constructor

问题 Let's assume we have some classes defined and available in global namespace. In example: class Point: def __init__(self, x, y): self.x = x self.y = y class Vector: def __init__(self, alpha, r): self.x = r * cos(alpha) self.y = r * sin(alpha) # and many others... How to do this: class_name = 'Point' x = 14.361 y = -8.100 code_str = 'class_object = ' + class_name + '(' + str(x) + ', ' + str(y) + ')' exec code_str # That evaluates to: "class_object = Point(14.361, -8.100)" print class_object.x,

问题 This question is regarding Function Stack Creation. Suppose we create a function fn(int a,char b) and call from main fn(A,B) , in this case when the function is called a fn. stack is created with return address, Stack pointer (etc) where local variables and parameters are created and on return is destroyed. I have a few questions: 1) For our parameterized constructor suppose myClass{ int a; char c; public: myClass(int a,char c) { this->a=a; this->c=c; } }; does the constructor myClass(int a

问题 Say i have 3 classes like this: |Abstract Class: Building| |int windows; | |int rooms; | | | |Abstract Class: House extends Building| |int familyMembers; | | |Class: MobileHome extends House| |int wheels; | Now i am trying to figure out the best way to structure my program, because obviously the number of windows and rooms will depend on the subclass of House , however all buildings have windows (at least for the sake of this program they do). So that is why they are in the building class but

问题 I have an issue, while trying few code snippets i came across a code class O { final int i; O() { i=10; } O(int j)// error here as THE BLANK FINAL FIELD i IS NOT INITIALIZED { j=20; System.out.println(j); } } class Manager3 { public static void main(final String[] args) { O n1=new O(); //O n2=new O(10); //n1.i=20; //System.out.println(j1.i); } } but if i comment the constructor with parameter i do not get any errors. My question is why am i getting this compile time error when i put both the

问题 Consider - public class Class_A { public void func() {...} public void func(int a){...} All three - Class_A a = new Class_A(); // legal a.func(); // legal a.func(1); // legal But After constructor with arg like public Class_A (int a){...} is added to Class_A , the default constructor become to be - Class_A a = new Class_A(); // The constructor Class_A() is undefined Thats force me to add public Class_A() {/*Do Nothing*/} into Class_A . Since each class has default constructor , why doesn't

问题 Suppose I have class A final { int& ir; public: A(int& x) : ir(x) { } void set(int y) { ir = y; } // non-const method! int get() const { return ir; } }; and const int i; Obviously I can't have A a(i); since that would breaks constness. But I also cannot have const A a(i); despite the fact that this will not break constness de-facto. C++ doesn't support "const-only" ctors, e.g. in this case one which would take a const int& . Is there a way to get const A a wrapping a reference to i - other

问题 This question already has answers here : stackoverflow error in class constructor (2 answers) Why am I getting a StackOverflowError exception in my constructor (3 answers) Closed 2 years ago . This is my code : public class ConstructorsDemo{ public static void main(String a[]){ Cons1 c1 = new Cons1(); } } class Cons1{ Cons1 c = new Cons1();// the error is in this line Cons1(){ //does somwthing } } So I get an infinite loop error here (Stackoverflow). However it's fine if I comment out any of

问题 SingleMonitorInfo::SingleMonitorInfo(MONITORINFOEX* lpMONITORINFOEX) :rcMonitorArea(lpMONITORINFOEX->rcMonitor), rcWorkArea(lpMONITORINFOEX->rcWork), dwStatusFlags(lpMONITORINFOEX->dwFlags), szDeviceName({ '\0' }), szMonitorName({ '\0' }), szMonitorDescription({ '\0' }), lpPixelArray(NULL) { wcscpy_s(SingleMonitorInfo::szDeviceName, 33, lpMONITORINFOEX->szDevice); SingleMonitorInfo::setStringMonitorNameAndDescription(lpMONITORINFOEX->szDevice); } I am rewriting my program using member

问题 I have a 3 classes, ParentClass , ClassA , ClassB . Both ClassA and ClassB are subclasses of ParentClass . I wanna try to create objects of type ClassA or ClassB using some kind of enumeration to identify a type, and then instantiate the object cast as the parent type. How can I do that dynamically? Please take a look at the code below, and the parts that say //what do I put here? . Thanks for reading! enum ClassType { ClassA, ClassB }; public abstract class ParentClass { public ParentClass()

问题 Before you mark this a duplicate, I have read this question and this question and they don't answer my question (and even seem to confuse me more, not to mention that they're both in Python 2 and I want to know about Python 3). From this question, understand why the following code, from typing import Hashable class UnorderedPair(frozenset): def __init__(self, left: Hashable, right: Hashable): self.left = left self.right = right super().__init__((left, right)) if len(self) != 2: raise