default-constructor

And how can I write my own array class to not need a default constructor for its elements? Right now, when I do the new [] to allocate space, I need a default constructor. std::vector does not. How do they do this magic? std::vector doesn't need the default constructor because it never uses it. Every time it needs to construct an element, it does it by using the copy constructor , because every time it has something to copy: either existing vector element or an element you yourself supplied for copying through a method's parameter (explicitly or implicitly, by relying on a default argument )

This question already has an answer here: Why do this() and super() have to be the first statement in a constructor? 19 answers I have the following 2 classes public class classA { classA() { System.out.println("A"); } } class classB extends classA { classB() { System.out.println("B"); } } and then running 1 classA c = new classB(); or 2 classB c = new classB(); always gives A B Why is this happening? At first glance, in either scenario, I would assume that only the classB constructor would be called and thus the only output would be B but this is clearly wrong. Aniket Thakur That is how Java

public class Sample { static int count = 0; public int abc; public Sample() { abc = ++Sample.count; } } I want to create an array of above class, and want each element in the array to be initialized by invoking the default constructor, so that each element can have different abc .So I did this: Sample[] samples = new Sample[100]; But this doesn't do what I think it should do. It seems this way the default constructor is not getting called. How to invoke default constructor when creating an array? I also would like to know what does the above statement do? You can't, basically. When you create

With C++11 std::array , do I have the guarantee that the syntax std::array<T, N> x; will default-initialize all the elements of the array ? EDIT : if not, is there a syntax that will work on all arrays (including zero-sized arrays) to initialize all elements to their default value? EDIT : on cppreference , the default constructor description says: (constructor) (implicitly declared) (public member function) default-constructs or copy-constructs every element of the array so the answer may be yes. But I would like to be sure of that according to the standard or future standard. By definition,