stumped by NullPointerException errors

From: David (dave_shattuck_at_hotmail.com)
Date: 05/07/04 

Date: 6 May 2004 17:00:21 -0700

Anyone up to a challenge? I am using pointers in Java so that one
object can update another. I have done this in the program I am
working on without a problem. Now, I am using it again and
encountering a NullPointerException error. It does not make sense.
Here's the logic I've been using:

Class 1 instantiates Class 2 using a constructor which allows Class 1
to pass a pointer of itself to Class 2

Class 2 saves the address of Class 1's pointer within a private member
variable "pc"

Class 1 has protected member function "memberfunction"

Class 2 is able to access Class 1 through the private member variable
"pc"

In code:

public class1 {
   class1() {
      class2(this);
   }

   protected void memberfunction() {
      // does something usefull
   }
}

public class2 {
   class1 pc;
   class2(class1 callback) {
      pc=callback;
   }

   private anotherfunction() {
      pc.memberfunction()
   }
}

Why, when I wrote my program (using threads which can access their
parent's member functions) I had no problem but now I am getting a
null pointer error? Can anyone think of reasons I would receive this
error using the scenerio above? This is a broad question - hopefully
I've given enough information for some answers!

David

Relevant Pages

  • stumped by NullPointerException errors
    ... Class 2 saves the address of Class 1's pointer within a private member ... Class 2 is able to access Class 1 through the private member variable ...
    (comp.lang.java.programmer)
  • stumped by NullPointerException errors
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    (comp.lang.java.help)
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