public ArrayList getAllClass() {
        ArrayList al = new ArrayList();
        DBUtil db = new DBUtil();
        try {
           Statement st = db.getConnection().createStatement("");     //这里说有问题
            
        } catch (Exception ex) {
            Logger.getLogger(ClassDAOImpl.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

db.getConnection().createStatement();

createStatement(""); 里的""是什么?一般是用不带参数的.如二楼所说.
我这里废话一下帮你顶~!