constructor

问题 What exactly is the difference between a final class and having a class constructor as private. I know both can't be subclassed(correct me if i am wrong). Is their any difference? 回答1: A final class cannot be extended. It prevents this final class FinalClass { } // and later class ExtendedClass extends FinalClass { // ERROR } This is useful for things like String - you wouldn't want someone to be able to overwrite the logic of String, one of the most commonly used Objects, and be able to, oh

问题 Say you are creating a java object like so: SomeClass someObject = null; someObject = new SomeClass(); At what point does the someObject become non-null? Is it before the SomeClass() constructor runs or after? To clarify a little, say if another thread was to check if someObject was null while the SomeClass() constructor was halfway through completion, would it be null or non-null? Also, what would be the difference if someObject was created like so: SomeClass someObject = new SomeClass();

问题 I have created 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 grapich methods. There isn't a constructor like Java for my class? // I want put it in a method like constructor java arrayPosition = [[NSMutableArray alloc] init]; currentPositionName = [NSString stringWithFormat:@"noPosition"]; 回答1: Yes, there is an initializer. It's called -init , and it goes a little something like

问题 This is more of a puzzle than question. I have the following code: public class PrivateBaseConstructor { public static class BaseClass { private BaseClass() { } } public static class DerivedClass extends BaseClass { public DerivedClass() { super(); // 1* } } } Here the call for super(); at 1* is allowed event though the base class constructor is private . If we write the classes as separate classes in same package: BClass.java public class BClass { private BClass() { } } DClass.java public

问题 I want to construct an object in the stack, using C++. Do you know what is the difference between these to ways of calling the constructor (with and without parenthesis): a) MyClass object ; b) MyClass object() ; I am using MFC and when constructing the global variable for the main app, if I use the latter way, I get an exception, I thought these two ways were equivalent. Thank you guys for any information. 回答1: This is one of those gotchas of C++. MyClass object(); is the way that a function

问题 I liked this question - Legitimate uses of the Function constructor - so I wanted to create a similar question regarding the Array constructor. Of course, the array literal notation is the correct way to create arrays. This would mean that the new Array notation should not be used. And "case closed". However, there is one specificity of the new Array form. If a natural number is passed in, an empty array is created and its length property is set to that number. So arr = new Array( 7 ); is

问题 Greetings, After reading the following article I have a question: https://developer.mozilla.org/en/Introduction_to_Object-Oriented_JavaScript In the inheritance example, the Person constructor doesn't take any parameters. How would this same example look if I were to add one and call it from the Student constructor? Thanks! 回答1: Well, a way that you can re-use the logic of the Person constructor is invoking it with call or apply, for example: function Person(gender) { this.gender = gender; }

问题 I want to learn how to create multiple threads with the new C++ standard library and store their handles into an array. How can I start a thread? The examples that I saw start a thread with the constructor, but if I use array, I cannot call the constructor. #include <iostream> #include <thread> void exec(int n){ std::cout << "thread " << n << std::endl; } int main(int argc, char* argv[]){ std::thread myThreads[4]; for (int i=0; i<4; i++){ //myThreads[i].start(exec, i); //?? create, start, run

问题 After compiling of c++ file (with global static object) I get in nm output this function: 00000000 t _Z41__static_initialization_and_destruction_0ii __static_initialization_and_destruction_0(int, int) /* after c++filt */ What is it? It will call __cxa_atexit() Can I disable generation of this function (and calling a __cxa_atexit() ) and put all constructor and destructor calls to .ctors and .dtors sections? 回答1: This doc file seems to tell ya all you'd wanna know about those functions: http:/

问题 I have an abstract base class with several optional parameters: abstract case class Hypothesis( requirement: Boolean = false, onlyDays: Seq[Int] = Nil, … ) extends Something {…} Do i really need to explicitly repeat all parameters with the additional keywords override val on top ‽ case class SomeHypothesis( anotherArg: SomeType, override val requirement: Boolean = false, override val onlyDays: Seq[Int] = Nil, … ) extends Hypothesis( requirement, onlyDays, … ) {…} Or is there a syntax like