java - Program crashes with empty text field -

i need trying fix code. thought simple (probably is) can't it. have simple adding calculator. works fine, if leave 1 or both number text fields empty, program crashes.

i have if statement, apparently not telling right thing.

public class mainactivity extends activity { double firstnum, secondnum, answernum;   @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     final edittext first = (edittext) findviewbyid(r.id.txtfirst);     final edittext second = (edittext) findviewbyid(r.id.txtsecond);       final textview answer = (textview) findviewbyid(r.id.txtanswer);        button calc = (button) findviewbyid(r.id.btncalc);     calc.setonclicklistener(new onclicklistener() {            @override         public void onclick(view v) {             // todo auto-generated method stub              // convert pulled info double using variable names             firstnum = double.parsedouble(first.gettext().tostring());             secondnum = double.parsedouble(second.gettext().tostring());              if (first == null || second == null)             {                 toast.maketext(mainactivity.this, "please enter value", toast.length_short).show();             }             else {              // add numbers             answernum = (firstnum + secondnum);             //set format             decimalformat total = new decimalformat ("###,###,###.##");             answer.settext("answer " + total.format(answernum));             }         }     }); } } 

if want validate edittext means try following code work fine.

public class mainactivity extends activity { double firstnum = 0; double secondnum = 0, answernum;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     final edittext first = (edittext) findviewbyid(r.id.edittext1);     final edittext second = (edittext) findviewbyid(r.id.edittext2);      final textview answer = (textview) findviewbyid(r.id.textview1);      button calc = (button) findviewbyid(r.id.button1);     calc.setonclicklistener(new onclicklistener() {          @override         public void onclick(view v) {             // todo auto-generated method stub               if (first.gettext().tostring().equals("")                     || second.gettext().tostring().equals("")) {                 toast.maketext(mainactivity.this, "please enter value",                         toast.length_short).show();             } else {                 firstnum = double.parsedouble(first.gettext().tostring());                 secondnum = double.parsedouble(second.gettext().tostring());                 answernum = (firstnum + secondnum);                 decimalformat total = new decimalformat("###,###,###.##");                 answer.settext("answer " + total.format(answernum));             }         }     }); } }