You are calling the method in a static context because you have used the class name rather than an object reference to call the getValue() function. You will need to use the current CD object for this call. Your method is almost correct though. You want to set the text of the value field to the result of cd.getValue(). The getValue() method will do the calculation for you, you just need the listeners to call that calculation at the right time and put the value into the field you want it displayed in.