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• Constructor being called again?

  - by Halo

  I have this constructor; public UmlDiagramEntity(ReportElement reportElement, int pageIndex, Controller controller) { super(reportElement.getX1(), reportElement.getY1(), reportElement.getX2(), reportElement.getY2()); setLayout(null); this.pageIndex = pageIndex; this.controller = controller; reportElements = reportElement.getInternalReportElements(); components = new ArrayList<AbstractEntity>(); changedComponentIndex = -1; PageListener p = new PageListener(); this.addMouseMotionListener(p); this.addMouseListener(p); setPage(); } And I have an update method in the same class; @Override public void update(ReportElement reportElement) { if (changedComponentIndex == -1) { super.update(reportElement); } else { reportElements = reportElement.getInternalReportElements(); if (components.size() == reportElements.size()) { if (!isCommitted) { if (reportElement.getType() == ReportElementType.UmlRelation) { if (checkInvolvementAndSet(changedComponentIndex)) { anchorEntity(changedComponentIndex); } else { resistChanges(changedComponentIndex); } return; } } ..................goes on When I follow the flow from the debugger, I see that when update is called, somewhere in the method, the program goes into the constructor and executes it all over again (super, pageIndex, etc.). Why does it go to the constructor :D I didn't tell it to go there. I can make a deeper analysis and see where it goes to the constructor if you want. By the way, changedComponentIndex is a static variable.

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• Java Constructor Style (Check parameters aren't null)

  - by Peter

  What are the best practices if you have a class which accepts some parameters but none of them are allowed to be null? The following is obvious but the exception is a little unspecific: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null || two == null) { throw new IllegalArgumentException("Parameters can't be null"); } //... } } Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } Here the constructor is neater, but now the constructor code isn't really in the constructor: public class SomeClass { public SomeClass(Object one, Object two) { setOne(one); setTwo(two); } public void setOne(Object one) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } //... } public void setTwo(Object two) { if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } } Which of these styles is best? Or is there an alternative which is more widely accepted? Cheers, Pete

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• C++: Constructor/destructor unresolved when not inline?

  - by Anamon

  In a plugin-based C++ project, I have a TmpClass that is used to exchange data between the main application and the plugins. Therefore the respective TmpClass.h is included in the abstract plugin interface class that is included by the main application project, and implemented by each plugin. As the plugins work on STL vectors of TmpClass instances, there needs to be a default constructor and destructor for the TmpClass. I had declared these in TmpClass.h: class TmpClass { TmpClass(); ~TmpClass(); } and implemented them in TmpClass.cpp. TmpClass::~TmpClass() {} TmpClass::TmpClass() {} However, when compiling plugins this leads to the linker complaining about two unresolved externals - the default constructor and destructor of TmpClass as required by the std::vector<TmpClass> template instantiation - even though all other functions I declare in TmpClass.h and implement in TmpClass.cpp work. As soon as I remove the (empty) default constructor and destructor from the .cpp file and inline them into the class declaration in the .h file, the plugins compile and work. Why is it that the default constructor and destructor have to be inline for this code to compile? Why does it even maatter? (I'm using MSVC++8).

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• Calling base class constructor

  - by The Void

  In the program below, is the line Derived(double y): Base(), y_(y) correct/allowed? That is, does it follow ANSI rules? #include <iostream> class Base { public: Base(): x_(0) { std::cout << "Base default constructor called" << std::endl; } Base(int x): x_(x) { std::cout << "Base constructor called with x = " << x << std::endl; } void display() const { std::cout << x_ << std::endl; } protected: int x_; }; class Derived: public Base { public: Derived(): Base(1), y_(1.2) { std::cout << "Derived default constructor called" << std::endl; } Derived(double y): Base(), y_(y) { std::cout << "Derived constructor called with y = " << y << std::endl; } void display() const { std::cout << Base::x_ << ", " << y_ << std::endl; } private: double y_; }; int main() { Base b1; b1.display(); Derived d1; d1.display(); std::cout << std::endl; Base b2(-9); b2.display(); Derived d2(-8.7); d2.display(); return 0; }

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• Java: design problem with final-value and empty constructor

  - by HH

  $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; // Design Problem? // I feel the initialization problem is just due to bad style. InitInt(){} InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } } public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Partial Solutions and Suggestions use "this" to access methods in the class, instead of creating empty constructor change final to non-final with final field value: initialize all final values in every constructor remove the empty constructor, keep your code simple and clean

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• C# ArrayList calling on a constructor class

  - by EvanRyan

  I'm aware that an ArrayList is probably not the way to go with this particular situation, but humor me and help me lose this headache. I have a constructor class like follows: class Peoples { public string LastName; public string FirstName; public Peoples(string lastName, string firstName) { LastName = lastName; FirstName = firstName; } } And I'm trying to build an ArrayList to build a collection by calling on this constructor. However, I can't seem to find a way to build the ArrayList properly when I use this constructor. I have figured it out with an Array, but not an ArrayList. I have been messing with this to try to build my ArrayList: ArrayList people = new ArrayList(); people[0] = new Peoples("Bar", "Foo"); people[1] = new Peoples("Quirk", "Baz"); people[2] = new Peopls("Get", "Gad"); My indexing is apparently out of range according to the exception I get.

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• Spring overloaded constructor injection

  - by noob

  This is the code : public class Triangle { private String color; private int height; public Triangle(String color,int height){ this.color = color; this.height = height; } public Triangle(int height ,String color){ this.color = color; this.height = height; } public void draw() { System.out.println("Triangle is drawn , + "color:"+color+" ,height:"+height); } } The Spring config-file is : <bean id="triangle" class="org.tester.Triangle"> <constructor-arg value="20" /> <constructor-arg value="10" /> </bean> Is there any specific rule to determine which constructor will be called by Spring ?

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• c++ Using const in a copy constructor?

  - by Anton

  I have never written copy constructor, so in order to avoid pain i wanted to know if what i have coded is legit. It compiles but i am not sure that it works as a copy constructor should. Also do i have to use const in the copy constructor or i can simply drop it. (What i dont like about const is that the compiler cries if i use some non const functions). //EditNode.h class EditNode { explicit EditNode(QString elementName); EditNode(const EditNode &src); } //EditNodeContainer.h class EditNodeContainer : public EditNode { explicit EditNodeContainer(QString elementName); EditNodeContainer(const EditNodeContainer &src); } //EditNodeContainer.cpp EditNodeContainer::EditNodeContainer(QString elementName):EditNode(elementName) { } //This seems to compile but not sure if it works EditNodeContainer::EditNodeContainer(const EditNodeContainer &src):EditNode(src) { } //the idea whould be to do something like this EditNodeContainer *container1 = new EditNodeContainer("c1"); EditNodeContainer *copyContainer = new EditNodeContainer(container1);

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• Java: design problem with private-final-int-value and empty constructor

  - by HH

  $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; //DUE to new Klowledge: Design Problem //I think having an empty constructor like this // is an design problem, shall I remove it? What do you think? // When to use an empty constructor? InitInt(){} public static void main(String[] args) { InitInt test = new InitInt(); System.out.println(test.getRight()); } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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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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• Would this constructor be acceptable practice?

  - by Robb

  Let's assume I have a c++ class that have properly implemented a copy constructor and an overloaded = operator. By properly implemented I mean they are working and perform a deep copy: Class1::Class1(const Class1 &class1) { // Perform copy } Class1& Class1::operator=(const Class1 *class1) { // perform copy return *this; } Now lets say I have this constructor as well: Class1::Class1(Class1 *class1) { *this = *class1; } My question is would the above constructor be acceptable practice? This is code that i've inherited and maintaining.

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• Constructor return value

  - by Ivan Gromov

  Could you tell me what is wrong with my class constructor? Code: CVector::CVector (int size_) { if (size_ > 0) { this->size = size_; this->data = new double[size]; for (int i = 0; i < size; i++) { (*this)(i) = i; } } cout << "constructor end" << endl; return; } Usage example: tvector = CVector(6); I get an access violation after "constructor end" output.

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• Why Java cannot find my constructor?

  - by Roman

  Well, maybe it is a stupid question, but I cannot resolve this problem. In my ServiceBrowser class I have this line: ServiceResolver serviceResolver = new ServiceResolver(ifIndex, serviceName, regType, domain); And compiler complains about it. It says: cannot find symbol symbol : constructor ServiceResolver(int,java.lang.String,java.lang.String,java.lang.String) This is strange, because I do have a constructor in the ServiceResolver: public void ServiceResolver(int ifIndex, String serviceName, String regType, String domain) { this.ifIndex = ifIndex; this.serviceName = serviceName; this.regType = regType; this.domain = domain; } ADDED: I removed void from the constructor and it works! Why?

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• variadic constructors

  - by FredOverflow

  Are variadic constructors supposed to hide the implicitly generated ones, i.e. the default constructor and the copy constructor? struct Foo { template<typename... Args> Foo(Args&&... x) { std::cout << "inside the variadic constructor\n"; } }; int main() { Foo a; Foo b(a); } Somehow I was expecting this to print nothing after reading this answer, but it prints inside the variadic constructor twice on g++ 4.5.0 :( Is this behavior correct?

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• Windows Live SkyDrive: How To Move or Copy Files Between Folders

  - by Gopinath

  Microsoft has very simple and easy to use interface to move files between folders in Windows Operating system. But their own cloud storage service,Windows Live SkyDrive, complicated these simple and daily used operations. We need a guide to figure out how to perform basic copy/move operations. Couple of years ago we wrote about moving files between folders in old version of SkyDrive but the guide does not hold good today as SkyDrive has gone through many user interface changes in the recent past. Today one of our readers asked us how to move/copy files in the latest version of SkyDrive and here are the steps to be followed 1. Login to your Windows Live SkyDrive 2. Select the file you want to Move or Copy by clicking on the information icon (see 2 in below image) 3. After selecting the information icon, expand Information section displayed on the right side panel to access Move and Copy options (see 3 in the below image). 4. To move the selected file to another folder, select Move option and Sky Drive will guide you through folder selection user interface for choosing the target folder. 5. Once you navigate to the target folder where you want to move the file click on “Move this file into <<Target Folder>>”. 6. You are done. Dear Microsoft, SkyDrive provides us tonnes of free storage but please make it’s user interface a bit better so that we don’t need to write guides to perform basic operations. Hope you listen to your customers. This article titled,Windows Live SkyDrive: How To Move or Copy Files Between Folders, was originally published at Tech Dreams. Grab our rss feed or fan us on Facebook to get updates from us.

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• Mac OSX snow leapord move to folder on keystroke

  - by Georges Oates Larsen

  On a weekly basis I have to organize thousands of photos (in groups of up to five thousand) into folders depending upon what they contain (to then narrow them down to the best photos of the same thing). This means I am constantly scanning through photos and organizing them into a folder. THe problem is, the process of stopping my scan, then dragging the photo all the way into a folder myself is bogging me down. Would it be possible to, for instance using something like applescript, or even going so far as using XCode/Cocoa, to create a shortcut that moves whatever I have selected in the finder to a pre-specified folder? Does somethign like this already exist?

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• Accessing the Private Constructor

  - by harigm

  I am java developer, went for an interview. I have been asked a question about the Private constructor 1) Can I access a Private Constructor of a Class and Instantiate the class. I was thinking and gave the answer directly--- "NO" But its wrong, can any one help Why NO? and How we can achieve this

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• Call a constructor from variable arguments with PHP

  - by zneak

  Hello guys, I have a function that takes variadic arguments, that I obtain from func_get_args(). This function needs to call a constructor with those arguments. However, I don't know how to do it. With call_user_func, you can call functions with an array of arguments, but how would you call a constructor from it? I can't just pass the array of arguments to it; it must believe I've called it "normally". Thank you!

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• Calling assignment operator in copy constructor

  - by stas

  Are there some drawbacks of such implementation of copy-constructor? Foo::Foo(const Foo& i_foo) { *this = i_foo; } As I remember, it was recommend in some book to call copy constructor from assignment operator and use well-known swap trick, but I don't remember, why...

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• behaviour of the implicit copy constructor / assignment operator

  - by Tobias Langner

  Hello, I have a question regarding the C++ Standard. Suppose you have a base class with user defined copy constructor and assignment operator. The derived class uses the implicit one generated by the compiler. Does copying / assignment of the derived class call the user defined copy constructor / assignment operator? Or do you need to implement user defined versions that call the base class? Thank you for your help.

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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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• Require a default constructor in java?

  - by jdc0589

  Is there any way to require that a class have a default (no parameter) constructor, aside from using a reflection check like the following? (the following would work, but it's hacky and reflection is slow) boolean valid = false; for(Constructor<?> c : TParse.class.getConstructors()) { if(c.getParameterTypes().length == 0) { valid = true; break; } } if(!valid) throw new MissingDefaultConstructorException(...);

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• Calling methods in super class constructor of subclass constructor?

  - by deamon

  Calling methods in super class constructor of subclass constructor? Passing configuration to the __init__ method which calls register implicitely: class Base: def __init__(self, *verbs=("get", "post")): self._register(verbs) def _register(self, *verbs): pass class Sub(Base): def __init__(self): super().__init__("get", "post", "put") Or calling register explicitely in the subclass' __init__ method: class Base: def __init__(self): self._register("get", "post") def _register(self, *verbs): pass class Sub(Base): def __init__(self): _register("get", "post", "put") What is better or more pythonic? Or is it only a matter of taste?

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• constructor in objective c

  - by zp26

  HI, I have create my iPhone apps but i have a problem. I have a classViewController where i have implemented my program. I must alloc 3 NSMutableArray but i don't want do it in a grapich methods. There isn't a constructor like java for my class? Thanks so much and sorry for my english XP // I want put it in a method like constructor java arrayPosizioni = [[NSMutableArray alloc]init]; nomePosizioneCorrente = [NSString stringWithFormat:@"noPosition"];

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• Calling MethodBase's Invoke on a constructor (reflection)

  - by Alix

  Hi everyone. First of all, sorry if this has been asked before. I've done a pretty comprehensive search and found nothing quite like it, but I may have missed something. And now to the question: I'm trying to invoke a constructor through reflection, with no luck. Basically, I have an object that I want to clone, so I look up the copy constructor for its type and then want to invoke it. Here's what I have: public Object clone(Object toClone) { MethodBase copyConstructor = type.GetConstructor( new Type[] { toClone.GetType() }); return method.Invoke(toClone, new object[] { toClone }); //<-- doesn't work } I call the above method like so: List list = new List(new int[] { 0, 1, 2 }); List clone = (List) clone(list); Now, notice the invoke method I'm using is MethodBase's invoke. ConstructorInfo provides an invoke method that does work if invoked like this: return ((ConstructorInfo) method).Invoke(new object[] { toClone }); However, I want to use MethodBase's method, because in reality instead of looking up the copy constructor every time I will store it in a dictionary, and the dictionary contains both methods and constructors, so it's a Dictionary<MethodBase>, not Dictionary<ConstructorInfo>. I could of course cast to ConstructorInfo as I do above, but I'd rather avoid the casting and use the MethodBase method directly. I just can't figure out the right parameters. Any help? Thanks so much.

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