The entire piece of code would make it easier. However I am willing to
jump off the cliff and suggest that for some reason size  isn't
constructed properly. Like maybe for some reason it is equal to null;

probably more like setA hasn't been initialised yet, but the code would be good

Let's say that the code snippet (we don't have the
entire code) is implementing the actionLister, then
you have to have a method called actionPerformed,
let's say that it's the one that throws the
nullPointerException (if it is) then add to that line
"throws nullPointerException", then put your code in
the try braces in the catch-try statement, then you
will run the program  without problems. Check the SDK
for the exact syntax. A nullPointerException is, just
my guess, the most common "error" in Java, probably
because of you don't access pointers the way you do in
C and C++.

What is the length. Is it a int  or a object.
Null Pointer Exception usually throws when u r trying something to assign to
a object when the memory for that object is not allocated.

the variable 'setA' is null...............

Thanks for the help I was able to get the problem
solved through the Java Beginners Club. It turns
out that I hadn't instantiated(spelling) the array
element. Thats all. I guess its a common error
for people starting out.

I think you don't instance the setA object. The secuence is:

- Declare: Objectxxx setA;
- Instance: setA = new Objectxxx();
- Use: setA.createSet(size);