question: protected boolean isValidIdentifier ( String identifier ) { if ( identifier . isEmpty ( ) ) return false ; for ( int i = 0 ; i < identifier . length ( ) ; i ++ ) { if ( ! Character . isDigit ( identifier . charAt ( i ) ) ) return false ; } return true ; }
target:  Returns whether the given string is a valid identifier within the JDBC authentication extension. Invalid identifiers may result in SQL errors from the underlying database when used in queries.