java - index out of bounds error why? -

the line x.set(7,y) in code below throwing indexoutofboundsexception, , can't figure out why. can help?

linkedlist<myclass> x = new linkedlist<myclass>(); x = myarraylist.get(7); iterator<myclass> itr = x.iterator(); myclass y = new myclass(); while (itr.hasnext()) {     y = itr.next();     if (z.methodcalltogetstr().equals(y.methodcalltogetstr()))//z myclass object     {         y.inccount();         x.set(7, y);         break; 

assuming myarraylist.get(7) creates 7 elements, these elements numbered 0 6. 7th 1 off end of list.