Accessing members and intertance

Question

Greetings:
I wrote up a couple of very simple classes to test my understanding of Accessing Inherited Members. In the "Java Programming Language 3rd Edition" page 75 it says "When you invoke a method through an object reference, the actual class of the object governs which implementation is used. When you access a field the declared type of the reference is used."
This is what I my trying to test and I managed to confuse myself and a co-worker very well. Please find my classes below and my questions futher below.
code:
package testadd;
class Car {
int zero2Sixty = 12;
void goFast() {
System.out.println(" Car goes fast. Zero to Sixty in: " + zero2Sixty);
void stepOnPetal() {
goFast();
int getZero2Sixty() {
return zero2Sixty;
class BMW extends Car {
int zero2Sixty = 8;
void goFast() {
System.out.println(" BMW goes fast. Zero to Sixty in: " + zero2Sixty);
// int getZero2Sixty() {
// return zero2Sixty;
// End
package testadd;
public class Untitled1 {
public Untitled1() {
public static void main(String[] args) {
Car aCar;
BMW bmer = new BMW();
aCar = bmer;
bmer.stepOnPetal() ;
bmer.goFast() ;
aCar.stepOnPetal() ;
aCar.goFast() ;
System.out.println("bmer.zero2Sixty:" + bmer.zero2Sixty );
System.out.println("aCar.zero2Sixty:" + aCar.getZero2Sixty() );
System.out.println("bmer.zero2Sixty:" + bmer.getZero2Sixty() );
// End
BMW goes fast. Zero to Sixty in: 8
BMW goes fast. Zero to Sixty in: 8
BMW goes fast. Zero to Sixty in: 8
BMW goes fast. Zero to Sixty in: 8
bmer.zero2Sixty:8
aCar.zero2Sixty:12
bmer.zero2Sixty:12
I do not understand why the last two methods return 12
What is the difference between the call to stepOnPetal and getZero2Sixty()?
Thanks in Advance.
Regards
kd

Answer 1

Hi,
The field zero2Sixty is duplicated. I.e The field exists in both classes.
stepOnPetal() always calls the goFast(), which is overridden in BMW, so it uses the correct value for the attribute zero2Sixty.
getZero2Sixty() is not overriden in BMW, so it returns the value in Car.
An easier answer it that the code you have written is the same as defining an attribute in car, and another one in bmw. They aren't related to each other.
/Kaj