Polymorphism and Constructors

I am an AP Java Student and I am practicing for my exam. I came across this question and I don't understand the answer:

Consider the following classes:

public class A
{
  public A() { methodOne(); }

  public void methodOne() { System.out.print("A"); }
}

public class B extends A
{
  public B() { System.out.print("*"); }

  public void methodOne() { System.out.print("B"); }
}

What is the output when the following code is executed:

A obj = new B();

The correct answer is B*. Can someone please explain to me the sequence of method calls?