Hidden fields though inheritance

Question

In the following code example:

class Parent { 
    int x =5;
    public Integer aMethod(){

        System.out.print(\"Parent.aMthod \");
        return x;
          


        

Answer 1

There's no polymorphic resolution being done when you access class member fields (instance variables) like p.x. In other words, you'll get the results from the class that's known at compile time, not what is known at run time.

For method calls this is different. They are dispatched at run time to an object of the actual class the reference points to, even if the reference itself has a super type. (in the VM this happens via the invokevirtual opcode, see e.g. http://java.sun.com/docs/books/jvms/second_edition/html/Instructions2.doc6.html#invokevirtual).