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• Perl - Calling subclass constructor from superclass (OO)

  - by Emmel

  This may turn out to be an embarrassingly stupid question, but better than potentially creating embarrassingly stupid code. :-) This is an OO design question, really. Let's say I have an object class 'Foos' that represents a set of dynamic configuration elements, which are obtained by querying a command on disk, 'mycrazyfoos -getconfig'. Let's say that there are two categories of behavior that I want 'Foos' objects to have: Existing ones: one is, query ones that exist in the command output I just mentioned (/usr/bin/mycrazyfoos -getconfig`. Make modifications to existing ones via shelling out commands. Create new ones that don't exist; new 'crazyfoos', using a complex set of /usr/bin/mycrazyfoos commands and parameters. Here I'm not really just querying, but actually running a bunch of system() commands. Affecting changes. Here's my class structure: Foos.pm package Foos, which has a new($hashref-{name = 'myfooname',) constructor that takes a 'crazyfoo NAME' and then queries the existence of that NAME to see if it already exists (by shelling out and running the mycrazyfoos command above). If that crazyfoo already exists, return a Foos::Existing object. Any changes to this object requires shelling out, running commands and getting confirmation that everything ran okay. If this is the way to go, then the new() constructor needs to have a test to see which subclass constructor to use (if that even makes sense in this context). Here are the subclasses: Foos/Existing.pm As mentioned above, this is for when a Foos object already exists. Foos/Pending.pm This is an object that will be created if, in the above, the 'crazyfoo NAME' doesn't actually exist. In this case, the new() constructor above will be checked for additional parameters, and it will go ahead and, when called using -create() shell out using system() and create a new object... possibly returning an 'Existing' one... OR As I type this out, I am realizing it is perhaps it's better to have a single: (an alternative arrangement) Foos class, that has a -new() that takes just a name -create() that takes additional creation parameters -delete(), -change() and other params that affect ones that exist; that will have to just be checked dynamically. So here we are, two main directions to go with this. I'm curious which would be the more intelligent way to go.

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• What is a good practice to access class attributes in class methods?

  - by Clem

  I always wonder about the best way to access a class attribute from a class method in Java. Could you quickly convince me about which one of the 3 solutions below (or a totally different one :P) is a good practice? public class Test { String a; public String getA(){ return this.a; } public setA(String a){ this.a = a; } // Using Getter public void display(){ // Solution 1 System.out.println(this.a); // Solution 2 System.out.println(getA()); // Solution 3 System.out.println(this.getA()); } // Using Setter public void myMethod(String b, String c){ // Solution 1 this.a = b + c; // Solution 2 setA(b + c); // Solution 3 this.setA(b + c); } }

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• Best way to insert items from a Derived class's constructor into a Base class's private std::vector?

  - by Will

  I have these classes: class Base { ... private: std::vector<X> v; }; class Derived { Derived(X*, int n); } where the constructor of Derived is passed an array of item Xs, which I need to insert into my vector v in the Base class. (X is a smart pointer) Currently I see two ways to do this: 1) Create a function in Base: InsertItem(X*) that will insert an item into the vector. 2) Create a vector in Derived that contains the full list, then get it into Base by moving the entire vector. I dont see any advantages to #2, but was wondering if #1 was a good solution, or if there are better ways to do this. Thanks!

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• Are raw C++ pointers first class objects?

  - by Shailesh Kumar

  According to Wikipedia: An object is first-class when it: can be stored in variables and data structures can be passed as a parameter to a subroutine can be returned as the result of a subroutine can be constructed at runtime has intrinsic identity (independent of any given name) Somebody had once told me that raw pointers are not first class objects while smart pointers like std::auto_ptr are. But to me, a raw pointer (to an object or to a function) in C++ does seem to me to satisfy the conditions stated above to qualify as a first class object. Am I missing something?

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• PHP Array To Class Static Public Values.

  - by what

  I want to make a class that has all the values of an array as a static object in that class. For example: $vars=array(... );//some array with actual values $Class_code='class MyClass{'; for($i=0; $i<count($vars); $i++){ $Class_code.='static public $'.strval($vars[i]).';'; } eval($Class_code.'}'); /* When I echo the line above it says that the vars for MyClass (MyClass::vars) are missing even with strval(). */ So, how can I get $vars[i] to be a string if strval didn't work?

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• How to initialise a STL vector/list with a class without invoking the copy constructor

  - by Warpspace

  I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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• How to find full module path of a class to import in other file

  - by Pooya

  I have method that returns module path of given class name def findModulePath(path, className): attributes = [] for root, dirs, files in os.walk(path): for source in (s for s in files if s.endswith(".py")): name = os.path.splitext(os.path.basename(source))[0] full_name = os.path.splitext(source)[0].replace(os.path.sep, '.') m = imp.load_module(full_name, *imp.find_module(name, [root])) try: attr = getattr(m, className) attributes.append(attr) except: pass if len(attributes) <= 0: raise Exception, "Class %s not found" % className for element in attributes: print "%s.%s" % (element.__module__, className) but it does not return the full path of the module, For example I have a python file named "objectmodel" in objects package,and it contains a Model class, So I call findModulePath(MyProjectPath,"Model"). it prints objectmodel.Model but I need objects.objectmodel.Model

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• Is extending a singleton class wrong?

  - by Anwar Shaikh

  I am creating a logger for an application. I am using a third party logger library. In which logger is implemented as singleton. I extended that logger class because I want to add some more static functions. In these static functions I internally use the instance (which is single) of Logger(which i inherited). I neither creates instance of MyLogger nor re-implemented the getInstance() method of super class. But I am still getting warnings like destructor of MyLogger can not be created as parent class (Loggger) destructor is not accessible. I want to know, I am I doing something wrong? Inheriting the singleton is wrong or should be avoided??

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• Console class in java Exception in reading password

  - by satheesh

  Hi, i am trying to use Console class in java. with this code import java.io.Console; public class ConsoleClass { public static void main(String[] args){ Console c=System.console(); char[] pw; pw=c.readPassword("%s","pw :"); for(char ch:pw){ c.format("%c",ch); } c.format("\n"); MyUtility mu =new MyUtility(); while(true){ String name=c.readLine("%s", "input?: "); c.format("output: %s \n",mu.doStuff(name)); } } } class MyUtility{ String doStuff(String arg1){ return "result is " +arg1; } } here i am getting NullPointerException when i tried to run in netbeans but i am not getting any Exception when tried to run in cmd with out netbeans IDE.Why?

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• consts and other animals

  - by bks

  Hello i have a cpp code wich i'm having trouble reading. a class B is defined now, i understand the first two lines, but the rest isn't clear enough. is the line "B const * pa2 = pa1" defines a const variable of type class B? if so, what does the next line do? B a2(2); B *pa1 = new B(a2); B const * pa2 = pa1; B const * const pa3 = pa2; also, i'm having trouble figuring out the difference between these two: char const *cst = “abc”; const int ci = 15; thank you

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• C#: reflection alternative for switch on enum in order to select namespace/class

  - by Am

  Hi, I have an interface named IHarvester. There are 3 implementations of that interface, each under their own namespace: Google Yahoo Bing A HarvesterManager uses the given harvester. It knows the interface and all 3 implementations. I want some way of letting the class user say in which harvester it wants to use. And in the code select that implementation, without a switch-case implementation. Can reflection save my day? Here is the code bits: // repeat for each harvester namespace Harvester.Google { public abstract class Fetcher : BaseHarvester, IInfoHarvester {...} } public enum HarvestingSource { Google, Yahoo, Bing, } class HarvesterManager { public HarvestingSource PreferedSource {get;set;} public HarvestSomthing() { switch (PreferedSource) .... // awful... } } Thanks.

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• Running a java program in linux terminal with -class path

  - by Arya

  Hello I've been trying for an hour to run the following program with a the postgresql classpath class Test{ public static void main(String[] args){ try { Class.forName("org.postgresql.Driver"); } catch (ClassNotFoundException cnfe) { System.err.println("Couldn't find Postgresql driver class!"); } } } The program compiled fine with the javac command, but I'm having a hard time running it with the postgresql classpath. I have "postgresql-9.0-801.jdbc4.jar" in the same directory as the file and I tried the following, but non of them worked java -classpath ./postgresql-9.0-801.jdbc4.jar Test java -classpath postgresql-9.0-801.jdbc4.jar Test java -classpath "postgresql-9.0-801.jdbc4.jar" Test What am I doing wrong? Regards!

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• How to call constructor of the current class and parent class at the same time?

  - by Siegfried

  public class A{ public A(int a, int b) {...} } public class B : A{ List a; List b; public B(){...} //constructor1 public B(int a, int b) : base(a,b){...} //constructor2 } My question is I need to initialize both list a and b in class B. If I put them in the constructor1, how can I call constructor1 in constructor2? I don't want to rewrite the initialization statements in constructor2 again. Thanks!

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• VS 2010 Entity Repository Error Class member EntityBase.id is unmapped.

  - by Steve

  In my project I have it set up so that all the tables in the DB has the property "id" and then I have the entity objects inherit from the EntityBase class using a repository pattern. I then set the inheritance modifier for "id" property in the dbml file o/r designer to "overrides" Public MustInherit Class EntityBase MustOverride Property id() As Integer End Class Public MustInherit Class RepositoryBase(Of T As EntityBase) Protected _Db As New DataClasses1DataContext Public Function GetById(ByVal Id As Integer) As T Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault End Function End Class Partial Public Class Entity1 Inherits EntityBase End Class Public Class TestRepository Inherits RepositoryBase(Of Entity1) End Class the line Return (From a In _Db.GetTable(Of T)() Where a.id = Id).SingleOrDefault however produces the error "Class member EntityBase.id is unmapped" when i use VS 2010 using the 4.0 framework but I never received that error with the old one. Any help would be greatly appreciated. Thanks in advance.

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• ActionScript Accessing Functions/Vars From Outside Of Class

  - by TheDarkIn1978

  how can i call public functions or vars of a sprite class from another class (or frame script)? i keep getting 1061: Call to a possibly undefined method (function i'm trying to call) through a reference with static type flash.display:Sprite. //Framescript var a:Sprite = new customRect(); addChild(a); a.getSide(); //.as file package { import flash.display.Sprite; public class customRect extends Sprite { public var side:Number; private function customRect() { var box:Sprite = new Sprite(); box.graphics.beginFill(); box.graphics.drawRect(0, 0, 200, 200); box.graphics.endFill(); side = box.width; } public function getSide():void { trace(side); } } }

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• C++ method chaining including class constructor

  - by jena

  Hello, I'm trying to implement method chaining in C++, which turns out to be quite easy if the constructor call of a class is a separate statement, e.g: Foo foo; foo.bar().baz(); But as soon as the constructor call becomes part of the method chain, the compiler complains about expecting ";" in place of "." immediately after the constructor call: Foo foo().bar().baz(); I'm wondering now if this is actually possible in C++. Here is my test class: class Foo { public: Foo() { } Foo& bar() { return *this; } Foo& baz() { return *this; } }; I also found an example for "fluent interfaces" in C++ (http://en.wikipedia.org/wiki/Fluent_interface#C.2B.2B) which seems to be exactly what I'm searching for. However, I get the same compiler error for that code. Thanks in advance for any hint. Best, Jean

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• why primitive type will call first rather than wrapper classes?

  - by kandarp

  Hello EveryOne, public class A { public void test(Integer i) { System.out.println("In Wrapper Method"); } public void test(int i) { System.out.println("In primitive Method"); } public static void main(String args[]) { A a = new A(); a.test(5); } } When I will call test method from main and pass integer argument, then it will call the method which accept primitive type as argument. I just want to know that why it call primitive type method rather than the method who accepts wrapper class as argument? Is there any rule, which java follow to call methods? Thanks,

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• C++ Beginner - 'friend' functions and << operator overloading: What is the proper way to overload an

  - by Francisco P.

  Hello, everyone! In a project I'm working on, I have a Score class, defined below in score.h. I am trying to overload it so, when a << operation is performed on it, _points + " " + _name is returned. Here's what I tried to do: ostream & Score::operator<< (ostream & os, Score right) { os << right.getPoints() << " " << right.scoreGetName(); return os; } Here are the errors returned: 1>c:\users\francisco\documents\feup\1a2s\prog\projecto3\projecto3\score.h(30) : error C2804: binary 'operator <<' has too many parameters (This error appears 4 times, actually) I managed to get it working by declaring the overload as a friend function: friend ostream & operator<< (ostream & os, Score right); And removing the Score:: from the function declaration in score.cpp (effectively not declaring it as a member). Why does this work, yet the code describe above doesn't? Thanks for your time! Below is the full score.h /////////////////////////////////////////////////////////// // Score.h // Implementation of the Class Score // Created on: 10-Mai-2010 11:43:56 // Original author: Francisco /////////////////////////////////////////////////////////// #ifndef SCORE_H_ #define SCORE_H_ #include <string> #include <iostream> #include <iostream> using std::string; using std::ostream; class Score { public: Score(string name); Score(); virtual ~Score(); void addPoints(int n); string scoreGetName() const; int getPoints() const; void scoreSetName(string name); bool operator>(const Score right) const; ostream & operator<< (ostream & os, Score right); private: string _name; int _points; }; #endif

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• FindBugs and CheckForNull on classes vs. interfaces

  - by ndn

  Is there any way to let FindBugs check and warn me if a CheckForNull annotation is present on the implementation of a method in a class, but not on the declaration of the method in the interface? import javax.annotation.CheckForNull; interface Foo { public String getBar(); } class FooImpl implements Foo { @CheckForNull @Override public String getBar() { return null; } } public class FindBugsDemo { public static void main(String[] args) { Foo foo = new FooImpl(); System.out.println(foo.getBar().length()); } } I just discovered a bug in my application due to a missing null check that was not spotted by FindBugs because CheckForNull was only present on FooImpl, but not on Foo, and I don't want to spot all other locations of this problem manually.

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• How to use the vtable to determine class type

  - by Alex Silverman

  I was recently on an interview for a position where C/C++ is the primary language and during one question I was told that it's possible to use the vtable to determine which class in a hierarchy a base pointer actually stores. So if, for example you have class A { public: A() {} virtual ~A() {} virtual void method1() {} }; class B : public A { public: B() {} virtual ~B() {} virtual void method1() {} }; and you instantiate A * pFoo = new B(), is it indeed possible to use the vtable to determine whether pFoo contains a pointer to an instance of A or B?

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• How to Execute Page_Load() in Page's Base Class?

  - by DaveDev

  I have the following PerformanceFactsheet.aspx.cs page class public partial class PerformanceFactsheet : FactsheetBase { protected void Page_Load(object sender, EventArgs e) { // do stuff with the data extracted in FactsheetBase divPerformance.Controls.Add(this.Data); } } where FactsheetBase is defined as public class FactsheetBase : System.Web.UI.Page { public MyPageData Data { get; set; } protected void Page_Load(object sender, EventArgs e) { // get data that's common to all implementors of FactsheetBase // and store the values in FactsheetBase's properties this.Data = ExtractPageData(Request.QueryString["data"]); } } The problem is that FactsheetBase's Page_Load is not executing. Can anyone tell me what I'm doing wrong? Is there a better way to get the result I'm after? Thanks

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• How to deal with constructor argument names?

  - by Bane

  Say I have a class that has some properties, like x, y, width and height. In its constructor, I couldn't do this: class A { public: A(int, int, int, int); int x; int y; int width; int height; }; //Wrong and makes little sense name-wise: A::A(int x, int y, int width, int height) { x = x; y = y; width = width; height = height; } First of all, this doesn't really make sense. Second, x, y, width and height become some weird values (-1405737648) when compiled using g++. It does work, however, if I append "a" to the argument names. What is the optimal way of solving these naming conflicts?

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• Access parent class from custom attribute

  - by madcapnmckay

  Hi, Is it possible to access a parent class from within an attribute. For example I would like to create a DropDownListAttribute which can be applied to a property of a viewmodel class in MVC and then create a drop down list from an editor template. I am following a similar line as Kazi Manzur Rashid here. He adds the collection of categories into viewdata and retrieves them using the key supplied to the attribute. I would like to do something like the below, public ExampleDropDownViewModel { public IEnumerable<SelectListItem> Categories {get;set;} [DropDownList("Categories")] public int CategoryID { get;set; } } The attribute takes the name of the property containing the collection to bind to. I can't figure out how to access a property on the parent class of the attribute. Does anyone know how to do this? Thanks

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• Make Java parent class not part of the interface

  - by Bart van Heukelom

  (This is a hypothetical question for discussion, I have no actual problem). Say that I'm making an implementation of SortedSet by extending LinkedHashMap: class LinkedHashSortedMapThing extends LinkedHashMap implements SortedSet { ... } Now programmers who use this class may do LinkedHashMap x = new LinkedHashSortedMapThing(); But what if I consider the extending of LinkedHashMap an implementation detail, and do not want it to be a part of the class' contract? If people use the line above, I can no longer freely change this detail without worrying about breaking existing code. Is there any way to prevent this sort of thing, other than favouring composition over inheritance (which is not always possible due to private/protected members)?

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• Other class view cannot be loaded into TabBar Controller

  - by SkyEagle888

  Hi, I am making a project with 3 child views that are switched by a TabBar. What I did Create a project (Window-Based) Add 3 child classes (Window-Based too) Add a Tab Bar Controller to MainWindow.xib For each view under Tab Bar Controller, the 'Class', 'Name', 'Title' and 'NIB Name' are all set to connect to the corresponding class Add @class, IBOutlet are done in AppDelegate.h and AppDelegate.m In didFinishLaunchingWithOptions, I called [window addSubView: tabBarController.view]; Save and Run -- Tab Bar with 3 items can be seen But ... the 3 child views ARE NOT LOADED and SHOWN ... :( Anything that I missed ? Million Thanks

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