You need to work out the order of invocation of the constructors. Write down which constructor is called and when. Then you can see what of the B object exists. The details are in the Java Language Specification. You will have to follow the links.
By the way: if this is an exam question (original or changed), you must tell us where it is from. It also shows the danger of calling methods not marked final or private from a constructor. It also shows the confusion which can occur when you have two fields of the same name. I hope you are posting this as an example of code you would never use in real life.