Help with data access

Question

Hi,
I am new to Java and stuck at a problem. Situation is like following-
package X
public abstract class A {
     A(int a) { this.a=p; }
     protected int p;
     abstract int func();
package Y
public class B extends A{
     B(int b) { super(b); }
     B() {}
     //p is accessible here
     int func() {
          D d=new D();
          d.func2();
    static void main() {
        func();
public abstract class C extends B{
public class D extends C implements interface{
     int func2() {}
}Now my problem is when I try to access p from func2(), I am getting a NullPointerException error. I am not initialising p anywhere through D()'s and B()'s no argument constructor. Is that the problem?

Answer 1

When you post code it doesn't help when the code doesn't actually reflect the problem.
The code you posted isn't legal java so given that it won't even compile you certainly can't get a null pointer exception from that. And where you commented the usage of 'p' you can't use it there so that doesn't help with guessing what you actual code might have looked like.
So all I can do is offer the following general advice.
Null pointer exceptions occur because a reference is null and it is de-referenced.. Thus if you do a line like the following.
xxx.p
Then 'xxx' is the only possible thing that can be null.
The stack trace of the exception will tell you the exact line that the problem occurred on.