Problem stringItem.setText()

[Fsirka]

I have a problem mobile applications
code:
else if (command == okCommand) {
int weight,percentage,price,result;
String s_weight,s_percentage,s_price,s_result;
s_weight=textField1.getString();
s_price=textField.getString();
s_percentage=textField2.getString();
weight=Integer.parseInt(s_weight);
percentage=Integer.parseInt(s_percentage);
price=Integer.parseInt(s_price);
result=10*price/(weight/percentage);
stringItem.setText("rhrhrhr"+result);
}
Problems
All the text fields are not null (textField="200";textField1=3;textField2=70)
result = 9
but when I press "OK" in mobil phone, then stringItem is null
Why ???
If I get object of stringItem in new form1 and I use "OK" for go from form to form1 , then it is good.
How can I do only once in form ?