java - how to invoke a new activity the moment the user enter exactly 4 digits of code into an editText box -

i invoke new activity moment user enter 4 digits of code edittext box.

how can catch exact moment user enter 4 , last digit , invoke action checks if code valid.

thanks,

gil.

use text watcher

    edittext.addtextchangedlistener(new textwatcher() {          @override         public void ontextchanged(charsequence s, int start, int before,                 int count) {             // todo auto-generated method stub          }          @override         public void beforetextchanged(charsequence s, int start, int count,                 int after) {             // todo auto-generated method stub          }          @override         public void aftertextchanged(editable s) {             // todo auto-generated method stub             //start activity             if (s.length()==4)                 startactivity(new intent(callingactivity.this,calledactivity.class));         }     });