I have a base class `A` and a derived class `B`.
How can I copy...in a single simple line...the fields from an object of type `A` into an object of type `B`?
I have a method,if that helps,that can build the object from the field values.
I do not want to use any type of reflection!

```
class A{
  String id; //and setter/getter
 }
class B extends A{
  String b; //and setter/getter
}
public A buildA(String id){
  A=new A();
  a.setId(id);
  return A();
}
// how to copy A=buildA("a") into a B type of object...
// I would avoid doing 
//public B voidB(String id, string b){
B=new B();
b.setId(
b.setB...
// Remark - I cannot do the init from constructor with fields!

```