Question

public class A extends B {
    private A(B b) {
        super(b);
    }

    public static A parse(string s) // question 1
    {
        B result = D.parse(s);

        return new A(result); // question 2
    }

}

Question 1: I don’t understand what type of constructor(?) is this.
What I think of a regular constructor looks something like public A(). But this one:

public static A parse(string s)

How should I interpret it?

Question 2: new A(result);
What does this “new” do when returning something?
Is this method returning and calling a private constructor?

Answer 1

Question 1: It’s not a constructor at all, it’s just a static method that creates an object.

Question 2: new is used to call the constructor on a class. new A(...) calls the A constructor passing in the arguments.

So what you have there in A is a class that cannot be instantiated in the normal way (because the constructor is private), but from which you can get instances by calling A.parse. parse is usually called a “factory” method in this case.