constructor

问题 Which is generally considered the more preferred method when trying to add a constructor with an additional parameter? A subclass or a wrapper? That being, creating a subclass of the class and then just using that subclass' constructor? Or adding a wrapper method which will take the extra parameter and return an object with that parameter set? Thank you for your time! EDIT: I don't have access to the superclass's code. 回答1: The answer is language dependent. In C#/.NET, you would typically use

问题 In c++11, Union supports non-POD member. I want to initialize a non-POD member in the constructor. On wikipedia c++11 page, it uses a placement 'new' to initialize a non-POD member. #include <new> // Required for placement 'new'. struct Point { Point() {} Point(int x, int y): x_(x), y_(y) {} int x_, y_; }; union U { int z; double w; Point p; // Illegal in C++03; legal in C++11. U() {new(&p) Point();} // Due to the Point member, a constructor definition is now required. }; I am wondering is

问题 This question already has answers here : “Least Astonishment” and the Mutable Default Argument (31 answers) Closed 5 years ago . Here is a python class: class TxdTest(object): def __init__(self, name = '', atrributes = []): self.name = name self.attributes = atrributes and then I use it like this: def main(): for i in range(3): test = TxdTest() print test.name print test.attributes test.name = 'a' test.attributes.append(1) so, what's the result? The result is: [] [1] [1, 1] Why the 'self

问题 public partial class RegistrationController : Controller { private readonly IPartnerRepository _partnerRepository; public RegistrationController(IPartnerRepository partnerRepository) { _partnerRepository =partnerRepository; }} I use autoface to the dependancy injection and i have this error: ` No parameterless constructor defined for this object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information

问题 #include <iostream> using namespace std; class X { public: X() { cout<<"Cons"<<endl; } X(const X& x){ cout<<"Copy"<<endl; } void operator=(const X& x){ cout<<"Assignment called"; } }; X& fun() { X s; return s; } int main(){ X s = fun(); return 0; } This code calls the copy constructor also. Why does this work? I recall that the first time I ran this program, it seg faulted. But after a while, it started calling this copy cons. and now works!! Wierd. But if I replace, fun() as follows: X fun()

问题 I have read in many sources and books that constructor is used to initialise the fields when an object is created. I have also read that JVM provides a default constructor if I don't mention one. What is the purpose of a constructor if it is not required to initialise the fields like the one I have mentioned below? I also understand that a constructor without parameter is required as it is necessary during object creation when an argument is not passed (when programmer-defined constructors

问题 In Java, can a method/constructor declaration appear inside another method/constructor declaration? Example: void A() { int B() { } } I think not, but I'd love to be reassured. 回答1: No . it is not compilable. 回答2: No this is not possible. For reference: http://download.oracle.com/javase/tutorial/java/javaOO/methods.html 回答3: Not directly, but you can have a method in a class in a method: class A { void b() { class C { void d() { } } } } 回答4: This is not possible in java. However this can

问题 I have made a Label subclass and need to initialize a few of its Properties. Some I can set in the constructor, but others are being reset in the designer code of the form, so they must be set after the designer has done its InitializeComponent but before the Paint event runs, which needs them in place. Of course the control should be self-sufficient, so I can't add anything to the form's code. I am using a workaround now: I set a flag bool needsInit = true; which I check in the Paint event.

问题 I have a bunch of Repository classes which all look a bit like the following. Note that I have omitted certain methods; I just want you to get a flavour. public class SuggestionRepository : ISuggestionRepository { private IUnitOfWork _unitOfWork; public SuggestionRepository(IUnitOfWork unitOfWork) { _unitOfWork = unitOfWork; } public Suggestion Load(int id) { Suggestion suggestion; suggestion = _unitOfWork.Load<Suggestion>(id); return suggestion; } public IQueryable<Suggestion> All { get {

问题 Lets say my file looks like this: #include <iostream> #include <string> using namespace std; class testclass{ public: string name; //testclass(const string& sref){ // name = sref; //} testclass(string str){ name = str; } ~testclass(){} }; int main(){ testclass t1("constStringRef"); cout << t1.name << '\n'; } What are the differences between constructor 1 and 2 given the following constructor-call: testclass tobj("tmemberstring"); Here is what i thought of: I know that passing by reference