NullPointer problem

Question

Hi, I was wondering if anyone out there could help, (and hope this is in the appropriate forum, I'm very new to this).
I'm creating a null pointer exception that I can't seem to get rid of.
1) I set a load of variables on an actionPerformed event in my GUI.
2) then I instantiate buyer1 (buyer1 is an instance variable in my code)
3) code] NaiiveBuyerTactic nbt1 =new NaiiveBuyerTactic();buyer1 is a class which creates a new tactic as an instance variable.
Below is the code which is causing problems:
setMaxPrice();
     NaiiveBuyer buyer1= new NaiiveBuyer(getMaxPrice(), getMinPrice(), getMaxTime(), getBeta());
     // the buyer then creates a tactic, note we now need to pass the tactic these values
     buyer1.nbt1.setPmax(getMaxPrice());
System.out.println("Buyer1s name: " + buyer1.getName()); // here it prints "buyer1s name: null" on the terminal...
     Mediator m1 = new Mediator(buyer1);// then pass another class the buyer1
     System.out.println("Nbt vals: "+buyer1.nbt1.pmax); // here it correctly prints all the new values to the terminalthen in the mediator class I have an instance variable for the buyer and an instance variable for its tactic.
I instantiate it like:
public Mediator(NaiiveBuyer buyer) {     
          NaiiveBuyer b1=buyer;
          NaiiveBuyer nbt1 = buyer.nbt1;
          Seller s1 = new Seller(150, 50, 10000, 0.7);
     When i use the line below I get a null pointer exception. I still have references to the buyer, so I don't think it has become ready for garbage collection.
Double iWrapCurr = new Double(b1.nbt1.bidGenerator(counter));Any help anyone could give would be gratefully received. Many thanks!

Answer 1

I know that the buyer is null, but I want to know why?
And it is this line that creates the exception as I have a test class, which sucessfully prints it all to the terminal.
public static void main(String[] args) {
NaiiveBuyerTactic bt = new NaiiveBuyerTactic();
bt.setPmax(100);
for (int z=0; z<50; z++){
bt.bidGenerator(z);     }
Double iWrapCurr = new
Double(b1.nbt1.bidGenerator(counter));
Well, either b1 or nbt1 are null (assuming that this
is the line that really creates the exception, and
not something in bidGenerator().