constructor

问题 Given: static class Question { // stuff List<Value> values static class Value { // stuff } When I run: Question question = new Question() question.id = "whatever" if (it == QuestionType.SELECT || it == QuestionType.MULTICHOICE) { question.values = [new Question.Value(), new Question.Value()] for (Question.Value v : question.values) { // stuff } question.values contains an array of Question objects and NOT Value. Intellij doesn't give me any error nor warnings. I tried evaluating "new Question

问题 I'm still confused about the behaviour of std::vector::resize() . Consider the following code (see also type requirements for std::vector<type>) struct A { A() : X(0) { std::cerr<<" A::A(); this="<<this<<'\n'; } A(A const&) { assert(0); } // is required but doesn't fire in vector::resize int X; }; int main() { std::vector<A> a; a.resize(4); // would not compile without A::A(A const&) or A::A(A&&) } Without A::A(A const&) or A::A(A&&) , the line with a.resize(4); doesn't compile. However, that

问题 What the difference between A a1(5); and A a2 = A(5) ? Both of the works, but I really want know the difference between them, because I used method 2 in one of my project and I suffered from a bug which is fixed after I change to method 1. Thanks in advance! class A { public: int val; A() : val(0) {} A(int newVal) : val(newVal) {} }; int main() { A a1(5); // method 1 A a2 = A(5); // method 2 } 回答1: A a1(5); // method 1 A a2 = A(5); // method 2 The first one is called direct initialization,

问题 For instance, if I have a class like this: namespace Sample { public Class TestObject { private Object MyAwesomeObject = new MyAwesomeObject(); } } Is there any benefit to set it up so that the property is set in the constructor like this? namespace Sample { public Class TestObject { private Object MyAwesomeObject; public TestObject() { MyAwesomeObject = new MyAwesomeObject() } } } 回答1: The two are (nearly) identical. When you define the initializer inline: private Object MyAwesomeObject =

问题 I'm trying to do some AOP over objects at construction time, and found IConstructorInterceptor, which would be perfect for what I want but it doesn't appear to work (in version 1.2 at least). I've also looked at both the IObjectPostProcessor & the IInstantiationAwareObjectPostProcessor, but I can't find any way to do processing on an object around construction time... The PostProcessPropertyValues method on the IInstantiationAwareObjectPostProcessor is close, but it only passes through setter

问题 I was reading an open-source code, and there was a constructor designed like this: public class FeatureSequence2FeatureVector extends Pipe implements Serializable { boolean binary; public FeatureSequence2FeatureVector (boolean binary) { this.binary = binary; } public FeatureSequence2FeatureVector () { this (false); } } This may be just a trivial preference matter, but what I would do is like this: public class FeatureSequence2FeatureVector extends Pipe implements Serializable { boolean binary

问题 I'm running the below applet . In it, the moment I add the constructor ( even empty ), the applet throws a runtime exception: MainFrame.class can't be instantiated, java.lang.InstantiationException If I remove the constructor, no exception in thrown. Can't I have a constructor present in an applet? public class MainFrame extends JApplet implements WindowListener, ActionListener { public void init() { System.out.println("Applet Step1"); String[] args = null; createAndShowGUI(args); } private

问题 I have a simple piece of code, that compiles in Delphi XE2 but not in XE3, and I don't know why. I have reduced the problematic code to a small bit and would like to know what's wrong with it in Delphi's opinion. Trying to compile a project containing this unit in Delphi XE 2 works fine, but in Delphi XE3 (trial), it gives "[dcc32 Error] AffineTransform.pas(26): E2382 Cannot call constructors using instance variables". The only "eccentric" thing I know of here is the use of the old-school

问题 My question has changed from the other one I have posted. I started out with multiple files and decided to put it all in one main.cpp file for now just to get it working. main.cpp: #include <iostream> using namespace std; class arrayListType { public: bool isEmpty() ; bool isFull() ; int listSize() ; int maxListSize() ; void print() ; bool isItemAtEqual(int location, int item) ; virtual void insertAt(int location, int insertItem) = 0; virtual void insertEnd(int insertItem) = 0; void removeAt

问题 I fear that this is a very basic question, however, I was not able to solve it yet. I have a class A // classA.h ... class ClassA { public: ClassA(); ClassA(int foo); private: int _foo; ... } // classA.cpp ClassA::ClassA() { _foo = 0; } ClassA::ClassA(int foo) { _foo = foo; } ... A second class B uses an instance of class A in the constructor: // classB.h ... #include "classA.h" #define bar 5 class ClassB { public: ClassB(); private: ClassA _objectA; ... } // classB.cpp ClassB::ClassB() {