Ok... I need help with something

When I push the button, I need to draw graph of function f(x) = a* x*x + b*x + c in the new window. a, b & c are in the text area.
The main problem is how to connect two classes... In one class I have variables a, b & c and the button, and in other class I have program which draws the graph, but I can't get the variables a,b,c from the first class to the second, therefore, the graph is always f(x) = 0 * x*x + 0*x + 0

I'm using BlueJ

I hope you understand what I'm saying. I'd appreciate any help