question: private int match ( ) throws ParsingException , IOException { int value = - 1 ; int lineno = st . lineno ( ) ; String sValue = null ; switch ( lookahead ) { case StreamTokenizer . TT_NUMBER : value = ( int ) st . nval ; if ( value < 0 ) { sValue = String . valueOf ( st . nval ) ; } lookahead = st . nextToken ( ) ; break ; default : sValue = st . sval ; break ; } if ( value <= 0 ) { throw new ParsingException ( lineno , "a non-negative number" , sValue ) ; } return value ; }
target:  Excepts to match a non-negative number.