Not familiar with the tool. There ought to be documentation telling you what you are returning.
Put another line in your catch(Error e) block like this:-
as required
here. I have used other lexical scanners, which produce some sort of return value. You ought to have a method to add something like this:-
. . . and you need to put a line in with each TOKEN: definition on the lines of "return getSymbol(INT_TYPE, Integer.parseInt(yytext()));"
As I said, there ought to be documentation with the tool on its website telling you what you are supposed to do, and there will probably be worked examples for you to study.
BTW: A digit or a character DOES NOT constitute a token.