AP Comp Sci problem

Question

Hi, I'm kind of a beginner to java, and i'm in comp sci 2. I'm looking for an answer to one of the questions that I got for my project. I think that it is just that I don't really understand all of the terminology related to the code. I have only been trained in basic java, and some of the things are a bit over my head...
The given code:
public class A {
private int i;
public A(int n) {
i=n;
public void methodA() {
System.out.println(i);
public class B extends A {
public B(int n) {
super(n);
public void methodA() {
System.out.println(i/2);
public void methodB() {
System.out.println("hello");
public class C {
A aRef;
A bRef;
void methodC1() {
System.out.println("hello again");
public void methodC2() {
The problem states:
"Write a sub-class of C called E. This class should have a constructor that accepts a reference of type A and assigns A to aRef, and a method called justTesting() which invokes method B() from aRef if it is an instance of class B."
I think I should basically start out with:
public class E extends C {
public E(...something...) {
aRef = new A();
public void justTesting() {
if (aRef instanceof B) {
B.methodB();
I'm not really sure about much of it, or whether i'm on the right track or completely off. But thanks for reading, and if you have a hint or correction that I could make, please keep in touch!

Answer 1

When you post code, please use [code] and [/code] tags as described in Formatting Help on the message entry page. It makes it much easier to read.
Resources for Beginners
Sun's basic Java tutorial
Sun's New To Java Center. Includes an overview of what Java is, instructions for setting up Java, an intro to programming (that includes links to the above tutorial or to parts of it), quizzes, a list of resources, and info on certification and courses.
http://javaalmanac.com. A couple dozen code examples that supplement The Java Developers Almanac.
jGuru. A general Java resource site. Includes FAQs, forums, courses, more.
JavaRanch. To quote the tagline on their homepage: "a friendly place for Java greenhorns." FAQs, forums (moderated, I believe), sample code, all kinds of goodies for newbies. From what I've heard, they live up to the "friendly" claim.
Bruce Eckel's Thinking in Java (Available online.)
Joshua Bloch's Effective Java
Bert Bates and Kathy Sierra's Head First Java. This one has been getting a lot of very positive comments lately.