The invalid character constant in this case is 'employee_name'. Single quotes in Java define a character constant, i.e. one character, e.g. 'a' or 'b' or '!'. 'employee_name' is a string of them so you have to use a String literal and double quotes, i.e. "employee_name".
When I said to use single quotes I meant in your SQL query string, e.g. String sql = "insert into table values ('string in sql')"; not in your Java code.