg0){ Log.v("btn:",btn); Log.v("int:",n); } //btn returns null; //int returns 1; But onCreate method not set variables.. Why not set main class variables like this.i=31 ?

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• Implement abstract class as a local class? pros and cons

  - by sinec

  Hi, for some reason I'm thinking on implementing interface within a some function(method) as local class. Consider following: class A{ public: virtual void MethodToOverride() = 0; }; A * GetPtrToAImplementation(){ class B : public A { public: B(){} ~B(){} void MethodToOverride() { //do something } }; return static_cast<A *>(new B()); } int _tmain(int argc, _TCHAR* argv[]) { A * aInst = GetPtrToAImplementation(); aInst->MethodToOverride(); delete aInst; return 0; } the reason why I'm doing this are: I'm lazy to implement class (B) in separate files MethodToOverride just delegates call to other class Class B shouldn't be visible to other users no need to worry about deleting aInst since smart pointers are used in real implementation So my question is if I'm doing this right? Thanks in advance!

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• How do i get (is it possible to) a reference to the class that creates an instance of another class.

  - by Cadde

  Odd situation... I need to create a new instance of a class that needs a member of the calling class. But i can't pass a reference to the calling class through the constructor. The solution i am looking for is something like this: Public Class ChildClass Public Sub New(args) _MyMember = GetMemberFromCallingClass() ... ... End Sub End Class I want this to work without having to manually pass any references or variables from the calling class to the new instance of ChildClass. Is this possible and if so, what should i look at to make this part of my code.

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• this pointer to base class constructor?

  - by Rolle

  I want to implement a derived class that should also implement an interface, that have a function that the base class can call. The following gives a warning as it is not safe to pass a this pointer to the base class constructor: struct IInterface { void FuncToCall() = 0; }; struct Base { Base(IInterface* inter) { m_inter = inter; } void SomeFunc() { inter->FuncToCall(); } IInterface* m_inter; }; struct Derived : Base, IInterface { Derived() : Base(this) {} FuncToCall() {} }; What is the best way around this? I need to supply the interface as an argument to the base constructor, as it is not always the dervied class that is the interface; sometimes it may be a totally different class. I could add a function to the base class, SetInterface(IInterface* inter), but I would like to avoid that.

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• Tip #19 Module Private Visibility in OSGi

  - by ByronNevins

  I hate public and protected methods and classes.  It requires so much work to change them in a huge project like GlassFish.  Not to mention that you may well have to support those APIs forever.  They are highly overused in GlassFish.  In fact I'd bet that > 95% of classes are marked as public for no good reason.  It's just (bad) habit is my guess. private and default visibility (I call it package-private) is easier to maintain.  It is much much easier to change such classes and methods around.  If you have ANY public method or public class in GlassFish you'll need to grep through a tremendous amount of source code to find all callers.  But even that won't be theoretically reliable.  What if a caller is using reflection to access public methods?  You may never find such usages. If you have package private methods, it's easy.  Simply grep through all the code in that one package.  As long as that package compiles ok you're all set.  There can' be any compile errors anywhere else.  It's a waste of time to even look around or build the "outside" world.  So you may be thinking: "Aha!  I'll just make my module have one giant package with all the java files.  Then I can use the default visibility and maintenance will be much easier.  But there's a problem.  You are wasting a very nice feature of java -- organizing code into separate packages.  It also makes the code much more encapsulated.  Unfortunately to share code between the packages you have no choice but to declare public visibility. What happens in practice is that a module ends up having tons of public classes and methods that are used exclusively inside the module.  Which finally brings me to the point of this blog:  If Only There Was A Module-Private Visibility Available Well, surprise!  There is such a mechanism.  If your project is running under OSGi that is.  Like GlassFish does!  With this mechanism you can easily add another level of visibility by telling OSGi exactly which public you want to be exposed outside of the module.  You get the best of both worlds: Better encapsulation of your code so that maintenance is easier and productivity is increased. Usage of public visibility inside the module so that you can encapsulate intra-module better with packages. How I do this in GlassFish: Carefully plan out at least one package that will contain "true" publics.  This is the package that will be exported by OSGi.  I recommend just one package. Here is how to tell OSGi to use it in GlassFish -- edit osgi.bundle like so:-exportcontents:     org.glassfish.mymodule.truepublics;  version=${project.osgi.version} Now all publics declared in any other packages will be visible module-wide but not outside the module. There is one caveat: Accessing "module-private" items outside of the module is controlled at run-time, not compile-time.  The compiler has no clue that a public in a dependent module isn't really public.  it will happily compile it.  At runtime you will definitely see fireworks.  The good news is that you don't have to wait for the code path that tries to use the "module-private" items to fire.  OSGi will complain loudly when that module gets loaded.  OSGi will refuse to load it.  You will see an error like this: remote failure: Error while loading FOO: Exception while adding the new configuration : Error occurred during deployment: Exception while loading the app : org.osgi.framework.BundleException: Unresolved constraint in bundle com.oracle.glassfish.miscreant.code [115]: Unable to resolve 115.0: missing requirement [115.0] osgi.wiring.package; (osgi.wiring.package=org.glassfish.mymodule.unexported). Please see server.log for more details. That is if you accidentally change code in module B to use a public that is really a "module-private" in module A, then you will see the error immediately when you try to test whatever you were changing in module B.

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• add a div.class in a child, only when the parent does not have other div.class

  - by armandfp

  i have a html code like this: <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> </div> and i need to add a div only on those divs that dont have that "checkclass", so it will like this: <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="newclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="checkclass"></div> </div> <div class="someclass"> <div class="childclass"></div> <div class="newclass"></div> </div> i tried with jquery something like: $('.someclase:not(children(hasClass(checkclass))').append('<div class="newclass"></div>'); $('.someclass:not(:children(.checkclass))').append('<div class="newclass"></div>'); $('.someclass > :not(.checkclass)').append('<div class="newclass"></div>'); but still nothing, any ideas?

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• Unique ID Defined by Most-Derived Class accessible through Base Class

  - by Narfanator

  Okay, so, the idea is that I have a map of "components", which inherit from componentBase, and are keyed on an ID unique to the most-derived*. Only, I can't think of a good way to get this to work. I tried it with the constructor, but that doesn't work (Maybe I did it wrong). The problem with any virtual, etc, inheritance tricks are that the user has to impliment them at the bottom, which can be forgotten and makes it less... clean. *Right phrase? If - is inheritance; foo is most-derived: foo-foo1-foo2-componentBase Here's some code showing the problem, and why CRTP can't cut it: (No, it's not legit code, but I'm trying to get my thoughts down) #include<map> class componentBase { public: virtual static char idFunction() = 0; }; template <class T> class component : public virtual componentBase { public: static char idFunction(){ return reinterpret_cast<char>(&idFunction); } }; class intermediateDerivations1 : public virtual component<intermediateDerivations1> { }; class intermediateDerivations2 : public virtual component<intermediateDerivations2> { }; class derived1 : public intermediateDerivations1 { }; class derived2 : public intermediateDerivations1 { }; //How the unique ID gets used (more or less) std::map<char, componentBase*> TheMap; template<class T> void addToMap(componentBase * c) { TheMap[T::idFunction()] = c; } template<class T> T * getFromMap() { return TheMap[T::idFunction()]; } int main() { //In each case, the key needs to be different. //For these, the CRTP should do it: getFromMap<intermediateDerivations1>(); getFromMap<intermediateDerivations2>(); //But not for these. getFromMap<derived1>(); getFromMap<derived2>(); return 0; } More or less, I need something that is always there, no matter what the user does, and has a sortable value that's unique to the most-derived class. Also, I realize this isn't the best-asked question, I'm actually having some unexpected difficultly wrapping my head around it in words, so ask questions if/when you need clarification.

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• copy array from one class to another class array

  - by shishir.bobby

  hi all, i hv an array ("array A", which contains 3 objects, fox ex, to,from,message) in class "A". and in class "B",i m having another array ("array B"),which fills tableview,of class "B" only. i need to fill tableview,with the values of class A's array (i.e array A,with the object values, to,from,message). how can i do it?? how to copy array from another class ? i hope i m clear with my question regards shishir

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• Why getResourceAsStream method is in Class class?

  - by anupsth

  Why public InputStream getResourceAsStream(String name) is in Class class? It just give inputstream of file which is in jar file and there is no relation with Class class. so it can be static method and it can be in any class.

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