Android - When i entered in EditText then value is not calculate in next EditText ? Any help will be appreciated

amntpaid Edittext value should be add in total editText.When i run this.it will not adding. Check my code.

                         String subtotal=String.valueOf(amntpaid);
                         String total =String.valueOf(totamnt);
                         total = total+subtotal;
                         String ncr=total+"";
                         totalamt.setText(ncr);